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PWM and audio

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wizard

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Hi,

Can somebody explain me if the below link is just a class D amplifier or what is called 'PWM' amplifier?
https://www.electro-tech-online.com/custompdfs/2008/12/MC68EZ328PWM.pdf

I know something about class D amplifiers, But not sure about the above link.

Besides, yesterday I made a Plasma arc speaker based on TL494 PWM chip.
It worked just fine and I was able to hear the Modulated music via the arc at 30 KV (the attached picture).
With the exception of the arc itself, I was wondering how a PWM modulator will work when the input is an audio frequency signal (sine wave for simplification)? Yes, I do know that PWM is modulation of duty cycle, but I am not sure about the output of the PWM with sound??

My main question:
As PWM is like 'AM' (both will affect the amplitude), Can I suppose that we will have any SIDEBAND on the output of the PWM like what we have on the output of acommon amplitude modulator?
Unfortunately I forgot to analyse the output of said PWM with my spectrum analyzer.

Thanks a bunch
 

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My main question:
As PWM is like 'AM' (both will affect the amplitude), Can I suppose that we will have any SIDEBAND on the output of the PWM like what we have on the output of acommon amplitude modulator?
Unfortunately I forgot to analyse the output of said PWM with my spectrum analyzer.

Thanks a bunch
PWM and AM are worlds apart. AM changes the amplitude of a sine wave carrier. PWM changes the duty cycle of a square wave carrier.
 
PWM and AM are worlds apart. AM changes the amplitude of a sine wave carrier. PWM changes the duty cycle of a square wave carrier.

Well, I do know that.

As I mentioned at the first post, both 'PWM' and 'AM change the amplitude of the voltage so that the amount of the voltage on the output is changed by the input signal (i.e modulating signal). PWM performs so by changes at it's duty cycle in accordance with the input signal, and AM does so by changes at the carrier amplitude in accordance with the input signal.
 
The voltage amplitude of the PWM signal does not change, only the averaged (filtered) power level of the signal which varies in proportion to the input modulating signal. PWM will produce sidebands but those are all near the high frequency pulse-width clock frequency. In normal listening you run the PWM through a low-pass filter (may just be the speaker inductance) which eliminates all the high frequencies, leaving only the audio input modulating frequency.
 
The voltage amplitude of the PWM signal does not change, only the averaged (filtered) power level of the signal which varies in proportion to the input modulating signal. PWM will produce sidebands but those are all near the high frequency pulse-width clock frequency. In normal listening you run the PWM through a low-pass filter (may just be the speaker inductance) which eliminates all the high frequencies, leaving only the audio input modulating frequency.

I think I told it too!

According to the PWM Sidebands, Can you let me know the formulation for?
In common AM there are 3 outputs, the carrier itself and 2 upper and lower sidebands which are: modulating signal + the carrier freq and modulating signal - the carrier freq. I am not sure of PWM though?!
 
That's funny, I am not able to find any info about PWM sidebands via Internet.
Maybe there are a lot of informations, but I am getting old:rolleyes:?!
 
That's funny, I am not able to find any info about PWM sidebands via Internet.
Maybe there are a lot of informations, but I am getting old:rolleyes:?!
I Googled "PWB sidebands" and came up with numerous hits, for example **broken link removed**, which shows the spectrum of such a signal.
 
Sidebands of PWM are the same as any other modulation.
The carrier is a pulse-wave so it has harmonics. The sidebands are the fundamental plus and minus the modulation frequency and each harmonic plus and minus the modulation frequency.
 
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