Design of filters using pseudo resistors for biomedical devices

The current state of the scientific and technical problem being solved is assessed, initial data are obtained, a 4th-order Sallen-Key filter and a filter with imitation of the inductors by an active circuit based on impedance converters using operational amplifiers and pseudo resistors are developed, and the results are compared. It is recommended to use the low-pass filter with imitation of the inductors in an electronic stethoscope, since it has, compared to the Sallen-Key filter, a less roll-off in the passband, greater attenuation in the stopband, a sharper drop in the frequency response in the transition region, better noise characteristics and a larger dynamic range. The filter with imitation of the inductors has lower nonlinear distortions and demonstrates operability with a spread of temperatures and element ratings, especially in the frequency range containing the main peaks of heartbeat and lung sounds, and the power consumption and hardware costs of such a filter are comparable to similar characteristics of the Sallen-Key filter.