For the settings I am using, the LOs are constants, so there are no counters in the design.
On Wed, Sep 24, 2008 at 6:38 AM, Aaron Parsons <[email protected] > wrote: > You might take a look at the counters that go into the look-up tables > that generate the sine/cosine LOs. I have a feeling that these > counters might not have resets, causing the two counters to come up at > random times relative to one another, shifting the phases of the > sin/cos and thus the real/imag components. This could be fixed by > propagating a sync into these counters. > > On Wed, Sep 24, 2008 at 1:44 AM, G Jones <[email protected]> wrote: > > Hi everyone, > > I just spent a long time struggling with this problem, so I wanted to > warn > > others in case you run into it. > > It seems that the 10.1 DDC blocks simulate fine in simulink, but > something > > goes wrong when building the design. The major symptom is that the filter > > does not have the expected rejection characteristics, and more > importantly, > > the real and imaginary outputs are not in quadrature for a single tone in > > the passband, as they should be. Again, in simulation things look fine. I > > even recorded actual ADC data and fed it into the simulation and the > output > > was exactly what I expected, but in hardware I kept getting a mirrored > > spectrum. Finally I captured the output of the DDC block and saw that the > > real and imaginary components are generally 180 degrees out of phase. > After > > building several iterations of the design, I finally decided to give 7.1 > a > > shot and it came out perfectly the first time. > > I am using the blocks with the LO set at 1 and decimating 4 simultaneous > ADC > > inputs down to 1 complex output. > > Please let me know if you've seen a problem like this and have an idea as > to > > where to start looking to fix it. I seached the map output to see if > > anything obvious was being optimized out but didn't find anything. > > > > Hope this helps someone, > > Glenn > > > > > > -- > Aaron Parsons > > 510-406-4322 (cell) > 787-878-2612 x329 (arecibo office) > 787-721-3991 (home) >
