PWM signal as a carrier wave

[maicael]

i was just wondering if a Pulse width modulation signal created from lets say a sine reference and a triangle carrier wave can be further compared to another reference signal to give a new PWM signal.it is just a thought as am not much of an electronics expert.so please be easy on me.

 

[simonbramble]

For a non electronics expert, that is quite a profound question. I see no reason why not.

A PWM waveform is normally generated by comparing a flat dc with a triangular waveform. If you modulate the dc, you modulate the duty cycle of the PWM, so by using a sinewave instead of a flat DC, you will create a sinewave modulated PWM.

If you are trying to further modulate the PWM you have just generated, it might be easier to further modulate the sinewave waveform in the first place.

 

[maicael]

thanks for the reply i really appreciate it.how do i further modulate a sine waveform in the first place.does that mean that the sine wave will be a carrier wave and if so what signal would be the reference signal

 

[unclejed613]

PWM wouldn't really make a good carrier wave by itself. being a pulse train means it has a lot of harmonic content. the harmonic content is highly variable because of the changes in the pulse width. however, in many modern AM transmitters, PWM is used as a method of creating AM modulation. what is done to do this is the AM transmitter generates a carrier wave, which goes into the final amplifier, and the supply voltage for the final amplifier is modulated by the PWM, and filtered, so that there are audio variations in the supply voltage of the final amplifier. the RF out is at the carrier frequency, modulated by audio. the PWM pulse train is filtered out and does not appear on the transmitter's output. this is much more efficient than a traditional AM modulator, which requires a large (audio power that is equal to the transmitter power) amplifier and very large modulation transformer.

i've actually seen one in use, and the original transmitter consisted of four cabinets, exciter, amplifier, modulator, and power supply. the one that replaced it used PWM, and consisted of three cabinets, exciter, PWM supply/modulator, and amplifier.

 

[Nigel Goodwin]

I think the OP needs to tell us what he's trying to do?, otherwise we're all just guessing.

But as for two forms of modulation, how about PWM with FM modulation of the triangle wave?.