You're still making no sense at all - tell us EXACTLY what you want to do, not how you imagine it needs to be done.Since i using PIC18F4331, i have been told that its output current is not constant. as i know, a precision amplifier can constant the current.
As it's only fed from a +ve 5V supply, obviously not.i have question about the PIC18F4331
Do the chip have 5 to -5 output? i mean the chip have negative output signal?