[sdiy] XOR as 'digital' ring modulator

Tim Ressel madhun2001 at yahoo.com
Thu Nov 11 00:09:41 CET 2010

Sorry, I was speaking theoretical so as not to confuse the reader with details. 
A true diode ring mixer uses diode switching to reverse the polarity of the 
carrier signal. Since it is a passive system, it has loss and not gain.


----- Original Message ----
From: Magnus Danielson <magnus at rubidium.dyndns.org>
To: synth-diy at dropmix.xs4all.nl
Sent: Wed, November 10, 2010 1:59:46 PM
Subject: Re: [sdiy] XOR as 'digital' ring modulator

On 11/10/2010 09:27 PM, Tim Ressel wrote:
> As a hopefully interesting side note, there are 2 ways to obtain the  "ring
> modulator" function. The popular one for the synth crowd is a  linear 
> like the AD633. The other way is by polarity reversal.  This is how true "ring
> modulators" work: the carrier signal goes  through an amplifier that has a
> selectable gain of + or - 1.  The  modulation signal's sign determines the 
> polarity: when the mod  signal is positive the gain is +1, when negative, -1.
> This is of course not nearly as clean as the linear multiplier, but hey, clean
> is over-rated.
> The XOR ring mod works as a true ring mod, as an XOR gate is a
> digitally-controlled inverter.
> We return you now to your regularly scheduled programming.

No. The true ring mod does not have gain which shift between +1 and -1. 
It has a gain shifting between those two extremes. A true ring mod 
actually always have losses.

Modern ring-mod equivalents such as Gilbert cells can also be made to do 
4-quadrature multiplications like the old double-balanced diode rings.

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