DelSig ADC Accuracy

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DelSig ADC Accuracy

Postby grimmjaw » Tue Oct 29, 2013 8:49 am

Hi,

I'm need some help in regards of the accuray of the DelSig ADC.
I'm using DelSig ADC in PSoC5LP to measured 4 channels,
The setup is as followed:
Differential input-->AMuxSeq-->DelSig ADC.
The ADC is configure as follow MultiSample, 20 Bit resolution, 182 SPS, input range +-6.144 with internal 1.024Volts.
I trying to measured on board 5v rail (i'm using PSoC5LP demo board btw) and getting 4.08V which is wrong.
Using DMM I'm getting 4.79V which make more sense.

Is the accuracy of the ADC that bad?Could the AMuxSeq play any role? :?:
thanks

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Re: DelSig ADC Accuracy

Postby bobmarlowe » Tue Oct 29, 2013 10:23 am

When I use ADCDelSig version 3.0 (latest) I may use up to 45 sps @20 bit resolution.
Additionally is displayed that the usable input range is GND + 100mV to VCC -250mV.

So I suggest you to update to latest (use Cypress Update Manager) and re-try.

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Re: DelSig ADC Accuracy

Postby grimmjaw » Tue Oct 29, 2013 1:37 pm

I'm using PSoC Creator 3 which I think has the latest component.
but the meaurements still way off

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Re: DelSig ADC Accuracy

Postby bobmarlowe » Wed Oct 30, 2013 1:12 am

I'm using PSoC Creator 3 which I think has the latest component.
Do not believe, check it, the version is displayed when hoovering with the mouse over the component. Otherwise: where do the the differences come from?

As I tried to tell you: The component is not able to measure 5.000V, the maximum is 4.750V and the lowest is 100mV.
Best would be for us to check when you upload your complete project here (File -> Create Workspace Bundle (minimal) and attach resulting file)


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Re: DelSig ADC Accuracy

Postby grimmjaw » Wed Oct 30, 2013 1:50 am

Hallo Bob,

I though the maximum range is 6*Vref=6.144V,no?
I tried measuring the 3.3V rail and got 3.339V Volt but from DMM the value is 3.293V
Anyway I have attached the workspace bundle.

Edit: I have also measured the Vref with DMM and got 1.023V, look okay to me
Attachments
Design02.cywrk.Archive01.zip
(513.87 KiB) Downloaded 128 times
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Re: DelSig ADC Accuracy

Postby grimmjaw » Wed Oct 30, 2013 3:20 am

It seem that I set the Vdda at 3.3V, that why I got a large offset.
By resetting Vdda to 5V I got better result :
4.89V at 4.79V.
3.39 at 3.29V
It seem at input range +-6.144 with internal 1.024Volts, the offset is around 100mV
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Re: DelSig ADC Accuracy

Postby bobmarlowe » Wed Oct 30, 2013 5:50 am

When you look at the picture of the configuration-window you can exactly see that there is a 100mV offset and that the maximum voltage is 4.750V when using rail-to-rail configuration.

ADC.jpg
ADC.jpg (57.7 KiB) Viewed 2925 times


When you set the Buffer Mode to "Bypass Buffer" the situation looks a bit different.

Additionally you should bypass tihe internal reference at port 0_3 or port 3_2 with a cap to increase the precision.


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Re: DelSig ADC Accuracy

Postby danadak » Wed Oct 30, 2013 1:02 pm

From the TRM -

DelSig Input Buffer.jpg
DelSig Input Buffer.jpg (87.08 KiB) Viewed 2906 times


Looks like specs over temp went more conservative to 100 mV.

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Re: DelSig ADC Accuracy

Postby grimmjaw » Tue Nov 05, 2013 5:59 am

erm..so it is in range.

Anyway, thanks for the help
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