Harmonic fold back improvement in the 4-path filter using band-pass charge domain sampler

In this paper we propose a method to improve the harmonic fold back (HFB) problem in a 4-path filter. A bandpass charge domain sampler (CDS) is used as a pre-filter for the 4-path filter. Producing notches around 3kf_s harmonics (f_s is the 4-path filter´s switching frequency and k=..., ±1, 0, ±1, ...) by pre-filter causes the folding of these frequency components to the 4-path filter pass-band be removed. The simulation results demonstrate that in the proposed structure the strongest harmonic folding occurs around 5f_s harmonic instead of 3f_s.