Explain the use analysis and application of switched capacitor filters

Use of switched capacitor filter

When using a switched capacitor filter, an analog low-pass filter should be connected to its input and output ends respectively. This is because the switched capacitor filter is an analog sampling data system, and its picture is shown in Figure 5.3-14. According to theoretical analysis, the maximum whisker rate of the input signal of the analog sampling system must be less than 1/2 of the sampling frequency fcx, otherwise aliasing distortion will occur. Therefore, before the switched capacitor filter, an anti-aliasing low-pass filter needs to be added to filter out frequency components higher than fcx/2. And because the output terminal of the switched capacitor filter is a sample-and-hold signal, in order to convert this signal into a continuous signal, a low-pass filter must be connected to the output terminal to filter out the switching signal components in the output signal. The filter is usually called a smoothing filter. Figure 5.3-15 shows the block diagram when a switched capacitor filter is used. Anti-aliasing filters and smoothing filters generally use RC active low-pass filters. The circuit form is usually the low-pass active filter circuit shown in Figure 5.2-1 in Section 2 of this chapter. This circuit has a simple structure and is convenient to use. It is integrated on the same MOS chip together with the switched capacitor filter.

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