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Figure 4- 109
Select modulation source
1)
Internal source
When using an internal modulation source, the modulation wave can be sine wave, square wave, ascending sawtooth
wave, descent sawtooth wave, arbitrary wave and noise, and is sine wave by default. After you use PWM function, the
modulation wave is sine wave by default. You can change it with the multi-functional control on the interface for using
PWM function or by pressing Wave.
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Square wave: duty ratio is 50%
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Ascending sawtooth wave: degree of symmetry is 100%
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Descent sawtooth wave: degree of symmetry is 0%
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Arbitrary wave: when selecting arbitrary wave as modulation waveform, function/arbitrary waveform generator
limits length of arbitrary wave to 32Mpts by automatic test count.
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Noise: white Gaussian noise
2)
External source
When using an external modulation source, the modulation wave and frequency will not show in the parameter list, when
an external waveform will be used to modulate carrier waveform. Duty ratio deviation of PWM is controlled by ±5V signal
level on the external analog modulation input terminal (Modulation In connector) on the back panel. For example, if duty
ratio deviation in parameter list is set to be 15%, duty ratio of carrier signal (pulse wave) increases by 15% when external
modulation signal is +5V. Lower external signal level generates less deviation.
Set duty ratio deviation
Duty ratio deviation is the deviation of the modulated waveform from the current carrier duty ratio. The range of PWM duty
ratio is 0%~49.99%, 20% by default. You can change it with the multi-functional control and direction keys on the interface
for using PWM function or by pressing Duty.
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Duty ratio deviation is change in duty ratio of modulated waveform relative to original pulse waveform (%).
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Duty ratio deviation should not be more than current duty ratio of pulse wave.
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The sum of duty ratio deviation and current duty ratio of pulse wave must be ≤99.99%.
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Duty ratio deviation is restricted by minimum duty ratio of pulse wave and the current edge time.