the reverse voltage of PD in the interconnect simulation


dear all
When I do a interconnect simulation,which have a photodetector in the system,I found the parameters of the PD wo can set are dark current,responsivity and thermal noise.What I want to konw is that whether can we set the working voltage of the PD in the interconnect simulation( As we all know,The PD is working at a reverse voltage). can you help me solve the question?Thanks a lot


Hi @jbwei,

Currently all the primitive photo-detector elements in the library can only be made frequency dependent (when you choose the “input parameter” to be “table”) but not voltage dependent. However, you can create your own compact model using the primitive photo-detector elements and the “Optical Modulator Lookup Table” element if you have some measurement data about the dependence. The lookup table modulator can load in the voltage versus power data hence make the photo-detector voltage dependent.

We also have the plan to include this feature in our LCML library in the future. I will definitely keep you in the loop about this.

I hope this could help :slight_smile: Please let me know if you have any troubles making your own compact model.


dear gwang
There are these parameter(including the responsivity ,dark current, thermal noise ) that can be modified about the photodetector in the interconnect simulation.As we all know, the thermal noise is a relationship between the dark current and 3dB bandwidth.If I set the value of the thermal noise and the dark current,can I calculate the 3dB bandwidth of thephotodetector? Which formula do you use to express the relationship about the three parameter? furthermore,I want to know whether there is a parameter that can express the sensitivity of the photodetector in the interconnect simulation.Hope to get your feedback.Thanks a lot.:slight_smile:


Hi @jbwei,

I think the 3 dB bandwidth of the PD is mainly related to the junction properties (RC properties) rather than the noises. We improved the photodetector models and now they support frequency dependent responsivity/sensitivity. And this relationship could be loaded form a file.

Let me know whether am I answering your questions :slight_smile:


dear gwang
Thanks for your feedback.It is right that the 3dB bandwidth of the PD is mainly related to the RC properties.But I think the thermal noise is also related to the 3dB bandwidth,which is like the formula below.

where IJn is the Johnson noise and the Isn is the shot noise,Id is the dark current,Ip is the photo current and B is the 3dB bandwidth.

Is the responsivity related to frequency? I think that the responsivity related to the reverse bias while the S21 parameter is related the 3dB bandwidth. if I want to load a file to the PD,how to write the file which contain the relationship between the frequency and S21 parameter and sensitivity?

Is it like the format as shown below?

frequency S21 sensitivity
xxxx xxxx xxxx


Hi @jbwei,

This photodetector model in the primitive element library is a simple model which does not capture all the physical properties of an actual photodetector design. You are right that according to Johnson -Nyquist noise, the actual thermal noise in the photodetector is related to the 3 dB BW and other noises as well. For this primitive element, you can only define the “dark current” and the “thermal noise”, then the shot noise is calculated accordingly. There is no place to define the 3 dB bandwidth (S21) for this model right now.

The responsivity is related to the reverse bias voltage, while it is also frequency dependent. You can define the frequency dependency in this model.

The file should contain two columns, for frequency and reponsivity, respectively, like the following:

#frequency responsivity
xxx xxx

Based on your request, I strongly suggest you to create your own PD compact model to fulfill the requirements. I will try to come up with a model for you and explain about it in an other reply. Meanwhile, please check out our LCML models and building methods to start building your own model:


dear gwang
thanks so much for your help.I will do some work to create my own PD in your guidance.If I have question ,I will ask you for you help .Thanks again for your help:slight_smile:


Hi @jbwei,

Hope everything is going well. I made this more sophisticated photodetector model for you (structure shown below); it basically meets all your requirements and you can tweak the parameters/data to fit it to your design purpose:

The following data files are loaded into the model to represent the corresponding information:

responsivity_freq.txt: loaded into the primitive PIN element (PIN) to represent the responsivity dependency on frequency.
3db_V.txt: loaded into the Low Pass Filter element (LPF) to represent the 3 dB bandwidth dependency on voltage.
IV.txt: loaded into the Lookup Table element (TABLE) to represent the IV feature of the photodetector.

If you want to include the noise relationship to other properties, you will need to calculate the dependency and implement it into the model. Here is a test file of this model: pd_example.icp (431.5 KB). Please download this file together with the data files to the same working directory. Please note that this is a toy model and the data file I provided may not based on actual measurement data.

Please play around with this model and let me know if you have further problems :slight_smile:


dear gwang
Thanks so much for your help.It will do much help for me to understand the PD model deeply in the interconnect.Thanks again for your support and guidance.:grinning: