Ultra-low distortion linearized pseudo-RC low-pass filter

Low distortion applications are increasingly demanded especially in the medical and audiovisual fields. Equally important, body sensors are more and more used in the medical, sports and space research fields. For instance, the breathing and heart rate signals fluctuate in the 0.5 to 5 Hz frequency range while several of the common biophysiological signals are situated between the 0.1 to 1 kHz spectrum like the electrooculography (EOG), the electroencephalography (EEG), the electrocardiogram (ECG), the electromyography (EMG). In this paper, an active low-pass filter using very high linear pseudo-resistors is presented. The pseudo-resistors allow the realization of very large resistances using small silicon area. More importantly, our proposed linearization technique provides tunable pseudo-resistors with very high linearity measured thanks to the total harmonic distortion (THD) of the output signal. Simulations results show that the proposed circuit's cutoff frequency is tunable in a wide range from 34 Hz to 20 kHz. In other words, we we were able to achieve a resistance value as high as 0.46 GO for a THD of −60 dB or 0.1%. Comparatively, for a cutoff frequency of 141 Hz and equivalent resistance of 0.11 GO, our filter achieves a THD as high as −83 dB or 0.007%.