Error in data size using CIC filter in Simulink R2020b: The number of input rows must be a multiple of the decimation factor

I am trying a simple Simulink model of an NCO generating a sin and cos which I then use in their own respective CIC decimator to generate quad and real output signals.

In the two product blocks (X) I get an error "The number of input rows must be a multiple of the decimation factor". I tried adding the convert blocks and specifying output type fixdt(1,20,18), but that didn't help. The NCO is generating the proper sin and cos with amplitude +/-1 and frequency 13.5MHz with a 256Mhz sample rate.

What is the trick to getting the CIC to work? I looked at a similar Matlab Example for a GSM dds and it worked, but there was nothing special done (that I could see) to make the CIC input data types correct. Please help, I've spent a day chasing this problem :(

Answer 1

[Walter Roberson]

You appear to be passing a 1 x 1 signal into decimation. Decimation works on a non-scalar.

You probably need to buffer the signals and decimate the result.

[Frank Rose]

For newbies, It would be helpful to show an example of how to do this.