TABLE OF CONTENTS There are two approaches to switched capacitor filter design. One uses integrators coupled together and the other uses cascades of first-order and second-order switched capacitor building blocks. This section will introduce some of the more well known first-order building blocks.
A general first-order transfer function in the s-domain is given as
We see that a first-order transfer function has one pole and one zero. If a 1 = 0, then the transfer function is low pass. If a 1 = 0, the transfer function is high pass. If neither a 1 nor a 0 is zero, the transfer function is a general first-order filter. Note that the zero can be in the RHP or LHP of the complex frequency domain.
The equivalent expression of Eq. (9.5-1) in the z-domain is given as
Figure 9.5-1(a) shows a switched capacitor low-pass circuit. We note that this circuit is identical to Fig. 9.3-4(a) except a switched capacitor, ? 2 C has been placed in parallel with the integrating capacitor, C. An easy way to understand and analyze this and similar circuits is to disconnect the ? 2 C switched capacitor from the output and redraw it as shown in Fig. 9.5-1(b). This circuit is simply a summing integrator and we can use previous methods to analyze it. The switches in the shaded boxes can be combined into a single pair of switches in the actual...
