I'm trying to to find the best way to force an inverting amplifier to postive saturation with a gate input, but otherwise leave the function of the op-amp intact. I've come up with a few ways to do this which all use some kind of current sink at the summing node. Using the open collector output of a comparator directly seemed the best way to go, but the offset contribution was significant in simulation. So now I'm not wondering if using a discrete mosfet or bjt is a better route. Unfortunately I need to control that with a positive 0 to 5V gate (from a schtmitt trigger), and the only way I can get this to work is with negative control voltages. Anybody have any suggestions for me?