3156B User Manual
Using the Instrument 3-20
Racal Instrument © 2005
It is different at higher frequencies as the number of points that are
being used for generating the waveforms are decreased according to
the following relationship:
Output Frequency = Sample Clock Frequency / Waveform Points
Sine the sample clock frequency has final value of 200MS/s, the only
way to increase frequency is by reducing the number of waveform
points. The reduction in number of points at higher frequency may
have a result on the resolution of which you intend to modify the
standard waveforms. For example, at 20MHz square wave, the
number of points that are available is only 10 and therefore the duty
cycle resolution is decreased to 10% increments.
There are two functions that allow you to find out the values of the
sample clock and the number of points that are used for a specific
function shape at certain frequency, these are:
ri3156B_query_std_sample_clock_freq
ri3156B_query_std_waveform_numb_points
The first function will provide information on the sample clock
frequency and the second, on the number of points in the waveform.
Note that the sample clock frequency setting cannot be changed when
you output a standard waveform from the built in library and therefore
this function provides entry to a query only
Generating
Arbitrary
Waveforms
The Model 3156B cannot generate arbitrary waveforms without first
loading them into its working memory. A description of the arbitrary
waveform function and an explanation of how to load waveforms into
memory are given in the following paragraphs.
What Are
Arbitrary
Waveforms?
Arbitrary waveforms are generated from digital data points which are
stored in memory. Each data point has a vertical resolution of 16 bits
(65536 points), i.e., each sample is placed on the vertical axis with a
precision of 1/65536.
The Model 3156B has waveform memory capacity of 1Meg point.
Each horizontal point has a unique address - the first being 00000 and
the last depends on the size of the memory. In cases where smaller
waveform length is required, the waveform memory can be divided
into smaller segments.
When the instrument is programmed to output arbitrary waveforms,
the clock samples the data points, one at a time, from address 0 to the
last address. The rate at which each sample is replayed is defined by
the sample clock rate parameter. The Model 3156B provides
programmable sample clock rates from 1S/s to 200MS/s.
