MSP430FR6047: Where does the accuracy limit come from?

Robert Storch

Part Number: MSP430FR6047

Hi,

currently, I'm investigating if the MSP430FR6047 is suitable for our application as a flowmeter (water application). We need very high accuracy in terms of ToF.

Did you investigate where the limit of approx. 35-40ps standard deviation of the single shot measurement is coming from?

Is it due to clock stability? Or SNR, i.e. does the receive chain of the AFE introduce too much noise? Or is the interpolator creating troubles?

If it is all of that - do you have an idea of the shares of each effect?

Thanks and best regards,

Robert

over 1 year ago

0 Dennis Lehman over 1 year ago

TI__Guru 60151 points

Hi Robert,

Let me reach out to one of our USS experts.

0 Robert Storch over 1 year ago in reply to Dennis Lehman

Prodigy 90 points

Ok, thanks. Looking forward to your answer.

0 Dennis Lehman over 1 year ago in reply to Robert Storch

TI__Guru 60151 points

Hi Robert,

From our USS expert:

The limitation comes from a combination of the finite SNR of the sigma-delta ADC, the clock jitter & the # of excitation pulses. The interpolation does add some amount of error due to fixed-point effects but that is a lot smaller compared to the effects of the finite SNR and the clock jitter. I am not sure if the contribution of the clock jitter and ADC SNR was individually studied at the design time.

0 Robert Storch over 1 year ago in reply to Dennis Lehman

Prodigy 90 points

Hi Dennis,

thanks for your reply. I assume that the effect of the number of excitation pulses is the increase in SNR, right?

Regarding clock jitter: do you know if this can be improved by the external crystal or is it the jitter of the PLL itself?

Regards,

Robert

0 Dennis Lehman over 1 year ago in reply to Robert Storch

TI__Guru 60151 points

Hi Robert,

Regarding the # pulses and SNR, you are correct. The jitter is due to the PLL. The oscillator input frequency is limited to 4 or 8MHz and is generated from either a resonator or crystal, and cannot be driven directly from another clock source.

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MSP430FR6047: Where does the accuracy limit come from?