19-1215; Rev 1; 4/98 155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers ____________________________Features ♦ 21nA Total RMS Noise ♦ 22kΩ Differential Transimpedance ♦ 180MHz Bandwidth ♦ 60mW Typical Power Consumption ♦ 60µA Peak Input Current ♦ Low, 85ps Pulse-Width Distortion ______________Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX3963CSA 0°C to +70°C 8 SO MAX3963C/D 0°C to +70°C* Dice *Dice are designed to operate over a 0°C to +100°C junction temperature (Tj) range, but are tested and guaranteed at TA = +25°C. __________________Pin Configuration TOP VIEW N.C. 1 IN 2 ________________________Applications MAX3963 8 VCC 7 OUT- FDDI N.C. 3 6 OUT+ 155Mbps ATM BYP 4 5 GND SO __________________________________________________Typical Application Circuit VCC 0.01µF VCC 1k 0.056µF (FILTER) OUT+ 100pF PHOTODIODE MAX3964 IN OUT- MAX3963 ( ) ARE FOR MAX3963C/D ONLY. GND BYP 0.056µF LIMITING AMPLIFIER CBYP 100pF (OPTIONAL) ________________________________________________________________ Maxim Integrated Products 1 For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX3963 _______________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 22kΩ. Input-referred noise of only 21nA allows detection of signals as small as 267nA, while pulse-width distortion is only 85ps with a 60µA 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 1kΩ 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 60Ω 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. MAX3963 155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers ABSOLUTE MAXIMUM RATINGS VCC ........................................................................-0.5V to +7.0V Continuous Current IN.......................................................................................5mA OUT+, OUT-....................................................................25mA BYP .......................................................................................5mA Continuous Power Dissipation (TA = +70°C) SO (derate 5.88mW/°C above +70°C) .........................471mW Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10sec) .............................+300°C Operating Junction Temperature (die) ..............-55°C to +150°C Processing Temperature (die) .........................................+400°C 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, 1kΩ load between OUT+ and OUT-, TA = 0°C to +70°C. Typical values are at VCC = 5.0V, TA = +25°C, unless otherwise noted.) (Note 1) TYP MAX Input Bias Voltage PARAMETER SYMBOL VIN Input = 0µA to 60µA CONDITIONS MIN 1.6 1.8 V Supply Current ICC Input = 0µA 12 20 mA Small-Signal Transimpedance z21 Differential output, input < 60µA 22 26.3 kΩ 17.5 Output Common-Mode Voltage VCC - 2.85 Power-Supply Rejection Ratio PSRR Output Resistance (per side) ROUT Maximum Differential Output Voltage VOD (MAX) f < 1MHz, referred to output V 35 45 UNITS dB 60 IIN = 80µA 68 Ω 2.2 V AC ELECTRICAL CHARACTERISTICS (VCC = +4.5V to +5.5V, CBYP = 100pF, CIN = 1.15pF, TA = +25°C, unless otherwise noted.) (Notes 2, 3) PARAMETER Small-Signal Bandwidth Pulse-Width Distortion RMS Noise Referred to Input SYMBOL BW-3dB PWD in CONDITIONS MIN TYP MAX UNITS 100 180 220 MHz IIN = 60µAp-p (Note 4) 85 160 ps (Note 5) 21 24.5 nA (Note 6) 37 COUT = 5pF nA Dice are tested at TA = +25°C 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 = +25°C. Note 1: Note 2: Note 3: Note 4: 2 _______________________________________________________________________________________ 155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers (VCC = 5.0V, CBYP = 100pF, CIN = 1.3pF, TA = +25°C, unless otherwise noted.) SMALL-SIGNAL TRANSIMPEDANCE vs. TEMPERATURE SUPPLY CURRENT vs. TEMPERATURE 1.8 22 21 VCC = 5.5V 13 12 VCC = 5V 11 20 10 20 30 40 50 60 70 1.2 1.0 0 10 20 30 40 50 60 0 70 10 20 30 40 50 60 TEMPERATURE (°C) PULSE-WIDTH DISTORTION vs. TEMPERATURE PULSE-WIDTH DISTORTION vs. INPUT CURRENT DIFFERENTIAL OUTPUT VOLTAGE vs. INPUT CURRENT 60 40 200 150 100 50 20 0 0 40 50 60 FREQUENCY RESPONSE BANDWIDTH vs. TEMPERATURE MAX3963-07 CIN = 1pF 200 -4 -5 -6 -7 BANDWIDTH (MHz) CIN = 11pF -50 CIN = 0.5pF CIN = 1pF 180 CIN = 1.5pF 160 140 100 100M FREQUENCY (Hz) *RELATIVE TO TRANSIMPEDANCE AT DC 50 100 150 26 24 CIN = 1.5pF 22 CIN = 1pF 20 CIN = 0.5pF 18 16 14 12 -8 -9 0 INPUT-REFERRED RMS NOISE 120 10M -100 INPUT CURRENT (µA) 220 -1 -3 -150 INPUT CURRENT (µAp-p) 1 -2 -1 10 20 30 40 50 60 70 80 90 100 TEMPERATURE (°C) 0 0 -2 0 70 1 MAX3963-09 30 INPUT-REFERRED NOISE* (nARMS) 20 MAX3963-08 10 MAX3963-06 MAX3963-05 250 70 2 DIFFERENTIAL OUTPUT VOLTAGE (V) 80 300 PULSE-WIDTH DISTORTION (ps) MAX3963-04 100 1M 1.4 TEMPERATURE (°C) IIN = 6OµAp-p 0 1.6 TEMPERATURE (°C) 120 PULSE-WIDTH DISTORTION (ps) VCC = 4.5V 10 0 TRANSIMPEDANCE* (dB) INPUT BIAS VOLTAGE (V) SUPPLY CURRENT (mA) TRANSIMPEDANCE (kΩ) 14 23 MAX3963-03 2.0 MAX3963-02 15 MAX3963-01 24 INPUT BIAS VOLTAGE (VIN) vs. TEMPERATURE 10 0 10 20 30 40 50 TEMPERATURE (°C) 60 70 0 10 20 30 40 50 60 70 TEMPERATURE (°C) *MEASURED WITH 4-POLE, 117MHz BESSEL FILTER _______________________________________________________________________________________ 3 MAX3963 __________________________________________Typical Operating Characteristics MAX3963 155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers ______________________________________________________________Pin Description PIN NAME FUNCTION 1, 3 N.C. 2 IN 4 BYP Connection for optional noise-reducing capacitor 5 GND Signal Ground 6 OUT+ Noninverting Voltage Output. Current flowing into IN causes VOUT+ to increase. 7 OUT- Inverting Voltage Output. Current flowing into IN causes VOUT- to decrease. 8 VCC Supply Voltage — FILTER* No Connect. No internal connection to the die. Signal Input Connection for 1kΩ filter resistor. This pad is accessible on the die only. *MAX3963C/D (die) only. VCC 1k (FILTER) VCC MAX3963 Q1 R1 RF 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 __________Applications Information Optical-Power Relations 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 10kΩ gain. 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%. Paraphase Amplifier Calculating Sensitivity and Overload 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 120Ω differential output impedance. The output emitter followers are designed to drive a 1kΩ 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 50Ω grounded load. The MAX3963 outputs may be AC coupled to a limiting amplifier. 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: Transimpedance Amplifier 12.7 in (re + 1) Sensitivity = 10log x 1000 dBm 2 ρ (r 1) e where ρ 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. 60µA Overload = 10log x 1000 dBm 2ρ Table 1. Optical-Power Relations* SYMBOL RELATION P1 Average Power PAVE Extinction Ratio re re = P1 / P0 Optical Power of a “1” P1 P1 = 2PAVE (re) / (re + 1) Optical Power of a “0” P0 P0 = 2PAVE / (re + 1) Signal Amplitude PINPUT PAVE = (P0 + P1) / 2 PINPUT = P1 - P0 = 2PAVE (re - 1) / (re + 1) *Assuming 50% average data duty cycle OPTICAL POWER PARAMETER PAVE P0 TIME Figure 2. Optical-Power Definitions _______________________________________________________________________________________ 5 MAX3963 _______________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. MAX3963 155Mbps Preamplifier for FDDI and ATM LAN Fiber Optic Receivers Output Filter Wire Bonding 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: 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. f -3dB = ___________________Chip Topography 1 2π ROUT COUT OUT- OUT+ GND where ROUT is the MAX3963 differential output resistance (typically 120Ω), 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 BYP 0.031" (0.79mm) 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 © 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.