19-1970; Rev 2; 1/02 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI Features ♦ 150mW Power Dissipation at 3.3V Supply ♦ 1.1µARMS Noise (-18dBm Sensitivity) ♦ 9GHz Bandwidth ♦ 2mAP-P Input Overload ♦ Received-Signal Strength Indication ♦ 8psP-P Typical Jitter Generation at 1.3mAP-P Input Current ♦ 600V/A Transimpedance Applications Ordering Information 10.3Gbps Ethernet Optical Receivers OC-192 VSR Optical Receivers Fibre-Channel Optical Receivers PART TEMP RANGE MAX3970U/D 0°C to +85°C PIN-PACKAGE Dice Note: Dice are designed to operate over a 0°C to +110°C junction temperature (TJ) range, but are tested and guaranteed at TA = +25°C. Typical Application Circuit 3.3V SUPPLY FILTERING VCC1 VCC2 MAX3970 FILTER 3.3V RF 200pF 0.01µF OUT+ IN OUT1.0V LIMITING AMPLIFIER 0.01µF RSSI ________________________________________________________________ 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 MAX3970 General Description The MAX3970 is a compact, low-power transimpedance amplifier (TIA) optimized for use in 10Gbps optical receivers. The TIA provides transimpedance at 600V/A with 50Ω differential CML outputs. The MAX3970 has a typical input-referred noise of 1.1µA, and when coupled with a high-speed photodiode, achieves -18dBm sensitivity and +2mA input overload. A received-signal strength indicator (RSSI) simplifies optical assembly. The circuit operates from a single 3.3V supply over a junction temperature range from 0°C to +110°C. MAX3970 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI ABSOLUTE MAXIMUM RATINGS Terminal Voltage Voltage VCC1 and VCC2 ...................................-0.3V to +5.0V Voltage at FILTER.................................-0.3V to (VCC1 + 0.3V) Voltage at OUT+, OUT-, RSSI ........................0V to (VCC + 0.5V) Input Current IN, TEST ............................................................-5mA to +5mA Operating Junction Temperature Range ...........-40°C to +125°C Storage Temperature Range .............................-60°C to +150°C Die Attach Process 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 = +3.0V to +3.6V, output loads = 50Ω to VCC, TJ = 0°C to +110°C. Typical values are at VCC = +3.3V, CIN = 0.25pF, LIN = 1.7nH, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER Supply Current Maximum DC Input Current SYMBOL in Z21 Small-Signal Bandwidth BW 100 DJ Input Bias Voltage VIN RSSI Gain RFILTER Maximum Differential Output Voltage VOD-MAX 62 130 1.45 1.45 f = 10GHz (Note 2) 11 µA pA/√Hz 43 50 58 Ω 450 600 875 Ω 9 13.2 GHz 70 150 kHz 7.4 IIN < 1.3mA 8 IIN = 2.0mA 16 22 0.9 0.96 IIN = 100µA to 1mA 900 1200 1500 IIN = 10µA to 100µA 1200 1800 3000 Input = 1mAP-P mA µAP-P 1.1 Differential output 10µAP-P < Input < 100µAP-P UNITS mA 1.1 RSSI Bandwidth Photodiode Filter Resistance 46 f = 10GHz (Note 2) Low-Frequency Cutoff Deterministic Jitter MAX f = 7.5GHz (Note 2) ROUT Small-Signal Transimpedance TYP 1.6 0.95 < linearity < 1.05 Input-Referred Noise Density Output Resistance (per side) MIN ICC IIN-MAX Input Linear Range Input-Referred RMS Noise CONDITIONS psP-P V V/A 10 70 330 410 500 kHz Ω 350 470 700 mVP-P Note 1: AC characteristics are guaranteed by design and characterization. Note 2: Input-referred noise is calculated as RMS output noise / (gain at f = 10MHz). Noise density is (input-referred noise) / √bandwidth. Noise measurements are made using 4-pole Bessel filters. 2 _______________________________________________________________________________________ 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI INPUT-REFERRED RMS NOISE CURRENT vs. AVERAGE INPUT CURRENT TJ = 100°C TJ = 50°C 0.3 0.4 0.5 0.6 MAX3970 toc02 5 10 100 1000 OUTPUT AMPLITUDE vs. TEMPERATURE 0 100 10 1000 INPUT = 1mAP-P, 00–11 PATTERN AT 10.0Gbps 600 500 400 300 200 -50 -25 0 25 50 1000 10000 DC TRANSFER FUNCTION OUTPUT VOLTAGE (mV) 10 100 AMPLITUDE (µAP-P) MAX3970 toc05 DETERMINISTIC JITTER vs. AVERAGE INPUT CURRENT 700 10 10000 DC INPUT CURRENT (µA) 20 15 10 1 0.7 30 20 1.0 CIN (pF) SIGNAL INPUT = 50µAP-P 75 100 300 DC CANCELLATION 250 CIRCUIT DISABLED, 200 VFILTER = GND 150 100 50 0 -50 -100 -150 -200 -250 -300 -2500 -1500 -500 500 1500 2500 INPUT CURRENT (µA) AMBIENT TEMPERATURE (°C) INPUT CURRENT (µA) EYE DIAGRAM (50µAP-P INPUT) EYE DIAGRAM (2.0mAP-P INPUT) SIMULATED FREQUENCY RESPONSE vs. INPUT INDUCTANCE 100mV/div MAX3970 toc09 70 65 LIN = 2.0nH 60 MAGNITUDE S21 (dB) 5mV/div 223 - 1PRBS 2mA INPUT MAX3970 toc08 223 - 1PRBS 50µA INPUT MAX3970 toc07 1 1.5 0 0.2 DIFFERENTIAL AMPLITUDE (mVP-P) 40 25 0.5 TJ = 0°C 0.9 2.0 INPUT = k28.5 PATTERN MAX3970 toc06 1.1 30 JITTER (psP-P) 1.2 0.8 0.1 JITTER (psP-P) 2.5 RMS NOISE CURRENT (µA) 1.3 1.0 3.0 MAX3970 toc01 NOISE IS MEASURED IN A BANDWIDTH OF 7.5GHz. MAX3970 toc04 INPUT-REFFERED NOISE (µARMS) 1.4 DETERMINISTIC JITTER vs. INPUT AMPLITUDE MAX3970 toc03 INPUT-REFERRED NOISE vs. CAPACITANCE 55 LIN = 1.5nH LIN = 1.0nH LIN = 0.5nH 50 45 40 35 30 25 20ps/div 20ps/div 1k 10k 100k 1M 10M 100M 1G 10G 100G FREQUENCY (Hz) _______________________________________________________________________________________ 3 MAX3970 Typical Operating Characteristics (VCC = +3.3V, TA = +25°C, input bondwire inductance = 1.0nH, unless otherwise noted. CIN is total source capacitance to die. All measurements made on MAX3970 EV Kit.) Typical Operating Characteristics (continued) (VCC = +3.3V, TA = +25°C, input bondwire inductance = 1.0nH, unless otherwise noted. CIN is total source capacitance to die. All measurements made on MAX3970 EV Kit.) LIN = 2.0nH LIN = 1.5nH 52 LIN = 1.0nH 50 LIN = 0.5nH 15 20 25 30 -0.20 IIN = 0, iIN = 0 MAX3970 toc12 MAX3970 toc11 ∆VCC 10 48 -0.25 VCC = +3.0V VCC = +3.3V -0.30 VCC = +3.6V -0.35 35 40 1G 10G -0.40 100k 100G 1M 10M 100M FREQUENCY (Hz) FREQUENCY (Hz) S22 vs. FREQUENCY OUTPUT VSWR (DIFFERENTIAL) 20 40 60 80 RSSI OUTPUT VOLTAGE vs. AVERAGE INPUT CURRENT 2.5 MAX3970 toc14 0 0 AMBIENT TEMPERATURE (°C) 3.0 MAX3970 toc13 10 1G 2.8 2.6 MAX3970 toc15 46 2.0 2.4 -10 VSWR -30 VRSSI (V) 2.2 -20 2.0 1.8 -40 1.5 1.0 1.6 1.4 0.5 1.2 -50 1.0 -60 100M 1G 0 0.8 100M 10G 1G SIMULATED SMALL-SIGNAL BANDWIDTH vs. CAPACITANCE 700 12 TJ = 50°C 10 9 TJ = 0°C TJ = 100°C 600 TRANSIMPEDANCE (V/A) -3dB BANDWIDTH (GHz) 13 7 6 1000 CURRENT (mA) MAX3970 toc17 14 8 500 SMALL-SIGNAL TRANSIMPEDANCE vs. TEMPERATURE MAX3970 toc16 15 11 0 10G FREQUENCY (Hz) FREQUENCY (Hz) 500 400 300 200 100 5 4 0 0.1 0.2 0.3 0.4 CIN (pF) 4 ∆VOUT COMMON-MODE VOLTAGE (V) PSRR = -20 LOG 5 SUPPLY REJECTION (dB) 56 MAGNITUDE S21 (dB) 0 MAX3970 toc10 58 54 OUTPUT COMMON-MODE VOLTAGE (REFERENCED TO VCC) vs. TEMPERATURE POWER-SUPPLY REJECTION RATIO vs. FREQUENCY SIMULATED FREQUENCY RESPONSE vs. INPUT INDUCTANCE MAGNITUDE S22 (dB) MAX3970 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI 0.5 0.6 0.7 -50 -25 0 25 50 75 100 AMBIENT TEMPERATURE (°C) _______________________________________________________________________________________ 1500 2000 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI PAD NAME FUNCTION BP1, BP2, BP18 VCC1 BP3 FILTER BP4 TEST BP5 IN BP6, BP7 GND1 BP8, BP9 GND2 Ground BP10, BP13 GND3 Ground BP11 OUT- Negative CML Output. Current flowing into IN causes OUT- to decrease. BP12 OUT+ Positive CML Output. Current flowing into IN causes OUT+ to increase. BP14, BP15 BP16 VCC2 Power Supply. Provides supply voltage to the output buffers. BP17 RSSI Received-Signal Strength Indicator. This pin provides a voltage proportional to the DC input current. Monitor this output during assembly to optimally align the photodiode to the optics. Power Supply. Provides supply voltage to input circuitry and bias to the photodiode via an internal 410Ω resistor. Provides bias voltage for the photodiode through a 410Ω resistor to VCC1. When grounded, this pin disables the DC cancellation circuit to allow a DC path from IN to OUT+ and OUT- for testing. Test Pad. This pad is connected to IN via a 1kΩ resistor. Amplifier Input. Accepts photodiode input current. Ground Detailed Description The MAX3970 transimpedance amplifier is optimized for 10Gbps fiber optic receivers. Figure 1 is a functional diagram of the MAX3970, which comprises a transimpedance amplifier, a voltage amplifier, an output buffer, a received-signal strength indicator, and a DCcancellation circuit. Transimpedance Amplifier Photodiode signal current flows into the summing node of a high-gain amplifier. Shunt feedback through RF converts this current into a voltage with a gain of approximately 400Ω. Schottky diodes clamp the output voltage for large input currents, as shown in Figure 2. DC Cancellation Circuit The DC cancellation circuit centers the input signal within the transimpedance amplifier’s linear range (Figure 3). Low-frequency feedback is employed to remove the input signal’s DC component. The DC cancellation circuit is internally compensated and therefore does not require external capacitors. This circuit minimizes pulse-width distortion for data sequences that exhibit a 50% mark density. A mark density significantly different from 50% will cause the MAX3970 to generate pulse-width distortion. Received-Signal Strength Indicator The voltage amplifier converts single-ended signals to differential signals and introduces approximately 4dB of gain. The received-signal strength indicator (RSSI) provides a voltage proportional to the DC input current. The RSSI circuitry is designed to drive a 10kΩ load and is used during the assembly process to optimally align the photodiode. The lowpass filter in the DC cancellation circuit determines the response time of the RSSI circuit. Output Buffer Design Procedure Voltage Amplifier The output buffer is optimized to drive a 100Ω differential load between OUT+ and OUT-. Although short-circuit protection is provided, this stage will not drive a 50Ω load to ground. For proper operation, the load must be AC-coupled. For large signals, the output buffer produces a limited, 500mVP-P differential output voltage. Terminate the MAX3970 outputs differentially for optimum supply-noise rejection. If a single-ended output is required, terminate the used and unused outputs similarly. Power Supply The MAX3970 requires wide-band power-supply decoupling. Power-supply bypassing should provide low impedance between VCC and ground for frequencies between 50kHz and 10GHz. Use LC filtering at the main supply terminal and decoupling capacitors as close to the die as possible. _______________________________________________________________________________________ 5 MAX3970 Pad Description MAX3970 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI RF MAX3970 420Ω TRANSIMPEDANCE AMPLIFIER VOLTAGE AMPLIFIER OUTPUT BUFFER 50Ω OUT+ IN OUT50Ω DC CANCELLATION CIRCUIT 1kΩ TEST RSSI BUF LOWPASS FILTER VCC1 BUF 410Ω FILTER DISABLE Figure 1. Functional Diagram AMPLITUDE AMPLITUDE INPUT FROM PHOTODIODE OUTPUT (LARGE SIGNALS) OUTPUT (SMALL SIGNALS) TIME TIME INPUT AFTER DC CANCELATION Figure 2. MAX3970 Limited Output Figure 3. Effects of DC Cancellation on Input Signal 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 MAX3970 contains an internal lowpass filter to reduce photodiode noise current and improve receiver sensitivity. An external capacitor connected between the FILTER pad and ground can further reduce this noise (see the Typical Application Circuit). Current generated by supply-noise voltage is divided between the filter capacitance and photodiode capacitance. Assuming the filter capacitance is much larger than the photodiode capacitance, the input noise current due to supply noise is: 6 INOISE = (VNOISE)(CPD) / (RFILTER)(CFILTER) where C FILTER is the external capacitance plus the internal 22pF capacitor. If the amount of tolerable noise is known, the filter capacitance can be easily selected: CFILTER = (VNOISE)(CPD) / (RFILTER)(INOISE) For example, with maximum noise voltage = 100mVP-P, CPD = 0.25pF, RFILTER = 410Ω, and INOISE selected to be 300nA (1/4 of the MAX3970's input noise): CFILTER = (100mV)(0.25pF) / (410Ω)(300nA) ≈ 200pF Thus, the required external filter capacitance is 200pF -22pF = 178pF. _______________________________________________________________________________________ 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI Output Coupling Capacitors The output coupling capacitors should be low impedance over a frequency range from 50kHz to 10GHz. For more information on selecting coupling capacitors, visit Maxim's website and follow the links to HFAN1.1, Choosing AC-Coupling Capacitors. The MAX3970 has two power-supply connections (VCC1 and VCC2) and three ground connections (GND1, GND2, and GND3). Maxim recommends connecting all power supply and ground pads. At a minimum, connect at least one pad from each section. The backside of the MAX3970 die is fully insulated and can be connected to VCC, ground, or left floating. Input Capacitance Noise and bandwidth are adversely affected by capacitance on the MAX3970’s input node as shown in Input Referred Noise vs. Capacitance and Small Signal Bandwidth vs. Capacitance in the Typical Operating Characteristics. Use any technique available to minimize input capacitance. Applications Information Interface Schematics Figures 4 through 7 show interface pads for the MAX3970. Back termination is provided by integrated 50Ω pullup resistors. Optical Power Relations Many MAX3970 specifications relate to the input signal amplitude. When working with fiber optic receivers, the input is sometimes expressed in terms of average optical power and extinction ratio. Figure 8 shows the relations that are helpful for converting optical power to optical modulation amplitude when designing with the MAX3970. Optical power relations are shown in Table 1 for an average mark density of 50% and an average duty cyle of 50%. VCC TEST 50Ω 50Ω OUT+ 1kΩ OUT- 12.5Ω IN 12.5Ω GND GND Figure 4. OUT Pads Figure 5. IN and TEST Pads _______________________________________________________________________________________ 7 MAX3970 Wire Bonding For high current density and reliable operation, the MAX3970 uses gold metalization. Connections to the die should be made with gold wire only. Aluminum bonding is not recommended. Die thickness is typically 8mils (0.203mm). Bondwire inductance between the photodiode and the IN pad can be optimized to obtain best performance. Higher inductance improves bandwidth while lower bondwire inductance reduces time domain ringing. See the Frequency Response vs. Input Inductance plot in the Typical Operating Characteristics. Bondwires on all other pads should be kept as short as possible (<30mil) to optimize performance. MAX3970 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI VCC VCC1 410Ω FILTER 22pF RSSI GND GND Figure 7. RSSI Pad Figure 6. FILTER Pad Input Optical Overload The overload is the largest input that the MAX3970 accepts while meeting specifications. Optical overload can be estimated in terms of average power with the following equation: OPTICAL POWER P1 2mA Overload = 10log × 1000 dBm 2×ρ PAVE Optical Linear Range The MAX3970 has high gain, and operates in a linear range for inputs not exceeding: P0 TIME Figure 8. Optical Power Relations 60µA(re + 1) Linear Range = 10log × 1000 dBm 2 × ρ × (re − 1) Optical Sensitivity Calculation The MAX3970 input-referred RMS noise current in generally determines the receiver sensitivity. To obtain a system bit error rate (BER) of 1 x 10-12, the signal-tonoise 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 2 × ρ × ( r 1 ) − e where ρ is the photodiode responsivity in A/W. 8 _______________________________________________________________________________________ 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI PARAMETER SYMBOL MAX3970 Table 1. Optical Power Relations* (129.8, 971.6) RELATION Average Power PAVG PAVG = (P0 + P1) / 2 Extinction Ratio re re = P1 / P0 Optical Power of a “1” P1 P1 = 2PAVG Optical Power of a “0” P0 Optical Modulation Amplitude PIN re MAX3970 (0, 799.4) re + 1 3 P0 = 2PAVG / (re+1) (512, 548.8) IN r −1 PIN = P1 − P0 = 2PAVG e re + 1 (0, 169.4) *Assuming a 50% average mark density. HF98Z (381.8, 0) Table 2. MAX3970 Bondpad Information COORDINATES PAD NAME X Y BP1 VCC1 0 799.4 BP2 VCC1 0 673.4 BP3 FILTER 0 547.4 BP4 TEST 0 421.4 BP5 IN 0 295.4 BP6 GND1 0 169.4 BP7 GND1 129.8 0 BP8 GND2 255.8 0 BP9 GND2 381.8 0 BP10 GND3 512 170.8 BP11 OUT- 512 296.8 BP12 OUT+ 512 422.8 BP13 GND3 512 548.8 BP14 VCC2 512 674.8 BP15 VCC2 512 800.8 BP16 VCC2 381.8 971.6 BP17 RSSI 255.8 971.6 BP18 VCC1 129.8 971.6 y x • ALL DIMENSIONS ARE IN microns. • PAD DIMENSIONS: METAL H = 102.4 microns W = 102.4 microns PASSIVATION OPENING 94.4 microns 94.4 microns • COORDINATES SPECIFY LOWER LEFT CORNER OF THE PAD. Figure 9. Bondpad Diagram _______________________________________________________________________________________ 9 MAX3970 10Gbps, 3.3V Low-Power Transimpedance Amplifier with RSSI Chip Topography VCC1 RSSI VCC2 VCC2 VCC1 VCC2 VCC1 GND3 FILTER OUT+ 0.053" (1.345mm) TEST IN OUT- GND1 GND3 DIE IDENTIFICATION GND1 GND2 GND2 0.034" (0.864mm) Chip Information TRANSISTOR COUNT: 125 PROCESS: SILICON GERMANIUM BIPOLAR 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 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.