clamper

I want a small cheap voltage clamper device. I'd like under 2 volts
drop at 1 mA, but minimal current at a few hundred millivolts.

I tried two small diodes in series, but that's terrible. Better is a
logic-level mosfet with gate connected to drain. It clamps nicely at
1.5 volts or so but conducts picoamps at a few hundred mV, over 1000:1
better than the diodes.

This will go between the force and sense leads of a 4-wire temperature
sensor thing so it automatically works in 2-wire or 4-wire mode.

The alternative is to use two SSRs and let the user explicitely
declare 2-w or 4-w mode.