Other Parts Discussed in Thread: LOG114, LOG101, LOG104
Hello,
I would like to use the LOG112 in a new design. I need best possible accuracy. I have a few questions about how to accomplish that.
1. I plan to measure over 5 decades, 1nA - 100uA. I plan to use Iref = 3.16uA (center of decade range). Is that the best value for Iref?
2. To measure voltage offset, I plan to drive I1 and I2 with 3.16uA, measure the voltage at VLOGOUT, and use that value to compensate for offset. Is that a good plan? Should I use a different value of input current?
3. To measure gain error, I plan to drive I1 with 31.6uA and I2 with 3.16uA, read the voltage at VLOGOUT, compensate it for previously measured offset, and divide it by nominal gain = 0.5V/dec. I don't know if that will work because Log Conformity error will be present (over 1 decade). Is there a better way?
4. I plan to generate Iref from a 2.5V reference. The 2.5V reference in the LOG112 is +/-0.5%. I plan to use a 0.05% reference like the LM4132A-2.5 to generate Iref. I will also use it to generate the test currents mentioned above. How does reference current error affect overall accuracy? In particular, what term should be added to Eqn. (9) on page 12 of the datasheet?
Thanks for your help!
Richard