19-3181; Rev 0; 2/04 3.2Gbps SFP Transimpedance Amplifiers with RSSI The MAX3724/MAX3725 transimpedance amplifiers provide a compact, low-power solution for communication up to 3.2Gbps. They feature 325nA input-referred noise at 2.1GHz bandwidth (BW) with 0.6pF input capacitance. The parts also have >2mAP-P AC input overload. Both parts operate from a single +3.3V supply and consume 93mW. The MAX3724/MAX3725 are in a compact 30-mil x 50-mil die and require no external compensation capacitor. A space-saving filter connection is provided for positive bias to the photodiode through an on-chip 580Ω resistor to V CC. These features allow easy assembly into a low-cost TO-46 or TO-56 header with a photodiode. The MAX3724 and MAX3748A receiver chip set provides an RSSI output using a Maxim-proprietary* interface technique. The MAX3724 preamplifier, MAX3748A postamplifier, and the DS1858/DS1859 SFP controller meet all the SFF-8472 digital diagnostic requirements. Features ♦ Wider Bandwidth than MAX3744/MAX3745 ♦ RSSI Implementation in 4-Pin TO-46 Header (MAX3724 and MAX3748A) ♦ 8psP-P Deterministic Jitter for <100µAP-P Input Current ♦ 325nARMS Input-Referred Noise at 2.1GHz Bandwidth ♦ 28mA Supply Current at +3.3V ♦ 2.5GHz Small-Signal Bandwidth ♦ 2.0mAP-P AC Overload ♦ Die Size: 30 mils x 50 mils (Identical to the MAX3744/MAX3745) Applications Ordering Information Up to 3.2Gbps SFF/SFP Optical Receivers PART Optimized for Small-Form-Factor Pluggable (SFP) Optical Receivers TEMP RANGE PIN-PACKAGE MAX3724E/D -40°C to +85°C Dice** MAX3725E/D -40°C to +85°C Dice** **Dice are designed to operate with junction temperatures of -40°C to +110°C but are tested and guaranteed only at TA = +25°C. *Patent pending. Typical Application Circuit SFP OPTICAL RECEIVER VCC 400pF 400pF VCC VCC FILTER OUT+ IN MAX3724 OUTGND 0.1µF MAX3748A IN- OUTRSSI 4-PIN TO CAN 0.1µF OUT+ IN+ DISABLE HOST BOARD VCC = 3.3V 4.7kΩ TO 10kΩ LOS 3.3kΩ MOD-DEF1 DS1858/ DS1859 MOD-DEF2 ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX3724/MAX3725 General Description MAX3724/MAX3725 3.2Gbps SFP Transimpedance Amplifiers with RSSI ABSOLUTE MAXIMUM RATINGS Power-Supply Voltage (VCC) .................................-0.5V to +6.0V Continuous CML Output Current (OUT+, OUT-) ............................................. -25mA to +25mA Continuous Input Current (IN)...............................-4mA to +4mA Continuous Input Current (FILTER).......................-8mA to +8mA Operating Junction Temperature Range (TJ) ....-55°C to +150°C Storage Ambient Temperature Range (TSTG) ...-55°C to +150°C Die Attach Temperature...................................................+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. ELECTRICAL CHARACTERISTICS (VCC = +2.97V to +3.63V and TA = -40°C to +85°C. Typical values are at VCC = +3.3V, source capacitance (CIN) = 0.85pF, and TA = +25°C, unless otherwise noted.) (Notes 1, 2) PARAMETER Supply Current SYMBOL ICC CONDITIONS MIN Including CML output current (IIN = 0) TYP MAX UNITS 28 41 mA Input Bias Voltage 1.0 Input Overload Input-Referred Noise (Note 4) (Note 3) IN 2 CIN = 0.85pF, BW = 933MHz 200 CIN = 0.85pF, BW = 2.1GHz (Note 3) 360 CIN = 0.85pF, BW = 18GHz (Note 3) CIN = 0.6pF, BW = 933MHz 200 CIN = 0.6pF, BW = 2.1GHz (Note 3) 325 Small-Signal Bandwidth (Note 3) Differential output, IIN = 40µAAVE BW Low-Frequency Cutoff Deterministic Jitter (Notes 3, 5) nARMS 440 635 2.8 3.5 -3dB, CIN = 0.6pF 2 2.5 -3dB, CIN = 0.85pF 1.8 2.3 -3dB, input current = 20µAAVE (Note 3) DJ 485 700 CIN = 0.6pF, BW = 18GHz (Note 3) Differential Transimpedance V mAP-P 4.5 GHz 30 100µAP-P < input ≤ 2.1Gbps, K28.5 pattern 2mAP-P 2.7Gbps, 231 - 1 pattern 11 10µAP-P < input ≤ 100µAP-P 8 2.7Gbps, 231 - 1 pattern kHz 33 15 2.1Gbps, K28.5 pattern kΩ 17 psP-P 12 Filter Resistance 510 580 690 Ω Differential Output Resistance (OUT+, OUT-) 85 100 115 Ω 220 280 400 mVP-P Maximum Differential Output Voltage 2 VOD Input > 50µAAVE, output termination 50Ω to VCC (output in limited state) _______________________________________________________________________________________ 3.2Gbps SFP Transimpedance Amplifiers with RSSI (VCC = +2.97V to +3.63V and TA = -40°C to +85°C. Typical values are at VCC = +3.3V, source capacitance (CIN) = 0.85pF, and TA = +25°C, unless otherwise noted.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP Single-Ended Output CommonMode Minimum Level (MAX3724) Relative to VCC, IIN = 1mAAVE 540 490 Output Data Transition Time Input > 200µAP-P 20% to 80% rise/fall time (Note 3) 70 Frequency ≤ 1GHz 17 1GHz < frequency ≤ 2GHz 10 Differential Output Return Loss Power-Supply Noise Rejection PSNR IIN = 0 (Note 6) RSSI Gain (MAX3724) ARSSI (Note 7) RSSI Gain Stability (MAX3724) f < 1MHz 46 1MHz ≤ f < 10MHz 34 10log(ARSSI/ARSSI-NOM) where ARSSI-NOM = ARSSI at 3.3V, +25°C (Note 3) MAX UNITS mV 100 ps dB dB 21 A/A 0.24 dB Note 1: Dice are designed to operate with junction temperatures of -40°C to +110°C but are tested and guaranteed only at TA = 25°C. Note 2: Source capacitance represents the total capacitance at the IN pad during characterization of the noise and bandwidth parameters. Note 3: Guaranteed by design and characterization. Note 4: Input-referred noise is: RMS output noise Gain at f = 100MHz Note 5: Deterministic jitter is the sum of pulse-width distortion (PWD) and pattern-dependent jitter (PDJ). Note 6: Power-supply noise rejection PSNR = -20log(∆VOUT / ∆VCC), where ∆VOUT is the differential output voltage and ∆VCC is the noise on VCC. Note 7: IOUT _ CM (IIN = 400µA) − IOUT _ CM (IIN = 0µA) ARSSI = 400µA IOUT + + IOUT − where IOUT _ CM = 2 RSSI range is from IIN = 6µA to 500µA _______________________________________________________________________________________ 3 MAX3724/MAX3725 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = +3.3V, CIN = 0.85pF, TA = +25°C, unless otherwise noted.) CIN = 0.85pF 500 CIN = 0.5pF 400 300 BW = 2.1GHz 200 700 0 600 500 CIN = 1.5pF CIN = 0.85pF 400 20 40 60 80 5 CIN = 0.5pF -5 -40 -20 0 20 40 60 80 100 -10 100M 1G 10G TEMPERATURE (°C) FREQUENCY (Hz) DETERMINISTIC JITTER vs. INPUT VOLTAGE SMALL-SIGNAL TRANSIMPEDANCE vs. TEMPERATURE EYE DIAGRAM INPUT = 20µAP-P, DATA RATE = 2.1Gbps MAX3724/25 toc04 50 45 40 35 30 25 20 2.7Gbps, 27-1PBRS 15 MAX3724/25 toc06 75 K28.5 PATTERN 70 10mV/div 65 10 2.1Gbps, K28.5 5 0 0.01 0.1 1 10 60 -40 -20 0 20 40 60 80 TEMPERATURE (°C) EYE DIAGRAM INPUT = 20µAP-P, DATA RATE = 3.2Gbps EYE DIAGRAM INPUT = 2mAP-P, DATA RATE = 2.1Gbps MAX3724/25 toc07 10mV/div EYE DIAGRAM INPUT = 2mAP-P, DATA RATE = 3.2Gbps MAX3724/25 toc08 MAX3724/25 toc09 K28.5 PATTERN 50mV/div 50ps/div 60ps/div 100 INPUT CURRENT (mAP-P) K28.5 PATTERN 4 15 10 0 300 100 20 TEMPERATURE (°C) TRANSIMPEDANCE (dB Ω) -20 30 25 200 -40 35 GAIN (dB) CIN = 1.5pF 40 MAX3724/25 toc02 700 800 MAX3724/25 toc05 INPUT-REFERRED NOISE (nARMS) UNFILTER INPUT-REFERRED NOISE (nARMS) MAX3724/25 toc01 800 600 OPTICAL FREQUENCY RESPONSE (70µm InGaAS PHOTODIODE, INPUT -22dBm) INPUT-REFERRED NOISE vs. TEMPERATURE MAX3724/25 toc03 INPUT-REFERRED NOISE vs. TEMPERATURE DETERMINISTIC JITTER (psP-P) MAX3724/MAX3725 3.2Gbps SFP Transimpedance Amplifiers with RSSI K28.5 PATTERN 50mV/div 60ps/div 50ps/div _______________________________________________________________________________________ 3.2Gbps SFP Transimpedance Amplifiers with RSSI SUPPLY CURRENT vs. TEMPERATURE S22 (dB) -15 MAX3725 -20 60 -25 50 40 30 20 -20 0 RSSI MAX3724, MAX3748A 400 350 300 250 40 60 80 100 -100 -50 0 50 100 INPUT CURRENT (mAP-P) BANDWIDTH vs. TEMPERATURE EYE DIAGRAM TEMPERATURE = +100°C INPUT = 20µAP-P DATA RATE = 2.7Gbps MAX3724/25 toc15 3 TA = +85°C -50 MAX3724/25 toc14 450 3dB BANDWIDTH MAX3748 RSSI OUTPUT (µA) 500 20 4 MAX3724/25 toc13 TA = -40°C 0 TEMPERATURE (°C) FREQUENCY (MHz) 550 50 -200 -40 500 1000 1500 2000 2500 3000 3500 4000 100 -150 0 0 150 -100 10 -30 200 MAX3724/25 toc12 MAX3724 -10 MAX3724/25 toc11 -5 70 SUPPLY CURRENT (mA) MAX3724/25 toc10 0 DC TRANSFER FUNCTION (VFILT = 0V) OUTPUT VOLTAGE (mVP-P) DIFFERENTIAL S22 vs. FREQUENCY 223 - 1 PRBS MAX3724 CIN = 0.6pF 2 6mV/div MAX3744 CIN = 0.6pF 1 200 150 0 0 500 1000 1500 2000 -40 -20 0 20 40 60 80 100 AVERAGE INPUT CURRENT (µA) TEMPERATURE (°C) OPTICAL EYE DIAGRAM INPUT = 0dBm, DATA RATE = 3.2Gbps OPTICAL EYE DIAGRAM INPUT = 0dBm, DATA RATE = 4.25Gbps MAX3724/25 toc16 MAX3724/25 toc18 K28.5 PATTERN 30mV/div 60ps/div OPTICAL EYE DIAGRAM INPUT = -18dBm, DATA RATE = 4.25Gbps MAX3724/25 toc17 K28.5 PATTERN 100mV/div 60ps/div K28.5 PATTERN 3mV/div 60ps/div 50ps/div _______________________________________________________________________________________ 5 MAX3724/MAX3725 Typical Operating Characteristics (continued) (VCC = +3.3V, CIN = 0.85pF, TA = +25°C, unless otherwise noted.) 3.2Gbps SFP Transimpedance Amplifiers with RSSI MAX3724/MAX3725 Pin Description MAX3724/ MAX3725 BOND PAD NAME 1, 3 VCC 2, 7 N.C. 4 IN 5 FILTER 6, 10 GND Supply Ground 8 OUT- Inverting Data Output. Current flowing into IN causes the voltage at OUT- to decrease. For the MAX3724, the common mode between OUT+ and OUT- is proportional to the average input current. 9 OUT+ Noninverting Data Output. Current flowing into IN causes the voltage at OUT+ to increase. For the MAX3724, the common mode between OUT+ and OUT- is proportional to the average input current. FUNCTION Supply Voltage No Connection TIA Input. Signal current from photodiode flows into this pin. Provides bias voltage for the photodiode through a 580Ω 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. VCC MAX3724 RF RF TRANSIMPEDANCE AMPLIFIER TRANSIMPEDANCE AMPLIFIER OUT+ OUT- IN DC CANCELLATION CIRCUIT VCC DC CANCELLATION CIRCUIT RSSI MAX3725 FILTER FILTER 50Ω OUT+ OUT- IN 50Ω 50Ω VCC 50Ω Figure 1. Functional Diagram Detailed Description The MAX3724/MAX3725 are transimpedance amplifiers designed for up to 3.2Gbps SFF/SFP transceiver modules. A functional diagram of the MAX3724/MAX3725 is shown in Figure 1. The MAX3724/MAX3725 comprise a transimpedance amplifier stage, a voltage amplifier stage, an output buffer, and a direct-current (DC) feedback cancellation circuit. The MAX3724 also includes a signal strength indicator (RSSI). To provide this signal in 6 a standard 4-pin TO header, the RSSI level is added to the common mode of the differential data output pins. Transimpedance Amplifier Stage The signal current at the input flows into the summing node of a high-gain amplifier. Shunt feedback through the resistor RF converts this current to a voltage. In parallel with the feedback resistor are two back-to-back Schottky diodes that clamp the output signal for large input currents, as shown in Figure 2. _______________________________________________________________________________________ 3.2Gbps SFP Transimpedance Amplifiers with RSSI AMPLITUDE MAX3724/MAX3725 AMPLITUDE INPUT FROM PHOTODIODE TIME TIME OUTPUT (SMALL SIGNALS) INPUT AFTER DC CANCELLATION OUTPUT (LARGE SIGNALS) Figure 2. MAX3724/MAX3725 Limited Output Voltage Amplifier Stage The voltage amplifier stage provides gain and converts the single-ended input to differential outputs. Figure 3. DC Cancellation Effect on Input VCC 100Ω 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 caused by large input signals. The DC cancellation circuit is internally compensated and therefore does not require external capacitors. OUT+ OUT- Output Buffer The output buffer provides a reverse-terminated voltage output. The buffer is designed to drive a 100Ω differential load between OUT+ and OUT-. The MAX3724 must be DC-coupled to the MAX3748A. See Figures 4 and 5. For optimum supply-noise rejection, the MAX3725 should be terminated with a matched load. If a singleended output is required, the unused output should be terminated to a 50Ω resistor to VCC. The MAX3725 does not drive a DC-coupled, 50Ω grounded load; however, it does drive a compatible 50Ω CML input. Figure 4. Equivalent Output MAX3724 VCC 50Ω 50Ω Signal-Strength Indicator OUT+ The MAX3724 produces a signal proportional to the average photodiode current. This is added to the common mode of the data outputs OUT+ and OUT-. This signal is intended for use with the MAX3748A to provide a ground-referenced RSSI voltage. OUT- Applications Information Signal-Strength Indicator The SFF-8472 digital diagnostic specification requires monitoring of input receive power. The MAX3748A and MAX3724 receiver chipset allows for the monitoring of the average receive power by measuring the average DC current of the photodiode. Figure 5. Equivalent Output MAX3725 _______________________________________________________________________________________ 7 MAX3724/MAX3725 3.2Gbps SFP Transimpedance Amplifiers with RSSI The MAX3724 preamp measures the average photodiode current and provides the information to the output common mode. The MAX3748A RSSI detect block senses the common-mode DC level of input signals IN+ and IN- and provides a ground-level-referenced output signal of the photodiode current. The advantage of this implementation is that it allows the TIA to be packaged in a low-cost conventional 4-pin TO-46 header. The MAX3748A RSSI output is connected to an analog input channel of the DS1858/DS1859 SFP controller to convert the analog information into a 16-bit word. The DS1858/DS1859 provide the received power information to the host board of the optical receiver through a 2-wire interface. The DS1859 allows for internal calibration of the receive power monitor. The MAX3724 and the MAX3748A have been optimized to achieve RSSI stability of better than 2.5dB within the 6µA to 500µA range of average input photodiode current. To achieve the best accuracy, Maxim recommends receive power calibration to be 6µA at the low end, and 500µA at the high end of the required range. Optical Power Relations Many of the MAX3724/MAX3725 specifications relate to the input signal amplitude. When working with optical receivers, the input is sometimes expressed in terms of average optical power and extinction ratio. Figure 6 and Table 1 show relations that are helpful for converting optical power to input signal when designing with the MAX3724/MAX3725. (Refer to Application Note HFAN–3.0.0: Accurately Estimating Optical Receiver Sensitivity.) Optical Sensitivity Calculation The input-referred RMS noise current (I N ) of the MAX3724/MAX3725 generally determines the receiver sensitivity. To obtain a system bit-error rate (BER) of 1E-12, the signal-to-noise ratio must always exceed 14.1. The input sensitivity, expressed in average power, can be estimated as: 14.1 × IN (re + 1) Sensitivity = 10log 1000 dBm ( r − ) 2 ρ 1 e where ρ is the photodiode responsivity in A/W and IN is RMS current in amps. Input Optical Overload The overload is the largest input that the MAX3724/ MAX3725 can accept while meeting deterministic jitter specifications. The optical overload can be estimated in terms of average power with the following equation: 2mARMS (re + 1) Overload = 10log 1000 dBm 2ρ(re − 1) Optical Linear Range The MAX3724/MAX3725 have high gain, which limits the output when the input signal exceeds 50µAP-P. The MAX3724/MAX3725 operate in a linear range (10% linearity) for inputs not exceeding: 50µARMS (re + 1) Linear Range = 10log 1000 dBm 2ρ(re − 1) Table 1. Optical Power Relations PARAMETER SYMBOL RELATION Average power PAVG Extinction ratio re PAVG = (P0 + P1) / 2 r e = P1 / P 0 Optical power of a 1 P1 P1 = 2PAVG(re) / (re + 1) Optical power of a zero P0 P0 = 2PAVG / (re + 1) Signal amplitude PIN PIN = P1 - P0; PIN = 2PAVG(re - 1) / (re + 1) Note: Assuming 50% average duty cycle and mark density. 8 _______________________________________________________________________________________ 3.2Gbps SFP Transimpedance Amplifiers with RSSI Photodiode Filter Supply voltage noise at the cathode of the photodiode produces a current I = CPD ∆V/∆t, which reduces the receiver sensitivity (C PD is the photodiode capacitance.) The filter resistor of the MAX3724/MAX3725, 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): INOISE = (VNOISE)(CPD) / (RFILTER)(CFILTER) If the amount of tolerable noise is known, the filter capacitor can be easily selected: CFILTER = (VNOISE)(CPD) / (RFILTER)(INOISE) For example, with maximum noise voltage = 100mVP-P, CPD = 0.85pF, RFILTER = 600Ω, and INOISE selected to be 350nA: CFILTER = (100mV)(0.85pF) / (600Ω)(350nA) = 405pF Wire Bonding For high-current density and reliable operation, the MAX3724/MAX3725 use gold metalization. Connections to the die should be made with gold wire only, using ballbonding techniques. Die thickness is typically 14 mils (0.4mm). TOP VIEW OF TO-46 HEADER CASE GROUND OPTICAL POWER PI 400pF TO 1000pF 400pF TO 1000pF VCC PHOTODIODE PAVG OUT+ OUT- PO TIME MAX3724 MAX3725 Figure 6. Optical Power Relations Figure 7. Suggested Layout for TO-46 Header _______________________________________________________________________________________ 9 MAX3724/MAX3725 Layout Considerations Noise performance and bandwidth are adversely affected by capacitance at the IN pad. Minimize capacitance on this pad and select a low-capacitance photodiode. Assembling the MAX3724/MAX3725 in die form using chip and wire technology provides the best possible performance. Figure 7 shows a suggested layout for a TO header for the MAX3724/MAX3725. The placement of the filter cap to minimize the ground loop of the photodiode is required to achieve the specified bandwidth. The OUT+ and OUT- bond wire lengths should also be minimized to meet the bandwidth specification. Special care should be taken to ensure that ESD at IN does not exceed 500V. 3.2Gbps SFP Transimpedance Amplifiers with RSSI MAX3724/MAX3725 Chip Topography GND VCC 1 N.C. 2 VCC 3 IN 4 FILTER 5 MAX3724 MAX3725 10 9 OUT+ 0.03in (0.76mm) 6 7 GND N.C. 8 OUT- 0.05in (1.26mm) Pad Coordinates Chip Information PAD COORDINATES (µm) X COORDINATES (µm) Y 1 1.4 495.6 2 0 336 3 0 224 4 0 112 5 0 0 6 494.2 -1.4 7 865.2 -1.4 8 1005.2 -1.4 9 1005.2 495.6 10 490 495.6 TRANSISTOR COUNT: 301 PROCESS: SiGe Bipolar SUBSTRATE: ISOLATED DIE THICKNESS: 0.014in ±0.001in 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. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.