Low-pass filtering circuit and method of using the same.

摘要

A filtering circuit having the behavior of a low-pass filter capable of having a long time constant. The filtering circuit comprises an input circuit (10) for receiving a voltage input signal to be filtered. A comparator circuit (11) is provided for monitoring the input signal relative to an analog output signal from an accumulator circuit (13) and providing an error signal representative of the difference of the input and output signals. The error signal is fed to a voltage controlled oscillator (17) to generate a frequency signal proportional to the error signal. A frequency dividing circuit (14) is provided to divide the frequency signal by a predetermined division factor to control the low cut-off frequency of the filtering circuit whereby to increase the response time thereof. An accumulator (13) is provided to integrate the frequency signal. An output circuit (33) provides an output of the stored integrated frequency signal to constitute the analog output signal.