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Dc offset and quality a PWM signal

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maicael

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can dc offset affect the quality of a pwm signal for example a triangle wave carrier with dc offset of 3volts above zero voltage compared to a sine reference with dc offset 2volts above the zero voltage.
will the pwm signal quality be affected or will the comparator that both signal are passed to correct this.just asking a thought as am not much of an electronics expert.thanks
 
The PWM signal is the comparator output, which is simply switching high and low, so the 'quality' is unaffected by input offsets. Offsets will, however, affect the duty cycle of the PWM signal.
 
If I got this right then yes sort of, on a pwm generator of the kind you imply a triangle wave is compared with a dc voltage to make a pwm signal, if you were to apply dc offset to the triangle wave it would have the same effect as adjusting the dc reference input to the comparator and change the pwm.
Ideally you dont want dc offset on the triangle wave, unless you want a minimum pwm duty cycle, and even then its a unusually complex way of doing it.
 
a positive offset on the triangle wave will shift the triangle with respect to the input, and will cause an offset after the output signal is filtered. if such an offset exists, it can be countered by a similar offset applied to the input. if the modulator is being run from a single supply and not a bipolar supply, both inputs will have an offset of 1/2 Vcc to begin with. just as long as the offset on the triangle, and on the input signal are the same, there will be no offset at the filtered output (except the 1/2 Vcc level because of single supply operation). so in the case of single supply operation, 1/2 Vcc is "zero", and any deviation from that is an offset.
 
No argument with that.
I was thinking more along the lines of a dimmer or speed control, maybe your thinking of audio or waveform generation Jed, same applies though.
 
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