CCS/PGA970EVM: waveform frequency error

Hello,

Are you making sure to populate the waveform table first then write this data to the device before generating the waveform?

Here are the full instructions as described in the PGA970GUI user's guide:

The waveform generation section of the ADC page is used to generate continuous Sine wave. Steps to
generate sine wave:
1. Specify required values in GAIN_CTRL, SEM, DAC_VCM, DIFF_VOCM, Skip Filter.
2. Specify required offset for the wave to be generated in WFM Bias. The range for this value is 0.82
to 0.88
3. Specify the amplitude for the sine wave in WFM Amplitude. The range of WFM Amplitude value
depends on the GAIN_CTRL, SEM and WFM_Bias Value in the following manner.
• In Single-Ended Mode
WFM_Amplitude < (WFM_Bias - 0.15)/GAIN_CTRL
• In Differential mode
WFM_Amplitude < 1.235 - WFM Bias
When GUI is initializing WFM Amplitude and WFM_BIAS controls will be loaded with typical
values. User can able to change the values during runtime and when entered value lies outside
limit or if it is not satisfying the above condition, Popup will be displayed and entered value will
be coerced to proper value.
4. Specify the frequency with which the wave has to be generated in WFM Frequency. The range for
frequency is 1 kHz to 20 kHz.
5. After specifying the waveform parameters, press Populate Waveform Table button. The Waveform
table gets populated with the values that has to be written to the Waveform RAM. No. of Samples
shows the number of samples required to generate quarter of the specified sine wave. The table
values can be edited and number of samples can also be specified manually through No. of
Samples edit box. There can be between 1 and 256.
6. To write the table values to the device, click the Write button at the bottom of waveform table.
7. Clear will erase the waveform table values. Save and Open is used to save the waveform data to a
text file or load the waveform data from a text file.
8. Click Generate button to generate the waveform. When the button is clicked, a set of registers
related to the waveform generation gets written to the device.
9. After the waveform generation starts, click the Stop button to stop the waveform generation

Please let me know if you are already following this procedure and still having trouble.

Regards,

Hi

I try,waveform frequency is not change.

Hi Scott,

I have recently purchased PGA970EVM just to evaluate. So far phase one of just getting waveform generator to work correctly seems consuming too much time. It is simple instructions but would not work the way it is suppose to be. I thought  the board is faulty, so returned and Farnell swapped a new board for me, same result. At P1 and P2, it is always 660 kHz. Nothing can change this frequency. I checked the waveform table RAM page 8 and 9 correct. data length is correct. communication is working good too. Disabling vref buffer effectively turned off the waveform (not Generate/ Stop).

Voltages are correct- VDD=12V, DVDD=1.8V, AVDD=2.92V, REF=2.52V. Waveform output signal is always reference to P2 (VCM). Any waveform generator output signal measurement reference to GND does not work, I don't know if that is correct! So I stick with referencing to P2.

I have tried your instruction above, and below- please help, I don't know what is missing/ done wrong.