| 摘要 |
An automatic gain control circuit, for amplifying an input signal so that it has a specific correspondence with a reference value (Vref), includes an input terminal (2) for receiving the input signal, a variable gain amplifier (4) for amplifying the input signal in response to a gain control signal, a peak detector (14) for detecting peaks in the amplified input signal, the peak detector (14) having an attack time constant (Ta) and a decay time constant (Td), and supplying a peak detector output signal (Vp) representative of the amplitude of the peaks in the amplified input signal, a comparator (20) for comparing the peak detector output signal (Vp) with the reference value (Vref) to form an error signal (e), and an integrator (30) for integrating the error signal (e) to form the gain control signal. The peak detector includes a controller for controlling the decay time constant in response to the error signal, the controller decreasing the decay time constant for increasing error signals, in a situation when the peak detector output signal (Vp) is larger than the reference value (Vref). The relationship, Td=cxTap, is maintained between the attack time constant Ta and the decay time constant Td of the peak detector, where c is a positive constant and p is a constant larger than 1. p is preferably equal to 2 and c satisfies the relation 20</=c</=200.
|
