User`s manual

Output Frequency

and Sample Rate

The output frequency of an arbitrary waveform is defined as:

= sample rate/waveform_points

For frequency sweeps the sample rate(s) are the start and stop frequencies.

For example, with an arbitrary waveform with 4096 amplitude points, a start

frequency of 4.096E6 and a stop frequency of 8.192E6 produces a sweep

from 1 kHz to 2 kHz.

For frequency-shift keying the sample rates are frequency1 and frequency2

specified by the

[SOURce:]FREQuency[1]:FSKey command. The output

frequencies are the sample rates divided by the number of amplitude points

in the arbitrary waveform.

AC Leveling The AFG has a 250 kHz output filter and a 10 MHz output filter. When the

filter has been selected and enabled, AC output leveling maintains the

amplitude at a constant level over the frequency sweep or frequency list.

AC leveling, which is performed by the

CALibration:STATe:AC ON

command (reset setting), applies to the sine wave function only.

AC Leveling

Amplitude Errors

When AC leveling is enabled during a sweep or frequency list, errors in the

output amplitude still occur during a frequency change. In most cases, the

errors are negligible. However, in applications where the step-to-step

frequency changes are large (10% or greater), or when frequency changes

occur near the filter’s cutoff frequency, the error is such that settling times

on the order of milliseconds are required for the output to settle to the

correct amplitude.

Table 4-1 shows typical (non-warranted) amplitude errors versus settling

times when a frequency change occurs. These “worst case” settling times

represent frequency changes (

freq

to freq

) of 10% and 1% from the filter’s

cutoff frequency.

160 Sweeping and Frequency-Shift Keying Chapter 4