Analog neagtive delay generator - please help

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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.

Re: Analog neagtive delay generator - please help



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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



Re: Analog neagtive delay generator - please help


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Well, so much for the stock market investment machine I was going to build!

--
Tim Wescott
Control system and signal processing consulting
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Re: Analog neagtive delay generator - please help



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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



Re: Analog neagtive delay generator - please help


John Larkin a écrit :
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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.

Re: Analog neagtive delay generator - please help


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Or a PLL.

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Ayup.

--
Tim Wescott
Control system and signal processing consulting
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Re: Analog neagtive delay generator - please help


The problem I am trying to solve is :
Consider an analog PLL and the reference signal is pure sinusoidal. In
a "locked in" mode, the VCO output will be a sinusoidal signal of
exactly same frequency as the reference signal, but has an added phase
(basically delay),
because of the way the VCO works. So is there a way to remove this
phase ??


On Mar 26, 9:20 pm, John Larkin

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Re: Analog neagtive delay generator - please help



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 > The problem I am trying to solve is :
 > Consider an analog PLL and the reference signal is pure sinusoidal. In
 > a "locked in" mode, the VCO output will be a sinusoidal signal of
 > exactly same frequency as the reference signal, but has an added phase
 > (basically delay),
 > because of the way the VCO works. So is there a way to remove this
 > phase ??
 >

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 consulting
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Re: Analog neagtive delay generator - please help


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.



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Re: Analog neagtive delay generator - please help


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Firstly, what is 'delay locked loop'?

When one needs a signal and a delayed copy of that signal, one uses
a delay line (simplest is just a long cable).  Then, the events
on the signal cable are occurring prior to those on the delay line,
and you can refer timings to the delay-line-output and
call the direct signal 'negative delay'.   That's  how an
oscilloscope can trigger on a pulse and still show the
lead-up to the pulse on the display.

Re: Analog neagtive delay generator - please help


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It is a delay line with a variable tap, or some sort of variable RC
delay, that is controlled in a similar manner to a PLL to get controlled
delay.

They're way popular in FPGAs these days, to de-skew clocks, double
clocks (by XORing a clock with a delayed version), have controlled phase
differences between clocks, and other useful things that you need if you
want to build really, really, really fast logic on a chip that's only
really, really fast.

--
Tim Wescott
Control system and signal processing consulting
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Re: Analog neagtive delay generator - please help



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It's a delay line in the feed back path of an oscillator.  A "digital PLL", if
you will.

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Re: Analog neagtive delay generator - please help


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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.

GB2%

Re: Analog neagtive delay generator - please help


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Bummer!

--
Tim Wescott
Control system and signal processing consulting
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