Differential charge-domain bilinear-Z switched-capacitor pseudo-N-path filters

The charge-domain bilinear-Z transformation is used in conjunction with a fully-differential pseudo-N-path filter design to create a design that has strong potential in the high-frequency bandpass domain. Both low-pass and high-pass N-path designs are examined theoretically and relative comparisons made of component and op-amp gain-sensitivity. Analysis by SWITCAP of component-sensitivity shows that the largest frequency-varying sensitivity is 0.064 dB per 1% component variation. A discrete prototype HP-two-path differential stray-insensitive filter was built as a test vehicle. Results are presented for a design with a bandpass center-frequency of two kHz and a bandwidth of 20 Hz. The clock feedthrough noise was shifted out of the passband by the use of z →z^-N transformation. Mirror frequency components were found to be about 55 dB below the signal level