ADS127L11EVM-PDK: Spectrum Analysis of High Speed Mode and Low Speed Mode

Masakazu Adachi

Intellectual 2500 points

Part Number: ADS127L11EVM-PDK

Hello Team,

I have a question about GUI. *Attached the capture

I have input the following signals, but the results are quite different in high speed mode and low speed mode.

-frequency: 1 kHz

-waveform: sinusoidal

-amplitude: ±0.834 V

In high speed mode, the first harmonic is set to 1kHz, but in low speed mode, 125Hz (one eighth of 1kHz) is caught as the first harmonic.

Since low speed mode is one eighth of the sampling of high speed mode, it seems to be related. I also notice that THD is extremely worse than in High Speed mode.

Please let me know what you think.

Regards,

Masakazu

over 2 years ago

0 Keith Nicholas over 2 years ago

TI__Mastermind 36150 points

Hello Masakazu,

The Master Clock Frequency needs set to 3MHz to operate in Low-speed mode. The device has been configured for low-speed, but the clock input is still operating at 24MHz, which is too high, causing poor performance in THD as well as the incorrect FFT.

Regards,
Keith Nicholas
Precision ADC Applications

0 Masakazu Adachi over 2 years ago in reply to Keith Nicholas

TI__Intellectual 2500 points

Hello Keith,

I understand. I will set the master clock to 3MHz and experiment.

Regards,

Masakazu

0 Keith Nicholas over 2 years ago in reply to Masakazu Adachi

TI__Mastermind 36150 points

Hello Masakazu,

O.k. Please let me know if you have additional questions.

Thanks,
Keith

0 Keith Nicholas over 2 years ago in reply to Masakazu Adachi

TI__Mastermind 36150 points

Hello Masakazu,

O.k. Please let me know if you have additional questions.

Thanks,
Keith

0 Masakazu Adachi over 2 years ago in reply to Keith Nicholas

TI__Intellectual 2500 points

Hello Keith,

I set the master clock to 3MHz and experiment.

However, in low speed mode, 125Hz (one eighth of 1kHz) is caught as the first harmonic.

Please let me know what you think.

Regards,

Masakazu

0 Keith Nicholas over 2 years ago in reply to Masakazu Adachi

TI__Mastermind 36150 points

Hello Masakazu,

This is a 'bug' in the software that I missed. We will get this corrected on a future version of the GUI software.

I hooked this up on the bench and was able to get it to work with the below settings. Keep the Master Clock set to 24MHz, and use the Clock divider option of 'Div by 8'. The software will correctly identify the sample rate to 23.44ksps and should provide correct results.

The below signal generator frequency is 2kHz, with an amplitude of 3.25Vrms.

Please let me know if this corrects the problem. Thanks!

Regards,
Keith

0 Masakazu Adachi over 2 years ago in reply to Keith Nicholas

TI__Intellectual 2500 points

Hello Keith,

I see. I'll confirm it.

Thank you.

Masakazu

0 Keith Nicholas over 2 years ago in reply to Masakazu Adachi

TI__Mastermind 36150 points

Hello Masakazu,

O.K. I will wait for your feedback.

Keith

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ADS127L11EVM-PDK: Spectrum Analysis of High Speed Mode and Low Speed Mode