Low-Pass Filters with Pseudo Resistors for Electronic Stethoscopes

This article is devoted to the design of a low-pass filter for an electronic stethoscope using pseudo resistors. A filter with imitation of inductors by an active circuit based on operational amplifiers with a bandwidth of 1 kHz has been chosen as a low-pass filter. Ripples in the bandwidth are 0.9 dB, and the stopband attenuation, starting at 10 kHz, is 77 dB. The efficiency of the filter is simulated at various temperatures and corner parameters. The values of nonlinear distortions and noise characteristics have been found, as well as the dynamic range of the filter equal to 44 dB, power consumption is 293 μW. The filter layout has been designed with an area of 68 000 μm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. It is possible to significantly reduce the filter chip area while maintaining acceptable filter characteristics, due to the use of pseudo resistors.