AnsweredAssumed Answered

Spice Opamp model noise

Question asked by fargo on Jan 7, 2014
Latest reply on Jan 8, 2014 by NeilJ

Hi,

 

I downloaded the spice model for AD8676 and tried to simulate the noise in LTspice.

 

My circuit is really simple (see attached pdf).

The opamp is connected as a unity gain buffer. The only resistor is an Rs from the positive input to ground.

I am using +/-15V supplies (I also checked with +/-5V supplies and get same results).

 

I then swept the Rs value from 1 to 1G and plotted V(onoise) at 1kHz.

From that I find:

Vn=21.3nV/rHz

In=21.5fA/rHz

 

The datasheet says

Vn = 2.8nV/rHz

In = 300fA/rHz

 

So the simulated voltage noise seems to be ~10x too high and current noise is 15x too low.

Am I doing something wrong or is there a problem with the model for AD8676?

 

Thanks,

John

Attachments

Outcomes