18F4520 A/D working weird

[TurboLS]

First of all about the frequency, this CCD is being run very slow... approximately 3.6kHz and as such, the frequency of the vout signal is also 3.6khz.

I will definitely take a look at the adcon 2 register to see if maybe that will fix the problem.

We were using a simple buffer with a negative feedback loop and powered with positive 18V and negative 18V.

I also read in the manual that the maximum input impedance for an analog signal is 2.5kohms. Does anyone know what the minimum or recommended impedance is>?

Thanks for everyone's help. Hopefully I can figure out a way to get the PIC to work with this setup.

[TurboLS]

Well, I slope coupled the input with a 1200pF cap and a 10k resistor and if go directly from that into a non-inverting x10 opamp circuit and then to the PIC, I can actually see a signal. As of yet, all I can get is noise on the A/D tho, so it may just be that I have to change the point at which I do the A/D operation in the software. I will be trying a combination of circuits with the slope coupler, amplifier, buffer, and sampling opamp circuitry.

Also, since I am running the chip so slow, I don't think the slew rate nor the ADCON2 register would be a problem.

[TurboLS]

also, do i expressly need the following line in my code?

ADCON0.0 = 1 ' enable a/d

Cuz I can do A/D without it, but I was just wondering if it might have been a config error. thanks.

[TurboLS]

I am pretty sure I just measure the impedance in parallel, but how do I do that (on the PORTA.0 A/D channel) with the PIC? thanks.