|
|
发表于 2009-6-11 04:55:16
|
显示全部楼层
eezm's circuit is essentially two simple log amps combined together to cancel their tempco. A8 is the one generating the output. A9 and the right half of ua726 forms the 2nd log amp: its output depends will go up and down with temperature. However, that signal is applied to the left half ua726's emitter, making it out of phase with A8's output, thus canceling out the tempco impact.
another approach is to build two identical log opamp (using a lm394 + a dual opamp), and use a differential amp to subtract the temp - caused thermal drift.
if you don't want to use matched pairs, you can replace the 1k resistor with a thermister with positive tempco (at +0.2mv/c) to offset the negative tempco from the diode / transistor. |
|
楼主
