Re: [casper] Simulation of tutorial3
Hi Ross Solved - too much gain in the quant causing all the problems seen - Need to work out why it had the effect it did but reducing it produces a perfect spectrum. We did see this when preparing for the last workshop. Tutorial 3 is set up for a wideband noise input where the input power is spread across the whole band. Putting in a sinusoid will cause saturation when requantising. It is important to calibrate your system based on the real input signal. Snapshot blocks at strategic places (post ADC, post FFT, post requantiser etc) are useful in this regard. Regards Andrew On Wed, May 15, 2013 at 6:58 PM, Ross Williamson wrote: 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 wrote: yes indeed a sync pulse does help significantly doh On Wed, May 15, 2013 at 12:36 PM, Jack Hickish 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 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) -- Ross Williamson Research Scientist - Sub-mm Group California Institute of Technology 626-395-2647 (office) 312-504-3051 (Cell)
Re: [casper] Simulation of tutorial3
Solved - too much gain in the quant causing all the problems seen - Need to work out why it had the effect it did but reducing it produces a perfect spectrum. On Wed, May 15, 2013 at 6:58 PM, Ross Williamson wrote: > 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 > wrote: >> yes indeed a sync pulse does help significantly doh >> >> On Wed, May 15, 2013 at 12:36 PM, Jack Hickish 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 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) -- Ross Williamson Research Scientist - Sub-mm Group California Institute of Technology 626-395-2647 (office) 312-504-3051 (Cell)
Re: [casper] Simulation of tutorial3
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 wrote: > yes indeed a sync pulse does help significantly doh > > On Wed, May 15, 2013 at 12:36 PM, Jack Hickish 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 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)
Re: [casper] Simulation of tutorial3
yes indeed a sync pulse does help significantly doh On Wed, May 15, 2013 at 12:36 PM, Jack Hickish 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 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)
Re: [casper] Simulation of tutorial3
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 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) > >
[casper] Simulation of tutorial3
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)
