Design Of Switched Capacitor Filters For Micro-sensors

Switched capacitor filter is a new kind of integrative active filter which was used widely in both civil and military areas. It is important to realize the integration, micromation, low cost and low power. Four kind of switched capacitor filters was designed and simulated based on the analysis of the principle of switched capacitor.A traditional RC active filter structure and SC Resistor Simulations were used in the one-order switched capacitor filters in this paper, which made the filter-circuit more exact and more easily to be integrated. A kind of Parasitic-insensitive resistor simulation was used as the SC Resistor Simulation. This kind of resistor simulation not only ignore the effect of the parasitic-capacitance but also helps circuit designers save a dedicated sample-and-hold at the input. A kind of switch was used in the filter circuits, which is made up of six MOS transistors. It not only meets the require of speed and exactness but also reduce the Charge Injection Effect. A kind of clock-time scheduling circuit was use in the filter circuits, which supply a non-overlapping clock pulses. It prevent the clock-time scheduling from disordering heavily because of the clock pulses overlapping. The results of the simulation of the filter circuits were shown that the circuits met the require of the design, and they can widely be used in low-frequency micro-sensors.A kind of low-Q two-order biquad switched capacitor filter was designed in this paper. This kind of filter can decide the frequency response(low-pass band-pass high-pass etc) of the filters by setting the position of the zeros and the poles, which makes the design facility and the total capacitance smaller. The results of the simulation of the filter circuits were shown that the circuits met the require of the design. Compare with traditional RC filters, it has smaller capacitance and it can be integrated in one chip more easily. So it can widely be used in many areas.We must specify the important parameters with respect to the op-amps used in the switched capacitor filters. With the consideration of the these condition, a six order switched capacitor low-pass filter was designed. After the designs of the structure of the filter, the orders, the distribution of zeros and poles, signal-flow-graph and capacitance value, the filter circuit was realized. The results of the simulation of the filter circuits were shown that the circuits met the require of the design, and compared with the filters with the same orders, they have better amplitude-frequency characteristics and decay rate. So they can widely be used in many kinds of micro-sensors in these frequency ranges.