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Original question:

FIR filter in TMS320F28335

TMS320F2812: Fixed Point Precision for DSP Library Functions

Ismail Halit KARAKAS
Prodigy 90 points
Part Number: TMS320F2812

I have a legacy design using the IQMath library with Q24 precision, it is generally using fir16_alt and Q15 precision for math operations.

I will add new FIR LPF and IIR HPF filters with FFT. I know Q15's precision is fairly enough for me so I can use fir16 and iir16 functions however,

could you please tell me if this causes an incompatibility issue with FFT32 precision and also IQMath precision needs to be changed

if further math operations are needed after FFT operations as well? Q15's precision is also enough for the operations I may need to do FFT outputs. 

I don't know using IQMath lib vey well, 

PS: The input for all operations above is 16bits External ADC values.

  • 0
    TI__Mastermind 26130 points

    Ismail,

    If you want to, you can change the Q value used by the IQMath library by changing the GLOBAL_Q value. Details are in the IQMath lib users guide. Relevant pic is pasted below.

    Yes, the Fixed point DSP library FFT has its own data precision assumptions which you will need to adhere to. These are mentioned in the Fixed point DSP user guide. So yes, if you are filtering followed by FFT or vice versa, you may need to perform some data conversion operations e.g. Q15 to Q31 etc.

    Thanks,

    Sira