Hi Liu: Thanks for your suggestion. We are using a 10 bit ADC card, so the input to PFB for us is fix_10_9.
The noise floor steps only become obvious if we use higher channels FFT, such as 32K, and accumulate for some time. Thanks Wan ________________________________ From: Zhiwei Liu [mailto:[email protected]] Sent: Wednesday, 13 January 2010 3:46 PM To: [email protected] Subject: Re: [casper] DC part of FFT output Hi Wan, Set your sine wave amplitude to a value less than 1, since the input to PFB should come from ADC which is FIX_8_7 I always set the amplitude to 0.4 for my simulation, never had a problem. Zhiwei On Tue, Jan 12, 2010 at 10:37 PM, Dan Werthimer <[email protected]<mailto:[email protected]>> wrote: hi wan, what are the levels of this output? if they are the least significant bits, then this is likely from round off noise. best wishes, dan On 1/12/2010 6:45 PM, [email protected]<mailto:[email protected]> wrote: Hi All: I use a matlab sine wave generator to generate a sine wave as an input to PFB and FFT. But I find I get a little DC output and a few small steps from FFT output. I am pretty sure there is no DC added into the input signal. So where these DC could be from? And why there is some small steps on the noise floor? For the details of spectrum output, please see the attached. Thanks Wan -- Zhiwei Liu
