18F4520 A/D working weird

[NavMicroSystems]

TurboLS,

give us an idea what you "analog signal" looks like and where it is comming from.

[TurboLS]

The analog signal is coming from a sample and hold op amp that is sampling an analog video signal coming from a CCD chip. Please click on the following link and look at the Vout signal on page 13 of the PDF. That is the signal we are getting before we attach the PIC chip.

http://www.kodak.com/global/plugins/...2ELongSpec.pdf

Then when we attach it, the signal gets loaded down and all we get is noise in the A/D. thanks again for takin a look.

[TurboLS]

I also tried putting the signal through a buffering op amp and that doesn't seem to help. For some reason, the A/D input of the PIC does not like the signal coming from output of the buffer, nor does it like the input of our sample and hold circuitry, nor the signal coming directly from the CCD. So we tried to amplify the signal before buffering it and the output just becomes noisy as hell with or without the PIC connected.

HELP!

[TurboLS]

Is there any way to set PORTA.0 as a low impedance input???

[NavMicroSystems]

we tried to amplify the signal before buffering it and the output just becomes noisy as hell with or without the PIC connected.

So it's not a PIC problem, it's more a problem with the output of your sensor.

Is there any way to set PORTA.0 as a low impedance input???

With external hardware.


It's still not really clear to me what you are trying to achieve.

What does the timing of the analog signal look like?

[TurboLS]

I would post the picture from that PDF file if I could. But the signal I get before the PIC is just like the one on page 13 labeled "Vout" and it is in phase with the horizontal clocks and the reset clock in that same corner of the page. I figured that putting the signal through a buffer would take care of the low impedance issue, but it doesn't. What external hardware would you recommend for lowering the impedance??

[mister_e]

opamp, transistors, mosfet, fet.... usually opamp