Design of a sixth order elliptical low pass filter in cascade design with Switched Capacitor second order stages of type biquad

Introduction

I can’t publish the Cadence files so the following README shows how to project a sixth order filter with Switched Capacitor in Cadence. For more information please see wiki, the italian language report or the presentation.

Switched capacitor filter

Filters generally consist of resistors, capacitors and inductors. Since the
resistive elements are difficult to implement in integrated form and occupy large areas, these are replaced by switched capacitors. You can see
that the switched capacitor behaves like a resistor of value R = 1/(f_clk*C). The switched capacitor filter to be designed must meet the following specifications.

Getting started

Prerequisites

• Matlab, Matlab Filter Designer

• Virtuoso Cadence 6

  How to use the Matlab code

1. Open Matlab
2. Open filter_design.m

3. Run the parts of the code to calculate the quality factor, the capacitances and the aspect ratio of the MOSFETs that constitute the real op-amp.

   Results

   Following the steps in wiki it’s possible to design a sixth order filter in Cadence with second order sections. The AC responses are shown below.

   

   First stage

   

   Second stage

   

   Third stage

   

   Total filter