Scripted Verilog-A Electrical Phase Shifter (Statistical) – Lumfoundry Template – Ansys Optics

This is an example of how the Verilog-A custom element model can be used to create a statistical phase shifter element. The Verilog-A custom element will be useful in cases where the models offered by CML Compiler do not offer capabilities/features needed or there is no model offered that can be used for a specific photonic device. In such cases, a custom Verilog-A model can be built to model the behavior of the desired photonic device.

Note: The Verilog-A custom element model is an advanced model. Please see other phase shifter examples in lumfoundry template for more typical phase shifter implementations.

Template: veriloga_scripted_eps, veriloga_scripted_eps_stat

Photonic Model: veriloga_scripted_element

Quality Assurance Test: None

Parameters: User defined (wg_length in this example)

Statistically Enabled Parameters: user-defined (delta_width and delta_height in this example)

Interoperability with Cadence Virtuoso:

Circuit design flows using INTERCONNECT model: No
Circuit design flow using photonic Verilog-A model: Yes

Required Data

The required data is collected as a struct with the following fields:

general

"general" is a struct with the following fields:

Field	Type	Description
prefix	string	A string containing the prefix of the model, which will be used within Virtuoso to provide incrementing element names for each successive element that is added to the schematic.

ports

"ports" is a struct with the following fields:

Field	Type	Description
port_X	struct with the fields described in the table below	Ports defined as port_X with X being an integer, describing the user-defined ports to be added to the model.

Each struct above consists of the following fields:

Field	Type	Description
name	string	The name of the port, which will be visible to the end user. This name should be consistent with the name that will be used for netlisting.
dir	string	The directionality of the port, either "Input", "Output", or "Bidirectional"
pos	string	The side of the model which the port will be displayed on, either "Left", "Right", "Top", or "Bottom"
loc	number	The placement of the port on the side defined by loc, provided as a coordinate between 0 and 1.
order	number	The order at which the port is listed in a netlist.

parameters

"parameters" is a struct with the following fields:

Field	Type	Description
parameter_X	struct with the fields described in the table below	parameter_X with X being an integer is user-facing parameters to be added to the model.

Each struct above consists of the following fields:

Field	Type	Description
name	string	The name of the parameter.
unit	string	The unit of the parameter.
default	number	The nominal value of the parameter.
visible_to_user	boolean	A flag to enable/disable the parameter in the model.
min	number	Minimum allowed value if the visible_to_user is set to True.
max	number	Maximum allowed value if the visible_to_user is set to True.

model_data

"model_data" is a struct with the following fields:

Field	Type	Description
photonic_model	String	The name of the photonic model used for this template. Please visit here for a list of all available photonic models.
veriloga_script_filename	string	The name of the Verilog-A script to be loaded, including the file extension (.va)
debug_mode	Boolean	A flag to add unencrypted Verilog-A models for debugging. If this flag is set to 1, CML Compiler adds unencrypted Verilog-A models for this element (both CML Compiler generated shell and user-defined model) to the library to facilitate debugging process. On the other hand, if this flag is set to 0, CML Compiler will encrypt Verilog-A files for this element.
mode_number	number	The number of supported modes in the user- provided Verilog-A module, which can be up to 2 modes. If the provided Verilog-A module supports one mode, CML Compiler will use the same module for the second mode response.
ele_eq_ctk (optional)	struct	This is an optional input in case electrical equivalent circuit is defined by the user for the photonic module. This struct has the following entries: subcircuit_name: A string with the name of the module defining the electrical equivalent circuit. port_connections: Given that with the presence of electrical equivalent circuit, the final external photonic model consists of both optical and electrical modules, this struct describes how the electrical equivalent circuit ports connect to the optical module and the external photonic model, with the following entries: opt_to_extrnal: a dictionary where each "key" is the index of an electrical port for the optical module, and each "value" is the index of the corresponding electrical port for the external photonic model. ele_to_external: a dictionary where each "key" is the index of an electrical port for the electrical equivalent circuit, and each "value" is the index of the corresponding electrical port for the external photonic model. ele_to_opt: a dictionary where each "key" is the index of an electrical port for the electrical equivalent circuit, and each "value" is the index of the corresponding electrical port for the optical module.

statistical

"statistical" is a struct with the fields below. This struct is optional and is only required for statistical compact models.

Note: To allow CML Compiler to build statistically enabled models, the statistical_parameter_status has to be defined in the Library master file. For more information, see Statistical CMLs.

Field	Type	Description
name	string	The name of the statistical parameter.
mean	number	The mean value of the statistical parameter.
corners	matrix	Corner values for the statistical parameter provided as a Cx1 matrix where C is the number of process corners defined in the library master file. Note: The values for the process corners should follow the same order as in the library master file.
LOCAL	struct	A struct describing the LOCAL level variation of the X-th statistical parameter with the following fields: distribution: a string that defines the type of the probability density function used to describe the LOCAL level variation. Currently, the only option is 'normal' (Gaussian). sigma: a number that defines the standard deviation of the LOCAL level variation. CORRGROUP: Name of the spatial correlation group that this statistical parameter belongs to. The correlation group must be defined in the library master file. Note: It is optional to provide a CORRGROUP for statistical parameters.
GLOBAL	struct	A struct containing the GLOBAL level variation of the X-th statistical parameter with the following fields: distribution: a string that defines the type of the probability density function used to describe the GLOBAL level variation. Currently, the only option is 'normal' (Gaussian). sigma: a number that defines the standard deviation of the GLOBAL level variation. GLOBALGROUP: Name of the GLOBALGROUP defined in the top level XML file. (If a GLOBALGROUP is provided , the description in the XML file is used instead of the data file). Note: It is optional to provide a GLOBAL level variation for statistical parameters.
slope_<model_parameter>	Number	The sensitivity of the <model_parameter> of with respect to the X-th statistical parameter defined as d_<model_parameter>\( / \)d_parameter_X. This model_parameter should also be present as delta_<model_parameter> in the user-defined Verilog-A model to define how it affects the behavior of the model.

User-defined Verilog-A script file

This file consists of the Verilog-A modules provided by the user in Verilog-A syntax with the following assumptions:

Optical module name: Module name should match the name of the script file.
Optical port bit orders: Each optical port should have 4 bits for models supporting one mode or 8 bits for models supporting two modes. The order of the bits are:
0:in_RE_m1 1:in_Im_m1 2:out_Re_m1 3:out_Im_m1 4:in_RE_m2 5:in_Im_m2 6:out_Re_m2 7:out_Im_m2
Please note that the 4^th to 7^th bit are optional for the case the model supports 2 modes.
Electrical equivalent circuit (if applicable): The name of this module should be defined in the .json source file under “subcircuit_name”.
Port orders:
1. Optical ports should be listed first and followed by electrical ports.
2. If there are no electrical equivalent circuit, it is assumed the port order of the external photonic model is identical to the internal optical module.
3. If electrical equivalent circuit is present, external photonic models and internal optical module don't need to have identical electrical port order (the connection will be described under port_connections in .json source file), but optical ports that come first need to be in the same order as the external model.
Statistical modelling [Only available for Cadence platform] : In a statistical model, the parameters must be specified in the .json source file. The sensitivity of each "model parameter" to the "statistical parameters" should be defined as "slope_<model_parameter>".

For each "slope_<model_parameter>", you need to define a "delta_<model_parameter>" in the user-defined module to indicate how it affects the model's behavior. For an example, please refer to the custom_veriloga_eps template.
CML Compiler will automatically connect the variations of the statistical parameters to the variations of "delta_<model_parameter>" given by:
delta_<model_parameter> = slope_<model_parameter> * statistical parameters

Scripted Verilog-A Electrical Phase Shifter (Statistical) – Lumfoundry Template