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Arbitrary
Waveforms
Figure 1-9, Typical Half Cycle Display
One of the main functions of the Racal model 2074 is generating
real-life waveforms. These are normally not sinewaves and squares
but user specific waveforms. Generating such waveforms require
external utilities such as MatLAB or even spreadsheets but having
the program alone is not enough for the 2074; Once the waveform
is computed and defined, it must be converted to a format which the
instrument can accept and coordinates downloaded to the
generator memory for re-play.
Arbitrary waveforms are stored as digital XY coordinates in a
special memory, normally referred to as working memory. Each
coordinate is referred to as waveform point, or waveform sample.
The waveform is better defined if it has many waveform points. For
example, with only 8 point, sine waveform will hardly resemble the
shape of a sinewave and will look more like an up-down staircase,
but with 100 points, the same sine waveform will look almost
perfect.
The final shape of the waveform is produced by a DAC (Digital to
Analog Converter) The waveform samples are clocked to the DAC
at a rate defined by the sample clock frequency. The output of the
DAC converts the digital data to analog levels and passes on the
signal to the output amplifier. The shape of the function is more or
less the same as it comes out of the DAC except it could be
amplified or attenuated, depending on the require amplitude level.
The size of the working memory is limited to the way the hardware
was designed. The 2074 has 1Meg points available as standard (2
Meg point optional) to build one or more waveforms. There is no
need to use the entire memory for only one waveform; The memory
can be divided into smaller segments loaded with different
waveforms while the instrument can be programmed to output one
segment at a time.
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