Cascaded Integrator Comb (CIC) Filters

Matlab/Octave code + article PDF

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What You Will Get

  • Matlab/Octave files to build and test a decimating CIC filter chain that include

  • 1st CIC chain

  • 2nd CIC chain (can be turned on and off)

  • Compensation filter for passband droop (includes a regular FIR option as well as a simple 3-tap filter for low latency)

  • Lowpass filter to satisfy the spectral mask (both FIR and IIR)

  • Separate scripts for simulation and verification of the whole chain

  • Time and frequency visualizations at the output of each block for debugging and analysis

For implementation of a Digital Downconverter (DDC), a Digital Upconverter (DUC) or some other signal processing application, DSP engineers usually need a few weeks to design, test and finalize the CIC stages along with a suitable compensation filter.

With the provided scripts, you can simply choose the parameters and evaluate the cascade response. These parameters, set separately for CIC-1 and CIC-2 (if turned on), include

  • signal bandwidth

  • sample rate

  • decimation rate

  • differential delay

  • number of stages

  • lowpass response

The complete article on CIC filters in PDF format (32 pages) is also included for an in-depth understanding.

If your design does not meet the desired specifications with one CIC chain, then a second CIC chain with different decimation rate, differential delay and number of stages can be included, an example of which is shown in the figure below.

Additional advantages of these resources include the following.

  • CIC decimation and interpolation bit growth scripts for proper register word widths at each stage

  • Group delay plots and latency numbers for investigating target delays in your application

  • Ability to do custom modifications, e.g., to incorporate suggestions from the FPGA team

  • Output plots at each stage of the chain to test proper functionality and identify or debug any potential issues

Using these scripts, your DSP team can design the system in a single day, saving you several weeks of effort and a considerable amount of money.