I'm trying to obtain a high impedance, several decades current pump for charging a capacitor from 1uA to 10mA, swing +/-5V.
I arranged two current mirrors like this and is working acceptable for simplicity, cost, etc.
Two options I tried so far:
1) Controlled FETs, but due to P/N mismatches, control curves are completely different :) I guess worse solution.
2) Using OA's to drive voltages across R5/R6 based on the fact that when approaches +5/-5, mirrors will be "disabled" and maximum charge time will be achieved.
Still not the best deal, OA's needs to be matched and control curve will be most of the time effective at 90% of voltage (near rail) due to log effect of linear charging the cap.
So I wonder if there is a brilliant idea here :))
Thank you in advance!