2ctiby

modified 6 years ago

PWM basic idea

281

03:35:54

Reference Signal: ... Orange trace is a combination of waves rather than showing just one regular sine wave.

Modulation Wave: ... Green trace is a fixed frequency sawtooth wave. (Triangle could be used instead).

The whole orange Reference Signal peak to peak is kept within the confines of the green Modulation Wave sawtooth peak to peak, so that every crossing of the signal above/below the sawtooth is detected.

The green sawtooth Modulation Wave frequency needs to be a lot higher than the Reference Signal frequency.

That on/off is output as a high/low square wave (blue trace): hence PWM

There are quite a few different ways to Modulate a signal. Here is another way:

A different variation can be seen if you flick the switch. Here, the Modulation Wave is now just a d.c. straight line instead of being a sawtooth.

Use the pot to alter the voltage height of that green Modulation line, up or down to 'trigger' the PWM. The width of the blue output square wave will alter accordingly, depending on how much of the signal is detected.

That broadcast PWM square wave would then be demodulated at the receiver, to obtain a replica of the original Reference Signal orange trace input.

published 6 years ago

hurz

6 years ago

Your slowest "reference signal" is 6kHz, sampling this with just 10kHz sawtooth is much to low, better said this is subsampling OR !underdampling! and cause wrong chaotic results. You need at least 12kHz sawtooth, better is much higher and with 100kHz it starts to look like PWM. Oversampling is essentiell cause PWM is a single bit digital to analog or A to D, this needs high oversampling rates, factors of upto 100. E.g. 6kHz would need 600kHz sampling. Sure this is difficult to demonstrate with EveryCicruit, but Undersampling is also not a good way to demonstrate.

2ctiby

6 years ago

@hurz ... yes, I did say that the Modulation Wave needs to be much higher than the Reference Signal. The visual here makes it all more easy to envisage, but it is as well to emphasise that aspect.

hurz

6 years ago

so why not demonstrate a higher sampling rate and a reconstruction of the "reference signal" at least lets say 6kHz sinewave.

2ctiby

6 years ago

The presentation here is to give the basic understanding of what occurs with a basic PWM. Added complications and reconstruction of signal is not appropriate here, other than to have such things stated ... which I did. If you personally would like to further the presentation, then go ahead with your own follow up.

hurz

6 years ago

so it does present nothing functional, just a chaotic blue signal which is not useful for anything, very funny your basic idea about presentations. One might say its bullshit

2ctiby

6 years ago

Clear off and do your own thing, and leave others to gain the basic PWM concept which this presentation describes.

hurz

6 years ago

adjustment for your crap http://everycircuit.com/circuit/4508296321695744

2ctiby

6 years ago

Your adjustment was not really needed for this 'basic' presentation. It also does not describe more than a single reference wave frequency, and it detracts from the switch operation that was mentioned.

hurz

6 years ago

what a surprise you do not understand and dont like 😜

2ctiby

6 years ago

What a surprise... the aggressive school bully continues bluffing knowledge and attacking others after 5 years learning nothing.

kiani

6 years ago

@2ctiby over simplifying is almost as bad as complicated.

hurz

6 years ago

Craplified?

kiani

6 years ago

With the best of intentions @2ctiby. The description part,, far too complicated long,, by the time you reach the ladt line, the first one is forgotten.. . A gggood circuit demo needs not such long descriptions,, (in my opinion ') and i don't know about FET s.,... I just used to work eith CADANCE doing stupid VLSI.

2ctiby

6 years ago

@kiani ... You admit that you don't know about Mosfets, but you critisise my help guidelines instead of studying them, whilst acting like some sort of authority on circuits which need deeply studied workings of mosfets... Perhaps it's time for you to be less vocal on EC.

zorgrian

6 years ago

[BLOCKED]

kiani

6 years ago

[BLOCKED]

kiani

6 years ago

[BLOCKED]

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