Knowing the voltage across a diode, I need to determine the current through it with a fair degree of accuracy over a range of about 1000x. Is any one type of diode better than another in terms of the accuracy of its logarithmic voltage gain with increasing forward current? This will be a production circuit, so consistancy between devices would also be good to avoid the need for individual calibration.
Thanks, Scott Kelley
Production spread on most diodes will give you a lot of grey hairs on this quite quickly. A solution might be to use a current mirror (with the diode being the 'programming side' as AoE so eloquently puts it) and using the other side as the input to a log amp (as an example).
Much depends on the current you have (what range) - a Wilson mirror gets around a couple of issues, and used to be commercially available (not cheap though - as mirrors must have guaranteed Vbe match, they tend to be expensive. See the MAT-xx series from Analog devices for an example of tightly matched transistors).
As I said, a lot will depend on the maximum current you are using.
Cheers
PeteS
Something I didn't mention - this will double the current (there will be equal current in the two transistors unless you can get or design matched ratio pairs where you can get a ratio of currents).
Cheers
PeteS
through
Are you going to have temperature compensation?
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