[sdiy] passive ring modulator transformers

Mon Jan 18 23:57:18 CET 2016

Hi Richie, Neil,

IMO it is incorrect to generally state that the diode ring modulator "operates
as a switching modulator".

More accurate would be "can be operated as a switching modulator" or (depending
on the application) "is intended as a switching modulator".

I did a Spice simulation just now.

With sine amplitudes of 1V of both input signals, the output is similar to what
you'd expect from a four quadrant multiplier: at any point in time the output
signal is approximately proportional to *both* input voltages (the ring
modulator is definitely not as distortion free as a double-balanced mixer
though).

If you choose a higher amplitude of the "center taps driving" signal of, say,
10V,  then it does start to act like a chopping modulator. Indeed, the inputs
are not interchangeable: the output signal remains proportional to the other
input signal.

If anyone wants to see for theirself, below are the contents of an .asc file
that you can load into LTSPICE IV. You may want to plot V(plusout)-V(minout),
V(n001) and V(n004).

By the way, I now look forward to build a circuit around a double balanced
modulator, equipped with switches to overdrive neither, one, or both inputs,
thus selecting the three "ring modulator" flavours "linear", "chopping", and
"xor" :)

Best regards
Simon

Version 4
SHEET 1 880 680
WIRE -96 96 -288 96
WIRE -48 96 -96 96
WIRE 176 96 0 96
WIRE 192 96 176 96
WIRE 272 96 256 96
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WIRE 480 96 416 96
WIRE -48 112 -48 96
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WIRE -48 192 -48 160
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IOPIN 480 96 Out
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IOPIN 480 288 Out
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SYMATTR Value 1N914
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TEXT -224 440 Left 2 !.tran 0 0.01 0

> Op 17 januari 2016 om 23:14 schreef Richie Burnett
> <rburnett at richieburnett.co.uk>:
>
>
> Thanks Neil. They are all pretty clear on the matter! A diode ring
> modulator (double-balanced mixer) operates as a switching modulator, not a
> product modulator like I had always thought. So it doesn't really matter
> what waveshape you feed into one of the inputs of a real diode ring
> modulator, as long as it has sufficient amplitude to commutate the diodes!
>
> -Richie,
>
> -----Original Message-----
> From: Neil Johnson
> Sent: Sunday, January 17, 2016 8:04 PM
> To: Richie Burnett
> Cc: Simon Brouwer ; synthdiy diy
> Subject: Re: [sdiy] passive ring modulator transformers
>
> Hi Richie,
>
> Here is some more light reading for you:
>
> The original Cowan patent:
> http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=2025158
>
> The wikipedia page:
> https://en.wikipedia.org/wiki/Ring_modulator
>
> My own take on things:
> http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=2&subsubmenu=12
>
> Cheers,
> Neil
>
>
> On 17 January 2016 at 19:50, Richie Burnett
> <rburnett at richieburnett.co.uk> wrote:
> > Fair enough :-) who am I to argue with minicircuits!!! I'm still not sure
> > whether that app note is actually saying that you *can* use a diode ring
> > mixer as a switching modulator if you have square waves conveniently
> > available instead of sines, or if they are saying that it *always*
> > operates in a switching mode regardless of the drive waveform. I guess
> > whether this mattersor not depends on what you're using it for.
> >
> > I've always thought of ring modulators as proportional devices. Albeit
> > ones that aren't particularly linear and distort a lot. And for the right
> > range of amplitudes in, you can get a decent approximation to a linear
> > multiplication function, as shown in the video you linked.
> >
> > It's interesting that they say pulse inputs actually reduce distortion
> > though! I know switching modulators are often used by the software defined
> > radio crowd so they obviously work fine that way.
> >
> > Cheers,
> >
> > -Richie,
> >
> > Sent from my Xperia SP on O2
> >
> > ---- Neil Johnson wrote ----
> >
> >>Hi Ritchie,
> >>
> >>> My point was that his two cases of a gain of +1 and -1 are just the
> >>> saturated gains.
> >>
> >>This Minicircuits document: https://www.minicircuits.com/app/AN00-011.pdf
> >>would seem to disagree with you:
> >>
> >>Q. I am a digital designer, dealing with pulses rather than sine
> >>waves. Is it necessary to
> >>furnish only sine waves to a double-balanced mixer?
> >>A.
> >>No. A double-balanced mixer operates as a switching device; pulses are
> >>fine, and may
> >>even reduce distortion.
> >>
> >>> The diode mixer or ring modulator is a proportional device, and in fact
> >>> Minicircuits even recommend a sinusoidal local oscillator signal at
> >>> +7dBm level for optimum operation. With harder LO drive the behaviour is
> >>> less linear and tends more towards the saturated switching behaviour,
> >>> with the addition of a whole load more distortion products in the
> >>> output.
> >>
> >>The +7dBm (level 7 device) spec is to do with conversion gain or loss,
> >>not about driving the diodes. Other mixers are designed to be run at
> >>higher levels, upto +27dBm for some devices (they tend to be rather
> >>more esoteric!).
> >>
> >>> Yes, that dafx paper is the one I was thinking about. Thanks for the
> >>> links! I only skimmed over it but it looked good.
> >>
> >>Hmmm...
> >>
> >>Cheers,
> >>Neil
> >>--
> >>http://www.njohnson.co.uk
>
>
>
> --
> --
> http://www.njohnson.co.uk
>
>
> -----
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