Fig. 1. Simulated LI curve.
Fig. 2. Simulated transient response.
SPICE3-based Circuit Simulator with Support for
High-Speed Optoelectronic Devices
P. V. Mena, A. X.-F. Xiang, S. M. Kang
University of Illinois at Urbana-Champaign
Department of Electrical and Computer Engineering
Beckman Institute for Advanced Science and Technology
405 N. Mathews Ave., Urbana, IL 61801
Part of the research effort of the OEIC/VLSI group in the Beckman Institute at the University of Illinois at Urbana-Champaign involves the development of CAD software for photonic design. CAD tools would provide important simulation capability when designing a photonic system. As more systems begin to incorporate optics alongside the requisite electronics, the ability to effectively model all of the devices within the design is extremely important, both at the circuit level (as discussed here) or at the system level. Work being done by the OEIC/VLSI group on the latter topic involves the use of iFROST: illinois FibeR-optic and Optoelectronic Systems Toolkit, developed by Brent K. Whitlock.
The group's work on circuit simulation centers on vSPICE, a circuit simulator which extends SPICE3 (originally developed at UC-Berkeley) to include support for a variety of high-speed optoelectronic devices such as laser diodes and photodetectors. Currently, the main models that have been implemented in vSPICE are the Curtice-Ettenburg MESFET model, an MSM photodetector model, and a large-signal laser diode model. Below we describe in more detail some of these models.
Contact: Andrew Xiang ( xiang@uiuc.edu )
The MESFET model by W. R. Curtice and M. Ettenburg was introduced in the early 1980's and uses the hyperbolic tangent curve to simulate the shape of the Ids vs. Vds curve and a cubic polynomial to adjust the height of the curve. A resistor from the drain to source terminals is included to control the transconductance in the pinch-off region. While the Statz-Raytheon model has fewer parameters and simpler device equations than the Curtice-Ettenburg model, the latter has a higher degree of accuracy due to its complicated polynomial. This model has been implemented in vSPICE as an addition to the regular MESFET models found in SPICE3.
Contact: Andrew Xiang ( xiang@uiuc.edu )
The performance of MSM photodetectors is mainly determined by the transit time of excess carriers and the capacitance associated with the device. The intrinsic impulse photoresponse of the photodetectors can be accurately modeled as a negative-sloped linear curve in the time domain when the space-charge perturbation of the electric field is negligible. This is true for most applications in which low illumination power is used. In our approach, direct use of convolution using a trapezoidal integration method is employed within vSPICE to perform transient simulation of MSM detectors. 1-D device simulation is done on MSM photodetectors to study the impulse response for the circuit model.
Contact: Pablo Mena
The quantum-well (QW) laser model in vSPICE is implemented as an equivalent circuit composed of both parasitic elements (series and parallel) and one of two possible intrinsic cavity models. The first cavity model is based on the two basic rate equations, one for QW carrier concentration, the other for photon density in the active region. The second cavity model includes a third rate equation for carriers in the barrier, or confinement, layers adjoining the QWs. Unimolecular, radiative, and Auger recombination are each accounted for in the model. Furthermore, one of four different gain terms can be chosen. These terms include both logarithmic gain expressions as well as linearized ones. Finally, the parasitic elements of the model can account for series resistance, additional series diode effects, and shunting resistance or capacitance.
Unlike a typical model implementation within SPICE, the laser model is included as a subcircuit within an input SPICE deck. A parsing program converts a ".Xmodel" statement into a subcircuit, thereby simplifying matters for the user. The use of a subcircuit allows the model to be implemented within other SPICE simulators such as HSPICE.
In Figs. 1 and 2 below we show some laser simulation results from SPICE.
| Fig. 1. Simulated LI curve. |
Fig. 2. Simulated transient response. |