Demystifying Switched Capacitor Circuits

Demystifying Switched-Capacitor Circuits

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4.2 Low-Order Switched-Capacitor Filters

First-Order SC Filters

A generic fi rst-order active SCF is shown in Figure 4.2. This is a three-in-one

fi ltering circuit that incorporates three different types of SCF: low-pass, all-pass, and

high-pass. Note that there are three specially labeled switches. For instance, the

switch labeled Φ

2

Φ

LP

will be turned on when both Φ

2

and Φ

LP

go to 1. Here, LP, AP,

and HP stand for low-pass, all-pass, and high-pass, respectively.

As the clocking scheme for this fi lter, Φ

AP

takes up a portion of Φ

LP

, whereas

Φ

HP

is not overlapping with Φ

LP

. In other words, when the circui ...