A Low Noise Low Distortion Automatic Gain Control Circuit

This paper presents a kind of Automatic Gain Control (AGC) circuits which can be used in speech signal acquisition system, it has high gain range, low noise and high linearity. The proposed AGC is based on feedback topologies and the gain is digital controlled. The design indexes are 1 V supply voltage, 0~40 dB gain range, 2 dB gain step, 8 kHz bandwidth. A π-type resistors network is used in the Programmable Gain Amplifier (PGA) as the passive feedback device to realize gain linearity in decibels and increase the gain accuracy. The hysteresis comparator eliminate the chattering effects when the output signal of Peak Detector changes rapidly around the threshold. The design is implemented in 0.18 μm CMOS and occupies an active area of 0.41 mm². The power consumption of AGC is about 0.17 mW at 1 V supply voltage. The gain of AGC loop ranges from 0 dB to 40.2 dB in 2 dB step with gain error not more than 0.2 dB. The total harmonic distortion (THD) is below -70 dB over the audio frequencies at 1 kHz, 0.4-Vpp differential output. The integrated noise in the audio range (20 Hz~20 kHz) is less than 5μVRMS when the gain of PGA is set at 0 dB.