AnsweredAssumed Answered

AD9361 Filter Wizard: 50MHz Passband

Question asked by mclark on Feb 28, 2018
Latest reply on Feb 28, 2018 by travisfcollins

I'm working with the No-OS driver and AD9361 on a custom board. I'm having a difficult time using the AD9361 Filter Wizard to design a 50MHz near-flat passband.

 

My RX/TX path clocks are setup as:

 

    // {BBPLL_FREQ, ADC_FREQ, R2_FREQ, R1_FREQ, CLKRF_FREQ, RX_SAMPL_FREQ

    {800000000,200000000,100000000,100000000,100000000,50000000}

 

This implies HB2 and HB1 are bypassed (or decimate-by-1), while HB3 and the PFIR are configured as decimate-by-2. The input sample rate at the PFIR is expected to be 100MHz, thus the PFIR should support a cutoff frequency greater than 25MHz, yet the Wizard's filter specification is always limited to 25MHz.

 

In any case, I designed the filter using the following Matlab command:

 

Transition band: [25MHz, 40MHz]

Hz = round((2^15-1)*firpm(31,[0 0.5 0.8 1],[1 1 0 0])) ,

 

but I still see a 6 dB roll-off starting around 20MHz. I understand this is probably due to other filtering in play, and will need to be compensated for. Is the Wizard not applicable for my application or is there something wrong with my reasoning?

 

Any feedback would be appreciated.

Thanks!

Outcomes