Like page 2 of this document?
http://mayaweb.upr.clu.edu/~mtoledo/newpages2/ElectronicsII_files/Docs/H
andouts/oscillators.pdf

That seems to be the simplest W-Bridge I've found, and just what you
described except with the feedback on the inverting input...

nick@veys.com | www.veys.com/nick

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Harold M Hallikainen
> Sent: Wednesday, February 20, 2002 3:09 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Sine wave generation from simple components.
>
>
>         Well, you could go with a Wein Bridge oscillator. It
> consists of a non-inverting amplifier with a gain of three
> (generally made with an op amp and a couple resistors), a
> series RC from the output to the input, and a parallel RC
> from the input to ground. At 1/(2piRC), the "gain" of the
> series/parallel network is 1/3 at an angle of 0 degrees. Make
> up the gain with the amplifier and it oscillates. You can put
> a small light bulb in place of the resistor between the
> inverting op amp input and ground go get automatic gain
> control. As the signal gets larger, the lamp current goes up,
> increasing resistance and decreasing gain). The lamp probably
> won't work at real low frequencies (it will follow the waveform).
>         A nice chip for generating sine waves is the XR2206.
> It has square, sine, and triangle wave outputs (you switch
> between triangle and sine). It has two timing resistors and
> another pin to select between the two, so it's nice for
> generating frequency shift keyed signals. You can also inject
> current into the timing resistor pins to do linear FM. It has
> an analog multiplier (balanced modulator) in the output, so
> you can generate AM, BSBSC AM, and BPSK. The sine/triange
> output has a source resistance of 600 ohms, ideal for driving
> phone lines and stuff.
>         Nice chip! I first used it in the mid 1970's.
>         Finally, if you want to move to a PIC, for a low
> frequency, you can use the PWM output to drive an LPF as a
> D/A. Then use a sine lookup table to output values for a sine
> wave. You could even do "variable phase addition" in the PIC
> to do direct digital synthesis... Of course, there are DDS
> chips available (for much higher frequencies).
>
> Harold
>
>
>
>
> FCC Rules Online at http://hallikainen.com/FccRules
> Lighting control for theatre and television at
> http://www.dovesystems.com
>
>
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