Fig. 6

Low-pass and notch filter. The schematic shows a second-order Sallen–Key low-pass filter and a Twin–T 50-Hz notch filter. These circuits are active filters providing amplification and signal bandwidth limitation mainly in the frequency range of 50 Hz. Both the two architectures exhibit several advantages and remarkable performance in ELF range. The passive components needed to implement these circuits are commercially standard values and exhibit low-noise performance. Signal bandwidth and total gain requirements are taken into account