A dual-loop automatic gain control for infrared communication system

This paper presents a dual-loop automatic gain control (AGC) employed in a 10 Mbps infrared communication system. The AGC is composed of an exponential-type variable-gain amplifier, a shaping filter, a gain/buffer stage, a noncoherent envelope detector, and a pair of integrators that provide dual loop bandwidths. The switch and two integrators are realized by a proposed switched integrator technique. The fast acquisition is accomplished by a 500 kHz loop bandwidth at the initial acquisition state and followed by a 50 kHz loop bandwidth at the steady state. The AGC is implemented in 0.6 μm SPTM CMOS technology. According to the post-layout simulation, it achieves an acquisition time of 5 μs and provides a constant output of 1V_pp at a 50 Ω load for 20 dB input signal amplitude range. The dual-loop AGC consumes 88 mW power from a single 3.3 V supply and occupies 1.8×1.8 mm² area.