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: 1V supply voltage, 0~40dB gain range, 2dB 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 0.18μm CMOS and occupies an active area of 0.41mm2. The power consumption of AGC is about 0.17mW at 1V supply voltage. The gain of AGC loop ranges from 0dB to 40.2dB in 2dB step with gain error not more than 0.2dB. The total harmonic distortion (THD) is below -70dB over the audio frequencies at 0.4-Vpp differential output. The integrated noise in the audio range (20 Hz~20 kHz) is less than 5μVRMS when the gain is set at 0dB.