I am building a circuit which has OPAMP and inputs to the OPAMP from the photodiode. I have replaced the photodiode with the equivalent circuit. Aim is to cancel the noise. Output should be the subtraction of two input currents. Attached the LTSpice file.

 

Although many here use LTSpice, not all do. You may get more help if you also include a screen grab of your schematic, preferably in .png format.

 

Attached .png file

 

Your TIA conversion G is quite low, re the 1k ohm fdbk R. And your 100M ohm
input Rs generating a lot of thermal noise, Mostly uncorrelated, so subtraction
not effective.

I am not an expert here, what am I missing.


Regards, Dana.

 

Aim is to cancel the noise.

What noise is that circuit cancel supposed to cancel?

 

The signals from the two photodiodes caused by light will subtract because they are opposite in polarity. However, the intrinsic noise from the two photodiodes will add as the RMS of two noise sources. This is because the two noise sources are uncorrelated. The LTSpice noise simulations will show this additive effect. This AAC article can get you started on simple noise simulations if you don't know how to do it in LTSpice.

https://www.allaboutcircuits.com/technical-articles/Noise-Analysis-Using-LTspice-Tutorial/

 

I have replaced the photodiode with the equivalent circuit

What is p-n transition area of your photodiode?
If it is 67 square centimeters and under sunlight,
then current will about 2A, like in your simulation.
Seems current in range 10~20uA will be more realistic.

 

Thanks for the link.
- The signals from the two photodiodes caused by light will subtract because they are opposite in polarity.
At the output of the photodiodes, signals are not getting subtracted. Please suggest me if i have done any mistake.

 

- The signals from the two photodiodes caused by light will subtract because they are opposite in polarity.
At the output of the photodiodes, signals are not getting subtracted

Graph 1
I1:
PULSE(165u 150u 3u 0 0 2u 8u 4)
165u = 15uA Data light + 150uA Background Light
150u = 0uA Data light + 150uA Background Light
I2:
150u = 150uA Background Light
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Graph 2
I1:
PULSE(16.5u 1.5u 3u 0 0 2u 8u 4)
16.5u = 15uA Data light + 1.5uA Background Light
1.5u = 0uA Data light + 1.5uA Background Light
I2:
1.5u = 1.5uA Background Light
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 

In the first graph, how come data light = 15 and background light = 150 u ?
In the second graph, how come data light = 13 and background light = 1.5 ?

 

Thank you. Where is the option to set data light and background light in LTSpice?
Can you please send me the tutorial link?

According to my understanding, here background light is the noise which we are cancelling. If data light is fed to two photodiodes, the signal also gets cancelled. That's the reason we are giving data light = 0u to another photodiode.
Can we show the dark noise, shot noise, thermal noise in LTSpice?
Can you share me the LTSpice file?

 

https://www.analog.com/en/technical-articles/transimpedance-amplifier-noise-considerations.html

https://www.ti.com/lit/an/sboa060/sboa060.pdf

The above might help.


Regards, Dana.

 

Thank you. Where is the option to set data light and background light in LTSpice?

hi,
Look at this image.
E

 

Well, seems it is about electronic noise, generated in photodiodes,
not about background (ambient) light.

Why not cool diode (diodes) by Peltier element up to -70°C?

Simulating noise in LTspice:
http://axotron.se/blog/voltage-and-current-noise-sources-in-ltspice-noise-simulations/
https://www.allaboutcircuits.com/technical-articles/Noise-Analysis-Using-LTspice-Tutorial/
https://www.digikey.com/en/videos/l/linear-technology/ltspice-iv-noise-simulations
http://www.gunthard-kraus.de/LTSwitcherCAD/SwitcherCAD-Tutorial_English/pdf-File/LTspice_4_e2.pdf

LTspice tutorial:
http://www.simonbramble.co.uk/lt_spice/ltspice_lt_spice_tutorial_1.htm
---------------------------------------------------------------------------

https://www.hamamatsu.com/resources/pdf/ssd/si_pd_circuit_e.pdf

 

If we want the circuit to operate in GHz frequency. Do we want to use the Rf in high frequency ?

 

If we want the circuit to operate in GHz frequency. Do we want to use the Rf in high frequency ?

Without Rf:

How to find the bandwidth for the circuit . I have chosen OPAMP of GBP = 4GHz. Feedback resistor chosen in 100k. I want to find total bandwidth using LTSpice?

Total Bandwidth with Rf = 100k:


Use LTspice.

 

Thank you so much. I can able to understand with your inputs.

How to find the bandwidth for the circuit . I have chosen OPAMP of GBP = 4GHz. Feedback resistor chosen in 100k. I want to find total bandwidth using LTSpice?

 

Can anyone know how to do AC analysis in LTspice for bandwidth characteristics?

 

Can anyone know how to do AC analysis in LTspice for bandwidth characteristics?

How about frequency response diagram?


See http://www.gunthard-kraus.de/LTSwitcherCAD/SwitcherCAD-Tutorial_English/pdf-File/LTspice_4_e2.pdf
pages 29 and 30.

 

Can you say the procedure ? How are you simulating frequency response ? What is dotted and solid line?