Disclosed is a bandpass filter with an input terminal including a sampling circuit for double sampling an input signal from said input terminal, an amplifier, and a conductive connection circuit whose input terminal is coupled to an output of said amplifier, for successively forming three different stages of conductive connection during a time period to form a filtering device with said amplifier. A double sampling bandpass delta-sigma modulator with an input terminal includes two said bandpass filters, a comparator circuit, a multiprocessor, and a feedback circuit which can reduce by half both the required number of amplifiers and the mismatch problems between capacitors and higher frequency operation, and can be easily achieved without additional analog circuits.
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