AUTOMATIC GAIN CONTROL CIRCUIT AND DATA STORAGE DEVICE USING THE CIRCUIT

PURPOSE:To reduce a reply time by suppressing fluctuation of a bias voltage attended with a transient response caused at the changeover of an operation of a write/read circuit and at the changeover of magnetic heads in a write read circuit (RAW circuit) of the data storage device. CONSTITUTION:An input stage of an automatic gain control circuit(AGC) 304 is provided with a low pass filter(LPF) 102 eliminating a high frequency component of an inputted read signal, a voltage comparator (COMP) 103 comparing its output with a prescribed voltage and outputting a signal corresponding to the quantity, and a clamp circuit 104 holding an input terminal voltage of a non-amplified signal of a voltage controlled amplifier to a specific voltage corresponding to the voltage of the input signal and releasing the voltage holding. Thus, fluctuation in a bias voltage attended with the transient response is detected and the voltage is forcibly restored to 0V rapidly.