4.9. Pulse width modulation (PWM)
In PWM, the pulse width of the carrier varies with the instantaneous voltage of the modulating signal, and
the waveform shape of the carrier must be pulse.
Before entering into PWM, users should firstly set the frequency and amplitude of carrier wave under
continuity function.
Press【PWM】key, the keyboard indicator of “PWM” will be on and the generator enters into pulse width
modulation function, the carrier wave is automatically set as pulse wave.
4.9.1. Modulation frequency:
Press【Menu】key to light “Mod_f” character and set modulation frequency value. In pulse width
modulation, modulation frequency is far lower than carrier frequency.
4.9.2. Pulse width deviation:
Press【Menu】key to light “Depth” indicator and set pulse width deviation value. It represents the
variation of carrier pulse width to the period of the pulse when the modulating waveform is with full
amplitude during PWM process, also the variation of the duty cycle. Name the maximum duty cycle of
modulated carrier as Dmax, and the minimum as Dmin, the pulse width deviation’s formula should be:
Pulse width deviation = Dmax - Dmin
If Dmax = 80%, Dmin = 20%, the pulse width deviation is 60%.
If Dmax = 50%, Dmin = 50%, the pulse width deviation should be 0%.
That is to say, when pulse width deviation is 0, the duty cycle of pulse wave is 50%.
4.9.3. Modulation waveform:
Press【Menu】key to light “Shape” character, the current modulation waveform sequence No. is shown,
input modulation waveform No. with the numeric keys or adjusting knob to select modulation waveform,
the modulation waveform may be any one of the 16 kinds of waveforms listed in the waveforms table in
section 4.2.9.
4.9.4. Sync output:
In PWM, the generator outputs a sync signal from the front panel “Sync” connector, which is a square
wave with TTL level and 50% duty cycle, its frequency is equal to modulating frequency and its phase is
referenced to the phase of the modulating signal.
In PWM, press【PWM】key, the “PWM” keyboard light will be off, and the generator exits PWM function
and returns back to continuity function.
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