A couple of more questions regarding simulation of tutorial3 - The setup has a 2^8 FFT (so 128 channels, 64 per vacc)
1) It looks as if the valid flag on Vacc is going high about 6 clock cycles before it should. This was tested by putting in an f=0.5 sine wave at the input to the adc (sample/period = 4, sample time = 1/4). The output from the vacc1 is at 38 rather than 32 and a DC component is also shifted by 6 (I'm not sure why there is a DC component). If you look at the latencies from the valid flag to dout there is 4 (so not quite 6) but I guess that gets us close - it is an error though and a think there should be a delay on the vacc valid line. 2) Maybe this is to be expected but if I shift the frequency below f=0.5, say f=0.25 then there are quite distinct harmonics present at f= 0.5 (about 1/8 of main freq) 0.75 (about half of main freq). I'm wondering if this is something to do with the discrete nature if the input sine-wave but I haven't thought too much about it. On Wed, May 15, 2013 at 1:04 PM, Ross Williamson <[email protected]> wrote: > yes indeed a sync pulse does help significantly.... doh.... > > On Wed, May 15, 2013 at 12:36 PM, Jack Hickish <[email protected]> wrote: >> Hi Ross, >> >> Have you looked upstream at, eg, the FFT output, to check there is a single >> spike coming out of that? Might also be worth making sure that you are >> simulating a sync pulse, and waiting long enough for data after the sync to >> propagate all the way through the design. >> >> Cheers, >> Jack >> >> >> On 15 May 2013 20:28, Ross Williamson <[email protected]> wrote: >>> >>> I'm trying to simulate tut3 by putting in a sine-wave at the input and >>> looking at the output of the accumulators - the acc_length is 2 and >>> FFT and pfb size is 12. Input parameters for the sine wave are: >>> >>> Sample based, Simulation Time >>> >>> Amplitude 0.1 >>> Bias 0 >>> Sample per period 100 >>> number of offset samples 0 >>> sample time 1/4 >>> Interpret vector parameters as 1-D checked >>> >>> I only look in the region where the output valid flag is high - The >>> problem is that I get a forest of lines out of both accumulators with >>> no obvious spike where the signal should be. It doesn't look like >>> there is clipping. I can post pictures of the scopes if needed but >>> I'm just wondering if I'm missing something obvious? >>> >>> >>> -- >>> Ross Williamson >>> Research Scientist - Sub-mm Group >>> California Institute of Technology >>> 626-395-2647 (office) >>> 312-504-3051 (Cell) >>> >> > > > > -- > Ross Williamson > Research Scientist - Sub-mm Group > California Institute of Technology > 626-395-2647 (office) > 312-504-3051 (Cell) -- Ross Williamson Research Scientist - Sub-mm Group California Institute of Technology 626-395-2647 (office) 312-504-3051 (Cell)
