The phase_shifter_electrical photonic model is tailored to electrical phase shifter elements and can also be used for optical attenuators. It provides the ability to model electrical phase shifters operating in depletion mode (reverse bias) or injection mode (forward bias) using either a travelling-wave electrode model or a lumped-electrode model, and allows parameterization of the active region length. This photonic model also supports temperature dependence for injection current in injection mode.
This model supports statistical modeling. Users can choose an arbitrary number of statistical parameters and define their influence on the effective and group index of the active waveguide as well as the insertion loss and Vpi_Lpi of the phase shifter, or attenuation efficiency of an optical attenuator. For information on statistical CMLs, see Statistical CMLs.
Lumfoundry Templates: Electrical Phase Shifter (Reverse Bias), Electrical Phase Shifter (Forward Bias), Electrical Phase Shifter (Statistical), Variable Optical Attenuator (Statistical)
Quality Assurance Test: phase_shifter_electrical QA
Statistical Modeling Support: neff (active wg), ng (active wg), IL, Vpi_Lpi (phase shifter), Attn_eff (optical attenuator)
Supported Parameters: length of the active region
Tuning Support: Vpi_Lpi (phase shifter), Insertion Loss, Attenuation Efficiency (optical attenuator).
Interoperability with Cadence Virtuoso:
- Circuit design flows using INTERCONNECT model: Yes.
- Circuit design flow using photonic Verilog-A model: Yes.
Advanced Options
The model is versatile and has several different options that can be enabled or disabled using different parameters included in the model data requirement. To see the list of data requirements for specific element configurations, please visit lumfoundry template pages.
Phase shifter/optical attenuator |
Phase shifter model: Attn_eff data does not exist Optical attenuator model: Attn_eff data exists |
Depletion/ Injection model (electrical phase shifter) |
Depletion: IV data does not exist Injection: IV data exists (temperature dependence of current also supported) |
Travelling wave/lumped model (depletion electrical phase shifter) |
Travelling wave model: Termination ports exist Lumped model: Termination ports do not exist |
Statistical/nominal model |
Statistical model: stat_parameters exist Nominal model: stat_parameters does not exist |
Model Information
- This model assumes thermal bandwidth to be constant over all bias range.
- Travelling-wave electrode model assumes small-signal RF operation.
- This model supports dual mode of operation.
- User can turn off internal electrical equivalent circuit using 'internal electrical equivalent' flag.
- Internal Model Diagram:
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Vpi Data Visualization:
The above plot shows the nonlinear nature of the effective index (neff) versus bias voltage (V) for a depletion type phase shifter. As the reverse bias is increased, the depletion layer width is increased resulting in smaller change in free carrier concentration in the waveguide, hence smaller effective index change. Therefore, the Vpi.L measured between bias points V1 and V2 would be smaller than when measured between V1 and V3.
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. The electrical bandwidth of the phase shifter is defined by an electrical low pass filter (LPF) inside the INTERCONNECT optical model. When running a Spectre-INTERCONNECT co-simulation, the phase shifter’s electrical bandwidth and loading effect can be alternatively described by an electrical equivalent circuit that is physically instantiated in Spectre, and in this case the LPF inside INTERCONNECT optical model is automatically turned off by default to avoid double counting the model’s electrical behavior. This is done by setting the built-in internal electrical equivalent flag to false when using Spectre-INTERCONNECT co-simulation.
Electrical equivalent circuit for a phase shifter model can be created by running CML Compiler with the “--interconnect_virtuoso” command line option. This section describes the electrical equivalent circuits for the depletion type and injection type phase shifters, respectively.
Depletion type pn junction phase shifter
Parameter | Description | Unit | Comments |
---|---|---|---|
Cj | Junction capacitance | F/m | Bias dependent |
Rj | Junction resistance | ohm-m | Series resistance of the pn junction. |
Cp | Parasitic capacitance | F | Capacitance between metal contacts. |
Rp | Contact resistance | ohm | Resistance of the metal contacts. |
The above figure shows the use of the electrical equivalent load and the optical device (PSPN_O) for co-simulation case. The junction capacitance voltage is used to bias the pn depletion phase shifter. For co-simulation, Spectre simulates the electrical characteristics from the equivalent electrical load model while INTERCONNECT simulates the optical device response of PSPN_O. In this case, the internal electrical LPF of PSPN_O must be turned off to avoid double counting the electrical bandwidth for the phase shifter device.
Injection type p-i-n junction phase shifter
The diode equivalent circuit is used to model the forward bias p-i-n junction phase shifter as shown below. Here, VCCS is a voltage controlled current source modeled by the diode parameters , Is, Ndiode and Vt using the diode equation given below. This electrical equivalent circuit is only created when running CML Compiler using the “--interconnect_virtuoso” command line option.
The parameters used to model the electrical equivalent circuit for the injection type phase shifter device are shown in the table below. Here, \(V_t\) is the thermal voltage used to model the IV curve, given by:
$$V_t = k*T/q $$
where \(k\) is the Boltzmann constant, \(T\) is the temperature, and \(q\) is the electron charge.
It should be noted that for the equivalent circuit compact model to pass QA for the device, its DC response should match with device IV_data and its AC response should match with device’s electrical_bandwidth_data.
Parameter | Description | Unit | Comments |
---|---|---|---|
Cj | Junction capacitance | F/m | Current dependent diffusion capacitance due to forward bias. |
Rs | Series resistance | Ohm | Temperature-dependent series resistance for a diode. |
Cp | Parasitic capacitance | F | Capacitance from electrical contact probes. |
Rp | Parasitic resistance | Ohm |
Resistance of from electrical contact probes. |
Ndiode | Diode ideality factor | - | Diode parameter to model the IV curve. |
Is | Reverse saturation current | A | Temperature-dependent reverse saturation current for the diode. |
The above figure shows the connection between the electrical equivalent load and the optical device (PSPIN_O) for co-simulation case. The diode voltage is used to drive the forward bias p-i-n phase shifter. For co-simulation, Spectre simulates the electrical characteristics from the equivalent electrical load model while INTERCONNECT simulates the optical device response of PSPIN_O. In this case, the internal electrical LPF of PSPIN_O must be turned off to avoid double counting the electrical bandwidth for the phase shifter device.
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 model for electrical phase shifters using Spectre, the electrical equivalent circuit model and the photonic model are implemented inside the compiled Verilog-A electrical phase shifter element. Spectre simulates both the electrical equivalent circuit for the phase shifter’s electrical characteristics and the photonic phase shifter model for its optical characteristics. The Verilog-A model for an electrical phase shifter element can be created by CMLC by executing it with --veriloga_virtuoso command line option.
The photonic Verilog-A model for a depletion type phase shifter is shown in the figure below.
The photonic Verilog-A model for an injection type phase shifter (PSPIN) element is shown in the figure below.