An analog front-end receiver with desensitization to input capacitance for free space optical communication

Optical wireless (OW) communication links are emerging as a promising broadband wireless access technology. This paper presents an analog front-end receiver that is designed to overcome challenges faced by high-speed optical wireless links requiring wide field-of-view (FOV), high dynamic range imaging receivers for signal acquisition/ tracking. This receiver employs a capacitive feedback transimpedance amplifier (TIA), with a self-biased automatic gain control (AGC) circuit to increase the input dynamic range. The receiver is designed for integration with wide FOV detectors with associated capacitance up to 5 pF and its performance is insensitive (within 5%) to an order of magnitude variation in input capacitance. The self-biased AGC allows 42 dB dynamic range in received optical power to accommodate varying link ranges and different OW system configurations. The receiver achieves a maximum gain of 52 dBOmega, -3 dB bandwidth of 523 MHz at 5 pF input capacitance, and variable TIA gain from 52 dBOmega to 32 dBOmega without instability. The input referred noise is 18.6 pA/radic(Hz) for 5 pF input capacitance. The front-end receiver is implemented in a 0.5 mum CMOS process and occupies an area of 0.06 mm² not including pads.