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Electrical Specifications Subject to Change
LTC2208 16-Bit, 130Msps ADC U
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
FEATURES

DESCRIPTIO
Sample Rate: 130Msps 78dBFS Noise Floor 100dB SFDR SFDR >83dB at 250MHz (1.5VP-P Input Range) PGA Front End (2.25VP-P or 1.5VP-P Input Range) 700MHz Full Power Bandwidth S/H Optional Internal Dither Optional Data Output Randomizer LVDS or CMOS Outputs Single 3.3V Supply Power Dissipation: 1.25W Clock Duty Cycle Stabilizer Pin Compatible 14-Bit Version 130Msps: LTC2208 (16-Bit), LTC2208-14 (14-Bit) 64-Pin QFN Package
The LTC(R)2208 is a 130Msps, sampling 16-bit A/D converter designed for digitizing high frequency, wide dynamic range signals up to input frequencies of 700MHz. The input range of the ADC can be optimized with the PGA front end. The LTC2208 is perfect for demanding communications applications, with AC performance that includes 78dBFS Noise Floor and 100dB spurious free dynamic range (SFDR). Ultra low jitter of 70fsRMS allows undersampling of high input frequencies with excellent noise performance. Maximum DC specs include 4LSB INL, 1LSB DNL (no missing codes) over temperature. The digital output can be either differential LVDS or single-ended CMOS. There are two format options for the CMOS outputs: a single bus running at the full data rate or demultiplexed buses running at half data rate. A separate output power supply allows the CMOS output swing to range from 0.5V to 3.3V. The ENC+ and ENC- inputs may be driven differentially or single-ended with a sine wave, PECL, LVDS, TTL or CMOS inputs. An optional clock duty cycle stabilizer allows high performance at full speed with a wide range of clock duty cycle.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
APPLICATIO S

Telecommunications Receivers Cellular Base Stations Spectrum Analysis Imaging Systems ATE
3.3V SENSE
VCM
2.2F
AIN+
1.25V COMMON MODE BIAS VOLTAGE
INTERNAL ADC REFERENCE GENERATOR
ANALOG INPUT
AIN-
+ -
S/H AMP
16-BIT PIPELINED ADC CORE
CORRECTION LOGIC AND SHIFT REGISTER
OUTPUT DRIVERS
OF CLKOUT D15 CMOS * OR * LVDS * D0
OGND
CLOCK/DUTY CYCLE CONTROL
VDD GND
3.3V
1F
1F
AMPLITUDE (dBFS)
ENC
ENC
PGA
SHDN
ADC CONTROL INPUTS
U
TYPICAL APPLICATIO
U
64k Point FFT, FIN = 15.1MHz, -1dB, PGA = 0
OVDD
0.5V TO 3.3V
1F
1F
2208 TA01
0
10
50 20 40 30 FREQUENCY (MHz)
60
2208 G03
DITH
MODE
LVDS
RAND
2208f
1
LTC2208
OVDD = VDD (Notes 1 and 2)
Supply Voltage (VDD) ................................... -0.3V to 4V Digital Output Ground Voltage (OGND)........ -0.3V to 1V Analog Input Voltage (Note 3) ..... -0.3V to (VDD + 0.3V) Digital Input Voltage .................... -0.3V to (VDD + 0.3V) Digital Output Voltage ................-0.3V to (OVDD + 0.3V) Power Dissipation............................................ 2000mW Operating Temperature Range LTC2208C ................................................ 0C to 70C LTC2208I .............................................-40C to 85C Storage Temperature Range ..................-65C to 150C Digital Output Supply Voltage (OVDD) .......... -0.3V to 4V
TOP VIEW
64 PGA 63 RAND 62 MODE 61 LVDS 60 OF+/OFA 59 OF-/DA15 58 D15+/DA14 57 D15-/DA13 56 D14+/DA12 55 D14-/DA11 54 D13+/DA10 53 D13-/DA9 52 D12+/DA8 51 D12-/DA7 50 OGND 49 OVDD
SENSE 1 GND 2 VCM 3 GND 4 VDD 5 VDD 6 GND 7 AIN+ 8 AIN- 9 GND 10 GND 11 ENC+ 12 ENC- 13 GND 14 VDD 15 VDD 16
65
48 D11+/DA6 47 D11-/DA5 46 D10+/DA4 45 D10-/DA3 44 D9+/DA2 43 D9-/DA1 42 D8+/DA0 41 D8-/CLKOUTA 40 CLKOUT+/CLKOUTB 39 CLKOUT -/OFB 38 D7+/DB15 37 D7-/DB14 36 D6+/DB13 35 D6-/DB12 34 D5+/DB11 33 D5-/DB10
ORDER PART NUMBER LTC2208CUP LTC2208IUP
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
CO VERTER CHARACTERISTICS
PARAMETER Resolution (No Missing Codes) Integral Linearity Error Differential Linearity Error Offset Error Offset Drift Gain Error Full-Scale Drift Transition Noise
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 4)
CONDITIONS
VDD 17 GND 18 SHDN 19 DITH 20 -/DB0 21 D0 DO+/DB1 22 D1-/DB2 23 D1+/DB3 24 D2-/DB4 25 D2+/DB5 26 D3-/DB6 27 D3+/DB7 28 D4-/DB8 29 D4+/DB9 30 OGND 31 OVDD 32
EXPOSED PAD IS GND (PIN 65) MUST BE SOLDERED TO PCB BOARD TJMAX = 125C, JA = 20C/W
UP PART MARKING* LTC2208UP
MIN 16

TYP 0.7 0.3 1 10 0.2 30 15 2.9
MAX 4 1 5 1.0
UNITS Bits LSB LSB mV V/C %FS
ppm/C ppm/C
Differential Analog Input (Note 5) Differential Analog Input (Note 6) External Reference Internal Reference External Reference
LSBRMS
2208f
2
U
W
U
U
WW
W
ABSOLUTE
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
U
LTC2208 A ALOG I PUT
SYMBOL VIN VIN, CM IIN ISENSE IMODE ILVDS CIN tAP tJITTER CMRR BW-3dB
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 4)
PARAMETER Analog Input Range (AIN+ - AIN-) Analog Input Common Mode Analog Input Leakage Current SENSE Input Leakage Current MODE Pin Pull-Down Current to GND LVDS Pin Pull-Down Current to GND Analog Input Capacitance Sample-and-Hold Acquisition Delay Time Sample-and-Hold Acquisition Delay Time Jitter Analog Input Common Mode Rejection Ratio Full Power Bandwidth CONDITIONS 3.135V VDD 3.465V Differential Input (Note 7) 0V AIN+, AIN- VDD 0V SENSE VDD MIN

DY A IC ACCURACY
SYMBOL SNR
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. AIN = -1dBFS. (Note 4)
PARAMETER Signal-to-Noise Ratio CONDITIONS 5MHz Input (2.25V Range, PGA = 0) 5MHz Input (1.5V Range, PGA = 1) 30MHz Input (2.25V Range, PGA = 0) 30MHz Input (1.5V Range, PGA = 1) 70MHz Input (2.25V Range, PGA = 0) 70MHz Input (1.5V Range, PGA = 1) 140MHz Input (2.25V Range, PGA = 0) 140MHz Input (1.5V Range, PGA = 1) 250MHz Input (2.25V Range, PGA = 0) 250MHz Input (1.5V Range, PGA =1 ) 5MHz Input (2.25V Range, PGA = 0) 5MHz Input (1.5V Range, PGA = 1) 30MHz Input (2.25V Range, PGA = 0) 30MHz Input (1.5V Range, PGA = 1) 70MHz Input (2.25V Range, PGA = 0) 70MHz Input (1.5V Range, PGA = 1) 140MHz Input (2.25V Range, PGA = 0) 140MHz Input (1.5V Range, PGA = 1) 250MHz Input (2.25V Range, PGA = 0) 250MHz Input (1.5V Range, PGA = 1) 5MHz Input (2.25V Range, PGA = 0) 5MHz Input (1.5V Range, PGA = 1) 30MHz Input (2.25V Range, PGA = 0) 30MHz Input (1.5V Range, PGA = 1) 70MHz Input (2.25V Range, PGA = 0) 70MHz Input (1.5V Range, PGA = 1) 140MHz Input (2.25V Range, PGA = 0) 140MHz Input (1.5V Range, PGA = 1) 250MHz Input (2.25V Range, PGA = 0) 250MHz Input (1.5V Range, PGA = 1) MIN TYP 77.7 75.3 77.6 75.2 77.5 75.1 76.9 74.8 75.4 73.8 100 100 95 100 90 95 85 90 78 83 100 100 100 100 100 100 95 95 90 90 MAX UNITS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB
2208f
SFDR
Spurious Free Dynamic Range 2nd or 3rd Harmonic
SFDR
Spurious Free Dynamic Range 4th Harmonic or Higher
U
WU
U
1 -1 -1
TYP 1.5 to 2.25 1.25
MAX 1.5 1 1
Sample Mode ENC+ < ENC- Hold Mode ENC+ > ENC-
10 10 6.5 1.4 -1.0 50
UNITS VP-P V A A A A pF pF ns fs RMS dB MHz
1V < (AIN+ = AIN-) <1.5V RS < 20
80 700
TBD
TBD
TBD
TBD
TBD
TBD
3
LTC2208 DY A IC ACCURACY
SYMBOL S/(N+D)
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. AIN = -1dBFS unless otherwise noted. (Note 4)
PARAMETER Signal-to-Noise Plus Distortion Ratio CONDITIONS 5MHz Input (2.25V Range, PGA = 0) 5MHz Input (1.5V Range, PGA = 1) 30MHz Input (2.25V Range, PGA = 0) 30MHz Input (1.5V Range, PGA = 1) 70MHz Input (2.25V Range, PGA = 0) 70MHz Input (1.5V Range, PGA = 1) 140MHz Input (2.25V Range, PGA = 0) 140MHz Input (1.5V Range, PGA = 1) 250MHz Input (2.25V Range, PGA = 0) 250MHz Input (1.5V Range, PGA = 1) 5MHz Input (2.25V Range, PGA = 0) 5MHz Input (1.5V Range, PGA = 1) 30MHz Input (2.25V Range, PGA = 0) 30MHz Input (1.5V Range, PGA = 1) 70MHz Input (2.25V Range, PGA = 0) 70MHz Input (1.5V Range, PGA = 1) 140MHz Input (2.25V Range, PGA = 0) 140MHz Input (1.5V Range, PGA = 1) 250MHz Input (2.25V Range, PGA = 0) 250MHz Input (1.5V Range, PGA = 1) 5MHz Input (2.25V Range, PGA = 0) 5MHz Input (1.5V Range, PGA = 1) 30MHz Input (2.25V Range, PGA = 0) 30MHz Input (1.5V Range, PGA = 1) 70MHz Input (2.25V Range, PGA = 0) 70MHz Input (1.5V Range, PGA = 1) 140MHz Input (2.25V Range, PGA = 0) 140MHz Input (1.5V Range, PGA = 1) 250MHz Input (2.25V Range, PGA = 0) 250MHz Input (1.5V Range, PGA = 1) MIN TYP 77.7 75.3 77.5 75.2 77.4 75 76.4 74.5 73.6 72.9 105 105 105 105 105 105 100 100 100 100 115 115 115 115 115 115 110 110 105 105 MAX UNITS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS dBFS
SFDR
SFDR
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 4)
PARAMETER VCM Output Voltage VCM Output Tempco VCM Line Regulation VCM Output Resistance CONDITIONS IOUT = 0 IOUT = 0 3.135V VDD 3.465V 1mA | IOUT | 1mA MIN 1.15 TYP 1.25 100 1 2 MAX 1.35 UNITS V
ppm/C
4
WU
TBD
TBD
Spurious Free at -25dBFS Dither "OFF"
TBD
TBD
Spurious Free at -25dBFS Dither "ON"
TBD
TBD
mV/ V
2208f
LTC2208 DIGITAL I PUTS A D DIGITAL OUTPUTS
SYMBOL PARAMETER ENCODE INPUTS (ENC+, ENC-) VID Differential Input Voltage VICM Common Mode Input Voltage RIN Input Resistance CIN Input Capacitance LOGIC INPUTS (DITH, PGA, SHDN, RAND) VIH High Level Input Voltage VIL Low Level Input Voltage IIN Digital Input Current CIN Digital Input Capacitance LOGIC OUTPUTS (CMOS MODE) OVDD = 3.3V VOH High Level Output Voltage VOL Low Level Output Voltage
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 4)
CONDITIONS
ISOURCE Output Source Current ISINK Output Sink Current OVDD = 2.5V VOH High Level Output Voltage VOL Low Level Output Voltage OVDD = 1.8V VOH High Level Output Voltage VOL Low Level Output Voltage LOGIC OUTPUTS (LVDS MODE) STANDARD LVDS VOD Differential Ouptut Voltage VOS Output Common Mode Voltage LOW POWER LVDS VOD Differential Ouptut Voltage VOS Output Common Mode Voltage
U
U
MIN 0.2
TYP
MAX
UNITS V V V k pF V V A pF
Internally Set Externally Set (Note 7) (See Figure 2) (Note 7) VDD = 3.3V VDD = 3.3V VIN = 0V to VDD (Note 7)

1.6 TBD 6 3 2 0.8 10 1.5
VDD = 3.3V VDD = 3.3V VOUT = 0V VOUT = 3.3V VDD = 3.3V VDD = 3.3V VDD = 3.3V VDD = 3.3V
IO = -10A IO = -200A IO = 160A IO = 1.6mA
3.1
3.299 3.29 0.01 0.10 -50 50 2.49 0.1 1.79 0.1
0.4
V V V V mA mA V V V V
IO = -200A IO = 1.60mA IO = -200A IO = 1.60mA
100 Differential Load 100 Differential Load 100 Differential Load 100 Differential Load

247 1.125 150 1.125
350 1.2 200 1.2
454 1.375 250 1.375
mV V mV V
2208f
5
LTC2208 POWER REQUIRE E TS
SYMBOL PARAMETER VDD Analog Supply Voltage PSHDN Shutdown Power STANDARD LVDS OUTPUT MODE OVDD Output Supply Voltage IVDD Analog Supply Current IOVDD Analog Supply Current PDIS Power Dissipation LOW POWER LVDS OUTPUT MODE OVDD Output Supply Voltage IVDD Analog Supply Current IOVDD Analog Supply Current PDIS Power Dissipation CMOS OUTPUT MODE OVDD Output Supply Voltage IVDD Analog Supply Current PDIS Power Dissipation
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. AIN = -1dBFS. (Note 9)
CONDITIONS
TI I G CHARACTERISTICS
SYMBOL fS tL tH
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 4)
PARAMETER Sampling Frequency ENC Low Time ENC High Time CONDITIONS
tAP Sample-and-Hold Aperture Delay LVDS OUTPUT MODE (STANDARD and LOW POWER) tD ENC to DATA Delay tC ENC to CLKOUT Delay tSKEW DATA to CLKOUT Skew tRISE Output Rise Time tFALL Output Fall Time Data Latency Data Latency CMOS OUTPUT MODE tD ENC to DATA Delay tC ENC to CLKOUT Delay tSKEW DATS to CLKOUT Skew Data Latency Data Latency
6
UW
MIN 3.135
SHDN = VDD

TYP 3.3 2 3.3 348 62 1350 3.3 348 31 1250
MAX 3.465
UNITS V mW V mA mA mW V mA mA mW V mA mW
3
3.6 383 69 1480 3.6 383 35 1375 3.6 383 1275
3
3
3.3 348 1150
UW
Duty Cycle Stabilizer Off Duty Cycle Stabilizer On Duty Cycle Stabilizer Off Duty Cycle Stabilizer On

MIN 1 3.65 2.6 3.65 2.6
TYP 3.846 3.846 3.846 3.846 -1 2.2 2.2 0 0.5 0.5 7 2.1 2.1 0 7 7
MAX 130 1000 1000 1000 1000
UNITS MHz ns ns ns ns ns ns ns ns ns ns Cycles ns ns ns Cycles Cycles
(Note 7) (Note 7) (tC-tD) (Note 7)

1.3 1.3 -0.6
3.5 3.5 0.6
(Note 7) (Note 7) (tC-tD) (Note 7) Full Rate CMOS Demuxed

1.3 1.3 -0.6
3.5 3.5 0.6
2208f
LTC2208 ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All voltage values are with respect to GND, with GND and OGND shorted (unless otherwise noted). Note 3: When these pin voltages are taken below GND or above VDD, they will be clamped by internal diodes. This product can handle input currents of greater than 100mA below GND or above VDD without latchup. Note 4: VDD = 3.3V, fSAMPLE = 130MHz, LVDS outputs, differential ENC+/ ENC- = 2VP-P sine wave with 1.6V common mode, input range = 2.25VP-P with differential drive (PGA = 0), unless otherwise specified. Note 5: Integral nonlinearity is defined as the deviation of a code from a "best fit straight line" to the transfer curve. The deviation is measured from the center of the quantization band. Note 6: Offset error is the offset voltage measured from -1/2LSB when the output code flickers between 0000 0000 0000 0000 and 1111 1111 1111 1111 in 2's complement output mode. Note 7: Guaranteed by design, not subject to test. Note 8: Recommended operating conditions.
ANALOG INPUT
ENC
-
ENC+ tD D0-D15, OF CLKOUT+ CLKOUT - tC N-7 N-6 N-5 N-4 N-3
W
LVDS Output Mode Timing All Outputs are Differential and Have LVDS Levels
tAP N+1 N+2 tL N+3 N+4 N tH
2208 TD01
TI I G DIAGRA UW
2208f
7
LTC2208 TI I G DIAGRA S W UW
Full-Rate CMOS Output Mode Timing All Outputs are Single-Ended and Have CMOS Levels
tAP ANALOG INPUT N+1 N+2 tH ENC- ENC+ tD N-7 tC N-6 N-5 N-4 N-3 tL N+3 N+4
N
DA0-DA15, OFA
CLKOUTA CLKOUTB
DB0-DB15, OFB
HIGH IMPEDANCE
2208 TD02
Demultiplexed CMOS Output Mode Timing All Outputs are Single-Ended and Have CMOS Levels
tAP ANALOG INPUT N tH ENC- ENC+ tD N-8 tD DB0-DB15, OFB tC
2208 TD03
N+1 N+2 tL N+3
N+4
DA0-DA15, OFA
N-6
N-4
N-7
N-5
N-3
CLKOUTA CLKOUTB
2208f
8
LTC2208 TYPICAL PERFOR A CE CHARACTERISTICS
Intergral Nonlinearity (INL) vs Output Code
2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 0 16384 32768 OUTPUT CODE 49152 65536 DNL ERROR (LSB) INL ERROR (LSB)
0 0.2 0.4 0.6 0.8 1 0 16384 49152 32768 OUTPUT CODE 65536
2208 G02
COUNT
64k Point FFT, FIN = 15.1MHz, -1dB, PGA = 0
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
0
10
50 20 40 30 FREQUENCY (MHz)
60
2208 G03
0
10
50 20 40 30 FREQUENCY (MHz)
60
2208 G04
AMPLITUDE (dBFS)
32k Point 2-Tone FFT, FIN = 21.14 MHz and 14.25MHz, -7dBFS, PGA = 0
0 -10 -20 -30 AMPLITUDE (dBFS) -40 -50 -60 -70 -80 -90 -100 -110 -120 0 10 50 20 40 30 FREQUENCY (MHz) 60
2208 G06
AMPLITUDE (dBFS)
-50 -60 -70 -80 -90 -100 -110 -120 0 10 50 20 40 30 FREQUENCY (MHz) 60
2208 G07
SFDR (dBFS)
UW
1 0.8 0.6 0.4 0.2
Differential Nonlinearity (DNL) vs Output Code
10000 9000 8000 7000 6000 5000 4000 3000 2000 1000
AC Grounded Input Histogram
0 32736 32740 32744 32748 32752 32756 OUTPUT CODE 2208 G14
64k Point FFT, 15.1MHz, -20dBFS, PGA = 0, Internal Dither "Off"
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
64k Point FFT, 15.1MHz, -20dBFS, PGA = 0, Internal Dither "On"
0
10
50 20 40 30 FREQUENCY (MHz)
60
2208 G05
32k Point 2-Tone FFT, FIN = 20.14 MHz and 14.25MHz, -25dBFS, PGA = 0
0 -10 -20 -30 -40
SFDR vs Input Level, FIN = 15MHz, PGA = 0, Dither "Off"
140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 -80 -70 -60 -50 -40 -30 -20 -10 0 INPUT LEVEL (dBFS) 2208 G08
2208f
9
LTC2208 TYPICAL PERFOR A CE CHARACTERISTICS
SFDR vs Input Level, fIN = 15MHz, PGA = 0, Dither "On"
140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 -80 -70 -60 -50 -40 -30 -20 -10 0 INPUT LEVEL (dBFS) 2208 G09 110 100 SFDR AND SNR (dBFS)
NORMALIZED FULL SCALE
SFDR (dBFS)
Input Offset Voltage vs Temperature, 5 Units
5 4 3 OFFSET VOLTAGE (mV) 2 IVDD (mA) 1 0 -1 -2 -3 -4 -5 -40 -20 0 20 40 60 TEMPERATURE (C) 80
2208 G12
380 360 340 320 300
AMPLITUDE (dBFS)
64K Point FFT, fIN = 30 MHz, -1dB, PGA = 0
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
0
10
40 30 20 50 FREQUENCY (MHz)
60
2208 G16
0
10
AMPLITUDE (dBFS)
10
UW
SNR and SFDR vs Duty Cycle
1.01
Normalized Full Scale vs Temperature, Internal Reference, 5 Units
1.005
90 80 SNR DCS OFF SNR DCS ON SFDR DCS OFF SFDR DCS ON 30 40 50 DUTY CYCLE (%) 60 70
1
70
0.995
60
0.99 -40
-20
0 20 40 60 TEMPERATURE (C)
80
2208 G11
IVDD vs Sample Rate, 5MHz Sine Wave, -1dB
420 400 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
64K Point FFT, fIN = 5 MHz, -1dB, PGA = 0
0
50 100 SAMPLE RATE (Msps)
150
2208 G13
0
10
40 30 20 50 FREQUENCY (MHz)
60
2208 G15
128K Point FFT, fIN = 30.1 MHz, -26dBFS, PGA = 0, Dither "On"
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
64K Point FFT, fIN = 70.1 MHz, -1dB, PGA = 0
40 30 20 50 FREQUENCY (MHz)
60
2208 G17
0
10
40 30 20 50 FREQUENCY (MHz)
60
2208 G18
2208f
LTC2208 TYPICAL PERFOR A CE CHARACTERISTICS
64K Point FFT, fIN = 70.1 MHz, -10dB, PGA = 0
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
0
10
40 30 20 50 FREQUENCY (MHz)
64K Point FFT, fIN = 70.1 MHz, -1dB, PGA = 1
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 105 100 AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
90 85 80 75 PGA = 0
PGA = 1
0
10
40 30 20 50 FREQUENCY (MHz)
60
2208 G22
70
AMPLITUDE (dBFS)
64K Point FFT, fIN1 = 67.2 MHz, -15dBFS, fIN2 = 74.4 MHz, -15dBFS, PGA = 0
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 0 -10 -20 -30 AMPLITUDE (dBFS) -40 -50 -60 -70 -80 -90 -100 -110 0 10 40 30 20 50 FREQUENCY (MHz) 60
2208 G25
AMPLITUDE (dBFS)
-120
0
10
AMPLITUDE (dBFS)
UW
60
64K Point FFT, fIN = 70.1 MHz, -20dB, PGA = 0
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
128K Point FFT, fIN = 70.1 MHz, -26dB, PGA = 0, Dither "On"
0
10
40 30 20 50 FREQUENCY (MHz)
60
2208 G20
0
10
40 30 20 50 FREQUENCY (MHz)
60
2208 G21
2208 G19
SFDR (HD2 and HD3) vs Input Frequency
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
64K Point FFT, fIN1 = 67.2 MHz, -7dBFS, fIN2 = 74.4 MHz, -7dBFS, PGA = 0
95
0
50
200 150 250 100 INPUT FREQUENCY (MHz)
300
2208 G23
0
10
40 30 20 50 FREQUENCY (MHz)
60
2208 G24
64K Point FFT, fIN = 140.1 MHz, -1dB, PGA = 1
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130
64K Point FFT, fIN = 140.1 MHz, -1dB, PGA = 0
40 30 20 50 FREQUENCY (MHz)
60
2208 G26
0
10
40 30 20 50 FREQUENCY (MHz)
60
2208 G27
2208f
11
LTC2208 TYPICAL PERFOR A CE CHARACTERISTICS
SFDR vs Input Level, fIN = 70.2MHz, PGA = 0, Dither "Off"
130 120 110 SFDR (dBc AND dBFS) SFDR (dBc AND dBFS) 100 90 80 70 60 50 40 30 -80 -70 -60 -50 -40 -30 -20 -10 INPUT LEVEL (dBFS) 0 130 120 110 SFDR (dBc AND dBFS) 100 90 80 70 60 50 40 30 -80 -70 -60 -50 -40 -30 -20 -10 INPUT LEVEL (dBFS) 0
SFDR vs Input Level, fIN = 140.2MHz, PGA = 1, Dither "On"
130 120 110 SFDR (dBc AND dBFS) 100 90 80 70 60 50 40
SNR AND SFDR (dBFS)
SNR AND SFDR (dBFS)
30 -80 -70 -60 -50 -40 -30 -20 -10 INPUT LEVEL (dBFS)
12
UW
SFDR vs Input Level, fIN = 70.2MHz, PGA = 0, Dither "On"
130 120 110 100 90 80 70 60 50 40
SFDR vs Input Level, fIN = 140.2MHz, PGA = 1, Dither "Off"
30 -80 -70 -60 -50 -40 -30 -20 -10 INPUT LEVEL (dBFS)
0
2208 G28
2208 G29
2208 G30
SNR and SFDR vs Sample Rate, fIN = 5MHz
110 105 100 95 90 85 80 75 0 70 0 25 50 75 100 125 150 175 200 SAMPLE RATE (Msps)
2208 G32
SNR and SFDR vs Supply Voltage (VDD), fIN = 5MHz
110 105 100 95 90 85 80 75 70 2.8 3 3.3 3.4 SUPPLY VOLTAGE (V) 3.6
2208 G33
LIMIT SFDR
LOWER
UPPER
SNR
SNR
2208 G31
2208f
LTC2208 PI FU CTIO S
For CMOS Mode. Full Rate or Demultiplexed SENSE (Pin 1): Reference Mode Select and External Reference Input. Tie SENSE to VDD to select the internal 2.5V bandgap reference. An external reference of 2.5V or 1.25V may be used; both reference values will set a full scale ADC range of 2.25V (PGA = 0). GND (Pins 2, 4, 7, 10, 11, 14, 18): ADC Power Ground. VCM (Pin 3): 1.25V Output. Optimum voltage for input common mode. Must be bypassed to ground with a minimum of 2.2F. Ceramic chip capacitors are recommended. VDD (Pins 5, 6, 15, 16, 17): 3.3V Analog Supply Pin. Bypass to GND with 1F ceramic chip capacitors. AIN+ (Pin 8): Positive Differential Analog Input. AIN- (Pin 9): Negative Differential Analog Input. ENC+ (Pin 12): Positive Differential Encode Input. The sampled analog input is held on the rising edge of ENC+. Internally biased to 1.6V through a 6.2k resistor. Output data can be latched on the falling edge of ENC+. ENC- (Pin 13): Negative Differential Encode Input. The sampled analog input is held on the falling edge of ENC -. Internally biased to 1.6V through a 6.2k resistor. Bypass to ground with a 0.1F capacitor for a single-ended Encode signal. SHDN (Pin 19): Power Shutdown Pin. SHDN = low results in normal operation. SHDN = high results in powered down analog circuitry and the digital outputs are placed in a high impedance state. DITH (Pin 20): Internal Dither Enable Pin. DITH = low disables internal dither. DITH = high enables internal dither. Refer to Internal Dither section of this data sheet for details on dither operation. DB0-DB15 (Pins 21-30 and 33-38): Digital Outputs, B Bus. DB15 is the MSB. Active in demultiplexed mode. The B bus is in high impedance state in full rate CMOS. OGND (Pins 31 and 50): Output Driver Ground. OVDD (Pins 32 and 49): Positive Supply for the Output Drivers. Bypass to ground with 1F capacitor. OFB (Pin 39): Over/Under Flow Digital Output for the B Bus. OFB is high when an over or under flow has occurred on the B bus. At high impedance state in full rate CMOS mode.
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CLKOUTB (Pin 40): Data Valid Output. CLKOUTB will toggle at the sample rate in full rate CMOS mode or at 1/2 the sample rate in demultiplexed mode. Latch the data on the falling edge of CLKOUTB. CLKOUTA (Pin 41): Inverted Data Valid Output. CLKOUTA will toggle at the sample rate in full rate CMOS mode or at 1/2 the sample rate in demultiplexed mode. Latch the data on the rising edge of CLKOUTA. DA0-DA15 (Pins 42-48 and 51-59): Digital Outputs, A Bus. DA15 is the MSB. Output bus for full rate CMOS mode and demultiplexed mode. OFA (Pin 60): Over/Under Flow Digital Output for the A Bus. OFA is high when an over or under flow has occurred on the A bus. LVDS (Pin 61): Data Output Mode Select Pin. Connecting LVDS to 0V selects full rate CMOS mode. Connecting LVDS to 1/3VDD selects demultiplexed CMOS mode. Connecting LVDS to 2/3VDD selects Low Power LVDS mode. Connecting LVDS to VDD selects Standard LVDS mode. MODE (Pin 62): Output Format and Clock Duty Cycle Stabilizer Selection Pin. Connecting MODE to 0V selects straight binary output format and disables the clock duty cycle stabilizer. Connecting MODE to 1/3VDD selects straight binary output format and enables the clock duty cycle stabilizer. Connecting MODE to 2/3VDD selects 2's complement output format and enables the clock duty cycle stabilizer. Connecting MODE to VDD selects 2's complement output format and disables the clock duty cycle stabilizer. RAND (Pin 63): Digital Output Randomization Selection Pin. RAND low results in normal operation. RAND high selects D1-D15 to be EXCLUSIVE-ORed with D0 (the LSB). The output can be decoded by again applying an XOR operation between the LSB and all other bits. This mode of operation reduces the effects of digital output interferance. PGA (Pin 64): Programmable Gain Amplifier Control Pin. Low selects a front-end gain of 1, input range of 2.25VP-P. High selects a front-end gain of 1.5, input range of 1.5VP-P. GND (Exposed Pad): ADC Power Ground. The exposed pad on the bottom of the package must be soldered to ground.
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LTC2208 PI FU CTIO S
For LVDS Mode. STANDARD or LOW POWER SENSE (Pin 1): Reference Mode Select and External Reference Input. Tie SENSE to VDD to select the internal 2.5V bandgap reference. An external reference of 2.5V or 1.25V may be used; both reference values will set a full scale ADC range of 2.25V (PGA = 0). GND (Pins 2, 4, 7, 10, 11, 14, 18): ADC Power Ground. VCM (Pin 3): 1.25V Output. Optimum voltage for input common mode. Must be bypassed to ground with a minimum of 2.2F. Ceramic chip capacitors are recommended. VDD (Pins 5, 6, 15, 16, 17): 3.3V Analog Supply Pin. Bypass to GND with 1F ceramic chip capacitors. AIN + (Pin 8): Positive Differential Analog Input. AIN - (Pin 9): Negative Differential Analog Input. ENC + (Pin 12): Positive Differential Encode Input. The sampled analog input is held on the rising edge of ENC+. Internally biased to 1.6V through a 6.2k resistor. Output data can be latched on the falling edge. ENC - (Pin 13): Negative Differential Encode Input. The sampled analog input is held on the falling edge of ENC -. Internally biased to 1.6V through a 6.2k resistor. Bypass to ground with a 0.1F capacitor for a single-ended Encode signal. SHDN (Pin 19): Power Shutdown Pin. SHDN = low results in normal operation. SHDN = high results in powered down analog circuitry and the digital outputs are set in high impedance state. DITH (Pin 20): Internal Dither Enable Pin. DITH = low disables internal dither. DITH = high enables internal dither. Refer to Internal Dither section of the data sheet for details on dither operation. D0-/D0+ to D15+/D15- (Pins 21-30, 33-38, 41-48 and 51-58): LVDS Digital Outputs. All LVDS outputs require differential 100 termination resistors at the LVDS receiver. D15+/D15- is the MSB.
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OGND (Pins 31 and 50): Output Driver Ground. OVDD (Pins 32 and 49): Positive Supply for the Output Drivers. Bypass to ground with 0.1F capacitor. CLKOUT+/CLKOUT - (Pins 39 and 40): LVDS Data Valid 0utput. Latch data on the rising edge of CLKOUT +, falling edge of CLKOUT -. OF+/OF- (Pins 59 and 60): Over/Under Flow Digital Output OF is high when an over or under flow has occurred. LVDS (Pin 61): Data Output Mode Select Pin. Connecting LVDS to 0V selects full rate CMOS mode. Connecting LVDS to 1/3VDD selects demultiplexed CMOS mode. Connecting LVDS to 2/3VDD selects Low Power LVDS mode. Connecting LVDS to VDD selects Standard LVDS mode. MODE (Pin 62): Output Format and Clock Duty Cycle Stabilizer Selection Pin. Connecting MODE to 0V selects straight binary output format and disables the clock duty cycle stabilizer. Connecting MODE to 1/3VDD selects straight binary output format and enables the clock duty cycle stabilizer. Connecting MODE to 2/3VDD selects 2's complement output format and enables the clock duty cycle stabilizer. Connecting MODE to VDD selects 2's complement output format and disables the clock duty cycle stabilizer. RAND (Pin 63): Digital Output Randomization Selection Pin. RAND low results in normal operation. RAND high selects D1-D15 to be EXCLUSIVE-ORed with D0 (the LSB). The output can be decoded by again applying an XOR operation between the LSB and all other bits. The mode of operation reduces the effects of digital output interferance. PGA (Pin 64): Programmable Gain Amplifier Control Pin. Low selects a front-end gain of 1, input range of 2.25VP-P. High selects a front-end gain of 1.5, input range of 1.5VP-P. GND (Exposed Pad Pin 65): ADC Power Ground. The exposed pad on the bottom of the package must be soldered to ground.
2208f
LTC2208 W
VDD
INPUT S/H
FIRST PIPELINED ADC STAGE
BLOCK DIAGRA
AIN+ AIN-
SECOND PIPELINED ADC STAGE
THIRD PIPELINED ADC STAGE
FOURTH PIPELINED ADC STAGE
FIFTH PIPELINED ADC STAGE
GND
DITHER SIGNAL GENERATOR
CORRECTION LOGIC AND SHIFT REGISTER
RANGE SELECT
SENSE
PGA
ADC CLOCKS
OVDD
CLKOUT+ CLKOUT- OF+ OF- D15+ D15-
ADC REFERENCE
VCM
BUFFER VOLTAGE REFERENCE
DIFFERENTIAL INPUT LOW JITTER CLOCK DRIVER
CONTROL LOGIC
OUTPUT DRIVERS
* * *
D0+ D0-
ENC+
ENC-
OGND
2208 F01
SHDN PGA RAND M0DE LVDS
DITH
Figure 1. Functional Block Diagram
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15
LTC2208
DYNAMIC PERFORMANCE Signal-to-Noise Plus Distortion Ratio The signal-to-noise plus distortion ratio [S/(N+D)] is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components at the ADC output. The output is band limited to frequencies above DC to below half the sampling frequency. Signal-to-Noise Ratio The signal-to-noise (SNR) is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components, except the first five harmonics. Total Harmonic Distortion Total harmonic distortion is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is expressed as: THD = -20Log(V22 + V32 + V42 + ... VN2)/V1 where V1 is the RMS amplitude of the fundamental frequency and V2 through VN are the amplitudes of the second through nth harmonics. Intermodulation Distortion If the ADC input signal consists of more than one spectral component, the ADC transfer function nonlinearity can produce intermodulation distortion (IMD) in addition to THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different frequency.
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If two pure sine waves of frequencies fa and fb are applied to the ADC input, nonlinearities in the ADC transfer function can create distortion products at the sum and difference frequencies of mfa nfb, where m and n = 0, 1, 2, 3, etc. For example, the 3rd order IMD terms include (2fa + fb), (fa + 2fb), (2fa - fb) and (fa - 2fb). The 3rd order IMD is defined as the ration of the RMS value of either input tone to the RMS value of the largest 3rd order IMD product. Spurious Free Dynamic Range (SFDR) Spurious Free Dynamic Range is difference between the peak harmonic or spurious noise that is the largest spectral component excluding the input signal and DC. This value is expressed in decibel relative to the RMS value of a full scale input signal. Full Power Bandwidth The Full Power bandwidth is that input frequency at which the amplitude of the reconstructed fundamental is reduced by 3dB for a full scale input signal. Aperture Delay Time The time from when a rising ENC + equals the ENC- voltage to the instant that the input signal is held by the sampleand-hold circuit. Aperture Delay Jitter The variation in the aperture delay time from convertion to conversion. This random variation will result in noise when sampling an AC input. The signal to noise ratio due to the jitter alone will be: SNRJITTER = -20log (2) * fIN * tJITTER
2208f
OPERATIO
LTC2208
CONVERTER OPERATION The LTC2208 is a CMOS pipelined multistep converter with a front-end PGA. As shown in Figure 1, the converter has five pipelined ADC stages; a sampled analog input will result in a digitized value seven cycles later (see the Timing Diagram section). The analog input is differential for improved common mode noise immunity and to maximize the input range. Additionally, the differential input drive will reduce even order harmonics of the sample and hold circuit. The encode input is also differential for improved common mode noise immunity. The LTC2208 has two phases of operation, determined by the state of the differential ENC+/ENC - input pins. For brevity, the text will refer to ENC+ greater than ENC - as ENC high and ENC+ less than ENC - as ENC low. Each pipelined stage shown in Figure 1 contains an ADC, a reconstruction DAC and an interstage amplifier. In operation, the ADC quantizes the input to the stage and the quantized value is subtracted from the input by the DAC to produce a residue. The residue is amplified and output by the residue amplifier. Successive stages operate out of phase so that when odd stages are outputting their residue, the even stages are acquiring that residue and vice versa. When ENC is low, the analog input is sampled differentially directly onto the input sample-and-hold capacitors, inside the "input S/H" shown in the block diagram. At the instant that ENC transitions from low to high, the voltage on the sample capacitors is held. While ENC is high, the held input voltage is buffered by the S/H amplifier which drives the first pipelined ADC stage. The first stage acquires the output of the S/H amplifier during the high phase of ENC. When ENC goes back low, the first stage produces its residue which is acquired by the second stage. At the same time, the input S/H goes back to acquiring the analog input. When ENC goes high, the second stage produces its residue which is acquired by the third stage. An identical process is repeated for the third and fourth stages, resulting in a fourth stage residue that is sent to the fifth stage for final evaluation. Each ADC stage following the first has additional range to accommodate flash and amplifier offset errors. Results from all of the ADC stages are digitally delayed such that the results can be properly combined in the correction logic before being sent to the output buffer.
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SAMPLE/HOLD OPERATION AND INPUT DRIVE Sample/Hold Operation Figure 2 shows an equivalent circuit for the LTC2208 CMOS differential sample and hold. The differential analog inputs are sampled directly onto sampling capacitors (CSAMPLE) through NMOS transitors. The capacitors shown attached to each input (CPARASITIC) are the summation of all other capacitance associated with each input. During the sample phase when ENC is low, the NMOS transistors connect the analog inputs to the sampling capacitors and they charge to, and track the differential input voltage. When ENC transitions from low to high, the sampled input voltage is held on the sampling capacitors. During the hold phase when ENC is high, the sampling capacitors are disconnected from the input and the held voltage is passed to the ADC core for processing. As ENC transitions for high to low, the inputs are reconnected to the sampling capacitors to acquire a new sample. Since the sampling capacitors still hold the previous sample, a charging glitch proportional to the change in voltage between samples will be seen at this time. If the change between the last sample and the new sample is small, the charging glitch seen at the input will be small. If the
LTC2208 VDD CSAMPLE 4.9pF CPARASITIC 1.8pF CSAMPLE 4.9pF CPARASITIC 1.8pF VDD AIN+ VDD AIN- 1.6V 6k ENC+ ENC- 6k 1.6V
2208 F02
APPLICATIO S I FOR ATIO W UU
Figure 2. Equivalent Input Circuit
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LTC2208
input change is large, such as the change seen with input frequencies near Nyquist, then a larger charging glitch will be seen. Common Mode Bias The ADC sample-and-hold circuit requires differential drive to achieve specified performance. Each input should swing 0.5625V for the 2.25V range (PGA = 0) or 0.375V for the 1.5V range (PGA = 1), around a common mode voltage of 1.25V. The VCM output pin (Pin 3) is designed to provide the common mode bias level. VCM can be tied directly to the center tap of a transformer to set the DC input level or as a reference level to an op amp differential driver circuit. The VCM pin must be bypassed to ground close to the ADC with 2.2F or greater. Input Drive Impedence As with all high performance, high speed ADCs the dynamic performance of the LTC2208 can be influenced by the input drive circuitry, particularly the second and third harmonics. Source impedance and input reactance can influence SFDR. At the falling edge of ENC the sample and hold circuit will connect the 4.9pf sampling capacitor to the input pin and start the sampling period. The sampling period ends when ENC rises, holding the sampled input on the sampling capacitor. Ideally, the input circuitry should be fast enough to fully charge the sampling capacitor during the sampling period 1/(2Fencode); however, this is not always possible and the incomplete settling may degrade the SFDR. The sampling glitch has been designed to be as linear as possible to minimize the effects of incomplete settling. For the best performance it is recommended to have a source impedence of 100 or less for each input. The source impedence should be matched for the differential inputs. Poor matching will result in higher even order harmonics, especially the second. INPUT DRIVE CIRCUITS Input Filtering A first order RC low pass filter at the input of the ADC can serve two functions: limit the noise from input circuitry and
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provide isolation from ADC S/H switching. The LTC2208 has a very broadband S/H circuit, DC to 700MHz; it can be used in a wide range of applications; therefore, it is not possible to provide a single recommended RC filter. Figures 3, 4a and 4b show three examples of input RC filtering at three ranges of input frequencies. In general it is desirable to make the capacitors as large as can be tolerated--this will help suppress random noise as well as noise coupled from the digital circuitry. The LTC2208 does not require any input filter to achieve data sheet specifications; however, no filtering will put more stringent noise requirements on the input drive circuitry. Transformer Coupled Circuits Figure 3 shows the LTC2208 being driven by an RF transformer with a center-tapped secondary. The secondary center tap is DC biased with VCM, setting the ADC input signal at its optimum DC level. Figure 3 shows a 1:1 turns ratio transformer. Other turns ratios can be used; however, as the turns ratio increases so does the impedance seen by the ADC. Source impedance greater than 50 can reduce the input bandwidth and increase high frequency distortion. A disadvantage of using a transformer is the loss of low frequency response. Most small RF transformers have poor performance at frequencies below 1MHz. Center-tapped transformers provide a convenient means of DC biasing the secondary; however, they often show poor balance at high input frequencies, resulting in large 2nd order harmonics.
VCM 2.2F 0.1F ANALOG INPUT T1 1:1 25 25 25 0.1F 12pF 25 AIN- 12pF
2208 F03
APPLICATIO S I FOR ATIO W UU
AIN+ 12pF
LTC2208
T1 = MA/COM ETC1-1T RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE EXCEPT 2.2F
Figure 3. Single-Ended to Differential Conversion Using a Transformer. Recommended for Input Frequencies from 5MHz to 50MHz
2208f
LTC2208
Figure 4a shows transformer coupling using a transmission line balun transformer. This type of transformer has much better high frequency response and balance than flux coupled center tap transformers. Coupling capacitors are added at the ground and input primary terminals to allow the secondary terminals to be biased at 1.25V. Figure 4b shows the same circuit with components suitable for higher input frequencies.
VCM 2.2F 0.1F ANALOG INPUT T1 1:1 0.1F 0.1F 4.7pF 4.7pF AIN+ LTC2208
AIN- 4.7pF
2208 F04a
T1 = MA/COM ETC1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE EXCEPT 2.2F
Figure 4a. Using a Transmission Line Balun Transformer. Recommended for Input Frequencies from 50MHz to 250MHz
VCM 2.2F 0.1F ANALOG INPUT T1 1:1 AIN- 2.2pF
2208 F04b
AIN+ 0.1F 2.2pF
0.1F
T1 = MA/COM ETC1-1-13 RESISTORS, CAPACITORS ARE 0402 PACKAGE SIZE EXCEPT 2.2F
Figure 4b. Using a Transmission Line Balun Transformer. Recommended for Input Frequencies from 250MHz to 500MHz
Direct Coupled Circuits Figure 5 demonstrates the use of a differential amplifier to convert a single ended input signal into a differential input signal. The advantage of this method is that it provides low frequency input response; however, the limited gain bandwidth of any op amp or closed-loop amplifier will degrade the ADC SFDR at high input frequencies. Additionally, wideband op amps or differential amplifiers tend to have
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high noise. As a result, the SNR will be degraded unless the noise bandwidth is limited prior to the ADC input.
VCM HIGH SPEED DIFFERENTIAL AMPLIFIER ANALOG INPUT 2.2F AIN+ 12pF LTC2208
APPLICATIO S I FOR ATIO W UU
+
CM
+ -
-
AIN- 12pF
2208 F05
AMPLIFIER = LTC6600-20, LTC1993, ETC.
Figure 5. DC Coupled Input with Differential Amplifier
Reference Operation Figure 6 shows the LTC2208 reference circuitry consisting of a 2.5V bandgap reference, a programmable gain amplifier and control circuit. The LTC2208 has three modes of reference operation: Internal Reference, 1.25V external reference or 2.5V external reference. To use the internal reference, tie the SENSE pin to VDD. To use an external reference, simply apply either a 1.25V or 2.5V reference voltage to the SENSE input pin. Both 1.25V and 2.5V applied to SENSE will result in a full scale range of 2.25VP-P (PGA = 0). A 1.25V output, VCM is provided for a common mode bias for input drive circuitry. An external bypass capacitor is required for the VCM output. This provides a high frequency low impedance path to ground for internal and external
RANGE SELECT AND GAIN CONTROL SENSE PGA
LTC2208
TIE TO VDD TO USE INTERNAL 2.5V REFERENCE OR INPUT FOR EXTERNAL 2.5V REFERENCE OR INPUT FOR EXTERNAL 1.25V REFERENCE
INTERNAL ADC REFERENCE
2.5V BANDGAP REFERENCE VCM 2.2F BUFFER 1.25V
Figure 6. Reference Circuit
2208 F06
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LTC2208
circuitry. This is also the compensation capacitor for the reference; it will not be stable without this capacitor. The minimum value required for stability is 2.2F. The internal programmable gain amplifier provides the internal reference voltage for the ADC. This amplifier has very stringent settling requirements and is not accessible for external use. The SENSE pin can be driven 5% around the nominal 2.5V or 1.25V external reference inputs. This adjustment range can be used to trim the ADC gain error or other system gain errors. When selecting the internal reference, the SENSE pin should be tied to VDD as close to the converter as possible. If the sense pin is driven externally it should be bypassed to ground as close to the device as possible with 1F ceramic capacitor.
1.25V VCM 2.2F 2 6 SENSE 2.2F LTC2208
3.3V 1F
LTC1461-2.5 4
2208 F07
Figure 7. A 2.25V Range ADC with an External 2.5V Reference
PGA Pin The PGA pin selects between two gain settings for the ADC front-end. PGA = 0 selects an input range of 2.25VP-P; PGA = 1 selects an input range of 1.5VP-P. The 2.25V input range has the best SNR; however, the distortion will be higher for input frequencies above 100MHz. For applications with high input frequencies, the low input range will have improved distortion; however, the SNR will be 1.8dB worse. See the typical performance curves section. Driving the Encode Inputs The noise performance of the LTC2208 can depend on the encode signal quality as much as for the analog input. The encode inputs are intended to be driven differentially, primarily for noise immunity from common mode noise
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sources. Each input is biased through a 6k resistor to a 1.6V bias. The bias resistors set the DC operating point for transformer coupled drive circuits and can set the logic threshold for single-ended drive circuits. Any noise present on the encode signal will result in additional aperture jitter that will be RMS summed with the inherent ADC aperture jitter. In applications where jitter is critical (high input frequencies), take the following into consideration: 1. Differential drive should be used. 2. Use as large an amplitude possible. If using transformer coupling, use a higher turns ratio to increase the amplitude. 3. If the ADC is clocked with a fixed frequency sinusoidal signal, filter the encode signal to reduce wideband noise. 4. Balance the capacitance and series resistance at both encode inputs such that any coupled noise will appear at both inputs as common mode noise. The encode inputs have a common mode range of 1.2V to VDD. Each input may be driven from ground to VDD for single-ended drive.
LTC2208 VDD TO INTERNAL ADC CLOCK DRIVERS VDD ENC+ 0.1F ENCODE INPUT T1 1:4 VDD 1.6V 6k ENC- 1.6V 6k
2208 F08
APPLICATIO S I FOR ATIO W UU
Figure 8. Transformer Driven Encode
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LTC2208
ENC+ 1.6V ENC- 0.1F
2208 F09
VTHRESHOLD = 1.6V
LTC2208
Figure 9. Single-Ended ENC Drive, Not Recommended for Low Jitter
3.3V MC100LVELT22 3.3V Q0 D0 ENC+ ENC- LTC2208
Q0
2208 F10
Figure 10. ENC Drive Using a CMOS to PECL Translator
Maximum and Minimum Encode Rates The maximum encode rate for the LTC2208 is 130Msps. For the ADC to operate properly the encode signal should have a 50% (5%) duty cycle. Each half cycle must have at least 3.65ns for the ADC internal circuitry to have enough settling time for proper operation. Achieving a precise 50% duty cycle is easy with differential sinusoidal drive using a transformer or using symmetric differential logic such as PECL or LVDS. When using a single-ended ENCODE signal asymmetric rise and fall times can result in duty cycles that are far from 50%. An optional clock duty cycle stabilizer can be used if the input clock does not have a 50% duty cycle. This circuit uses the rising edge of ENC pin to sample the analog input. The falling edge of ENC is ignored and an internal falling edge is generated by a phase-locked loop. The input clock duty cycle can vary from 30% to 70% and the clock duty cycle stabilizer will maintain a constant 50% internal duty cycle. If the clock is turned off for a long period of time, the duty cycle stabilizer circuit will require one hundred clock cycles for the PLL to lock onto the input clock. To use the clock duty cycle stabilizer, the MODE pin must be connected to 1/3VDD or 2/3VDD using external resistors.
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The lower limit of the LTC2208 sample rate is determined by droop of the sample and hold circuits. The pipelined architecture of this ADC relies on storing analog signals on small valued capacitors. Junction leakage will discharge the capacitors. The specified minimum operating frequency for the LTC2208 is 1Msps. DIGITAL OUTPUTS Digital Output Modes The LTC2208 can operate in four digital output modes: standard LVDS, low power LVDS, full rate CMOS, and demultiplexed CMOS. The LVDS pin selects the mode of operation. This pin has a four level logic input, centered at 0, 1/3VDD, 2/3VDD and VDD. An external resistor divider can be used to set the 1/3VDD and 2/3VDD logic levels. Table 1 shows the logic states for the LVDS pin.
Table 1. LVDS Pin Function
LVDS 0V(GND) 1/3VDD 2/3VDD VDD Digital Output Mode Full-Rate CMOS Demultiplexed CMOS Low Power LVDS LVDS
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Digital Output Buffers (CMOS Modes)
Figure 11 shows an equivalent circuit for a single output buffer in CMOS Mode, Full-Rate or Demultiplexed. Each buffer is powered by OVDD and OGND, isolated from the ADC power and ground. The additional N-channel transistor in the output driver allows operation down to low voltages. The internal resistor in series with the output makes the output appear as 50 to external circuitry and eliminates the need for external damping resistors. As with all high speed/high resolution converters, the digital output loading can affect the performance. The digital outputs of the LTC2208 should drive a minimum capacitive load to avoid possible interaction between the digital outputs and sensitive input circuitry. The output should be buffered with a device such as a ALVCH16373 CMOS latch. For full speed operation the capacitive load should be kept under 10pF. A resistor in series with the
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LTC2208
output may be used but is not required since the ADC has a series resistor of 43 on chip. Lower OVDD voltages will also help reduce interference from the digital outputs.
LTC2208 VDD VDD OVDD 0.5V TO VDD 0.1F OVDD DATA FROM LATCH PREDRIVER LOGIC TYPICAL DATA OUTPUT OGND
2208 F11
Figure 11. Equivalent Circuit for a Digital Output Buffer
Digital Output Buffers (LVDS Modes) Figure 12 shows an equivalent circuit for an LVDS output pair. A 3.5mA current is steered from OUT+ to OUT- or vice versa, which creates a 350mV differential voltage across the 100 termination resistor at the LVDS receiver. A feedback loop regulates the common mode output voltage to 1.20V. For proper operation each LVDS output pair must be terminated with an external 100 termination
LTC2208 3.5mA VDD VDD
DATA FROM LATCH
PREDRIVER LOGIC
Figure 12. Equivalent Output Buffer in LVDS Mode Low Power LVDS
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resistor, even if the signal is not used (such as OF+/OF- or CLKOUT+/CLKOUT-). To minimize noise the PC board traces for each LVDS output pair should be routed close together. To minimize clock skew all LVDS PC board traces should have about the same length. In Low Power LVDS Mode 1.75mA is steered between the differential outputs, resulting in 175mV at the LVDS receivers 100 termination resistor. The output common mode voltage is 1.20V, the same as standard LVDS Mode. Data Format The LTC2208 parallel digital output can be selected for offset binary or 2's complement format. The format is selected with the MODE pin. This pin has a four level logic input, centered at 0, 1/3VDD, 2/3VDD and VDD. An external resistor divider can be user to set the 1/3VDD and 2/3VDD logic levels. Table 2 shows the logic states for the MODE pin.
Table 2. MODE Pin Function
MODE 0(GND) 1/3VDD 2/3VDD VDD Output Format Straight Binary Straight Binary 2's Complement 2's Complement Clock Duty Cycle Stabilizer Off On On Off
OVDD 3.3V 0.1F OVDD 43 10k 10k OVDD 43 100 LVDS RECEIVER 1.20V
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+ -
2208 F12
OGND
LTC2208
Overflow Bit An overflow output bit (OF) indicates when the converter is over-ranged or under-ranged. In CMOS mode, a logic high on the OFA pin indicates an overflow or underflow on the A data bus, while a logic high on the OFB pin indicates an overflow on the B data bus. In LVDS mode, a differential logic high on OF+/OF- pins indicates an overflow or underflow. Output Clock The ADC has a delayed version of the encode input available as a digital output, CLKOUT. The CLKOUT pin can be used to synchronize the converter data to the digital system. This is necessary when using a sinusoidal encode. In both CMOS modes, A bus data will be updated as CLKOUTA falls and CLKOUTB rises. In demultiplexed CMOS mode the B bus data will be updated as CLKOUTA falls and CLKOUTB rises. In Full Rate CMOS Mode, only the A data bus is active; data may be latched on the rising edge of CLKOUTA or the falling edge of CLKOUTB. In demultiplexed CMOS mode CLKOUTA and CLKOUTB will toggle at 1/2 the frequency of the encode signal. Both the A bus and the B bus may be latched on the rising edge of CLKOUTA or the falling edge of CLKOUTB. Digital Output Randomizer Interference from the ADC digital outputs is sometimes unavoidable. Interference from the digital outputs may be from capacitive or inductive coupling or coupling through the ground plane. Even a tiny coupling factor can result in discernible unwanted tones in the ADC output spectrum. By randomizing the digital output before it is transmitted off chip, these unwanted tones can be randomized, trading a slight increase in the noise floor for a large reduction in unwanted tone amplitude. The digital output is "Randomized" by applying an exclusive-OR logic operation between the LSB and all other data output bits. To decode, the reverse operation is applied; that is, an exclusive-OR operation is applied between the
D15 D15/D0
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LSB and all other bits. The LSB, OF and CLKOUT output are not affected. The output Randomizer function is active when the RAND pin is high.
CLKOUT CLKOUT OF OF D14 D14/D0 D2
APPLICATIO S I FOR ATIO W UU
* * *
D2/D0
D1
D1/D0
RAND = HIGH, SCRAMBLE ENABLED
RAND
D0
2208 F13
D0
Figure 13. Functional Equivalent of Digital Output Randomizer
Output Driver Power Separate output power and ground pins allow the output drivers to be isolated from the analog circuitry. The power supply for the digital output buffers, OVDD, should be tied to the same power supply as for the logic being driven. For example, if the converter is driving a DSP powered by a 1.8V supply, then OVDD should be tied to that same 1.8V supply. In CMOS mode OVDD can be powered with any logic voltage up to the VDD of the ADC. OGND can be powered with any voltage from ground up to 1V and must be less than OVDD. The logic outputs will swing between OGND and OVDD. In LVDS Mode, OVDD should be connected to a 3.3V supply and OGND should be connected to GND.
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LTC2208
PC BOARD FPGA CLKOUT
OF
D15/D0 D15 LTC2208 D14/D0 D14
D2/D0
* * *
D1/D0 D1
D0
Figure 14. Descrambling a Scrambled Digital Output
LTC2208 AIN+ ANALOG INPUT AIN
-
ANALOG SUMMATION S/H AMP
CLOCK/DUTY CYCLE CONTROL
ENC
ENC
Figure 15. Functional Equivalent Block Diagram of Internal Dither Circuit
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Internal Dither The LTC2208 is a 16-bit ADC with a very linear transfer function; however, at low input levels even slight imperfections in the transfer function will result in unwanted tones. Small errors in the transfer function are usually a result of ADC element mismatches. An optional internal dither mode can be enabled to randomize the input location on the ADC transfer curve, resulting in improved SFDR for low signal levels. As shown in Figure 15, the output of the sample-and-hold amplifier is summed with the output of a dither DAC. The dither DAC is driven by a long sequence pseudo-random number generator; the random number fed to the dither DAC is also subtracted from the ADC result. If the dither DAC is precisely calibrated to the ADC, very little of the dither signal will be seen at the output. The dither signal that does leak through will appear as white noise. The dither DAC is calibrated to result in less than 0.5dB elevation in the noise floor of the ADC, as compared to the noise floor with dither off.
D2 D0
2208 F14
APPLICATIO S I FOR ATIO W UU
16-BIT PIPELINED ADC CORE
DIGITAL SUMMATION
OUTPUT DRIVERS
CLKOUT OF D15 * * * D0
PRECISION DAC
MULTIBIT DEEP PSEUDO-RANDOM NUMBER GENERATOR
2208 F15
DITH DITHER ENABLE HIGH = DITHER ON LOW = DITHER OFF
LTC2208
Grounding and Bypassing The LTC2208 requires a printed circuit board with a clean unbroken ground plane; a multilayer board with an internal ground plane is recommended. The pinout of the LTC2208 has been optimized for a flowthrough layout so that the interaction between inputs and digital outputs is minimized. Layout for the printed circuit board should ensure that digital and analog signal lines are separated as much as possible. In particular, care should be taken not to run any digital track alongside an analog signal track or underneath the ADC. High quality ceramic bypass capacitors should be used at the VDD, VCM, and OVDD pins. Bypass capacitors must be located as close to the pins as possible. The traces
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connecting the pins and bypass capacitors must be kept short and should be made as wide as possible. The LTC2208 differential inputs should run parallel and close to each other. The input traces should be as short as possible to minimize capacitance and to minimize noise pickup. Heat Transfer Most of the heat generated by the LTC2208 is transferred from the die through the bottom-side exposed pad. For good electrical and thermal performance, the exposed pad must be soldered to a large grounded pad on the PC board. It is critical that the exposed pad and all ground pins are connected to a ground plane of sufficient area with as many vias as possible.
Evaluation Boards
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APPLICATIO S I FOR ATIO W U U
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LTC2208 U
UP Package 64-Lead Plastic QFN (9mm x 9mm)
(Reference LTC DWG # 05-08-1705)
0.70 0.05 7.15 0.05 8.10 0.05 9.50 0.05 (4 SIDES)
PACKAGE DESCRIPTIO
PACKAGE OUTLINE
0.25 0.05 0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
9 .00 0.10 (4 SIDES)
0.75 0.05
R = 0.115 TYP
63 64 0.40 0.10 1 2
PIN 1 TOP MARK (SEE NOTE 5)
PIN 1 CHAMFER
7.15 0.10 (4-SIDES)
0.200 REF
0.25 0.05 0.50 BSC
(UP64) QFN 1003
0.00 - 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION WNJR-5 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE, IF PRESENT 4. EXPOSED PAD SHALL BE SOLDER PLATED 5. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 6. DRAWING NOT TO SCALE
BOTTOM VIEW--EXPOSED PAD
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LTC2208 U
COMMENTS 72dB SNR, 87dB SFDR, 48-Pin TSSOP Package 76.3dB SNR, 90dB SFDR, 48-Pin TSSOP Package Up to 500MHz IF Undersampling, 87dB SFDR Up to 500MHz IF Undersampling, 90dB SFDR 600MHz BW, 75dBc Distortion at 70MHz 350mW, 79dB SNR, 100dB SFDR 450mW, 79dB SNR, 100dB SFDR 650mW, 78dB SNR, 100dB SFDR 850mW, 78dB SNR, 100dB SFDR 1200mW, 78dB SNR, 100dB SFDR 890mW, 67.5dB SNR, 9mm x 9mm QFN Package 910mW, 67.5dB SNR, 9mm x 9mm QFN Package 230mW, 73dB SNR, 5mm x 5mm QFN Package 320mW, 61.6dB SNR, 5mm x 5mm QFN Package 395mW, 61.6dB SNR, 5mm x 5mm QFN Package 320mW, 70.2dB SNR, 5mm x 5mm QFN Package 395mW, 70.2dB SNR, 5mm x 5mm QFN Package 320mW, 72.5dB SNR, 5mm x 5mm QFN Package 395mW, 72.4dB SNR, 5mm x 5mm QFN Package 445mW, 73dB SNR, 9mm x 9mm QFN Package DC to 3GHz, 21dBm IIP3, Integrated LO Buffer 450MHz 1dB BW, 47dB OIP3, Digital Gain Control 10.5dB to 33dB in 1.5dB/Step 4.5V to 5.25V Supply, 25dBm IIP3 at 900MHz, NF = 12.5dB, 50 Single-Ended RF and LO Ports
2208f
TYPICAL APPLICATIO
RELATED PARTS
PART NUMBER LTC1747 LTC1748 LTC1749 LTC1750 LT1993 LTC2204 LTC2205 LTC2206 LTC2207 LTC2208 LTC2220 LTC2220-1 LTC2249 LTC2250 LTC2251 LTC2252 LTC2253 LTC2254 LTC2255 LTC2299 LT5512 LT5514 LT5522 DESCRIPTION 12-Bit, 80MSPS ADC 14-Bit, 80Msps ADC 12-Bit, 80Msps Wideband ADC 14-Bit, 80Msps Wideband ADC High Speed Differential Op Amp 16-Bit, 40Msps ADC 16-Bit, 65Msps ADC 16-Bit, 80Msps ADC 16-Bit, 105Msps ADC 16-Bit, 130Msps ADC 12-Bit, 170Msps ADC 12-Bit, 185Msps ADC 14-Bit, 65Msps ADC 10-Bit, 105Msps ADC 10-Bit, 125Msps ADC 12-Bit, 105Msps ADC 12-Bit, 125Msps ADC 14-Bit, 105Msps ADC 14-Bit, 125Msps ADC Dual 14-Bit, 80Msps ADC DC-3GHz High Signal Level Downconverting Mixer Ultralow Distortion IF Amplifier/ADC Driver with Digitally Controlled Gain 600MHz to 2.7GHz High Linearity Downconverting Mixer
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
LT/TP 0805 500 * PRINTED IN USA
FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2005
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