The photodetector_simple photonic model was created to model photodetector (PD) elements. It supports photodetector elements with up to two optical inputs, as well as multiple (up to two) electrical anode ports. It provides an ability to model photodetectors which include both shot and thermal noise, as well as saturation effects. This model can also include second and third order harmonic responsivities that arise from nonlinearities in the system.
The photodetector_simple photonic model supports statistical modeling. Users can choose an arbitrary number of statistical parameters and define their influence on the responsivity, electro-optic bandwidth and dark current of the photo detector. For information on statistical CMLs, see Statistical CMLs.
Note: If harmonic responsivity data is included, statistical support will be disabled.
Lumfoundry Templates: Photodetector, Photodetector (Statistical), Harmonic Photodetector
Quality Assurance Test: photodetector_simple QA
Statistical Modeling Support: responsivity, bandwidth, dark current
Supported Parameters: None
Tuning Support: None
Interoperability with Cadence Virtuoso:
- Circuit design flows using INTERCONNECT model: Yes.
- Circuit design flow using photonic Verilog-A model: Yes (not for harmonic models).
Model Information
- This model supports thermal noise, shot noise and power saturation.
- This model does not support pcells.
- The low power current of the photodetector, \(I_{ph}\), can be calculated by:
$$I_{ph} = C_1P + (C_2P)^2 + (C_3P)^3 $$
where \(P\) is the optical power incident on the photodetector, and \(C_1\), \(C_2\), and \(C_3\) are the linear, second, and third order responsivities, respectively.
Electrical Equivalent Circuit for INTERCONNECT model
The INTERCONNECT model can be used in the Cadence Virtuoso platform for PIC (photonic integrated circuits) and EIC (electronic integrated circuits) co-design and co-simulation. Electrical bandwidth of the photodetector is defined by an electrical low pass filter (LPF) inside the INTERCONNECT optical model. When running a Spectre-INTERCONNECT co-simulation, the electrical bandwidth and loading effect of the photodetector can be alternatively described by an electrical equivalent circuit, which is physically instantiated in Spectre, and in this case the LPF inside INTERCONNECT optical model must be turned off to avoid double counting the photodetector’s electrical bandwidth.
This section describes the use of an electrical equivalent circuit for the case of Spectre-INTERCONNECT co-simulation. The below figure shows a schematic of the electrical equivalent circuit for a photodetector, which can be created by running CML Compiler with the “--interconnect_virtuoso” command line option.
Parameter |
Description |
Unit |
Comments |
Cj |
Junction capacitance |
F |
Bias dependent |
Rj |
Junction resistance |
ohm |
|
Cp |
Parasitic capacitance |
F |
|
Rp |
Contact resistance |
ohm |
|
The figure below shows the use of the electrical equivalent circuit and the optical INTERCONNECT model for co-simulation case. The Cj voltage biases the optical INTERCONNECT model. In co-simulation, Spectre simulates the electrical equivalent circuit for its electrical bandwidth and loading effect, while INTERCONNECT simulates the optical INTERCONNECT model. In this case, the internal electrical LPF of the optical INTERCONNECT model must be turned off to avoid double counting the photodetector’s electrical bandwidth.
Electrical equivalent circuit for Photonic Verilog-A model
The photonic Verilog-A model is compatible with Cadence Virtuoso design platform and its Spectre simulator. When simulating the photonic Verilog-A PD model using Spectre , the electrical equivalent circuit and the photonic PD model are implemented inside the compiled photonic Verilog-A PD model as shown below. Spectre simulates both the electrical equivalent circuit for the PD’s electrical characteristics and the photonic PD model for its optical characteristics. The Verilog-A model for a PD element can be generated through CMLC by executing it with --veriloga_virtuoso command line option.