Keysight EXG and MXG X-Series Signal Generators User’s Guide 205
Basic Digital Operation for N5172B/82B with Options 653/655/656/657
Scaling a Waveform
Setting Waveform Scaling
Waveform scaling differs from waveform runtime scaling in that it permanently affects waveform
data and only applies to waveform segments stored in BBG media. You scale the waveform either
up or down as a percentage of the DAC full scale (100%). If you scale your waveforms using this
method, you may also need to change the waveform runtime scaling value to accommodate this
scaling.
When you scale, the signal generator permanently modifies the waveform file’s sample values so
that they conform to the desired scaling value. When you initiate scaling, the signal generator
performs the following actions:
— locates the waveform file’s absolute peak sample value
— determines its current percentage of full scale
— calculates the ratio of the desired scale value to the determined absolute peak sample scale
value
— multiplies each sample in the waveform file by this ratio
When you scale a waveform, you can create fractional data, lose data, or both. Fractional data
occurs almost every time you reduce or increase the scaling value, and causes quantization errors.
Quantization errors are more noticeable when scaling down, since you are closer to the noise floor.
You lose data when either the signal generator rounds fractional data down or the scaling value is
derived using the results from a power of two. This means that scaling a waveform in half (power of
two: 2
1
= 2) causes each waveform sample to lose one bit. The waveform data modifications are not
correctable and may cause waveform distortion. It is always best to make a copy of the original file
prior to applying scaling.
Use the following examples to apply waveform scaling to a waveform file. While this process uses
the factory–supplied waveform RAMP_TEST_WFM, it is the same for any waveform file.
Copy a Waveform File
1. Display the waveform files in BBG media: Press File > Catalog Type > More > Volatile
Segments.
2. Highlight the waveform RAMP_TEST_WFM.
3. Press Copy File.
Peak sample
85% of full scale—Prescaling
60% of full scale–Post scaling
DAC full scale 100%
Scaled sample value = scaling ratio × prescale sample val
Scaling ratio = desired scale val / current scale val
= 60 / 85
= 0.70588
Each sample in the waveform is multiplied by 0.70588 to
reach the 60% post scaling waveform amplitude.
Original ramp waveform
Scaled ramp waveform
= Samples
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