The principle circuit of a switched capacitor filter has been demonstrated in the figure 25.5 shown below The basic low-pass filter is made up of 2 capacitors, along with CMOS switches that are turned on alternately by a built-in clock oscillator. The clock runs at more than a few tens of kilohertz.
The switch C1 samples the input voltage when the 1st switch is closed & the 2nd switch is open. This voltage may be +ve or -ve depending on the phase of the input signal at that instant. An instant later the switches change state & the charge on C1 is equalized with the charge on C2, which came from the preceding sampling.
