On Sat, 3 May 2008 20:36:23 -0700 (PDT), rickman <gnuarm@gmail.com> wrote:>On May 3, 10:31 pm, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote: >> On Mon, 28 Apr 2008 15:08:06 -0700 (PDT), Rudheesh Raghav >> >> >> >> <rudhees...@gmail.com> wrote: >> >Hi all, >> >> > I would like to have some help from you in this topic. >> >> >I have converted a 12.1MHz analog IF signal to baseband using an >> >105MSPS ADC and a Virtex-4 FPGA. But I'm getting a DC offset of about >> >20% of peak to peak value. >> >> >The BW of the Signal is 200 KHz. >> >> >What is the best method of DC offset Cancellation?? >> >> >Can I do averaging over a period of time and subtract the average or >> >can I use a High Pass Filter?? >> >> >If averaging is the correct way, How long I should average?? >> >> > thanks in advance >> >> >Rudheesh >> >> Hello Rudheesh, >> You might have a look at the "DSP Tips & Tricks" >> column in the March 2008 issue of the IEEE Signal >> Proc. magazine. That column is an article titled >> "DC Blocker Algorithms", written by our own Randy Yates, >> some other guy. Perhaps it'll be of some use to you. >> >> Goos Luck, >> [-Rick-] > >Can you recommend a way to get that article without spending $13? I >guess even though I am an IEEE member, I still have to pay for >articles from magazines I don't subscribe to.Hi, Yes, there is a way. It's legal for the authors to distrubute copies of their articles. Please send me a private E-mail & I can solve you problem. Regards, [-Rick-]
DC Offset Cancellation in Digital Baseband
Started by ●April 28, 2008
Reply by ●May 4, 20082008-05-04
Reply by ●May 4, 20082008-05-04
On Sun, 4 May 2008 02:58:36 -0700 (PDT), Rudheesh Raghav <rudheeshrk@gmail.com> wrote:>On May 4, 7:31�am, Rick Lyons <R.Lyons@_BOGUS_ieee.org> wrote: >> On Mon, 28 Apr 2008 15:08:06 -0700 (PDT), Rudheesh Raghav >> >> >> >> <rudhees...@gmail.com> wrote: >> >Hi all, >> >> > � � � � I would like to have some help from you in this topic. >> >> >I have converted a 12.1MHz analog IF signal to baseband using an >> >105MSPS ADC and a Virtex-4 FPGA. But I'm getting a DC offset of about >> >20% of peak to peak value. >> >> >The BW of the Signal is 200 KHz. >> >> >What is the best method of DC offset Cancellation?? >> >> >Can I do averaging over a period of time and subtract the average or >> >can I use a High Pass Filter?? >> >> >If averaging is the correct way, How long I should average?? >> >> > � � � � � � � � � � � � � � � � thanks in advance >> >> >Rudheesh >> >> Hello Rudheesh, >> � �You might have a look at the "DSP Tips & Tricks" >> column in the March 2008 issue of the IEEE Signal >> Proc. magazine. �That column is an article titled >> "DC Blocker Algorithms", written by our own Randy Yates, >> some other guy. �Perhaps it'll be of some use to you. >> >> Goos Luck, >> [-Rick-] > >Hi Rick, > > Thank you for the information. > >What may be the possible sources of DC Offset in a Digital Down >Converter except from DC offset in the source?Hi, Humm, it may be possible that, depending on the signal being down-converted, that (1) amplitude mismatch and/or (2) non-90 degree phasing of the oscillators in "quadrature oscillator" may cause a DC bias error in the down-converted signal. I'm blurting things out here of the top of my head, so I wouldn't trust me if I were you. I'm tryin' to think of phrases you can 'Google on'. Maybe: phase mismatch phase offset quadrature oscillators amplitude mismatch It seems to me that "down-coverter" and "up-converter" tutorials on the Internet should discuss the effects of "imperfect oscillators". Good Luck, [-Rick-]
Reply by ●May 9, 20082008-05-09
> Hi, > � Humm, it may be possible that, depending on the > signal being down-converted, that (1) amplitude > mismatch and/or (2) non-90 degree phasing of the oscillators > in "quadrature oscillator" may cause aDCbias error > in the down-converted signal. > I'm blurting things out here of the top of my head, > so I wouldn't trust me if I were you. > > I'm tryin' to think of phrases you can 'Google on'. > Maybe: > > phase mismatch > phaseoffset > quadrature oscillators > amplitude mismatch > > It seems to me that "down-coverter" and > "up-converter" tutorials on the Internet should > discuss the effects of "imperfect oscillators". > > Good Luck, > [-Rick-]Hi Rick, Thank you for the information. I am looking on my NCO for it's phase and amplitude characteristics. and There is no chance for a beginner like me to distrust the author of a best selling DSP book. Rudheesh
