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- Newsgroups: sci.electronics
- Path: sparky!uunet!van-bc!rsoft!agate!ames!network.ucsd.edu!munnari.oz.au!uniwa!gude
- From: gude@uniwa.uwa.edu.au (David J W Emrich)
- Subject: Circuit to multiply audio signals wanted.
- Message-ID: <1992Sep6.161205.16290@uniwa.uwa.edu.au>
- Summary: Anyone out there remember op-amp multipliers?
- Keywords: multiply modulate
- Organization: University of Western Australia
- Date: Sun, 6 Sep 1992 16:12:05 GMT
- Lines: 44
-
- Hi Netland...
-
- I have a little problem that I can't solve immediately, coz I havent'
- got/can't find the relevant text book.
-
- Here is the outlay... I have two (later maybe more) audio signals, that
- are amplitude limited to 2V peak to peak, but no low-frequency
- limitations. (Eg DC to 20kHz). I want to "multiply" the two signals
- together, which, if I remember rightly, is the same as modulating one
- signal with the other. Since modulation is symmetric, if 100%
- modulation is used, I figure that is the same as multiplying them
- together. I know there is an op-amp circuit somewhere to do exactly
- what I want, but I can't remember, (it was 8 years since I started
- Engineering, and I haven't used much of it since. Poor old memory...)
-
- The only tricky bits are:
- 1) if _either_ one of the inputs is 0v (i.e. no signal), then the output
- must be as close to 0 as possible. I seem to remember some modulation
- circuits that still let one signal through at about 10% for zero
- modulation input.
-
- 2) Ideally, I should be able to switch the inputs over (i.e. swap roles
- from "carrier" to "modulation") with no discernible difference in
- output. This isn't totally necessary, I will probably end up with a
- computer controlled soft-switcher to swap signals around later, but it
- would be nice in the early stages.
-
- 3) If possible, it should be easily expanded to handle more than two
- inputs, hopefully without cascading, coz I don't want too many booster
- amplifiers to bring the signal back up to 2v after every stage.
-
-
- Can anyone remember their op-amp theory, or alternatively suggest a
- good, _current_ electronics text that covers this sort of thing?
-
- Please respond to email address below, I don't think too many others
- will want to wade through this stuff!
-
- Thanks in advance.
-
-
- [dav] aka
- David Emrich
- gude@uniwa.uwa.edu.au
-