Hello,
The LTSpice noise simulation of AD8603 gives around twice the noise density @ 1 kHz. It should be 22 nV/sqrt(Hz) flat and start the 1/f then below 1 kHz. See sim below connected as follower. Thanks.
From data sheet:
Marcelo
Hello,
The LTSpice noise simulation of AD8603 gives around twice the noise density @ 1 kHz. It should be 22 nV/sqrt(Hz) flat and start the 1/f then below 1 kHz. See sim below connected as follower. Thanks.
From data sheet:
Marcelo
Hello marcelobaru ,
Can you provide me your circuit schematic? I have simulated this on my end and got a voltage noise density plot similar to AD8603's datasheet. 
Datasheet plot: 
From the simulation and the datasheet's TPC plot, we can see a voltage noise density of about 27 nV/sqrt(Hz) @ 1kHz frequency.
Regards,
Paul
Hi,
I'm sorry, is this the correct file? The circuit looks like this when I opened the file:
Can you send a snippet/picture of your circuit in LTSpice as well? Thanks! 
Regards,
Paul
Hi Paul,
Not sure why your symbol is different. Are you using LTSpice XVII?
Netlist:
* C:\temp\Noise AD8603.asc
V§+3.3VA N001 0 3.3
Vnoise N002 0 1.65 AC 1 0
XU10 N002 Voutaux N001 0 Voutaux AD8601
.noise V(Voutaux) Vnoise dec 100 300 5000
.lib ADI.lib
.backanno
.end
Hello,
Yes. I am using LTSpice XVII. I'm sorry, I forgot that I have to download AD8603's model from analog.com since I couldn't find the part on the component's Library. I have autogenerated a symbol from the .cir file (netlist) that I have downloaded from here AD8603 Datasheet and Product Info | Analog Devices that's why I have a different symbol.
I have already fixed this on my end and created a symbol using the .cir file.
I have also simulated your circuit on my end and here is the result:
From my simulation, I am also getting about 27 nV/sqrt(Hz) @ a frequency of 1 kHz.
I'm thinking that the model that you are using is not updated. Can you try downloading the part's model from here: AD8603 Datasheet and Product Info | Analog Devices under Tools and Simulations
After downloading, open the .cir file using LTSpice and autogenerate a symbol from the netlist.
After generating the symbol, it should look like this: 
By viewing the Pin table, we can see the Pin Names and their corresponding SpiceOrders. (For SpiceOrder 1 -> non-inverting input, SpiceOrder 2 -> inverting input, etc.)
Click save, then close. After that, use this model on your circuit by navigating through Components. Let me know if the result of your simulation changes. Thank you
Best Regards,
Paul
Thanks Paul. I can't autogenerate the symbol. It is grayed out. Any thoughts why?
Hello marcelobaru ,
You're welcome Happy to hear that I was able to help you.
Regards,
Paul
Hello marcelobaru ,
You're welcome Happy to hear that I was able to help you.
Regards,
Paul
