A current detecting circuit for linear-mode InGaAs APD arrays

This paper presents a current detecting circuit for linear-mode InGaAs Avalanche Photo Diode (APD) array, which is the interface between APD and readout circuit. The detecting circuit adopts a Regulated Cascode (RGC) transimpedance preamplifier (TIA) for its high gain and wide bandwidth, and a differential voltage amplifier with high common-mode rejection ratio and strong capability in depressing the noise influence is used to further amplify the sensed signal generated by the preamplifier effectively. A gated control technique is also used to reduce the average power consumption. The circuit is designed and fabricated in TSMC 0.35μm CMOS technology, and the power consumption is 0.73mW with the operating voltage of 3.3V. The core area of the circuit is only 55μm×90μm. The proposed circuit is successfully used in a 8×8 APD array readout circuit, and the experimental result shows that the current sensitivity is 5.2μA.