Analog Devices AD6642 User Manual page 10

Evaluation Board User Guide
Adjusting the Amplitude of the Input Signal
The next step is to adjust the amplitude of the input signal for
each channel as follows:
1. Adjust the amplitude of the input signal so that the fundamental
is at the desired level. (Examine the Fund Power reading in the
left panel of the Graph – AD6657 Average FFT window; see
Figure 13.)
Figure 13. Graph – AD6657 Average FFT Window of VisualAnalog
2. Repeat this procedure for Channel B, Channel C, and/or
Channel D.
3. Click the disk icon within the Graph – AD6657 Average
FFT window to save the performance plot data as a .csv
formatted file. See Figure 14 for an example.
0
–20
–40
–60
–80
–100
–120
0 10 20 30
FREQUENCY (MHz)
Figure 14. Typical FFT, AD6657
4. If using the NSR feature, first change the settings in the ADC A,
ADC B, ADC C, and/or ADC D pages (see Figure 15) to
the desired settings.
f
= 185MSPS
S
f
= 30.3MHz @ –1dBFS
IN
SNR = 65.7dB (66.7dBFS)
SFDR = 89.7dBc
SECOND
HARMONIC THIRD
HARMONIC
40 50 60 70 80 90
Figure 15. SPIController, Example ADC A Page – NSR Settings
5. Repeat this procedure for Channel B, Channel C, and/or
Channel D.
6. Click on the button circled in the FFT Analysis box (see
Figure 16) in Visual Analog to bring up the options for
setting the NSR.
Figure 16. VisualAnalog – [Canvas – (AD6657 FFT)*] Main Window –
7. Configure the settings in the FFT Analysis to match the
settings selected for the NSR in the SPIController (see
Figure 17).
Figure 17. VisualAnalog, FFT Analysis Settings
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Showing AD6657 Average FFT Analysis
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