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From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Analog signal elay element: Question
Message-ID: <15976@milton.u.washington.edu>
Date: 7 Feb 91 03:02:41 GMT
References: <16663@venera.isi.edu>
Organization: University of Washington, Seattle
Lines: 22

In article <16663@venera.isi.edu> sllu@ISI.EDU (Shih-Lien Lu) writes:

>What are some ways to implement delays for analog signals (dealy in 1 ns
>resolution)?
>One possible way is to have the equiv. of an R/2R ladder.
>Is there any other way, in particular, to implement on an IC?

	You can use a SAW (surface acoustic wave) device with multiple
taps (select the tap for the required delay).  There is an interesting
property of GaAs: it is piezoelectric.  So, at least one company
(whose name I can get, given time to look up the guy who told me...)
which has a GaAs SAW device with multiple taps connected through
multiplying D/A converters to a summing junction.  They are
doing real-time FIR filtering that way.
	A linear CCD device with variable input clock frequency
could do it, but only for low-frequency input signals.
	A modulated light beam can be delayed by bouncing it off
a mirror (and moving the mirror); a Scotchlite retroreflective
panel moved 15 cm would give you a nanosecond's delay.  This, of
course, would mean mechanical motion for change in delay time.

	John Whitmore