[sdiy] quadrature sine wave oscillator question

[Czech Martin]

I'm not sure if we are talking about the same thing...

In the moment I'm not talking about frequency control,
this can be done via pots or multipliers, as you say.

I'm talking about the possibility to derive INSTANTANEOUS
amplitude information out of such a quadrature thing.
All other sine wave designs get a very much delayed information
on amplitude (i.e. peak detector and LPF).

m.c.

-----Original Message-----
From: jhaible at debitel.net [mailto:jhaible at debitel.net]
Sent: Dienstag, 25. März 2003 12:02
To: Czech Martin
Cc: Sdiy (E-mail)
Subject: Re: [sdiy] quadrature sine wave oscillator question


There's a schematic for this in Tietze/Schenk 
Halbleiterschaltungstechnik. But it shows
generic multipliers. It's an interesting circuit,
but you probably need very good multipliers
(offset voltage!) to get the required operation,
so I never tried it, and used a triangle VCO
+ waveshaper instead.

JH.


> has anybody dealt whith those?
> 
> This looks like a state var filter, but the Q
> regulation is set up so that a sine wave can build
> up.
> 
> To prevent heavy saturation and distortion a amplitude
> regulation is needed, like in all low distortion designs
> be it Wien bridge or else.
> 
> Unfortunately the gain/phase characteristics change
> a lot if the frequency is changed a lot, so
> the regulator must work fast.
> 
> Usually this is done via saturation devices (zeners etc.).
> This will cause some distortion.
> Or by some peak detector and very slow lowpass filter.
> 
> If the quadrature outputs are squared und summed up,
> this term will be DC (ideal) and can be taken for
> instanteneous amplitude regulation:
> 
> SQR(sin(x)) + SQR(cos(x)) = 1
> 
> I know there was a single chip or hybride package for
> this. Has anybody tried to build an audio range quadrature
> VCO using this method?
> 
> Cheers
> Martin Czech
> 
> CAD/CAE Library Group
> Micronas GmbH
> Hans-Bunte-Str 19
> D 79108 Freiburg
> Tel.: +49-761-517-2422
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>  
> 
> 
> 




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