A New Type of Digital Programmable Bandpass Filter

A new type of digital programmable bandpass filter is introduced, which is made up of a PC active filter with a high pass filter and a low pass one in series. In traditional PC active filters, digital variables cannot be used to control the cutoff frequencies. A D/A converter is used instead of the adjustable resistance so that the resistance can be altered by digital variables and the cutoff frequency changed. This filter can be directly interfaced, e.g. with a MCS -51 single chip microcomputer. It has been applied in an intelligent instrument, attaining satisfactory results.