19-1790; Rev 0; 8/00 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier Features ♦ 490nA (typ) Input-Referred Noise ♦ 2000MHz Bandwidth ♦ 2mA Input Overload ♦ 100Ω Differential Output Impedance ♦ 112mW Power Dissipation at +3.3V ♦ Integrated Filter Resistor ♦ CML Outputs ♦ Single +3.0V to +5.5V Supply Voltage Ordering Information Applications SDH/SONET Transmission Systems PART TEMP. RANGE MAX3864ESA -40°C to +85°C 8 SO -40°C to +85°C Dice* MAX3864E/D PIN Preamplifier Receivers PIN-PACKAGE * Dice are designed to operate with junction temperatures of -40°C to +140°C but are tested and guaranteed only at TA = +25°C. APD Preamplifier Receivers 2.5Gbps ATM Receivers Pin Configuration Regenerators for SDH/SONET TOP VIEW VCC 1 8 GND 7 OUT+ 3 6 OUT- FILTER 4 5 GND N.C. 2 MAX3864 IN SO Typical Application Circuit VCC 0.01µF 750Ω CFILTER 400pF VCC FILTER 0.1µF OUT+ PHOTODIODE IN 100Ω OUT- MAX3864 0.1µF LIMITING AMPLIFIER GND ________________________________________________________________ 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. MAX3864 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 750Ω 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. MAX3864 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier 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 = +85°C) 8-Pin SO package (derate 6.7mW/°C above +85°C) ..436mW Storage Temperature Range .............................-55°C to +150°C Operating Junction Temperature ......................-55°C to +150°C Processing Temperature (die) .........................................+400°C Lead Temperature (soldering, 10s) .................................+300°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 = +3.0V to +5.5V, 100Ω load between OUT+ and OUT-, 0.1µF coupling capacitors on OUT+ and OUT-, TA = -40°C to +85°C, unless otherwise noted. Typical values are at +3.3V, source capacitance = 0.85pF, and TA = +25°C.) (Note 1) PARAMETER CONDITIONS Input Bias Voltage MIN TYP MAX 0.66 0.83 0.99 V 34 63 mA Supply Current UNITS Transimpedance Differential, measured with 40µAp-p input 2100 2750 3400 Ω Output Impedance Single ended (per side) 48 50 52 Ω Maximum Differential Output Voltage Input = 2mAp-p with 100Ω differential output termination 220 380 575 mVp-p 600 750 930 Filter Resistor Ω AC Input Overload 2 mAp-p DC Input Overload 1 mA Input-Referred RMS Noise Input-Referred Noise Density 490 Bandwidth = 2.0GHz (Note 2) Small-Signal Bandwidth 1525 Low-Frequency Cutoff -3dB, input ≤ 20µADC Transimpedance Linear Range Gain at 40µAp-p is within 5% of the smallsignal gain Deterministic Jitter Power-Supply Rejection Ratio (PSRR) 668 nA 11 pA/√(Hz) 2000 MHz 30 kHz µAp-p 40 3.13V < VCC < 5.5V (Note 3) 24 67 3.0V ≤ VCC ≤ 3.13V (Note 3) 24 77 Output referred, f < 2MHz, PSRR = -20log(∆VOUT/∆Vcc) 50 ps dB 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. 2 _______________________________________________________________________________________ 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier INPUT-REFERRED RMS NOISE vs. TEMPERATURE 500 CIN = 1.0pF CIN = 0.5pF CIN IS SOURCE CAPACITANCE PRESENTED TO DIE, INCLUDES PACKAGE PARASITIC, PIN DIODE, AND PARASITIC INTERCONNECT CAPACITANCE. 300 250 -20 0 20 40 60 80 70 60 50 40 30 20 10 80 0 1 100 10 100 1k 10k JUNCTION TEMPERATURE (°C) FREQUENCY (MHz) INPUT-REFERRED RMS NOISE CURRENT vs. DC INPUT CURRENT SMALL-SIGNAL TRANSIMPEDANCE vs. TEMPERATURE 69 700 600 500 400 300 68 67 2.2 66 65 64 63 1.7 1.6 1.5 0 60 CIN IS SOURCE CAPACITANCE PRESENTED TO DIE, INCLUDES PACKAGE PARASITIC, PIN DIODE, AND PARASITIC INTERCONNECT CAPACITANCE. 1.4 -40 DC INPUT CURRENT (µA) -20 0 20 40 60 80 100 -40 INPUT = 2mA 460 VCC = 3.0V AT TA = -40°C 0 20 40 60 80 100 EYE DIAGRAM (INPUT = 2mAp-p) MAX3864 toc11 MAX3864 toc07 EYE DIAGRAM (INPUT = 2mAp-p) INPUT = 213 -1 PRBS WITH 72 CID -20 JUNCTION TEMPERATURE (°C) AMBIENT TEMPERATURE (°C) DIFFERENTIAL OUTPUT AMPLITUDE vs. TEMPERATURE 480 CIN = 1.5pF 1.8 61 500 CIN = 0.5pF 1.9 62 1000 CIN = 1.0pF 2.0 100 100 10,000 2.1 200 10 1000 BANDWIDTH vs. TEMPERATURE BANDWIDTH (GHz) TRANSIMPEDANCE dBΩ) 800 100 2.3 MAX3864 toc05 900 10 INPUT CURRENT AMPLITUDE (µAp-p) 70 MAX3864 toc04 1000 1 MAX3864 toc03 MAX3864 toc02 60 50 -40 INPUT-REFERRED NOISE (nARMS) 65 55 200 DIFFERENTIAL OUTPUT AMPLITUDE (mVp-p) 90 MAX3864 toc06 350 70 INPUT = 213 -1 PRBS WITH 72 CID VCC = 3.13V AT TA = -40°C MAX3864 toc12 400 100 PEAK-TO-PEAK JITTER (ps) TRANSIMPEDANCE (dBΩ) CIN = 1.5pF 450 75 MAX3864 toc01 INPUT-REFERRED NOISE (nARMS) 600 550 DETERMINISTIC JITTER vs. INPUT AMPLITUDE FREQUENCY RESPONSE 440 420 50mV/div 400 50mV/div 380 360 340 320 300 -40 -20 0 20 40 60 80 100 80ps/div 80ps/div AMBIENT TEMPERATURE (°C) _______________________________________________________________________________________ 3 MAX3864 Typical Operating Characteristics (VCC = 3.3V, TA = +25°C and MAX3864 EV kit source capacitance = 0.85pF, unless otherwise noted). Typical Operating Characteristics (continued) VCC = 3.3V, TA = +25°C and MAX3864 EV kit source capacitance = 0.85pF, unless otherwise noted). EYE DIAGRAM (INPUT = 2mAp-p) 10mV/div MAX3864 toc10 INPUT = 223 -1 PRBS 200 DIFFERENTIAL OUITPUT VOLTAGE (mVp-p) MAX3864 toc09 MAX3864 toc08 INPUT = 223 -1 PRBS DC TRANSFER FUNCTION EYE DIAGRAM (INPUT = 20µAp-p) 50mV/div MAX3864 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier 100 0 -100 -200 80ps/div -100 80ps/div -50 0 50 100 INPUT CURRENT (µA) Pin Description PIN NAME 1 VCC Supply Voltage FUNCTION 2 N.C. No Connection 3 IN Amplifier Input 4 FILTER Provides bias voltage for the photodiode through a 750Ω 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. 5 GND Ground 6 OUT- Inverting Output. Current flowing into IN causes VOUT- to decrease. 7 OUT+ Noninverting Output. Current flowing into IN causes VOUT+ to increase. 8 GND Ground 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. 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). 4 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 100Ω differential load between OUT+ and OUT-. The output voltage is divided between internal 50Ω 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. _______________________________________________________________________________________ 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864 MAX3864 RF = 1k TRANSIMPEDANCE AMPLIFIER VOLTAGE AMPLIFIER OUTPUT BUFFER 50Ω OUTPUT FILTER OUT+ OUT- IN 50Ω LOWPASS FILTER VCC VCC GND DISABLE 750Ω DC CANCELLATION CIRCUIT FILTER Figure 1. Functional Diagram AMPLITUDE AMPLITUDE INPUT FROM PHOTODIODE TIME TIME OUTPUT (SMALL SIGNALS) INPUT (AFTER DC CANCELLATION) OUTPUT (LARGE SIGNALS) 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 50Ω to VCC. The MAX3864 will not drive a DC-coupled, 50Ω grounded load. 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). 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 _______________________________________________________________________________________ 5 MAX3864 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier where ρ is the photodiode responsivity, including fiberto-photodiode coupling efficiency in A/W and IN in µA. For example, if SNR = 12.7, IN = 0.490µA, re = 10, and ρ = 1, then sensitivity is -24dBm. POWER PI Input Optical Overload PIN PAVG PO TIME Figure 4. Optical Power Relations Optical Linear Range Table 1. Optical Power Relations PARAMETER SYMBOL RELATION Average Power PAVE Extinction Ratio re PAVE = (P0 + P1) / 2 r e = P1 / P0 Optical Power of a 1 P1 P1 = 2PAVEre / (re + 1) Optical Power of a 0 P0 P0 = 2PAVE / (re + 1) Signal Amplitude PIN PIN = P1 - P0 = 2PAVE (re - 1) / (re + 1) 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 × IN (re + 1) Sensitivity =10log dBm 2ρ(re − 1) × 1000 6 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 × 1000 Overload = 10log dBm 2ρ The MAX3864 has high gain, which limits the outputs when the input signal exceeds 40µAp-p. The MAX3864 operates in a linear range for inputs not exceeding: 40µAp - p(re + 1) × 1000 Linear Range = 10log dBm 2ρ(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. 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. _______________________________________________________________________________________ 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864 TOP VIEW OF TO-46 HEADER VCC VCC CFILTER VCC 200Ω PHOTODIODE OUT+ OUT- IN MAX3864 GND CASE IS GROUND Figure 5. Suggested Layout for TO-46 Header Figure 6. Equivalent Input Circuit Photodiode Filter Wire Bonding 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): 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 ) If the amount of tolerable noise is known, the filter capacitor can be easily selected: CFILTER = (VNOISE )(CPD ) (RFILTER )(INOISE ) For example, with a maximum noise voltage equal to 100mVp-p, CPD = 0.85pF, RFILTER = 750Ω, and INOISE selected to be 250nA (half of the MAX3864’s input noise): CFILTER = (100mV)(0.85pF) = 453pF (750Ω)(250nA) _______________________________________________________________________________________ 7 MAX3864 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier VCC 50Ω 50Ω OUT+ OUT- GND Figure 7. Equivalent Output Circuit 8 _______________________________________________________________________________________ 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier OUT+ OUT- GND GND VCC INPUT Chip Information TRANSISTOR COUNT: 320 PROCESS: BIPOLAR (SILICON GERMANIUM) 50mils 1.27mm FILTER 30mils (0.762mm) _______________________________________________________________________________________ 9 MAX3864 Chip Topography 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier SOICN.EPS MAX3864 Package Information 10 ______________________________________________________________________________________ 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier MAX3864 NOTES ______________________________________________________________________________________ 11 MAX3864 2.5Gbps, +3V to +5.5V, Wide Dynamic Range Transimpedance Preamplifier 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 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.