Compact sub-hertz OTA-C filter design with MOS interface-trap charge pump

Single-ended and differential OTA configurations are biased with MOSFET interface-trap charge-pumping current generators to achieve very low transconductances for tunable sub-hertz OTA-C filter implementation. The paper reviews the basic physics of the current generator, presents the transconductor circuits, and two OTA-C filter configurations based on these transconductors. One of the filters is a lowpass with an experimentally determined lowest cutoff frequency of 0.18Hz, and the other is a fully differential bandpass with individually tunable lower and upper cutoff frequencies measured down to 0.3Hz. The former has one 15pF filter capacitor, and occupies an area of 0.0346mm/sup 2/, whereas the latter contains four such capacitors, and occupies an area of 0.188mm/sup 2/.