SWITCHED CAPACITOR FILTERS TUTORIAL






SWITCHED CAPACITOR FILTER


The switched capacitor filters have became popular because they require no external reactive components, capacitors or Inductors. In fact, the operation of these filters is based on the ability of on-chip capacitors and MOS (Metal oxide Semiconductor) switches to simulate resistors. The value of these on-chip simulating capacitors can be closely matched to other capacitors on the IC, which results in integrated filters whose cutoff frequencies are proportional to and determined only by the external clock frequency. In addition, the cutoff or center frequencies of switched capacitor filters can be programmed to fall anywhere within an extremely wide range of frequencies, typically more than a 200,000:1 range. Also the center frequencies can be very accurately determined. In short, switched capacitor filters offer the following advantages:
  • Low system cost

  • Low external component count

  • High accuracy

  • Excellent temperature stability
 The only drawback of switched capacitor filters is that they generate more noise than standard active filter circuits.

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