ADC Steps PicoScope5444B

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steiemi
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Joined: Wed Apr 18, 2018 6:34 am

ADC Steps PicoScope5444B

Post by steiemi » Wed Apr 25, 2018 2:49 pm

Hi,

I've analysed the ADC steps of all resolutions (8, 12, 14, 15 and 16) and found some interesting points and questions.
I've put a triangular Signal with Vpp = 2V on one channel A with an ADC range of +-1V and oversampled it so that i got the complete spectrum back with all ADC values.

Here an example of an spectrum with a Resolution of 14-bit:
Results_14bit.PNG
I got ADC-steps of 0.1525 mV, but every 4th or 5th value has an step of 0.12207 mV and on the edges 0.0305 mV. And if you count all steps, you can only get 3118 Steps. Why does not the ADC use the hole spectrum of 16384 values?
If the ADC performed steps of 0.12207 mV, you could get a linear graph over the hole spectrum and use 16383.5 values! Why is not it?

The same problem exists with the 8-, 12- and 15-bit resolution. Only the 16-bit resolution is linear with steps of 0.0305 mV and a number of 655534 values!

Here an conclusion of my tests:
Conclusion_test.PNG
Now the questions:
Why does the ADC not only use steps at 0.06104 mV at a resolution of 15 bits, so you can have the hole spectrum with 32767 values?
Why is this the same for 14-bit?
Is it possible to solve this problem?


Many thanks!

Martyn
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Re: ADC Steps PicoScope5444B

Post by Martyn » Wed Apr 25, 2018 9:29 pm

Are you using the internal signal generator / arbitrary waveform generator, which is 14 bit, for the triangle waveform ?
Martyn
Technical Support Manager

steiemi
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Joined: Wed Apr 18, 2018 6:34 am

Re: ADC Steps PicoScope5444B

Post by steiemi » Thu Apr 26, 2018 6:05 am

Yes, but the signal generator resolution of 14-bit shouldn't be a problem or?
Especially for the 8- and 12-bit mode

I will also do some measurements with an analog signal generator ....
Last edited by steiemi on Thu Apr 26, 2018 6:51 am, edited 1 time in total.

Martyn
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Posts: 3288
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: ADC Steps PicoScope5444B

Post by Martyn » Thu Apr 26, 2018 6:48 am

During the factory calibration of units a digital gain is calculated, for each range, to ensure that the device can meet the published specifications. What you are seeing is the application of this digital gain to the ADC values returned from the device.

If you require more information please email support@picotech.com
Martyn
Technical Support Manager

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