TMS320F28035: Software Phase Locked Loop - DDSRFSPLL

Jack,

We have some C2000 teams members on travel, they should be back in the office tomm so worst case you can expect a reply by then.

Best,

Matthew

Matthew, thanks.

Dear Matthew and Champs,

May I get some update about this?

Regards,

Jack

Dear Champs,

May I get further update about this?

Hi Jack,

Jack Tan80 said:

1. For the low pass filter parameter, how does the k1 and k2 obtained in docs? When I use the wf = 30, fs = 10Khz, I get k1 = 0.001497753369945 and k2 =-0.997004493260110 which is different from docs.

I did a quick calculation and your results seem correct for me.

Jack Tan80 said:

2. For the low pass filter in code, from the z tranform, I got the formular as below:

lpf = k1*(xn + xn_1) - k2*yn_1;

yn_1 = lpf;

xn_1 = xn;

But the code in docs and ti example is

Could you point out specifically which part are you talking about in the appnote? 

Regards,

Chen

Hi Chen,

For the sencond question, I'm talking the ti's reference code (SPLL_3ph_DDSRF_F.h) about the low pass filter.

The formular in ti's code is different from the result from linear transformation, the example code is:

spll_obj.y[1]=(spll_obj.d_p_decoupl*spll_obj.k1) - (spll_obj.y[0]*spll_obj.k2); \
spll_obj.d_p_decoupl_lpf=spll_obj.y[1] + spll_obj.y[0]; \
spll_obj.y[0]=spll_obj.y[1]; \

From the linear transformation, the formular should be:

lpf = k1*(spll_obj.d_p_decoupl + xn[0]) - k2*yn[0];

yn[0] = lpf;

xn[0] = spll_obj.d_p_decoupl;

Regards,

Jack

Hi Chen,

This is directly from linear transform, I found that ti's example code is the same with the formula.

Thanks,

Jack