Principle
Pulse-width modulation uses a rectangular pulse wave whose pulse width is modulated resulting in the variation of the average value of the waveform. If we consider a pulse waveform with a low value, a high value and a duty cycle D (see figure 1), the average value of the waveform is given by:
As is a pulse wave, its value is for and for . The above expression then becomes:
This latter expression can be fairly simplified in many cases where as . From this, it is obvious that the average value of the signal is directly dependent on the duty cycle D.
The simplest way to generate a PWM signal is the intersective method, which requires only a sawtooth or a triangle waveform (easily generated using a simple oscillator) and a comparator. When the value of the reference signal (the red sine wave in figure 2) is more than the modulation waveform (blue), the PWM signal (magenta) is in the high state, otherwise it is in the low state.
Read more about this topic: Pulse-width Modulation
Famous quotes containing the word principle:
“As in an icicle the agnostic abides alone. The vital principle is taken out of all endeavor for improving himself or bettering his fellows. All hope in the grand possibilities of life are blasted.”
—Anna Julia Cooper (18591964)
“Now, what I want is, Facts. Teach these boys and girls nothing but Facts. Facts alone are wanted in life. Plant nothing else, and root out everything else. You can only form the minds of reasoning animals upon Facts: nothing else will ever be of any service to them. This is the principle on which I bring up my own children, and this is the principle on which I bring up these children. Stick to Facts, sir!”
—Charles Dickens (18121870)
“An evident principle ... is the principle of justice to all peoples and nationalities, and their right to live on equal terms of liberty and safety with one another, whether they be strong or weak.”
—Woodrow Wilson (18561924)