High-Speed ADCs

Q&A Strange things with AD9281

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Strange things with AD9281

nigelwright7557 on Sep 16, 2019

I am using the ad9281 as the basis for a USB oscilloscope.

The first problem is noise if I go above 10MHz clocking.

If I reduce the clock speed the noise goes down.

The other problem is with 1 volt in I am getting code 166 out when it should be 128.

Vref is 2 volts.

I am using a PIC micro to clock the a2d then I just read data in to PIC port b so its pretty basic really.

Any advice would be appreciated.

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nigelwright7557 Sep 18, 2019 +1 verified

I got stuck into the various problems with my system.

1/ My op amp circuit was too close to the PIC clock circuit and was picking up 8MHz.

2/ AD9283 required better decoupling.

3/ The /AIN pin is not biased…

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0 nigelwright7557 on Sep 18, 2019 11:02 PM over 1 year ago

I got stuck into the various problems with my system.

1/ My op amp circuit was too close to the PIC clock circuit and was picking up 8MHz.

2/ AD9283 required better decoupling.

3/ The /AIN pin is not biased centrally and I had to put an extra resistor in two bias it centrally.

4/ The PIC clock seems to interfere with the AD9283 clock and using a different frequency PIC clock resulted in much less noise.
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0 nigelwright7557 on Sep 18, 2019 11:02 PM over 1 year ago

I got stuck into the various problems with my system.

1/ My op amp circuit was too close to the PIC clock circuit and was picking up 8MHz.

2/ AD9283 required better decoupling.

3/ The /AIN pin is not biased centrally and I had to put an extra resistor in two bias it centrally.

4/ The PIC clock seems to interfere with the AD9283 clock and using a different frequency PIC clock resulted in much less noise.
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