Analysis of capacitance spread reduction techniques for 50-Hz switched-capacitor notch filters

摘要

This paper presents an overview of design techniques to reduce the capacitance spread of SC notch filters. Three of these techniques are used in the design of a 50-Hz notch filter, intended for an internet of things (IoT) water management sensor node. In this application, due to the high sampling frequency required by the acquisition channel's ADC, the filter'sF(s)/f(p)ratio becomes excessively large, resulting in a capacitance spread of 3225.8, if a conventional SC implementation is used. Using charge division networks, with up to seven share/reset cycles, the filter's capacitance spread is reduced by a factor 12.9 and the total capacitance by 5.9, and a total power dissipation of approximately 262 mu W, for a supply voltage of 0.9 V. Using capacitive T-cell networks, the filter's capacitance spread is reduced by a factor 40.5 and the total capacitance by 14.2. Using partial charge transfer networks, the filter's capacitance spread is improved by a factor 41.6, and the total capacitance by 10.0. The filter's total power consumption, using the last two techniques, is approximately 11 mu W.