powerex06.in : GTO Turn-off Transient

Requires: S-Pisces/MixedMode
Minimum Versions: Atlas 5.34.0.R

This example illustrates the simulation of a Gate Turn-Off Thyristor (GTO). The device is embedded in a realistic power device circuit. The interaction between the circuit elements and the active device is important in accurately simulating GTO behavior. The steady state behavior is simulated first. This is used as the initial condition for the transient analysis. This example shows:

• GTO structure definition with Atlas
  
• The SPICE-like command syntax for MixedMode circuit simulation
  
• GTO steady state solution
  
• GTO transient turn-off process

Atlas is used to define the GTO structure including mesh, materials, electrodes, and doping. The mesh rect statement defines a rectangular mesh with grid lines at the locations specified by the x.m and y.m statements. Using the region statement, the mesh is divided into three regions: two silicon and one insulator. The electrode statement defines the cathode, anode and gate electrodes. The doping statements define the doping profiles. Note the definition of implant type, junction position and characteristic length. The net profile is n+ p n p+ from the cathode on top to anode on the bottom. The gate is contacted to the p region. This structure is saved and will be used as a device by MixedMode.

In this simulation, the MixedMode circuit simulator uses Atlas to calculate the transient characteristics of a GTO under the specified circuit conditions. First, a steady-state simulation of the GTO circuit is performed. The .begin and .end statements indicate the beginning and end of the MixedMode syntax. The MixedMode commands are similar to those used in SmartSpice. Circuit components, topology, and analysis are defined here. In general, the circuit component definition consists of three parts: the type of component, the lead or terminal node assignments, and the component value or model name. For example, the first component definition in this simulation is a dc current source. i1 defines the component as current source number one, 0 and 1 are the two circuit nodes for this component and 400 indicates that the current source value is 400 amps.

This circuit can be divided in two parts: input, and output. The input circuit connects to the cathode and anode of the GTO. It includes current source i1 , voltage source v1 , resistors r1 r2 r3 , diodes d1 d2 d3 , inductors l1 l2 l3 , and capacitor c1. The output or switching circuit connects to the GTO gate and anode and includes voltage sources v1 v2 v3 , diode d4 , resistors r2 r4 , and inductor l4 . The GTO component itself is specified by the agto statement. This statement specifies a device to be analyzed by Atlas. The a part of the agto command specifies that this is a device statement. The gto portion simply defines the device name. The option infile= indicates which device structure file is to be used. Other command line options exist. Please refer to the MixedMode section of the Atlas user's manual for a complete list.

The .nodeset statement defines the initial values for node voltages and the .save outfile= statement saves the result to the indicated file. Since this is the steady state solution, no output log data file is needed. Since standard diode parts are used in this circuit, the .model dd statement is used to specify additional characteristics. Note that dd was the model name given in the diode component definition statement. Additionally, the .options command sets the solution method to a modified two-level Newton using the m2ln parameter.

To completely specify the simulation, the physical models used by Atlas must be specified. The model statement is used to turn on the appropriate transport models. This set includes analytic: the analytic concentration dependent mobility model, fldmob: the lateral electric field-dependent mobility model, consrh: Shockley-Read-Hall recombination using concentration dependent lifetimes, auger: recombination accounting for high level injection effects, and bgn: band gap narrowing. The material statement is used to override default material parameters. In this case, the carrier recombination fixed lifetimes are set and for region three, the permittivity is set to that of air (1). Finally, an impact ionization model is enabled using the impact statement with the selb option. This specifies that the Selberherr impact ionization model is to be used. Note that for each of these commands, the device name and region can be specified.

The final part of this example is the transient simulation of the gate turn-off. The description of the circuit is similar to the steady state part. The gate turn-off is simulated by pulsing the GTO gate output resistance r4 from 1 mega-ohm to 1 micro-ohm over 100 ns. This is defined by the additional command line options on the r4 command line. The result of the essentially shorted resistor r4 is that a negative pulse is applied to the gate which initiates the GTO turn-off process. The .tran statement controls the overall transient simulation time.

Terminal characteristics of the GTO, circuit node voltages and circuit element currents are are saved in the .log file and can be observed with TonyPlot. The turnoff speed is seen by plotting the GTO anode and gate current.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.