19-4765; Rev 0; 7/98 KIT ATION EVALU E L B AVAILA 622Mbps, Low-Noise Transimpedance Preamplifier for LAN and WAN Optical Receivers The MAX3760 is internally compensated and requires few external components. In die form it includes a space-saving filter connection, which provides positive bias for the photodiode through a 1kΩ resistor to VCC. These features, combined with the die aspect ratio and dimensioning, allow the MAX3760 to assemble easily into a TO-style header with a photodiode. The MAX3760 is designed to be used with either the MAX3761 or the MAX3762 limiting-amplifier ICs. When combined with a photodiode, the chipset forms a complete 5V, 622Mbps receiver. The MAX3760 is available in die form and in an 8-pin SO package. ____________________________Features ♦ 73nA RMS Input-Referred Noise ♦ 560MHz Bandwidth ♦ 1mA Peak Input Current ♦ 6.5kΩ Gain ♦ Operation from -40°C to +85°C ♦ 100mW Typical Power Consumption ♦ Single +5V Supply Ordering Information PART MAX3760ESA MAX3760E/D TEMP. RANGE PIN-PACKAGE -40°C to +85°C -40°C to +85°C 8 SO Dice* *Dice are designed to operate over a -40°C to +100°C junction temperature (T j ) range, but are tested and guaranteed at TA = +25°C. ________________________Applications Typical Application Circuit 622Mbps ATM LAN Optical Receivers +5V 622Mbps WAN Optical Receivers 0.01µF VCC Pin Configuration (FILTER) 1k MAX3761 MAX3762 MAX3760 TOP VIEW 0.01µF 100pF OUT+ INREF VCC 1 8 COMP 7 OUT+ INREF 3 6 OUT- GND 4 5 GND IN 2 MAX3760 SO LIMITING AMPLIFIER 100Ω (OPTIONAL) IN OUT- GND 0.01µF COMP* ( ) INDICATE PINS AVAILABLE ONLY ON THE DIE. *NOT CONNECTED ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 For small orders, phone 408-737-7600 ext. 3468. MAX3760 General Description The MAX3760 is a transimpedance preamplifier for 622Mbps ATM applications. It operates from a single +5V supply and typically consumes only 100mW power. The preamplifier converts a small photodiode current to a differential voltage. A DC cancellation circuit provides a true differential output swing over a wide range of input current levels, thus reducing pulsewidth distortion. 6.5kΩ transimpedance gain and 560MHz bandwidth, combined with low 73nA input-referred noise, provide -31.5dBm typical sensitivity in 1300nm receivers. The circuit accepts a 1mAp-p input current, resulting in a typical optical overload of -3dBm. The device operates over an extended temperature range of -40°C to +85°C. MAX3760 622Mbps, Low-Noise Transimpedance Preamplifier for LAN and WAN Optical Receivers ABSOLUTE MAXIMUM RATINGS VCC ........................................................................-0.5V to +7.0V Continuous Current IN, FILTER ..........................................................-5mA to +5mA OUT+, OUT-...................................................-25mA to +25mA Voltage at INREF ...................................................-0.5V to +0.5V Voltage at COMP........................................-0.5V to (VCC + 0.5V) Continuous Power Dissipation (TA = +85°C) SO (derate 5.88mW/°C above +85°C) ..........................383mW Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C Operating Junction Temperature Range (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, COMP = GND, 100Ω load between OUT+ and OUT-, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VCC = +5.0V, TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Input Bias Voltage VIN Input = open 0.8 0.95 V Supply Current ICC Input = open 20 30 mA Small-Signal Transimpedance z21 Differential output, input <10µA 5.2 6.5 7.8 kΩ Differential Output Offset VOS IIN = 500µA, COMP = open -25 25 mV Output Impedance (per side) ZOUT 50 60 Ω 550 950 mV 800 1000 1200 20 45 Output Common-Mode Level Maximum Differential Output Voltage FILTER Resistance Power-Supply Rejection Ratio VCC - 2.0 VOUT(MAX) 40 IIN = 500µA, total peak-to-peak, differential signal RFILTER PSRR f < 1MHz, referred to output V Ω dB Note 1: Dice are tested at TA = +25°C. AC ELECTRICAL CHARACTERISTICS (VCC = +4.5V to +5.5V, COMP = open, CIN = 0.75pF, outputs terminated differentially into 100Ω, 8-pin SO package in MAX3760 EV kit, TA = +25°C, unless otherwise noted. Typical values are at VCC = +5V.) (Notes 2, 3) PARAMETER Small-Signal Bandwidth SYMBOL Low-Frequency Cutoff Pulse-Width Distortion RMS Noise Referred to Input Data-Dependent Jitter CONDITIONS BW PWD in DDJ MIN TYP 455 565 MAX UNITS MHz 20µA average input current 50 (Note 4) 75 200 ps CIN = 0.75pF (Notes 3, 5) 73 93.5 nA 200 kHz ps Note 2: AC characteristics are guaranteed by design and characterization. Note 3: CIN is the source capacitance presented to the die. Includes package parasitic, photo diode, and parasitic interconnect capacitance. Note 4: Input is a 622Mbps 1-0 pattern, signal amplitude = 0 to 1mA, extinction ratio (re) = 10. Note 5: Measured with a 4-pole, 470MHz Bessel filter. 2 _______________________________________________________________________________________ 622Mbps, Low-Noise Transimpedance Preamplifier for LAN and WAN Optical Receivers SMALL-SIGNAL GAIN vs. FREQUENCY 78 76 90 CIN = 0.75pF 70 CIN = 0.25pF 60 70 68 100 66 50 64 50 62 470MHz BANDWIDTH 40 60 -40 30 -5 65 0 10k 100 1M 100k 100M 10M 1G 10G 0 600 800 INPUT SIGNAL AMPLITUDE (µAp-p) INPUT-REFERRED RMS NOISE CURRENT vs. DC INPUT CURRENT TRANSIMPEDANCE vs. AMBIENT TEMPERATURE TYPICAL BANDWIDTH vs. JUNCTION TEMPERATURE 250 200 150 6500 6000 CIN = 1.25pF 480 460 CIN IS SOURCE CAPACITANCE PRESENTED TO DIE. INCLUDES PACKAGE PARASITIC, PIN DIODE, AND PARASITIC INTERCONNECT CAPACITANCE 420 5000 -40 1.00 2.15 4.64 10.0 21.5 46.4 100 215 464 1000 MAX760toc06 CIN = 0.75pF 500 440 0 -20 0 20 40 60 80 -40 100 30 -5 100 65 DC INPUT CURRENT (µA) AMBIENT TEMPERATURE (°C) JUNCTION TEMPERATURE (°C) TYPICAL EYEWIDTH vs. INPUT SIGNAL DATA-DEPENDENT JITTER vs. INPUT SIGNAL AMPLITUDE OUTPUT COMMON-MODE VOLTAGE vs. AMBIENT TEMPERATURE 223 - 1 PRBS 622Mbps re = 10 600 1.3 -1.4 -1.6 400 1.2 TA = -40°C REFERENCED TO VCC -1.2 VOLTAGE (V) TA = +25°C JITTER (ps pp) TA = +85°C MAX3760-09 1.5 -1.0 MAX3760-08 800 MAX3760 toc07 1.6 1000 520 5500 100 CIN = 0.25pF IN TO-56 HEADER 3dB BANDWIDTH (MHz) TRANSIMPEDANCE (Ω) 300 540 MAX3760-05 7000 MAX3760toc04 CIN = 0.75pF 470MHz BANDWIDTH 50 EYEWIDTH (ns) 400 FREQUENCY (Hz) 350 1.4 200 JUNCTION TEMPERATURE (°C) 450 INPUT-REFERRED NOISE (nA) 72 PWD (ps) CIN = 1.25pF re = 10 622Mbps, ONE-ZERO PATTERN 150 74 80 400 200 MAX3760-02 CIN IS SOURCE CAPACITANCE PRESENTED TO DIE. INCLUDES PACKAGE PARASITIC, PIN DIODE, AND PARASITIC INTERCONNECT CAPACITANCE GAIN (dB) INPUT-REFERRED NOISE (nA) 100 80 MAX3760-01 110 PULSE-WIDTH DISTORTION vs. INPUT SIGNAL AMPLITUDE MAX3760-03 INPUT-REFERRED NOISE vs. JUNCTION TEMPERATURE -1.8 -2.0 -2.2 -2.4 200 -2.6 1.1 -2.8 0 1.0 10 20 50 100 150 200 250 300 400 500 600 INPUT SIGNAL (µA) -3.0 0 200 400 600 800 INPUT SIGNAL AMPLITUDE (µAp-p) 1000 -40 -20 0 20 40 60 80 100 AMBIENT TEMPERATURE (°C) _______________________________________________________________________________________ 3 MAX3760 __________________________________________Typical Operating Characteristics (MAX3760 EV kit, VCC = +5.0V, COMP = open, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (MAX3760 EV kit, VCC = +5.0V, COMP = open, TA = +25°C, unless otherwise noted.) MAXIMUM OUTPUT SIGNAL AMPLITUDE vs. AMBIENT TEMPERATURE MAX3760-10 800 MAX OUTPUT SIGNAL AMPLITUDE (mVp-p) 700 600 500 400 -40 -20 0 20 40 60 80 100 AMBIENT TEMPERATURE (°C) EYE DIAGRAM (INPUT = 1mA) EYE DIAGRAM (INPUT = 10µA) 223 - 1 PRBS 500mV MAX3760-12 50mV MAX3760-11 MAX3760 622Mbps, Low-Noise Transimpedance Preamplifier for LAN and WAN Optical Receivers 223 - 1 PRBS 10mV/ div 100mV/ div -50mV 200ps/div -500mV 200ps/div Pin Description 4 PIN NAME 1 VCC FUNCTION Supply-Voltage Input 2 IN 3 INREF Signal Input 4, 5 GND Ground 6 OUT- Inverting Voltage Output. Current flowing into the input causes OUT- to decrease. 7 OUT+ Noninverting Voltage Output. Current flowing into the input causes OUT+ to increase. 8 COMP Compensation Capacitor Connection. Connection for optional external compensation capacitor for DCcancellation circuit. Add capacitance here to reduce the low-frequency cutoff of the DC cancellation circuit. Connect COMP directly to GND to disable the DC cancellation circuit. — FILTER Filter Connection. Provides positive bias for photodiode through a 1kΩ resistor to VCC (see the Designing Filters section). Available on the die only. Input Reference Connection. Connect to photodetector AC ground. _______________________________________________________________________________________ 622Mbps, Low-Noise Transimpedance Preamplifier for LAN and WAN Optical Receivers MAX3760 VCC D1 RF 1k MAX3760 (FILTER) VCC VCC Q2 R1 OUT- TRANSIMPEDANCE AMPLIFIER IN Q1 PARAPHASE AMP VCC INREF Q3 R2 OUT+ R3 R4 DC CANCELLATION AMPLIFIER Q4 GND COMP GND ( ) INDICATE PINS AVAILABLE ON DIE ONLY. Figure 1. Functional Diagram Detailed Description The MAX3760 is a transimpedance amplifier designed for 622Mbps fiber optic applications. As shown in the Functional Diagram (Figure 1), it comprises a transimpedance amplifier, a paraphase amplifier with emitterfollower outputs, and a DC cancellation circuit. Transimpedance Amplifier The signal current at the input flows into a high-gain amplifier’s summing node. Shunt feedback through RF converts this current to a voltage with 6.5kΩ gain. Diode D1 clamps the output voltage for large input currents. INREF is a direct connection to the input transistor’s emitter, and must be connected directly to the photodetector AC ground return for best performance. Paraphase Amplifier The paraphase amplifier converts single-ended signals to differential signals and introduces a voltage gain of 2. This signal drives a pair of internally biased emitter followers, Q2 and Q3, which form the output stage. Resistors R1 and R2 provide back-termination at the output, delivering a 100Ω differential output impedance. The output emitter followers are designed to drive a 100Ω differential load between OUT+ and OUT-. The MAX3760 can also be terminated with higher output impedances for increased gain and output voltage swing. The MAX3760 will not drive a 50Ω load to ground. For best noise rejection, terminate the MAX3760 with differential loads. DC Cancellation Circuit The DC cancellation circuit removes the input signal’s DC component by employing low-frequency feedback. This feature centers the input signal within the transimpedance amplifier’s dynamic range, thereby reducing pulse-width distortion on large input signals. The paraphase amplifier’s output is sensed through resistors R3 and R4, then filtered, amplified, and fed back to the base of transistor Q4. The transistor draws the input signal’s DC component away from the transimpedance amplifier’s summing node. The MAX3760 DC cancellation loop is internally compensated and does not require external capacitors in most 622Mbps applications. Add external capacitance at the COMP pin to reduce the DC cancellation circuit’s frequency response and improve data-dependent jitter. Connecting the COMP pin directly to GND disables the circuit. The DC cancellation circuit can sink up to 1mA at the input. _______________________________________________________________________________________ 5 MAX3760 622Mbps, Low-Noise Transimpedance Preamplifier for LAN and WAN Optical Receivers The MAX3760 minimizes pulse-width distortion for data sequences exhibiting a 50% duty cycle. A duty cycle significantly different from 50% will cause the MAX3760 to generate pulse-width distortion. DC cancellation current is drawn from the input and creates noise. This is not a problem for low-level signals with little or no DC component. Preamplifier noise increases for signals with significant DC component (see Typical Operating Characteristics). The MAX3760 operates with the photodetector cathode connected to VCC, as shown in the Typical Application Circuit. Connecting the photodetector anode to GND and the cathode to IN defeats the DC cancellation circuit and causes pulse-width distortion. Input Reference INREF is the reference point for IN. Connect it as close as possible to the photodetector diode’s AC ground. The photodetector’s AC ground is usually the ground of the photodetector’s filter capacitor. The total length from INREF, through the filter capacitor and the diode, and back to the input should be no more than 2cm. Applications Information Optical Power Definitions Many of the MAX3760’s specifications relate to the input signal amplitude. When working with fiber optic receivers, the optical input is usually expressed in terms of average optical power and extinction ratio. Use the relations given in Table 1 to convert optical power to input signal when designing with the MAX3760. 1mA Overload = 10log 1000 dBm 2ρ Linear Range The MAX3760 has high gain, which limits the output when the input signal exceeds 20µAp-p. It operates with 90% linearity for inputs not exceeding the following: ( ) 20µA r + 1 e 10log 1000 dBm ρr - 1 e ( ) Table 1. Optical Power Relations PARAMETER SYMBOL RELATION Average Power PAVE Extinction Ratio re re = P1 / P0 Optical Power of a “1” P1 P1 = 2PAVE Optical Power of a “0” P0 P0 = 2PAVE / (re + 1) Signal Amplitude PIN PIN = P1 - P0 = 2PAVE PAVE = (P0 + P1) / 2 Note: Assuming a 50% average input duty cycle. Calculating Sensitivity, Overload, and Linear Range Sensitivity Calculation The MAX3760’s input-referred RMS noise current (in) generally dominates the receiver sensitivity. In a system where the bit error rate (BER) is 1E - 10, the signal-tonoise ratio must always exceed 12.7. The sensitivity, expressed in average power, can be estimated as: 12.7in (re + 1) Sensitivity = 10log 1000 dBm 2ρ(re - 1) Where ρ is the photodiode responsivity in A/W. Input Overload The overload is the largest input that the MAX3760 accepts while meeting specifications. It is calculated as: 6 re (re + 1) OPTICAL POWER P1 PAVE P0 TIME Figure 2. Optical Power Definitions _______________________________________________________________________________________ (re ) - 1 (re + 1) 622Mbps, Low-Noise Transimpedance Preamplifier for LAN and WAN Optical Receivers 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. Take care to bypass VCC and to connect the GND pin to the ground plane with the shortest possible traces. Designing a Low-Capacitance Input Noise performance and bandwidth will be adversely affected by stray capacitance at IN. Make every effort to minimize capacitance on this node. Select a lowcapacitance photodiode and use good high-frequency design and layout techniques. The MAX3760 is optimized for 0.75pF of capacitance on the input—approximately the capacitance of a low-cost photodetector packaged in a header. When using the MAX3760 in the SO package, note that the package capacitance is about 0.3pF. The PC board between the MAX3760 input and the photodetector will add parasitic capacitance. Keep the input line short, and remove power and ground planes beneath it. For the best possible performance, assemble the MAX3760 in die form using chip-and-wire technology, or package the die in a TO header. These techniques minimize parasitic capacitance, resulting in the lowest noise. supply-noise voltage is divided between CFILTER and CPHOTO. The input noise current due to supply noise is as follows (assuming the filter capacitor is much larger than the photodiode capacitance): INOISE = (VNOISE )(CPHOTO ) (RFILTER )(CFILTER ) If the amount of tolerable noise is known, the filter capacitor is easy to select, as follows: CFILTER > (VNOISE )(CPHOTO ) (RFILTER )(INOISE ) For example, with maximum noise voltage = 10mVRMS, CPHOTO = 0.75pF, RFILTER = 1kΩ, and INOISE selected to be 30nA (half the MAX3760’s input noise): (10mV)(0.75pF) (1000)(30E - 9) CFILTER = = 250pF TOP VIEW OF TO-56 HEADER VCC CFILTER Designing Filters The MAX3760’s noise performance is strongly affected by the circuit’s bandwidth, which changes over temperature and varies from lot to lot. Receiver sensitivity can be improved by adding filters to limit this bandwidth. Filter designs range from a one-pole filter using a single capacitor to more complex filters using inductors. The simple filter provides a moderate rolloff with minimal components, while the complex filter provides a sharper rolloff and better transient response. A simple 530MHz filter can be created by placing a 6pF capacitor between the OUT+ and OUT- pins. Supply-voltage noise at the photodiode cathode produces a current, I = C PHOTO ∆V/∆t, which reduces receiver sensitivity (CPHOTO is the photodiode capacitance.) The MAX3760’s FILTER resistor, combined with an external capacitor, can be used to reduce this noise (see Typical Application Circuit). Current generated by PHOTODIODE OUT- OUT+ CASE IS GROUND Figure 3. Suggested Layout for TO-56 Header _______________________________________________________________________________________ 7 MAX3760 Power Supply The MAX3760 can operate from a power-supply voltage (VCC - GND) between 4.5V and 5.5V. GND can be any stable voltage, including -5.0V, as found in many systems using ECL interface levels. Wire Bonding For high current density and reliable operation, the MAX3760 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 4 mils square, with 6 mil pitch. Die thickness is 15 mils. ___________________Chip Topography INREF FILTER IN GND VCC GND COMP OUT- OUT+ 0.042" (1.05mm) 0.030" (0.75mm) TRANSISTOR COUNT: 131 SUBSTRATE CONNECTED TO GND Package Information SOICN.EPS MAX3760 622Mbps, Low-Noise Transimpedance Preamplifier for LAN and WAN Optical Receivers 8 _______________________________________________________________________________________