Is "Photodiode Circuit Design Wizard" simulating resistor noise properly?

Hello "Photodiode Circuit Design Wizard" maintainers,

I made a design with a photo diode with a small shunt resistance (100k). The noise density simulation is optimistic by at least x10 at the output (V/rHz).

Below is the design and source code.

The claim is that the noise in 100kOhm is sqrt(4kT/100k) = sqrt(1.7e-20/1e5) = 0.4pA/rHz. Referred to the output this becomes: 0.4pA*6.65Mohm/rHz = 2.7uV/rHz.

This is not what is on the simulation in the wizard. LtSpice confirrms the 2.7uV/rHz.

I would expect the resistors to be correctly simulated even when a bit abnormal.

And a suggestion for the presentation in the graphs. Please add minor-scale - tags to the axis - log scale is hard to read without.

br henning


"Name": "ADA4523 - wrong",
"Description": "photo amp - seems not to simulate R noise correctly",
"Tool": "PD",
"Design": {
"photodiode": {
"sensor": "",
"reverseVoltage": 0,
"biasPreference": "positive",
"capacitance": "1e-12",
"shuntResistance": "100000",
"peakCurrent": "3e-7",
"peakVoltage": 2,
"speedPreference": "bandwidth",
"speed": "1000",
"peaking": 0.707107,
"stages": "2",
"opAmps": [
"stage": "stage_1",
"opAmp": "ADA4528-1",
"locked": true,
"found": true,
"valid": true
"stage": "stage_2",
"opAmp": "ADA4528-1",
"locked": false,
"found": true,
"valid": true
"CreatedDate": "2020-06-26 04:23:26 PM",
"UpdatedDate": "2020-06-26 04:23:26 PM"

Top Replies