A CMOS Analog Front-end Receiver with Desensitization to Input Capacitance for Broadband Optical Wireless Communication

Line-of-sight optical wireless channels are emerging as a promising broadband wireless access technology. This paper describes a front-end transimpedance amplifier (TIA) that is designed to overcome challenges faced by high-speed optical wireless links requiring receivers with wide field-of-view (FOV) and high dynamic range for signal acquisition/tracking. This transimpedance amplifier employs a capacitive feedback configuration, with a selfbiased automatic gain control (AGC) circuit to increase the input dynamic range. The transimpedance amplifier is designed for integration with wide FOV detectors with associated capacitance up to 5pF and its performance is insensitive (within 5%) to an order of magnitude variation in input capacitance. The self-biased AGC allows 42dB dynamic range in received optical power to accommodate varying link ranges and different optical wireless (OW) system configurations. A test chip was implemented in a lowcost 0.5-μm CMOS process and achieves a maximum TIA gain of 52dBΩ , -3dB bandwidth of 523MHz at 5pF input capacitance, and variable TIA gain from 52dBΩ to 36dBΩ without instability. Noise measurements show input-referred noise current spectral density of 22pA/ √ Hz for 5pF input capacitance. Optical measurements show good eye diagrams at 750Mb/s. The power dissipation is 53mW from dual 3.3V and 1.8V supply voltages.