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Tx FIR filter set-up wrt predistortion

Category: Hardware
Product Number: AD9361

We want to use the 128 tap Tx channel FIR filter for pre-distortion to compensate for PA distortion but the Analog MatLab tool does not seem to allow us to do that.  Is this a limitation of the MatLab tool or a limitation of the FIR filter in the AD9361?

For now we just need to confirm whether or not this FIR filter can do the job we need it to, tuning it is another problem we will tackle later.



  • The FIR filter supports  a maximum of 128 taps, but the FIR taps are calculated based on the input sampling rate, which is a limitation to the number of taps that can get selected.

    from UG:

    The Tx FIR calculates 16 taps per clock cycle. This limits the number of available taps to the ratio of DAC_CLK to the input data rate multiplied by 16. For example, with an input data rate of 25 MHz and DAC_CLK equal to 100 MHz, the ratio of the DAC_CLK to the input data rate is 100/25 or 4. In this scenario, the total number of taps available is 64.
    Another limitation is the memory inside of the filter. The total number of operations that can be performed is limited to 64 per clock cycle. This means that the number of taps available is limited to 64 with an interpolation factor set to 1. If an interpolation rate greater than 1 is used, the memory space can be used to include more taps.