N-path and pseudo-N-path cells for switched-current signal processing

Novel switched-current N-path and pseudo-N-path cells are proposed, which allow the transformation of a z-domain low-pass reference filter into a bandpass one. The three types of cells, a forward Euler, backward Euler, and bilinear integrator, perform the z→-z and z→-z^N transformations, which avoid clock-feedthrough noise in the realized filter passband. The pseudo-N-path cells operate on the circulating-delay principle, which avoids mirror-frequency noise due to path mismatches and require only standard biphase clocks to operate. The effects of circuit nonidealities are studied and performance comparisons are made with a conventional narrow-band bandpass filter. The robust frequency stability characteristic makes the cells suitable for narrow-band bandpass applications. Results of an HSPICE simulation example is given for a sixth-order pseudo-N-path filter