A fast-settling high linearity auto gain control for broadband OFDM-based PLC system

A fast-settling high-linearity automatic gain control (AGC) for broadband OFDM-based (Orthogonal Frequency Division Multiplexing) powerline communication (PLC) transceiver is presented in this paper. The high peak-to-average power ratio (PAPR) of OFDM signals makes conventional closed-loop AGCs impractical for the stringent settling-time constraints. A novel AGC algorithm is proposed incorporating with a linear power detector and a charge-redistribution converter to determine the gain of the pseudo-exponential programmable gain amplifier (PGA). Fabricated in 90-nm CMOS technology, the PGA has been measured to exhibit a constant 3-dB bandwidth of 350 MHz with dB-linear gain ranging from -20 to 20 dB. The measured settling time of gain acquisition is less than 0.1 μs, which meets the stringent criteria of short settling time of OFDM-based system. The proposed AGC consumes 3.7 mW through a 1.2-V supply, and occupies 0.07 mm² active area.