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19-1493; Rev 0; 7/99
ANUAL N KIT M LUATIO ATA SHEET EVA WS D FOLLO
Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer
General Description Features
o 800MHz to 1000MHz RF Frequency Range o +2.7V to +5.5V Single-Supply Operation o Integrated LNA + Mixer + LO Buffer o Logic-Controlled LNA Bypass Switch Reduces Supply Current o LNA Performance (High/Low Gain) Gain: +15dB/-12dB NF: 1.4dB/12dB Input IP3: -4dBm/+16dBm o Mixer Performance (High/Low Gain) Gain: 6dB/4.6dB NF: 13dB/12dB Input IP3: +7dBm/-1.5dBm o Supply Current 8.5mA (High Gain) 3.8mA (Low Gain) o <0.1A Supply Current in Shutdown Mode o 0.8s Receiver Enable Time
MAX2685
The MAX2685's low-noise amplifier (LNA) and downconverter mixer comprise the major blocks of an RF front-end receiver. Optimized for 900MHz operation, the device's low noise figure, high gain, and high linearity make it ideal for cellular, cordless, and wireless data applications. A low supply current of 8.5mA (high-gain mode) and 3.8mA (low-gain mode) plus a low operating supply voltage range of +2.7V to +5.5V make it suitable for use in 3-cell NiCd or 1-cell lithium-ion (Li+) battery applications. A low-power shutdown mode further extends battery life by reducing supply current below 0.1A. The MAX2685 includes an LNA, LNA bypass switch, downconverter mixer, and local-oscillator (LO) buffer. The LNA has a low noise figure of 1.4dB, a high gain of 15dB, and an input third-order intercept point (IP3) of -4dBm. The mixer has a noise figure of 13dB, a gain of 6dB, and an input IP3 of +7dBm. In addition, an LNA bypass switch allows two levels of gain, reducing power consumption when high gain is not needed. The downconverter mixer has a single-ended RF input port and differential IF output ports. Differential operation of the IF ports offers improved even-order harmonic rejection and increased immunity to noise. An LO buffer allows the LO port to be driven with only -8dBm of LO power. The MAX2685 is offered in a space-saving 16pin QSOP package.
Ordering Information
PART MAX2685EEE TEMP. RANGE -40C to +85C PIN-PACKAGE 16 QSOP
Applications
Cellular/Cordless Phones Wireless Data 900MHz ISM-Band Radios 868MHz European ISM Band
Pin Configuration
TOP VIEW
Functional Diagram
LNAOUT MIXIN LNA
GND LNAIN GND GAIN VCC SHDN LO GND
1 2 3 4 5 6 7 8
16 15 14 13 12
LNAOUT VCC GND MIXIN GND GND IFOUT+ IFOUTGAIN LNAIN
MIXER IFOUT+ IFOUTLNA BYPASS
MAX2685
11 10 9
MAX2685
VCC SHDN GND POWER MANAGEMENT
LO BUFFER
QSOP
LO
________________________________________________________________ Maxim Integrated Products
1
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Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer MAX2685
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V LNAIN Input Power (50 source)...................................+10dBm LO Input Power (50 source) ........................................+10dBm MIXIN Input Power (50 source) ...................................+10dBm IFOUT+, IFOUT- to GND ..........................................-0.3V to +6V LNAOUT to GND ......................................................-0.3V to +6V GAIN, SHDN to GND..................................-0.3V to (VCC + 0.3V) Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derate 8.3mW/C above +70C)............667mW Junction Temperature ......................................................+150C Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(VCC = +2.7V to +5.5V, V SHDN = +2V, VGAIN = +2V, LNAIN = LNAOUT = MIXIN = LO = unconnected, IFOUT+ = IFOUT- = VCC, TA = -40C to +85C. Typical values are at TA = +25C and VCC = +3V, unless otherwise noted.) PARAMETER Supply Voltage Range Operating Supply Current Shutdown Supply Current Logic Input Voltage High Logic Input Voltage Low Logic Input Current GAIN = VCC GAIN = GND SHDN = GND GAIN, SHDN GAIN, SHDN V SHDN = VGAIN = 0 to 5.5V 0.01 2.0 0.5 1 CONDITIONS MIN 2.7 8.5 3.8 0.1 TYP MAX 5.5 14.1 6.4 1.0 UNITS V mA A V V A
AC ELECTRICAL CHARACTERISTICS
(MAX2685 EV kit, VCC = V SHDN = +3V, fLNAIN = fMIXIN = 880MHz, fLO = 960MHz, PLNAIN = -30dBm, PLO = -8dBm, PMIXIN = -25dBm, differential IFOUT operation, Zo = 50, TA = +25C, unless otherwise noted.) PARAMETER LOW-NOISE AMPLIFIER (LNA) RF Frequency Range (Note 1) LNA Gain LNA Gain Variation over Temperature LNA Noise Figure LNA Input IP3 LNA Input 1dB Compression LNAOUT Port Return Loss DOWNCONVERTER MIXER RF Frequency Range (Note 1) Mixer Conversion Gain GAIN = VCC GAIN = GND 800 4.7 2.5 6.1 4.6 1000 7.0 6.0 MHz dB GAIN = VCC GAIN = GND GAIN = VCC, TA = TMIN to TMAX (Note 2) GAIN = VCC GAIN = GND GAIN = VCC (Note 3) GAIN = GND (Note 4) GAIN = VCC GAIN = VCC GAIN = GND 800 13 -14 15 -12 0.9 1.4 12.2 -4.1 +16.2 -18.4 -18.6 -11.3 1000 16.2 -10.3 1.6 MHz dB dB dB dBm dBm dB CONDITIONS MIN TYP MAX UNITS
2
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Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2685 EV kit, VCC = V SHDN = +3V, fLNAIN = fMIXIN = 880MHz, fLO = 960MHz, PLNAIN = -30dBm, PLO = -8dBm, PMIXIN = -25dBm, differential IFOUT operation, Zo = 50, TA = +25C, unless otherwise noted.) PARAMETER Mixer Conversion Gain Variation over Temperature Mixer Noise Figure (SSB) Mixer Input IP3 (Note 5) LO Port Return Loss LO-to-LNAIN Isolation LO-to-MIXIN Isolation LNAOUT-to-MIXIN Isolation OVERALL SYSTEM Receiver Enable Time Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: (Note 6) 0.8 s SHDN = VCC or GND CONDITIONS GAIN = VCC, TA = TMIN to TMAX (Note 2) GAIN = VCC GAIN = GND GAIN = VCC GAIN = GND MIN TYP 1 13 12.1 7 -1.5 11 53 31 28 MAX 2 UNITS dB dB dBm dB dB dB dB
MAX2685
This is the recommended operating frequency range. Maximum and minimum limits are guaranteed by design and device characterization and are not production tested. Two tones at 880MHz and 880.1MHz, -30dBm per tone. Two tones at 880MHz and 880.1MHz, -10dBm per tone. Two tones at 880MHz and 880.1MHz, -25dBm per tone. Time from SHDN = high, until the cascaded receive gain is within 1dB of its final value. Measured with 47pF blocking capacitors on LNAIN and LNAOUT. Matching network removed from IFOUT output.
Typical Operating Characteristics
(MAX2685 EV kit, VCC = V SHDN = +3V, fLNAIN = fMIXIN = 880MHz, fLO = 960MHz, PLNAIN = -30dBm, PLO = -8dBm, PMIXIN = -25dBm, differential IFOUT operation, Zo = 50, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX2685 toc01
SHUTDOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX2685 toc02
LNA GAIN vs. SUPPLY VOLTAGE
GAIN = HIGH 15 10 TA = +25C TA = -40C TA = +85C
MAX2685 toc03
10 9 8 SUPPLY CURRENT (mA) 7 6 5 4 3 2 1 0 2.5 3.0 3.5 4.0 4.5 5.0 GAIN = LOW TA = +25C TA = -40C GAIN = HIGH TA = +85C TA = -40C TA = +85C TA = +25C
10 SHUTDOWN SUPPLY CURRENT (nA) 9 8 7 TA = +85C SHDN = GND
20
GAIN (dB)
6 5 4 3 2 1 0
5 0 -5 -10 TA = +25C T = -40C A GAIN = LOW TA = +85C
TA = +25C
TA = -40C 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
-15 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
5.5
SUPPLY VOLTAGE (V)
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Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer MAX2685
Typical Operating Characteristics (continued)
(MAX2685 EV kit, VCC = V SHDN = +3V, fLNAIN = fMIXIN = 880MHz, fLO = 960MHz, PLNAIN = -30dBm, PLO = -8dBm, PMIXIN = -25dBm, differential IFOUT operation, Zo = 50, TA = +25C, unless otherwise noted.)
LNA INPUT IP3 vs. SUPPLY VOLTAGE
GAIN = LOW TA = +25C TA = +85C GAIN (dB)
MAX2685 toc04
LNA GAIN vs. FREQUENCY
15 10 5 0 -5 NOISE FIGURE (dB) GAIN = HIGH
MAX2685 toc05
LNA NOISE FIGURE vs. FREQUENCY
1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2
MAX2685 toc06
20 15
20
2.0
TA = -40C INPUT IP3 (dBm) 10 5 0 -5 -10 2.5 3.0 TA = -40C 3.5 4.0 TA = +25C
GAIN = HIGH
TA = +85C
-10 -15 GAIN = LOW
1.1 1.0 870 880 890 900 910 920 930 940 950 960 FREQUENCY (MHz)
4.5
5.0
5.5
-20 800 825 850 875 900 925 950 975 1000 FREQUENCY (MHz)
SUPPLY VOLTAGE (V)
LNA REVERSE ISOLATION vs. FREQUENCY
MAX2685 toc07
LNA INPUT RETURN LOSS vs. FREQUENCY
MAX2685 toc08
LNA OUTPUT RETURN LOSS vs. FREQUENCY
-2 OUTPUT RETURN LOSS (dB) -4 -6 -8 -10 -12 -14 -16 -18 -20 GAIN = HIGH 800 840 880 920 960 1000 GAIN = LOW
MAX2685 toc09
0 -5 REVERSE ISOLATION (dB) -10 -15 -20 -25 -30 -35 GAIN = HIGH GAIN = LOW
-5 -6 INPUT RETURN LOSS (dB) -7 -8 -9 -10 -11 -12 -13 -14 -15 800 840 880 920 960 GAIN = LOW GAIN = HIGH
0
-40 800 825 850 875 900 925 950 975 1000 FREQUENCY (MHz)
1000
FREQUENCY (MHz)
FREQUENCY (MHz)
MAX2685 toc11
MAX2685 toc10
6.5 6.0
TA = -40C
GAIN = HIGH
8 6 INPUT IP3 (dBm) 4
TA = +85C TA = +25C GAIN = HIGH TA = -40C
TA = +25C GAIN (dB) 5.5 5.0 4.5 4.0 3.5 800 HI LO 3.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) TA = +25C TA = +85C TA = +85C TA = -40C
GAIN = LOW
2 TA = +85C 0 -2 -4 -6 -8 -10 2.5 3.0
TA = +25C GAIN = LOW TA = -40C
GAIN = LOW 1000 800 1000 GAIN = HIGH
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
4
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MAX2685 toc12
LNA S11 vs. FREQUENCY (800MHz to 1000MHz UNMATCHED)
MIXER GAIN vs. SUPPLY VOLTAGE
7.0 10
MIXER INPUT IP3 vs. SUPPLY VOLTAGE
Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer
Typical Operating Characteristics (continued)
(MAX2685 EV kit, VCC = V SHDN = +3V, fLNAIN = fMIXIN = 880MHz, fLO = 960MHz, PLNAIN = -30dBm, PLO = -8dBm, PMIXIN = -25dBm, differential IFOUT operation, Zo = 50, TA = +25C, unless otherwise noted.)
MAX2685
MIXER GAIN vs. IF FREQUENCY
MAX2685 toc13
MIXER GAIN vs. LO POWER
GAIN = HIGH
MAX2685 toc14
8 6 4 2 GAIN = HIGH
7 6 5 GAIN (dB) 4 3 2 GAIN = LOW
GAIN (dB)
0 -2 -4 -6 -8 -10 -12 60 70 BANDWIDTH DETERMINED BY DIFFERENTIAL-TO-SINGLE-ENDED CONVERTER CIRCUIT 80 IF FREQUENCY (MHz) 90 100 GAIN = LOW
1 0 -15 -10 -5 0 LO POWER (dBm)
MIXER NOISE FIGURE vs. LO POWER
MAX2685 toc15
LO PORT RETURN LOSS vs. FREQUENCY
-6 -7 RETURN LOSS (dB) -8 -9 -10 -11 -12 -13 -14 -15
MAX2685 toc16
15.0 14.5 14.0 NOISE FIGURE (dB) 13.5 13.0 12.5 12.0 11.5 11.0 10.5 10.0 -15 -10 -5 GAIN = HIGH GAIN = LOW
-5
0
750
800
850
900
950
1000 1050 1100
LO POWER (dBm)
FREQUENCY (MHz)
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Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer MAX2685
Pin Description
PIN 1, 3, 8, 11, 12, 14 2 NAME GND LNAIN FUNCTION Ground. Connect to ground plane with a low-inductance connection. RF Input to LNA and LNA Bypass Switch. Requires an external matching network and a series DC-blocking capacitor. Gain Control Logic-Level Input. Drive high to enable the LNA, open the LNA bypass switch, and increase the receiver's gain. Drive low to disable the LNA, close the LNA bypass switch, and reduce the receiver's gain. Supply Voltage. Bypass VCC to GND at each pin with a 47pF capacitor as close to the pin as possible. Shutdown Control Logic-Level Input. Drive high or connect to VCC for normal operation. Drive low to place the device in low-power shutdown mode. Local-Oscillator Input to Downconverter Mixer. Requires a series DC-blocking capacitor and an impedance-setting resistor (typically 75 to ground). Inverting Side to Downconverter Mixer's Differential Open-Collector IF Output. Requires a pull-up inductor to VCC for proper biasing, as well as a matching network to ensure optimum output power. Noninverting Side of Downconverter Mixer's Differential Open-Collector IF Output. Requires a pull-up inductor to VCC for proper biasing, as well as a matching network to ensure optimum output power. RF Input to Downconverter Mixer. Requires an external matching network and series DC-blocking capacitor. LNA Output. Internally matched to 50. LNAOUT has an internal blocking capacitor.
4 5, 15 6 7 9 10 13 16
GAIN VCC SHDN LO IFOUTIFOUT+ MIXIN LNAOUT
300pF 1 LNA INPUT 880MHz 0.1F 12nH 2 3 GAINCONTROL INPUT VCC 47pF SHUTDOWN INPUT 330pF LO INPUT 960MHz 6 SHDN 4 5 GND LNAIN GND GAIN VCC LNAOUT VCC GND MIXIN 16 15 14 300pF 13 3.3pF MIXER INPUT 880MHz LNA OUTPUT VCC 47pF
MAX2685
GND GND IFOUT+ 12 11 12pF 10 R* 680nH 820nH IF OUTPUT 80MHz VCC 1000pF 6pF 6pF
7
LO 9
75
8
GND
IFOUT-
*OPTIONAL FOR BROADBAND MATCH.
Figure 1. Typical Operating Circuit
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Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer
Detailed Description
The MAX2685 consists of five major components: a low-noise amplifier (LNA), an LNA bypass switch, a downconverter mixer, a local-oscillator (LO) buffer, and a power-management block.
LNA Bypass Switch and Gain Control
When a large input signal is present, enable the LNA bypass function to increase linearity and reduce supply current. Set GAIN low to enable the LNA bypass function.
MAX2685
Low-Noise Amplifier (LNA)
The LNA is a wideband, single-ended cascode amplifier that operates over a wide range of frequencies. The input of the LNA (LNAIN) requires an appropriate matching network and a DC-blocking capacitor. The typical operating circuit shown in Figure 1 is optimized for frequencies around 880MHz, requiring only a 0.1F capacitor in series with a 12nH inductor. See Table 1 for the LNA "S" parameters for matching to other frequencies. The output of the LNA (LNAOUT) is internally biased to VCC. It is internally matched to 50 and incorporates an internal DC-blocking capacitor.
Receive Mixer
The downconverter mixer is a wideband, single-balanced design with a low noise figure and high linearity. The RF signal at the MIXIN port is mixed with the signal at the LO port, and is downconverted to an IF frequency at the differential IF port.
RF Input The MIXIN input requires a simple external matching network and a series DC-blocking capacitor. See Figure 1 for a matching network example, optimized for 880MHz operation. Table 2 lists mixer "S" parameters for matching to other frequencies.
Table 1. LNA Typical S-Parameters (VCC = +3V, TA = +25C)
FREQUENCY (MHz)
|S11|
MAG
S11 PHASE (degrees)
|S21|
MAG
S21 PHASE (degrees)
|S12|
MAG
S12 PHASE (degrees)
|S22|
MAG
S22 PHASE (degrees)
High-Gain Mode (GAIN = VCC) 800 840 880 920 960 1000 800 840 880 920 960 1000 0.761 0.753 0.747 0.733 0.719 0.693 0.625 0.621 0.619 0.611 0.608 0.607 -64.5 -68.6 -73.2 -78.0 -82.8 -87.5 -45.6 -48.1 -50.9 -53.3 -55.5 -57.5 4.98 5.06 5.07 4.91 4.68 4.40 0.188 0.195 0.199 0.200 0.200 0.200 177.9 167.2 156.6 146.6 137.7 130.3 73.0 65.5 58.1 51.6 46.1 41.2 0.018 0.022 0.026 0.030 0.035 0.039 0.191 0.198 0.201 0.202 0.201 0.200 -163.7 -167.1 -171.3 -175.7 178.0 171.0 71.9 64.2 56.7 50.3 44.7 40.0 0.376 0.264 0.172 0.149 0.200 0.263 0.483 0.423 0.370 0.337 0.322 0.317 -107.3 -107.0 -94.6 -62.9 -42.4 -38.8 -91.3 -91.3 -89.9 -86.1 -80.9 -76.7
Low-Gain Mode (GAIN = GND)
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Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer MAX2685
Table 2. Mixer Typical S-Parameters (VCC = +3V, TA = +25C)
RF FREQUENCY (MHz) High-Gain Mode (GAIN = VCC) 800 840 880 920 960 1000 Low-Gain Mode (GAIN = GND) 800 840 880 920 960 1000 0.275 0.268 0.262 0.255 0.254 0.245 142.8 144.1 145.5 147.7 149.0 156.9 10 40 80 110 170 240 0.996 0.995 0.993 0.989 0.987 0.982 -0.5 -1.8 -3.2 -4.2 -6.2 -7.9 0.355 0.352 0.351 0.349 0.352 0.353 152.7 153.7 154.5 155.8 156.2 156.9 10 40 80 110 170 240 0.996 0.994 0.993 0.989 0.988 0.983 -0.4 -1.8 -3.2 -4.2 -6.2 -8.0 S11 MAG
|S11|
PHASE (degrees)
IF FREQUENCY (MHz)
|S22|
MAG (IFOUT+ Port Only)
S22 PHASE (IFOUT+ Port Only) (degrees)
8
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Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer
Local-Oscillator Input The LO port is the high-impedance input of the localoscillator buffer. It requires a series DC-blocking capacitor and a shunt resistor to ground to set the input impedance. See the Typical Operating Characteristics for a graph of LO Port Return Loss vs. Frequency. IF Output Port The mixer's downconverted output appears on the differential IFOUT+ and IFOUT- pins. The differential output can be converted to a single-ended output, as shown in the MAX2685 evaluation kit (EV kit). Refer to the Detailed Description in the MAX2685 EV kit data sheet.
Applications Information
Layout Considerations
A properly designed PC board is an essential part of any RF/microwave circuit. Note the IC's high-frequency inputs and outputs, and be sure to decouple the DC supply and control pins. For power-supply traces and connections, a star topology works well. Each VCC node in the circuit has its own path to the central V CC node and a decoupling capacitor that provides a low impedance at the RF frequency of interest. The central VCC also has a large decoupling capacitor. This provides good isolation between the different sections of the MAX2685.
MAX2685
Shutdown
Drive SHDN low to disable all device functions and place the MAX2685 in low-power shutdown mode. Drive SHDN high or connect it to VCC to enable all device functions.
Chip Information
TRANSISTOR COUNT: 295
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9
Low-Cost, 900MHz, Low-Noise Amplifier and Downconverter Mixer MAX2685
Package Information
QSOP.EPS
10
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