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2.5 Gbps High Sensitivity Transimpedance Amplifier with AGC

M02024 Product Brief - 34685 M02024

Low-power, high-sensitivity 2.5 Gbps TIA forGPON and OC48 applications

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Key Features

> -29 dBm Sensitivity > Photodiode current monitor

The M02024 transimpedance amplifier (TIA) withautomatic gain control (AGC) is fabricated in sub-micron CMOS for high performance. The device targets a sensitivity of -29dBm, enabling the use of low cost PIN diodes to meet the GPON Class B+ standard. In order to satisfy such high sensitivity and goodoptical overload requirements, automatic gain control (AGC) is implemented in the M02024. The AGC monitors the output amplitude and auto- matically reduces the TIA gain when the photodiode current exceeds the AGC threshold, maintaining the output at a constant level. With an input overload capability greater than +6 dBm, the AGC allows more than 35 dB of dynamic range, providing a low-cost solution for longer- reach 2.5 Gbps GPON/ATM/SONET systems that formerly required an APD. For even greater sen- sitivity, the M02024 may be used with an APD.The TIA consists of a high gain single-endedCMOS amplifier with a feedback resistor. The feedback creates a virtual low impedance at the input, and nearly all of the input current passes through the feedback resistor, defining the volt- age at the output. Advanced CMOS design techniques are employed to maintain the stability of this stage across all input conditions. An on- chiplow dropout linear regulator has been incorporated into the design to give excellent noise rejection up to several MHz. Higher frequency noise is removed by the inte-grated filter, eliminating the need for an external capacitor on the photodiode cathode.The circuit is intended to be configured for usewith PIN photodiodes in the “grounded cathode” configuration with the anode connected to the input of the TIA and the cathode connected to the PINK terminal. The PINK terminal provides ~2V reverse DC bias to reduce the photodiode capacitance. Operation with an external photodi- ode bias supply is also possible, as required by avalanche photodiodes.A replica of the average photodiode current isavailable at the MON pad for photo-alignment, monitoring average power and 'Loss of Signal' detection.For optimum system performance, the M02024die should be mounted with the photodetector inside a lensed TO-Can or other optical sub- assembly.

> Data rates to 2.5 Gbps > Internal or external bias forphotodiode > Integrated filter, eliminatesneed for a capacitor on thephotodiode cathode > Single +3.3V supply > Same pad layout and diesize asM02011/13/14/15/16 > AGC provides dynamicrange of 35 dB > +6 dBm Input overload

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