What's this system/circuit called? [debunked]

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[EDIT: This doesn't work. Do not read!]

What is this circuit called? Seems to be a simple way to output a sine wave, so it must have some standard name. I couldn't find it in The Art of Electronics, probably because I don't know what to look for...

note: ATtiny can be any PWM generator (ie: 555's, etc.)

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Last Edited: Thu. Nov 4, 2010 - 12:25 AM
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Its called Lowpass FIltered PWM, or any similar name you would like to attach to it.

I would not call the output "beat frequency" because that implies two signals into a mixer (in the RF sense- as in "multiplier", not the audio sense), looking at the difference component. Similarly, it is not inherently a sine generator; you can use it for (almost) any continuous, single-valued, periodic waveform you like. Come to think of it, it does not even have to be periodic; you can generate a random sequence (ie, "noise") which I guess will really be pseudo-random and then quasi-periodic.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Jim,

do you think adjective "balanced" could be used when describing the above circuit?

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The way it is drawn suggests "balanced". If the PWM modulation is balanced, then it would function as balanced, whether the PWM signals are exactly balanced/complementary or not.

I am not sure balanced mode would help much of anything unless the load requires balanced input.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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The word "differential" comes to my mind before the word "balanced" does.

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Agree!

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Right; PWM is an incorrect term. I'm thinking of a 50% pulse train with no width modulation (not balanced, either). Maybe that's why my "PWM beat" searches didn't find what I was looking for. Also, this circuit will only make an [beat frequency] envelope, roughly modulated at pulse frequencies. Like this:

Guess I need a few more knocks to the forehead. Thanks Jim!

SPICE (MacSpice) code to generate the above:

[Not A] Simple Differential RC Sine Wave Generator

Vp1	1 0		0 PULSE(0 5 5ns 5ns 5ns 99us 198us)
Vp2	2 0		0 PULSE(0 5 5ns 5ns 5ns 101us 202us)

R1	1 3		220
R2	2 4		220

C1	3 4		100nF

.control
delete all
op
tran 50ns 30ms 10ms
plot v(3, 4)
.endc
.END