I have been checking the input current noise with bias cancellation enabled and disabled. The data sheet shows that with bias cancellation enabled (VSHDN = V+) the current noise is bigger:
Following fig 3 in the data sheet I made this simulation in LTspice, using REQ = 10k so that the current noise will dominate.
The voltage on the SHDN pin is set first to 3.8V for bias cancellation disabled then to 5V for bias cancellation enabled. So the noise should be lower then higher. But in the simulation the first run (green trace) is higher:
The noise at 100mHz is 54uV/rtHz with REQ at 10k. Equivalent to 5400pA/rtHz. That is about the value shown on the graph in the data sheet for bias cancellation enabled (green line).
I am wondering if the LTC6228 spice model has the SHDN pin inverted for the noise model, or I am misunderstanding how it works?
Here's the simulation file:
Any help appreciated!
Added simulation file
[edited by: Kentxu at 8:00 PM (GMT 0) on 16 May 2020]