You can use the equations on the next page to determine specific
waveform lengths and modulation frequencies when more precise
control is needed. Normally, you should not have to perform these
calculations.
The function generator incorporates an internal 8-bit (
7 bits peak)
digital-to-analog converter (
DAC) to create an analog copy of the
modulation signal for amplitude modulation (
AM). This signal is
internally applied to a conventional four-quadrant analog multiplier
circuit to achieve amplitude modulation. Similarly, the generator uses
digital signal processing to combine the carrier and modulation signals
for frequency modulation (
FM). The FM modulation signal maintains
12-bit resolution for frequency values.
The following equations and example describe the capabilities and
limitations of the 33120A’s internal modulation signal generator.
Parameter Definitions:
Maximum Point Clock (C) = 5 MSa/ s (for AM)
1.25 MSa/ s (for FM)
Modulation Prescaler (S) = integer numbers (truncated) from 1, 2, 3, ... 2
20
Constant (k) = 4,900 (for AM)
624 (for FM)
Modulation Frequency (F) = 10 mHz to 20 kHz (for AM)
10 mHz to 10 kHz (for FM)
Points (P) = values from 2,000 to 4,000
even numbers only (rounded down)
Chapter 7 Tutorial
Modulation
294
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