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AN2168 - PSoC® 1 - Understanding Switched Capacitor Filters | Cypress Semiconductor

AN2168 - PSoC® 1 - Understanding Switched Capacitor Filters

Last Updated: 
Nov 23, 2017
AN2168 presents the theory behind switched capacitor filters, and provides guidelines and examples for implementing these filters in PSoC 1 devices.

A filter is a device that passes or rejects certain frequencies of a signal.  Four common types of filters are:

  • Low Pass Filters
  • Band Pass Filters
  • High Pass Filters
  • Notch Filters

This Application note discusses how these filters can be implemented using the Switched Capacitor Blocks in PSoC 1.  The application note discusses the following topics.

  • Basics of filters like universal filter transfer function, various variables that construct a filter (Roll off Frequency, Damping, High pass coefficient, Band pass coefficient and Low pass coefficient)
  • Detailed mathematical analysis of how the filters are implemented in PSoC 1 SC Blocks
  • A tool FilterCalc.exe which can be used to calculate capacitor values for given roll off frequency, damping value and column clock
  • Using FilterCalc.exe to configure a Low pass filter and a Band pass filter
  • Excel spreadsheet wizard that simplifies the task of configuring filters
  • Examples for Low pass filter and Band pass filters using the spread sheet
  • Construction of a Notch filter and Elliptical filter

Please refer  AN2041 – Understanding PSoC 1 Switched Capacitor Analog Blocks for more details about the basics of switched capacitor blocks.

The zip file that may be found in the Related Files section, has example projects for each type of filter, example filter wizard spread sheet and the FilterCalc application.

Example Project

Supported H/W and S/W Supported PSoC1 Devices
PSoC Designer Version H/W Kit CY8C20xxx CY8C21xxx CY8C22xxx CY8C23xxx CY8C24xxx CY8C27xxx CY8C28xxx CY8C29xxx
Yes 5.1 CY3210-PSoCEVAL1         x23A, x94 x43 x x66


In the following video, Dave explains filter choices with a PSoC Designer project.