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| Ultra low current Instrumentation Amp |
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| mfusaro:
I'm looking for a Instrumentation Amp that has a supply current around 1 uA, no other special requirements. The lowest current I could find is 30 uA. There are plenty of sub uA opamps, why do Instrumentation Amps need so much current? Thanks! |
| Kleinstein:
Internally an instrumentation amp is made from something like 2-3 OPs. In addition to the amplifier there are also resistors to set the gain, that need current when the input votlage is not zero. So it would need rather high resistors and thus causing high noise. High resistors are also not so easy to make on a chip. It is not impossible, but relatively expensive. 2 OPs + resistors may be an option - especially with low requirements on accurcy. |
| Marco:
What's the common mode voltage and source impedance? The single opamp+mosfet high side current sense circuit is a difference amplifier, CMRR is not dependent on resistor matching either, only gain is. |
| voltsandjolts:
The lowest power amplifier is one that is not there ;D If you are using a sigma-delta ADC, maybe you don't need the IAmp. |
| mfusaro:
Thanks for all the responses. This is a low side 4 wire current sense application. The common mode voltage is near zero and the sense resistor is 0.1 ohm. The output of the amp will feed the ADC input of a ultra low power microprocessor that is sleeping. |
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