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19-1215; Rev 1; 4/98
155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers
_______________General Description
The MAX3963 is a low-noise transimpedance preamplifier for FDDI and 155Mbps ATM optical receivers. The MAX3963's dynamic range is optimized for use in multimode LED-based applications. The preamplifier converts a small photodiode current to a differential voltage, with typical transimpedance of 22k. Input-referred noise of only 21nA allows detection of signals as small as 267nA, while pulse-width distortion is only 85ps with a 60A input signal. In a 1300nm multimode receiver, with responsivity of 0.7A/W, the MAX3963's dynamic range spans from -36dBm to -13.7dBm. The circuit operates from a single +5V supply, and typically consumes only 60mW power. The MAX3963 die includes a filter connection, which provides positive bias for the photodiode through a 1k resistor to VCC. This feature, combined with the small die size, allows the MAX3963 to fit easily into a TO-style package with a photodiode. The differential outputs are back terminated with 60 per side, allowing the easy use of filters to improve sensitivity. The MAX3963 is designed to be used with the MAX3964 limiting amplifier IC. It is available in an 8-pin SO package and as dice.
____________________________Features
21nA Total RMS Noise 22k Differential Transimpedance 180MHz Bandwidth 60mW Typical Power Consumption 60A Peak Input Current Low, 85ps Pulse-Width Distortion
MAX3963
______________Ordering Information
PART MAX3963CSA MAX3963C/D TEMP. RANGE 0C to +70C 0C to +70C* PIN-PACKAGE 8 SO Dice
*Dice are designed to operate over a 0C to +100C junction temperature (Tj) range, but are tested and guaranteed at TA = +25C.
__________________Pin Configuration
TOP VIEW
N.C. 1 IN 2 N.C. 3 BYP 4
8
VCC OUTOUT+ GND
________________________Applications
FDDI 155Mbps ATM
MAX3963
7 6 5
SO
__________________________________________________Typical Application Circuit
VCC 0.01F
1k (FILTER) 100pF PHOTODIODE
VCC 0.056F OUT+
MAX3964
IN OUT-
MAX3963
GND
BYP CBYP 100pF (OPTIONAL)
0.056F
LIMITING AMPLIFIER
( ) ARE FOR MAX3963C/D ONLY.
________________________________________________________________ Maxim Integrated Products
1
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155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers MAX3963
ABSOLUTE MAXIMUM RATINGS
VCC ........................................................................-0.5V to +7.0V Continuous Current IN.......................................................................................5mA OUT+, OUT-....................................................................25mA BYP .......................................................................................5mA Continuous Power Dissipation (TA = +70C) SO (derate 5.88mW/C above +70C) .........................471mW Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C Operating Junction Temperature (die) ..............-55C to +150C Processing Temperature (die) .........................................+400C
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 = +4.5V to +5.5V, CBYP = 100pF, 1k load between OUT+ and OUT-, TA = 0C to +70C. Typical values are at VCC = 5.0V, TA = +25C, unless otherwise noted.) (Note 1) PARAMETER Input Bias Voltage Supply Current Small-Signal Transimpedance Output Common-Mode Voltage Power-Supply Rejection Ratio Output Resistance (per side) Maximum Differential Output Voltage PSRR ROUT VOD (MAX) IIN = 80A f < 1MHz, referred to output 35 45 60 68 2.2 SYMBOL VIN ICC z21 Input = 0A Differential output, input < 60A 17.5 CONDITIONS Input = 0A to 60A MIN TYP 1.6 12 22 VCC - 2.85 MAX 1.8 20 26.3 UNITS V mA k V dB V
AC ELECTRICAL CHARACTERISTICS
(VCC = +4.5V to +5.5V, CBYP = 100pF, CIN = 1.15pF, TA = +25C, unless otherwise noted.) (Notes 2, 3) PARAMETER Small-Signal Bandwidth Pulse-Width Distortion RMS Noise Referred to Input Note 1: Note 2: Note 3: Note 4: SYMBOL BW-3dB PWD in COUT = 5pF IIN = 60Ap-p (Note 4) (Note 5) (Note 6) CONDITIONS MIN 100 TYP 180 85 21 37 MAX 220 160 24.5 UNITS MHz ps nA nA
Dice are tested at TA = +25C only. AC characteristics are guaranteed by design. CIN is the total capacitance at IN. COUT is the differential output capacitive load. PWD = [(width of wider pulse) - (width of narrower pulse)] / 2. Input is a 155Mbps 1-0 pattern, with rise time approximately 2ns. Note 5: Measured with a 117MHz, 3-pole Bessel filter. Note 6: Measured with COUT = 5pF, TA = +25C.
2
_______________________________________________________________________________________
155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers
__________________________________________Typical Operating Characteristics
(VCC = 5.0V, CBYP = 100pF, CIN = 1.3pF, TA = +25C, unless otherwise noted.)
MAX3963
SMALL-SIGNAL TRANSIMPEDANCE vs. TEMPERATURE
MAX3963-01
SUPPLY CURRENT vs. TEMPERATURE
MAX3963-02
INPUT BIAS VOLTAGE (VIN) vs. TEMPERATURE
MAX3963-03
24
15
2.0
14 VCC = 5.5V INPUT BIAS VOLTAGE (V) VCC = 4.5V TRANSIMPEDANCE (k) SUPPLY CURRENT (mA) 23
1.8
13
1.6
22
12 VCC = 5V
1.4
21
11
1.2
20 0 10 20 30 40 50 60 70 TEMPERATURE (C)
10 0 10 20 30 40 50 60 70 TEMPERATURE (C)
1.0 0 10 20 30 40 50 60 70 TEMPERATURE (C)
PULSE-WIDTH DISTORTION vs. TEMPERATURE
MAX3963-04
PULSE-WIDTH DISTORTION vs. INPUT CURRENT
MAX3963-05
DIFFERENTIAL OUTPUT VOLTAGE vs. INPUT CURRENT
DIFFERENTIAL OUTPUT VOLTAGE (V)
MAX3963-06
120 IIN = 6OAp-p PULSE-WIDTH DISTORTION (ps) 100 80 60 40 20 0 0 10 20 30 40 50 60
300 250 200 150 100 50 0
2
PULSE-WIDTH DISTORTION (ps)
1
0
-1
-2 0 10 20 30 40 50 60 70 80 90 100 INPUT CURRENT (Ap-p) -150 -100 -50 0 50 100 150 INPUT CURRENT (A)
70
TEMPERATURE (C)
FREQUENCY RESPONSE
MAX3963-07
BANDWIDTH vs. TEMPERATURE
MAX3963-08
INPUT-REFERRED RMS NOISE
24 22 20 18 16 14 12 10 CIN = 1.5pF CIN = 1pF CIN = 0.5pF
MAX3963-09
1 0 -1 TRANSIMPEDANCE* (dB) CIN = 1pF
220 200 BANDWIDTH (MHz) 180 160 140 120 100
26 INPUT-REFERRED NOISE* (nARMS)
CIN = 0.5pF CIN = 1pF CIN = 1.5pF
-2 -3 -4 -5 -6 -7 -8 -9 1M 10M
CIN = 11pF
100M
0
10
20
30
40
50
60
70
0
10
20
30
40
50
60
70
FREQUENCY (Hz) *RELATIVE TO TRANSIMPEDANCE AT DC
TEMPERATURE (C)
TEMPERATURE (C) *MEASURED WITH 4-POLE, 117MHz BESSEL FILTER
_______________________________________________________________________________________
3
155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers MAX3963
______________________________________________________________Pin Description
PIN 1, 3 2 4 5 6 7 8 -- NAME N.C. IN BYP GND OUT+ OUTVCC FILTER* No Connect. No internal connection to the die. Signal Input Connection for optional noise-reducing capacitor Signal Ground Noninverting Voltage Output. Current flowing into IN causes VOUT+ to increase. Inverting Voltage Output. Current flowing into IN causes VOUT- to decrease. Supply Voltage Connection for 1k filter resistor. This pad is accessible on the die only. FUNCTION
*MAX3963C/D (die) only.
VCC 1k (FILTER) VCC
MAX3963
Q1 RF R1 OUT+
IN
BYP
VCC TRANSIMPEDANCE AMPLIFIER PARAPHASE AMPLIFIER Q2 REFERENCE R2 OUT-
( ) ARE FOR MAX3963C/D ONLY.
Figure 1. Functional Diagram
4
_______________________________________________________________________________________
155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers
_______________Detailed Description
The MAX3963 transimpedance amplifier is designed for 155Mbps fiber optic applications. Figure 1 is a functional diagram of the MAX3963, which comprises a transimpedance amplifier and a paraphase amplifier with emitter-follower outputs.
__________Applications Information
Optical-Power Relations
Many of the MAX3963 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. The relations shown in Table 1 are helpful for converting optical power to input signal when designing with the MAX3963. These relations are true if the average data duty cycle is 50%.
MAX3963
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 with a 10k gain.
Paraphase Amplifier
The paraphase amplifier converts single-ended signals to differential signals and introduces a 2x voltage gain. This signal drives a pair of internally biased emitter followers, Q1 and Q2, which form the output stage. Resistors R1 and R2 provide back termination at the output, providing a 120 differential output impedance. The output emitter followers are designed to drive a 1k differential load between OUT+ and OUT-. Higher output impedances can also be driven, resulting in slightly increased gain and output voltage swing. The MAX3963 will not drive a 50 grounded load. The MAX3963 outputs may be AC coupled to a limiting amplifier.
Calculating Sensitivity and Overload
Sensitivity Calculation The MAX3963's input-referred RMS noise current (in) generally dominates receiver sensitivity. In a system where the bit error rate is 1E-10, the signal-to-noise ratio must always exceed 12.7. The sensitivity, expressed in average power, can be estimated as shown in the following equation: 12.7 in (re + 1) Sensitivity = 10log x 1000 dBm 2 (re - 1) where is the photodiode responsivity in A/W. Input Overload The overload is the largest input that the MAX3963 accepts while meeting specifications. A larger input causes increased pulse-width distortion. 60A Overload = 10log x 1000 dBm 2
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 PINPUT RELATION
P1 OPTICAL POWER
PAVE = (P0 + P1) / 2 re = P1 / P0 P1 = 2PAVE (re) / (re + 1) P0 = 2PAVE / (re + 1) PINPUT = P1 - P0 = 2PAVE (re - 1) / (re + 1)
PAVE
P0 TIME
*Assuming 50% average data duty cycle
Figure 2. Optical-Power Definitions
_______________________________________________________________________________________
5
155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers MAX3963
Output Filter
The MAX3963's noise can be reduced by filtering the output signal. For digital communications systems, a linear-phase filter with -3dB lowpass response of (0.7 x data rate) is recommended. A single-pole filter implemented with a capacitor across the outputs also reduces noise, and consumes less board space than a linear-phase filter. The following equation represents the filter frequency: f -3dB = 1 2 ROUT COUT
Wire Bonding
For high current density and reliable operation, the MAX3963 uses gold metalization. Make connections to the die with gold wire only, using ball-bonding techniques. Wedge bonding is not recommended. Die-pad size is 4mils square, with 6mil pitch. Die thickness is 15mils.
___________________Chip Topography
OUTOUT+ GND
where ROUT is the MAX3963 differential output resistance (typically 120), and COUT is the differential output load capacitance. For 155Mbps receivers, an 11pF capacitor is recommended.
Layout Considerations
Use good high-frequency design and layout techniques. The use of a multilayer circuit board with separate ground and VCC planes is recommended. Bypass VCC and connect the GND pin to the ground plane with traces kept as short as possible. Ensure that commonmode output capacitance is less than 2pF per output.
0.031" (0.79mm)
Low-Capacitance Input Design Considerations
Noise performance and bandwidth are adversely affected by stray capacitance on the input node. Every effort must be made to minimize capacitance on this pin. Select a low-capacitance photodiode, and use good high-frequency design and layout techniques. The MAX3963 is optimized for 1.0pF of capacitance on the input, approximately the capacitance of a photodetector diode packaged in a header. When using the SO package version of the MAX3963, the package capacitance is about 0.3pF. This means that great care must be used to reduce input capacitance. The PC board between the MAX3963 input and the photodiode can add parasitic capacitance. Keep the input line short, and remove power and ground planes beneath it. Assembling the MAX3963 in die form provides the best possible performance. Parasitic capacitance can be reduced to a minimum, resulting in the lowest noise and the best bandwidth.
VCC
IN
FILTER 0.031" (0.79mm)
BYP
TRANSISTOR COUNT: 116 SUBSTRATE CONNECTED TO GND
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.
6 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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