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19-1790; Rev 0; 8/00
2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier
General Description
The MAX3864 is a transimpedance preamplifier for applications in SDH/SONET systems operating up to 2.5Gbps. It features 490nA (typ) input-referred noise, 2.0GHz bandwidth, and 2mA input overload. The MAX3864 operates from a single +3.0V to +5.5V supply. It includes an integrated low-frequency compensation capacitor, as well as a filter connection that provides positive bias through a 750 resistor to VCC. These features save external components, simplifying design and assembly into a TO-46 header with a photodiode. The MAX3864 has a typical optical dynamic range of -24dBm to 0dBm using a PIN photodetector. o 490nA (typ) Input-Referred Noise o 2000MHz Bandwidth o 2mA Input Overload o 100 Differential Output Impedance o 112mW Power Dissipation at +3.3V o Integrated Filter Resistor o CML Outputs o Single +3.0V to +5.5V Supply Voltage
Features
MAX3864
Ordering Information
PART MAX3864ESA MAX3864E/D TEMP. RANGE -40C to +85C -40C to +85C PIN-PACKAGE 8 SO Dice*
Applications
SDH/SONET Transmission Systems PIN Preamplifier Receivers APD Preamplifier Receivers 2.5Gbps ATM Receivers Regenerators for SDH/SONET
* Dice are designed to operate with junction temperatures of -40C to +140C but are tested and guaranteed only at TA = +25C.
Pin Configuration
TOP VIEW
VCC 1 N.C. IN 2 8 7 GND OUT+ OUTGND
MAX3864
3 6 5 FILTER 4
SO
Typical Application Circuit
VCC 0.01F 750 CFILTER 400pF FILTER PHOTODIODE IN OUT+ 100 OUT-
VCC 0.1F
MAX3864
GND
0.1F
LIMITING AMPLIFIER
________________________________________________________________ Maxim Integrated Products
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC - GND) .................................-0.5V to +6.0V IN Current..............................................................-4mA to +4mA FILTER Current......................................................-8mA to +8mA Voltages at OUT+, OUT- .................(VCC - 1.5V) to (VCC + 0.5V) Continuous Power Dissipation (TA = +85C) 8-Pin SO package (derate 6.7mW/C above +85C) ..436mW Storage Temperature Range .............................-55C to +150C Operating Junction Temperature ......................-55C to +150C Processing Temperature (die) .........................................+400C Lead Temperature (soldering, 10s) .................................+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.
ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +5.5V, 100 load between OUT+ and OUT-, 0.1F coupling capacitors on OUT+ and OUT-, TA = -40C to +85C, unless otherwise noted. Typical values are at +3.3V, source capacitance = 0.85pF, and TA = +25C.) (Note 1)
PARAMETER Input Bias Voltage Supply Current Transimpedance Output Impedance Maximum Differential Output Voltage Filter Resistor AC Input Overload DC Input Overload Input-Referred RMS Noise Input-Referred Noise Density Small-Signal Bandwidth Low-Frequency Cutoff Transimpedance Linear Range Deterministic Jitter Power-Supply Rejection Ratio (PSRR) -3dB, input 20ADC Gain at 40Ap-p is within 5% of the smallsignal gain 3.13V < VCC < 5.5V (Note 3) 3.0V VCC 3.13V (Note 3) Output referred, f < 2MHz, PSRR = -20log(VOUT/Vcc) 40 24 24 50 67 77 ps dB Bandwidth = 2.0GHz (Note 2) 1525 Differential, measured with 40Ap-p input Single ended (per side) Input = 2mAp-p with 100 differential output termination 2100 48 220 600 2 1 490 11 2000 30 668 CONDITIONS MIN 0.66 TYP 0.83 34 2750 50 380 750 MAX 0.99 63 3400 52 575 930 UNITS V mA mVp-p mAp-p mA nA pA/(Hz) MHz kHz Ap-p
Note 1: Source capacitance represents the total capacitance at the IN pin during characterization of noise and bandwidth parameters. Noise and bandwidth will be affected by the source capacitance. See the Typical Operating Characteristics for more information. Note 2: Input-referred noise is calculated as (RMS output noise) / (Gain at f = 10MHz). Noise density is (Input-Referred Noise) / (Bandwidth)1/2. No external filters are used for the noise measurements. Note 3: Deterministic jitter is defined as the arithmetic sum of pulse-width distortion and pattern dependent jitter measured with a repeating 20-bit pattern of 00111110101100000101 (K28.5). See Typical Operating Characteristics.
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier
Typical Operating Characteristics
(VCC = 3.3V, TA = +25C and MAX3864 EV kit source capacitance = 0.85pF, unless otherwise noted).
INPUT-REFERRED RMS NOISE vs. TEMPERATURE
MAX3864 toc01
MAX3864
FREQUENCY RESPONSE
MAX3864 toc02
DETERMINISTIC JITTER vs. INPUT AMPLITUDE
90 PEAK-TO-PEAK JITTER (ps) 80 70 60 50 40 30 20 10
MAX3864 toc03
600 INPUT-REFERRED NOISE (nARMS) 550 500 450 400 350 300 250 200 -40 -20 0 20 40 60 80 CIN = 1.0pF CIN = 0.5pF CIN = 1.5pF
75
100
TRANSIMPEDANCE (dB)
70
65
60
CIN IS SOURCE CAPACITANCE PRESENTED TO DIE, INCLUDES PACKAGE PARASITIC, PIN DIODE, AND PARASITIC INTERCONNECT CAPACITANCE. 100
55
50 1 10 100 FREQUENCY (MHz) 1k 10k JUNCTION TEMPERATURE (C)
0 10 100 1000 10,000 INPUT CURRENT AMPLITUDE (Ap-p)
INPUT-REFERRED RMS NOISE CURRENT vs. DC INPUT CURRENT
MAX3864 toc04
SMALL-SIGNAL TRANSIMPEDANCE vs. TEMPERATURE
69 TRANSIMPEDANCE dB) 68 67 66 65 64 63 62 61 60
MAX3864 toc05
BANDWIDTH vs. TEMPERATURE
2.2 2.1 BANDWIDTH (GHz) 2.0 1.9 1.8 1.7 1.6 1.5 1.4 CIN IS SOURCE CAPACITANCE PRESENTED TO DIE, INCLUDES PACKAGE PARASITIC, PIN DIODE, AND PARASITIC INTERCONNECT CAPACITANCE. -40 -20 0 20 40 60 80 100 CIN = 1.5pF CIN = 1.0pF
MAX3864 toc06 MAX3864 toc12
1000 900 INPUT-REFERRED NOISE (nARMS) 800 700 600 500 400 300 200 100 0 1 10 100
70
2.3 CIN = 0.5pF
1000
-40
-20
0
20
40
60
80
100
DC INPUT CURRENT (A)
AMBIENT TEMPERATURE (C)
JUNCTION TEMPERATURE (C)
DIFFERENTIAL OUTPUT AMPLITUDE vs. TEMPERATURE
MAX3864 toc07
EYE DIAGRAM (INPUT = 2mAp-p)
INPUT = 213 -1 PRBS WITH 72 CID VCC = 3.0V AT TA = -40C
MAX3864 toc11
EYE DIAGRAM (INPUT = 2mAp-p)
INPUT = 213 -1 PRBS WITH 72 CID VCC = 3.13V AT TA = -40C
DIFFERENTIAL OUTPUT AMPLITUDE (mVp-p)
500 480 460 440 420 400 380 360 340 320 300 -40 -20 0 20 40 60 80 INPUT = 2mA
50mV/div
50mV/div
100
80ps/div
80ps/div
AMBIENT TEMPERATURE (C)
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
Typical Operating Characteristics (continued)
VCC = 3.3V, TA = +25C and MAX3864 EV kit source capacitance = 0.85pF, unless otherwise noted).
EYE DIAGRAM (INPUT = 2mAp-p)
MAX3864 toc08
EYE DIAGRAM (INPUT = 20Ap-p)
DIFFERENTIAL OUITPUT VOLTAGE (mVp-p)
INPUT = 223 -1 PRBS
MAX3864 toc09
DC TRANSFER FUNCTION
MAX3864 toc10
INPUT = 223 -1 PRBS
200
100
50mV/div
10mV/div
0
-100
-200 80ps/div 80ps/div -100 -50 0 50 100 INPUT CURRENT (A)
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME VCC N.C. IN FILTER GND OUTOUT+ GND Supply Voltage No Connection Amplifier Input Provides bias voltage for the photodiode through a 750 resistor to VCC. When grounded, this pin disables the DC cancellation amplifier to allow a DC path from IN to OUT+ and OUT- for testing. Ground Inverting Output. Current flowing into IN causes VOUT- to decrease. Noninverting Output. Current flowing into IN causes VOUT+ to increase. Ground FUNCTION
Detailed Description
The MAX3864 transimpedance amplifier is designed for 2.5Gbps fiber optic applications. As shown in Figure 1, the MAX3864 comprises a transimpedance amplifier, a voltage amplifier, an output buffer, an output filter, and a DC cancellation circuit.
Voltage Amplifier
The voltage amplifier converts single-ended signals to differential signals and introduces a voltage gain.
Output Buffer
The output buffer provides a back-terminated voltage output. The buffer is designed to drive a 100 differential load between OUT+ and OUT-. The output voltage is divided between internal 50 load resistors and the external load resistor. In the typical operating circuit, this creates a voltage-divider with a ratio of 1/2. The MAX3864 can also be terminated with higher output impedances, which increases gain and output voltage swings.
Transimpedance Amplifier
The signal current at the input flows into the summing node of a high-gain amplifier. Shunt feedback through RF converts this current to a voltage. Schottky diodes clamp the output voltage for large input currents (Figure 2).
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
MAX3864
RF = 1k TRANSIMPEDANCE AMPLIFIER IN 50 VOLTAGE AMPLIFIER OUTPUT BUFFER OUTPUT FILTER OUT+ OUT-
50
LOWPASS FILTER VCC DISABLE 750 FILTER DC CANCELLATION CIRCUIT
VCC GND
Figure 1. Functional Diagram
AMPLITUDE
AMPLITUDE
INPUT FROM PHOTODIODE
TIME OUTPUT (SMALL SIGNALS) INPUT (AFTER DC CANCELLATION) OUTPUT (LARGE SIGNALS)
TIME
Figure 2. Limited Output
Figure 3. DC Cancellation Effect on Input
For optimum supply-noise rejection, the MAX3864 should be terminated with a differential load. If a singleended output is required, the unused output should be terminated with 50 to VCC. The MAX3864 will not drive a DC-coupled, 50 grounded load.
Output Filter
The MAX3864 includes a one-pole lowpass filter that limits the circuit bandwidth and improves noise performance.
DC Cancellation Circuit
The DC cancellation circuit uses low-frequency feedback to remove the DC component of the input signal (Figure 3). This feature centers the input signal within the
transimpedance amplifier's linear range, thereby reducing pulse-width distortion (PWD) on large input signals. The DC cancellation circuit is internally compensated and therefore does not require external capacitors. This circuit minimizes PWD for data sequences that exhibit a 50% duty cycle and mark density. A duty cycle or mark density significantly different from 50% causes the MAX3864 to generate PWD. DC cancellation current is drawn from the input and creates noise. For low-level signals with little or no DC component, this is not a problem. Amplifier noise will increase for signals with significant DC component (see Typical Operating Characteristics).
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
POWER PI
where is the photodiode responsivity, including fiberto-photodiode coupling efficiency in A/W and IN in A. For example, if SNR = 12.7, IN = 0.490A, re = 10, and = 1, then sensitivity is -24dBm.
Input Optical Overload
PAVG PIN
PO
TIME
The overload is the largest input that the MAX3864 accepts while meeting deterministic jitter specifications. The optical overload can be estimated in terms of average power with the following equation (assumes re = ): 2mAp - p x 1000 Overload = 10log dBm 2
Figure 4. Optical Power Relations
Optical Linear Range
The MAX3864 has high gain, which limits the outputs when the input signal exceeds 40Ap-p. The MAX3864 operates in a linear range for inputs not exceeding: 40Ap - p(re + 1) x 1000 Linear Range = 10log dBm 2(re - 1)
Table 1. Optical Power Relations
PARAMETER Average Power Extinction Ratio Optical Power of a 1 Optical Power of a 0 Signal Amplitude SYMBOL PAVE re P1 P0 PIN RELATION PAVE = (P0 + P1) / 2 r e = P1 / P0 P1 = 2PAVEre / (re + 1) P0 = 2PAVE / (re + 1) PIN = P1 - P0 = 2PAVE (re - 1) / (re + 1)
Layout Considerations
Use good high-frequency design and layout techniques. The use of a multilayer circuit board with separate ground and power planes is recommended. Connect the GND pins to the ground plane with the shortest possible traces. Noise performance and bandwidth will be adversely affected by capacitance at the IN pin. Minimize capacitance on this pin, and select a low-capacitance photodiode. Assembling the MAX3864 in die form using chip and wire technology provides the best possible performance. Figure 5 shows the recommended layout for a TO header. The SO package version of the MAX3864 is offered as an easy way to characterize the circuit and to become familiar with the circuit's operation, but it does not offer optimum performance. When using the SO version of the MAX3864, the package capacitance adds approximately 0.3pF at the input. The PC board between the MAX3864 input and the photodiode also adds parasitic capacitance. Keep the input line short, and remove power and ground planes beneath it.
Note: Assuming a 50% average input duty cycle and mark density.
Applications Information
Optical Power Relations
Many of the MAX3864 specifications relate to the input signal amplitude. When working with fiber optic receivers, the input is usually expressed in terms of average optical power and extinction ratio. Figure 4 shows relations that are helpful for converting optical power to input signal when designing with the MAX3864. Optical power relations are shown in Table 1; the definitions are true if the average duty cycle and mark density of the input data are 50%.
Optical Sensitivity Calculations
The MAX3864 input-referred RMS noise current (IN) generally determines the receiver sensitivity. To obtain a system bit-error rate (BER) of 1E-10, the minimum signal-to-noise ratio (SNR) is 12.7. The input sensitivity, expressed in average power, can be estimated as: SNR x IN (re + 1) Sensitivity =10log dBm 2(re - 1) x 1000
GND
Connect GND as close to the AC ground of the photodetector diode as possible. The photodetector AC ground is usually the ground of the filter capacitor from the photodetector cathode. The total loop (from GND, through the bypass capacitor and the diode, and back to IN) should be no more than approximately 1/5th of a wavelength.
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
TOP VIEW OF TO-46 HEADER VCC VCC CFILTER VCC 200
PHOTODIODE
OUT-
OUT+ IN
MAX3864 GND CASE IS GROUND
Figure 5. Suggested Layout for TO-46 Header
Figure 6. Equivalent Input Circuit
Photodiode Filter
Supply voltage noise at the photodiode cathode produces a current I = CPD V / t, which reduces the receiver sensitivity (C PD is the photodiode capacitance). The filter resistor of the MAX3864, combined with an external capacitor, can be used to reduce this noise (see the Typical Application Circuit). Current generated by supply noise voltage is divided between CFILTER and CPD. The input noise current due to supply noise is (assuming the filter capacitor is much larger than the photodiode capacitance):
Wire Bonding
For high current density and reliable operation, the MAX3864 uses gold metalization. Connections to the die should be made with gold wire only, using ballbonding. Wedge bonding is not recommended. Die thickness is typically 15mils (0.375mm).
INOISE =
(VNOISE )(CPD ) (RFILTER )(CFILTER ) (VNOISE )(CPD ) (RFILTER )(INOISE ) (100mV)(0.85pF) = 453pF (750)(250nA)
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If the amount of tolerable noise is known, the filter capacitor can be easily selected:
CFILTER =
For example, with a maximum noise voltage equal to 100mVp-p, CPD = 0.85pF, RFILTER = 750, and INOISE selected to be 250nA (half of the MAX3864's input noise):
CFILTER =
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
VCC
50
50
OUT+
OUT-
GND
Figure 7. Equivalent Output Circuit
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier
Chip Topography
OUT+ OUT-
Chip Information
TRANSISTOR COUNT: 320 PROCESS: BIPOLAR (SILICON GERMANIUM)
MAX3864
GND
GND
50mils 1.27mm
VCC
INPUT
FILTER
30mils (0.762mm)
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
Package Information
SOICN.EPS
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
NOTES
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2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864
NOTES
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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