Keysight CXG, EXG, and MXG X-Series Signal Generators Programming Guide 211
Creating and Downloading Waveform Files
Understanding Waveform Data
There is no single scaling value that is optimal for all waveforms. To achieve
the maximum dynamic range, select the largest scaling value that does not
result in a DAC over–range error. There are two ways to scale the I/Q data:
— Reduce the input values for the DAC.
— Use the SCPI command
:RADio:ARB:RSCaling <val>
to set the
waveform amplitude as a percentage of full scale.
To further minimize overshoot problems, use the correct FIR filter for your
signal type and adjust your sample rate to accommodate the filter response.
2’s Complement Data Format
The signal generator requires signed values for the input data. For binary data,
two’s complement is a way to represent positive and negative values. The most
significant bit (MSB) determines the sign.
— 0 equals a positive value (01011011 = 91 decimal)
— 1 equals a negative value (10100101 = –91 decimal)
Like decimal values, if you sum the binary positive and negative values, you get
zero. The one difference with binary values is that you have a carry, which is
ignored. The following shows how to calculate the two’s complement using
16–bits. The process is the same for both positive and negative values.
The signal generator factory preset for scaling is 70%. If you reduce the
DAC input values, ensure that you set the signal generator scaling
(:RADio:ARB:RSCaling) to an appropriate setting that accounts for the
reduced values.
FIR filter capability is only available on vector signal generator models
with an installed baseband generator option.
Convert the decimal value to binary.
23710 = 01011100 10011110
Notice that 15 bits (0–14) determine the value and bit 16 (MSB) indicates a positive value.
Invert the bits (1 becomes 0 and 0 becomes 1).
10100011 01100001
Add one to the inverted bits. Adding one makes it a two’s complement of the original binary value.
10100011 01100001
+
00000000 00000001
10100011 01100010
The MSB of the resultant is one, indicating a negative value (–23710).
Test the results by summing the binary positive and negative values; when correct, they produce zero.
01011100 10011110
+ 10100011 01100010
00000000 00000000
Summary of Contents for X-Series
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