Problem with noise in A/D conversion

[maxturk]

Posted on September 11, 2003 at 10:35

Problem with noise in A/D conversion

[maxturk]

Posted on July 22, 2003 at 12:15

Hi everybody, I've a problem with A/D conversion caused by noise from a switching circuit for step motor control. When the motor is on, the conversion get corrupted. I've used a regulator for Vcc, decoupled mass and alimentation, avoided ground loop, optoisolated micro from switching part, filtered with an LC filter the analog input and also mediated the conversion; situation is improved, but still the conversion isn't stable: does anyone have other suggestion to obtain a valid result?

Thanks

[marco32]

Posted on July 23, 2003 at 08:58

Hello Jarod,

Could it be that the ADC input is nearly an PWM motor control output?

Marco

[sjo]

Posted on July 23, 2003 at 12:36

What kind of conversion are you taking, are you taking a sample/average?

Remember the st6 ad is +- 2lsb.

You could try a 256 sample loosing the lower 2bits.

Regards

SJO

[maxime2399]

Posted on July 23, 2003 at 15:50

You should check if there is some ST6 I/Os with injected current at the time of the conversion.

If one of the ST6 I/O body diode is conducing, it will add some noise internally on the ADC reference and may change your conversion by up to 0.6V.

In order to avoid this:

- first try to reduce the injected current in the device

- if you cannot, add an external diode to avoid the current inside the ST6 pin.

[biuro4]

Posted on September 11, 2003 at 10:35

Hi,

Try put the 47nF - 100nF capasitor to the ADC input pin and ground, should help, also you can connect 10k ressistor between GND and this pin