Square Waveform Generation; Pulse Waveform Generation - Agilent Technologies 33250A User Manual

Chapter 7 Tutorial

Square Waveform Generation

Square Waveform Generation
To eliminate distortion due to aliasing at higher frequencies, the 33250A
uses a different waveform generation technique to create square waves.
For frequencies above 2 MHz, square waveforms are created by routing
a DDS-generated sine wave into a comparator. The digital output from
the comparator is then used as the basis for the square wave output.
The duty cycle of the waveform can be varied by changing the comparator's
threshold. For frequencies below 2 MHz, different waveshapes are
loaded into waveform memory to minimize jitter.
Waveform Anti-Aliasing
DAC Filter
Comparator
Threshold
Voltage DAC
Square Waveform Generation Circuitry

Pulse Waveform Generation

To eliminate distortion due to aliasing at higher frequencies, the 33250A
also uses a different waveform generation technique to create pulse waves.
For pulse waveform generation, clock cycles are counted to derive both
the period and pulse width. To achieve fine period resolution, the clock
frequency is varied from 100 MHz to 200 MHz by a phase-locked loop
(see the following page). To achieve fine period width resolution, an
analog delay (0 to 10 ns) is applied to the trailing edge. The rising and
falling edge times are controlled by a circuit that varies the charging
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currents in a capacitor. Period, pulse width, and edge time are controlled
independently, within certain limits.
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