An all pass filter is a filter that passes all frequencies with equal gain while changing the phase of signals at different frequencies. Typically, the phase is shifted as a function of frequency. An all pass filter is often defined in terms of quarter wavelength delay (the delay at which the input and output are phase shifted by 90°. The all pass filter can be used to compensate for undesired phase shifts, implementation of a notch comb filter (achieved by mixing the filter output with an unfiltered version of the signal), and to converted a mixed phase filter’s output into a minimum phase filter.
Triad Semiconductor designs full custom mixed signal ASICs with all types of filters including continuous time, switched capacitor, gm-c, RF and sampled IF filters. Our design team has experience designing filters for precision low frequency applications, high-fidelity audio, telephony, cellphone, medical and high-volume consumer applications.