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SECTION 3
3.4.8
Waveform Selection, Square-Wave
Duty Cycle, and Synchronous
Out-
put
Waveform
Selection
Pressing the FCTN key displays the existing main syn-
thesizer waveform along with its corresponding number
and enables main synthesizer waveform selection. Avail-
able main synthesizer waveforms include: DC, SIN (Q >
i-L,r\l,&nd\.
To select a waveform with the numeric keys, simply
press the numeric key that corresponds to the desired
waveform. For example, press 1 to select a sine wave. The
waveform will change immediately when the corre-
sponding key is pressed. It is not necessary to press a
units key.
When the Model 3933A displays the existing waveform,
and FUNCTION parameter selection is enabled, you can
change the waveform by turning the MODIFY knob.
Turning the knob clockwise increases waveform num-
bers, while turning the knob counterclockwise decreases
waveform numbers. The number changes by a value of
one for each detent. When the highest or lowest
waveform numbers are reached, the number will wrap
around to the lowest or highest selection. Allowable se-
lections range from zero through five.
For all AC waveforms, the p-p value of the amplitude
will remain unchanged when you change the waveform.
If the output range mode is AUTO, and amplitude is
either rms or dBV, the amplitude will be converted to p-p
units when the waveform is changed.
Square-wave
Duty Cycle
The duty cycle is the ratio of the waveform high-level du-
ration to one complete cycle of the waveform. This ratio is
expressed as a percentage. For example, a 1OkHz square
wave has a time period of 100psec. If the high portion of
the waveform has a period of 30pec, the duty cycle is
30/100x100=30%.
Two square-waveform duty cycle modes are available: a
duty cycle fixed at 50%, and one with a variable-duty-cy-
cle. The duty cycle applies only to the square-wave func-
tion (waveform 31, although the duty cycle can be pro-
grammed while other waveforms are selected.
To change the duty cycle, press then DUTY key. When
the display indicates duty cycle, enter the new value
via
the numeric keypad, or modify the duty cycle with the
MODIFY knob. The allowable variable range is 5.0%
to
95.0%. If the Model 3933A is set to variable duty cycle, it
will remain in that mode even if you set the duty cycle to
50%. To select the fixed 50% duty cycle mode, press
SHIFT FXD50. In the duty cycle display mode, the Model
3933A displays "FXD" for the 50% fixed mode or "VAR"
for the variable duty cycle mode.
When the Model 3933A is in the variable duty cycle
mode, the upper-frequency limit is lMHz, and the maxi-
mum jitter is below 150nsec. The Model 3933A has a reso-
lution of 0.1% for duty cycle display, but the hardware
resolution is 0.4% (8 bits). As a result, if you make a duty
cycle change lower than the hardware resolution factor,
only the displayed value will change, not the duty cycle
of the actual output.
Synchronous
Output
Figure 3-10 illustrates the phase relationship between the
waveform and outputs at frequencies below IkHz. Typi-
cal jitter between the main synthesizer waveform output
and the main synthesizer synchronous output is about
9Snsec.
3-28
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