1
Getting
Started
Functional Description
1-7
Functional
Description
Detailed functional description is given following the general
description of the features and functions available with the 5251.
Output Functions
Model 5251 is completely digital. There are no analog functions
resident in its hardware circuits. Data has to be downloaded to the
instrument for it to start generating waveforms. The instrument can
generate a few standard functions such as sine wave, triangular
wave and square wave. Each time that a standard function is
required, the instrument calculates its coordinates and places them
in the waveform memory. Therefore, every time a standard function
is selected, minimal time is required for the controller to compute
the function and load its data to the waveform memory.
Frequency
Waveform frequency and sample clock are programmed with 14
digits, limited only by 1
μ
S/s. Frequency accuracy of the output
waveform is determined by the clock reference, CLK10, which
provides 1 ppm accuracy and stability over time and temperature.
Amplitude
The output level may be programmed from 200 mV to 20 Vp-p into
open circuit, or 100 mV to 10 V into 50
Ω
. Offset may be applied to
the output to shift the signal either positive or negative. Offset and
amplitude are inter-related, so make sure you understand the
offset-amplitude ranges before you apply offset to your signal.
Trigger Modes
Besides its normal continuous mode, the 5251 responds to a
variety of trigger sources. The output waveform may be gated,
triggered, or generate a counted burst of waveforms. A built-in re-
trigger generator has a programmable delay time. Once triggered,
the firmware issues automatic trigger intervals. The re-trigger
interval is measured from the end of the signal to the start of the
next signal. Having this feature eliminates the need for external
trigger sources. The re-trigger generator can be programmed from
200 ns to 20 seconds intervals with incremental resolution of 20 ns.
Arbitrary Waveforms
The Model 5251 generates arbitrary waveforms with 16 bits of
vertical resolution. Any waveform it generates must first be loaded
to its waveform memory. The arbitrary waveform memory is a bank
of 16-bit words. Each word represents a point on the horizontal
scale. Each word has a horizontal address that can range from 0 to
2,097,152 and a vertical address that can range from -16383 to
+16384 (16 bits). Using a high speed clocking circuit, the digital
contents of the arbitrary waveform memory is extracted and routed
to the Digital to Analog Converter (DAC). The DAC converts the
digital data to an analog signal, and the output amplifier completes
the task by amplifying or attenuating the signal at the output
connector.
Summary of Contents for 5251
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