MSP432P401R: Oversampling on MSP432P401R

artem dmitriev5

Part Number: MSP432P401R

Hello!

I want to get 14 bit resolution (it is necessary to measure 200mv changes) on MSP432P401R. I need 2 channels with sample speed at least 100ksps with 14bit.

Is it possible to do it with this controller? There is a http://www.ti.com/lit/an/slaa694a/slaa694a.pdf exmaple but i can't get 14 bit resolution on MSP432P401R Launchpad board. Differences between samples can be about 6.

over 7 years ago

0 Amit Ashara over 7 years ago

TI__Guru**** 244400 points

Hello Artem,

Yes, it is possible to have 2 channels, with each channel sampling at 100 Ksps with the MSP432P401R device. Let me look at the example code and update.

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

I have MSP32P401 bard, Operational amplifier OPA365, Reference Voltage REF2030 and battery with voltage dividers (On photo). Can i test oversampling under this conditions? i tried to use code from http://www.ti.com/lit/an/slaa694a/slaa694a.pdf but i don't have DAC8560EVM for test. It is really important to measure 0.2mV changes (I made a mistake before).

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem,

I would suggest using the example in the SDK for ADC sampling to see if you are getting the resolution. We can investigate from that point.

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

I can't get 14bit resolution in my conditions . Can you test adc accuracy with 4x oversampling in your lab, please? For example, it is necessary to prove the customer that adc can feel 200uV changes if input voltage is lower 1mV (for example 200, 400, 600, 800uV) and also the same in the middle of dynamic range (for example 200uV changes starting from 1.2v). The OSR can be 4x maximum. I think it can be quickly investigated if you have necesssary equipment.

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem,

Can you please attach the CCS project or code that you are using for configuring the ADC?

Also can you please provide the schematic of the ADC input stage, i.e. op-amp, filter, etc?

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

As i said i used slightly changed code from from this document www.ti.com/.../slaa694a.pdf (link http://www.ti.com/lit/zip/slaa694
I think it is not worth to provide the schematics because connections between chips via wires is incorrect (necessary to use precision voltage source at least or precision DAC eval board for example). I just tried how it will work with components that i found.

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem,

I am not sure about your last post, but does it mean that the issue is resolved on your side?

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

No, i just mean that i think it would be great if you can check ability to reach 200uv precision on your lab equipment, if it is possible of course. For one of the customer it is important to use microcontroller with 200uV precision ADC with 2 channels and at least 100ksps per channel.

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

Can you do small investigation based on http://www.ti.com/lit/zip/slaa694 example,please? If no, let me know please.

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem,

I can see it working with GND and 3.3V connected to the Analog Pin. I will check with a separate source to see if it reads the values of say 1.200V, 1.202V and 1.198V to make sure we have the 200 uV resolution.

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem.

You are using an external reference voltage source. What is the value of the reference source?

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

Hello!
Reference is 3v.

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

Thank you!
But can you check this also for for example 200, 400, 600, 800uV ? In the middle of range it is necessary to check 1.200V, 1.2002V and 1.1998V to make sure you have the 200 uV resolution (not 1.200V, 1.202V and 1.198V, because it is 2mv precision).

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Aretm,

You very first post mentioned 200mV resolution but later it was shown as 200 uV. So I assume it is 200 uV.

Now for a 1MSPS you may get 14-bit ADC with a lower ENOB. So the resolution assuming an ideal world case is 3V/(2^14) = 183.1 uV

Now we can add 1 bit with every an oversampling factor of 4. Hence you may get 91.55 uV with 250 KSPS and 45.775 uV with 62.5 KSPS.

But to be able to achieve such values, your setup needs to have excellent reference source and noise immunity. The free wires just do not cut it. Also the ENOB will be lesser than actual value, so getting 200 uV resolution per step may be something that is a little out of reach.

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

Did you document any investigations?

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem,

The above observations in my last post was based on the experiment to be conducted. The experiments have not been started yet.

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

Hello!
Are you planning to do any investigations on this week?
Thank you!

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem,

I checked with another co-worker of mine. With a Single Ended analog signal, being sampled at 100 KSPS and 3V reference, it is not possible to achieve the 200 uV resolution. The resolution per bit is 2^11.5 in single ended mode at 1 MSPS. With a 3V reference it amounts to 1.0358 mV per bit which is outside of the requirement. By oversampling at 4X, the sampling rate would be 250 KSPS and the resolution per bit will improve to 517.9 uV. Any further oversampling will reduce the sampling rate to below 100 KSPS as required by your application.

However if you are doing a differential signal conversion, it may still be possible to achieve the resolution.

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

Hello! thank you!

But in case of differential input I can use only 13bit to mesure unipolar voltage?

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem,

But with oversampling and if it is OK to go 16x oversampling you can raise the accuracy to an ENOB of 15 bits. BTW, why do you needt 100 KSPS if it is measuring the battery voltage?

0 artem dmitriev5 over 7 years ago in reply to Amit Ashara

Intellectual 330 points

It is not the measuring battery voltage. I just wanted to estimate adc precision for the customer. But i don't have suitable equipment for this experiment. I tried to use a battery as voltage source.

0 Amit Ashara over 7 years ago in reply to artem dmitriev5

TI__Guru**** 244400 points

Hello Artem,

Theoretically speaking the ADC resolution is defined as Vref/2^(ENOB). With oversampling of 4x you add 1 ENOB. Hence if the 1MSPS ENOB for single ended mode of sampling is 11.2 bits then at 250 KSPS (which is 4x over sampling) it would be 12.2 bits.

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MSP432P401R: Oversampling on MSP432P401R