Input Current of CMOS Opamp

[cherryic]

The attachment is the datasheet of Intersil ICL7611, which is a 1.4 MHz low power CMOS Opamp, but what confuses me is that it is said it has an ultra low input current. As far as I know, the gate current of MOSFET is zero, so where does this kind of input current come from?

Regards,
Cherryic

 

[manish12]

biasing required it. for keeping proper working condition.

 

[jonashat]

May be leakage current..

 

[cherryic]

biasing required it. for keeping proper working condition.

Would you please provide me some more details about this issue?

 

[elantra]

sometimes the ESD structure will have some leakage current under certain condition.

 

[Guest]

we suppose that current of MOST at gate terminal is zero. but in fact, for sub-micron processes because of low thickness of gate oxide, there is a very little current at this terminal, particularly in high frequencies. for more information you can refer to device level books about MOS.
I think the best is Tsividis's book about modeling of the MOS transistors.

Regards,
SAZ

 

[bicave]

Low input current means current consumption your OPAMP sink from Powe supply. right?
we don't think about high or low frequency. The input to Gate of mosfet equal zero.

 

[cherryic]

Any other suggestions? Where does this input current come from? I am still confused.

Regards,
Cherryic

 

[chang830]

Any other suggestions? Where does this input current come from? I am still confused.

Regards,
Cherryic

yes, it is to descrbe leakage current. See from other view, it is to describe the input impedence.

For ideal opa, we hope the input impedence is very very large.The less bias current means the larger input impedence, that's we expected for opa.

From the datasheet, you maybe noticed it has given the input impedence~1e12 ohm. Put 1V bias voltage, you get easily the input bias current ~1pA, just as in the spec.

 

[memsgg]

It comes from leakage from gate oxide layer, very low, but exists!!

 

[cherryic]

Any other suggestions? Where does this input current come from? I am still confused.

Regards,
Cherryic

yes, it is to descrbe leakage current. See from other view, it is to describe the input impedence.

For ideal opa, we hope the input impedence is very very large.The less bias current means the larger input impedence, that's we expected for opa.

From the datasheet, you maybe noticed it has given the input impedence~1e12 ohm. Put 1V bias voltage, you get easily the input bias current ~1pA, just as in the spec.

Your reply really helps a lot!!! I've got it now.