ADS1675: Quantifying ADC Performance

Richard Coulter

Part Number: ADS1675
Other Parts Discussed in Thread: PSIEVM

I have a working ADS1675 design, and I'd like to quantify performance of the ADC and my amplifier. I'm feeding a test signal from an Agilent Function Generator, but I suspect its output SFDR is less than the ~103dB specified dynamic range of the ADS1675 running at 2MSPS. I'm seeking recommendations for an effective test setup to fully quantify the dynamic range of my hardware. Is there a recommended function generator? Some way to filter the function generator's output? Anything related to test setup would be appreciated. Thank you!

3 months ago

0 Keith Nicholas 3 months ago

TI__Guru 50930 points

Hello Richard,

Welcome to the TI E2E community.

We use Audio Precision signal generators, specifically the APx555 series.

https://www.ap.com/analyzers-accessories/apx555

The signal generator section has a THD+N (22kHz BW) spec of -117dB.

The previous generation can also be used, the AP2700 series.

https://www.ap.com/analyzers-accessories/2700-series

We also have a fixed 2kHz precision signal source evaluation board, the PSIEVM, that can be used for quick checks, but THD+N for this product is around -104dB.

https://www.ti.com/tool/PSIEVM

Regards,
Keith Nicholas
Precision ADC Applications

0 Richard Coulter 3 months ago in reply to Keith Nicholas

Prodigy 10 points

Hi Keith,

Thanks for the quick reply. It looks like those sig gens run up to about 204kHz, but THD starts to climb above -100dB with sine waves above 100kHz. Sorry, I should have mentioned that we are running in the 100kHz to 500kHz range. Are there any sig gens or sources that would suit?

Thanks,
Rich

+1 Keith Nicholas 3 months ago in reply to Richard Coulter

TI__Guru 50930 points

Hello Rich,

I am not aware of any signal generators that have better than 106dB SNR+THD and can support greater than 200kHz which is why we typically specify wideband delta-sigma ADCs with test frequency less than 200kHz. However, there may be some newer products on the market.

For higher input signal frequency, we will use a low noise RF generator, such as the R&S SMB100B, with an external bandpass filter to improve THD and SFDR.

https://www.rohde-schwarz.com/us/products/test-and-measurement/analog-signal-generators/rs-smb100b-rf-and-microwave-signal-generator_63493-553988.html

https://www.allenavionics.com/product-details/bandpass-lc-filters

Regards,
Keith

+1 Richard Coulter 3 months ago in reply to Keith Nicholas

Prodigy 10 points

Thanks for the additional reply, Keith. The ADS1675 datasheet has a couple Spectral Response plots (Figures 19 and20 in SBAS416D) for Fin = 1600kHz, where THD is around 120dB below the input signal. Do you have any insight into how those plots were obtained? Again, I appreciate the dialogue.

Thanks,
Rich

+1 Keith Nicholas 3 months ago in reply to Richard Coulter

TI__Guru 50930 points

Hi Rich,

These measurements would have used a low noise RF generator and an external bandpass filter. I was not able to find the exact equipment used, but this is the setup we use for higher frequency measurements. The input level is adjusted to -0.5dB of full scale, and 65536 points are collected and then run through an FFT algorithm to produce the plots in the datasheet.

Regards,
Keith

0 Richard Coulter 3 months ago in reply to Keith Nicholas

Prodigy 10 points

Thanks yet again, Keith. Very helpful!

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ADS1675: Quantifying ADC Performance