Analog neagtive delay generator - please help
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From: Fred Bartoli on 27 Mar 2010 09:17 John Larkin a �crit : > On Fri, 26 Mar 2010 09:26:24 -0700, Tim Wescott <tim(a)seemywebsite.now> > wrote: > >> John Larkin wrote: >>> On Fri, 26 Mar 2010 09:09:27 -0700 (PDT), Daku <dakupoto(a)gmail.com> >>> wrote: >>> >>>> Could some analog guru please help ? Digital circuits can use a delay >>>> locked loop to generate a negative delay - is there any corresponding >>>> analog circuit to achieve the same result ? Any hints, suggestions >>>> would be invaluable. Thanks in advance for your help. >>> What kind of signal do you want to delay? If it's a periodic clock, >>> all sorts of phase shifters or delay lines will work. A 0.75T delay >>> line looks like a -0.25T delay. Or invert phase and delay 0.25, same >>> result. >>> >>> If it's a general signal, it's impossible. >>> >>> John >>> >>> >> Well, so much for the stock market investment machine I was going to build! > > Even a small negative delay could be put into a feedback loop to get > arbitrary long negative delays, enough to see the Drudge Report a week > in advance. > > John > > Cool. So with a small TLine put in a feedback loop will give looong delay line? And maybe varying the loop gain will make the delay variable? Better patent that before others do. -- Thanks, Fred.
From: Daku on 27 Mar 2010 11:27 Thanks for the insight. I do remember the phase detector output vs. phase graph fom Paul Gray's book. However, I wish to verify a few more issues: 1. A reference signal and 90 degree phase shifted VCO output, when fed into the phase detector produces a zero error - so what signal is being fed into the loop filter ?? 2. Suppose I split the raw VCO output (just before adding the 90 degree phase) and try to use it for something - what is the phase difference between this and the reference input the the phase detector ?? Thanks for the helpful insight and suggestions. On Mar 27, 9:48 am, Tim Wescott <t...(a)seemywebsite.now> wrote: > That depends on your phase detector. If you're talking about a classic > mixer-style phase detector that returns zero error when the VCO is 90 > degrees off from the reference -- yes. > > So you can solve that, either by making a network that phase shifts the > VCO by 90 degrees before applying it to the phase detector, or -- if > your reference is also a pure tone -- by using a digital reference > detector that returns zero error when the phases match. > > -- > Tim Wescott > Control system and signal processing consultingwww.wescottdesign.com
From: stratus46 on 1 Apr 2010 00:50 On Mar 26, 9:09 am, Daku <dakup...(a)gmail.com> wrote: > Could some analog guru please help ? Digital circuits can use a delay > locked loop to generate a negative delay - is there any corresponding > analog circuit to achieve the same result ? Any hints, suggestions > would be invaluable. Thanks in advance for your help. A very common instance of this is 'advanced sync' used in television to make a video source create a signal early so by the time it goes through processing it's at the desired time. As Larkin said, it only works with a periodic signal. AND, that 'advanced' signal is only delayed 'almost' 1 time period back so it seems advanced. It's not - so Tim Westcott can't have his investment machine. G²
From: Tim Wescott on 1 Apr 2010 01:37
stratus46(a)yahoo.com wrote: > On Mar 26, 9:09 am, Daku <dakup...(a)gmail.com> wrote: >> Could some analog guru please help ? Digital circuits can use a delay >> locked loop to generate a negative delay - is there any corresponding >> analog circuit to achieve the same result ? Any hints, suggestions >> would be invaluable. Thanks in advance for your help. > > A very common instance of this is 'advanced sync' used in television > to make a video source create a signal early so by the time it goes > through processing it's at the desired time. As Larkin said, it only > works with a periodic signal. AND, that 'advanced' signal is only > delayed 'almost' 1 time period back so it seems advanced. It's not - > so Tim Westcott can't have his investment machine. Bummer! -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com |