Patent ID: 7477099

Claim:
A filter adjustment circuit for adjusting response characteristics of an analog filter circuit having an analog amplifier capable of variably adjusting a gain in accordance with a value of a control signal inputted to a control terminal, the filter adjustment circuit comprising: reference signal generating means for generating an input signal to be inputted to the analog filter circuit and a reference signal as a comparison target and outputting the input signal and the reference signal; converting means for converting an output signal from the analog filter circuit operating on receiving the input signal and the reference signal from the reference signal generating means to signals in accordance with respective amplitude values of these signals; holding means for holding the two output signals from the converting means in time series; timing generating means for generating an update timing signal indicative of an update timing of the control signal to be inputted to the control terminal of the analog filter circuit based on a state transition of a filter output time-series signal held in the holding means or on a state transition of a reference time-series signal held in the holding means; and a control signal generating means for receiving the filter output time-series signal and the reference time-series signal each held in the holding means as well as the update timing signal from the timing generating means, generating the control signal to be inputted to the control terminal of the analog filter circuit based on a state of the received filter output time-series signal and on a state of the received reference time-series signal, and outputting the control signal to the analog filter circuit in accordance with a reception timing of the update timing signal.