hspice book hspice ch13 1 Thu Jul 23 19 10 43 1998 Chapter 13 Using Diodes Use diode models to describe pn junction diodes within MOS and bipolar integrated circuit environments and discrete devices You can use four types of models and a wide range of parameters to model standard junction diodes Zener diodes Silicon diffused junction diodes Schottky barrier diodes Nonvolatile memory diodes tunneling current Note See Chapter 15 Introducing MOSFET Chapter 16 Selecting a MOSFET Model and Chapter 22 Performing Behavioral Modeling for other MOSFET and standard discrete diodes Diode model types include the junction diode model and the Fowler Nordheim model The junction diode model has two variations geometric and nongeometric This chapter provides an overview of element and model parameters and scaling effects for the geometric and nongeometric junction diodes The following topics are covered in this chapter Understanding the Diode Types Using Model and Element Statements Specifying Junction Diodes Calculating Temperature Effects Using Diode Equations Using the Fowler Nordheim Diode Converting National Semiconductor Models Star Hspice Manual Release 1998 2 13 1 hspice book hspice ch13 2 Thu Jul 23 19 10 43 1998 Understanding the Diode Types Using Diodes Understanding the Diode Types Use the geometric junction diode to model IC based standard silicon diffused diodes Schottky barrier diodes and Zener diodes Use the geometric parameter to specify pn junction poly and metal capacitance dimensions for a particular IC process technology Use the nongeometric junction diode to model discrete diode devices such as standard and Zener diodes The nongeometric model allows you to scale currents resistances and capacitances using dimensionless area parameters The Fowler Nordheim diode defines tunneling current flow through insulators Use it to model diode effects in nonvolatile EEPROM memory 13 2 Star Hspice Manual Release 1998 2 hspice book hspice ch13 3 Thu Jul 23 19 10 43 1998 Using Diodes Using Model and Element Statements Using Model and Element Statements Use model and element statements to select the diode models The model statement s LEVEL parameter selects the type of diode model used LEVEL 1 selects the nongeometric junction diode model LEVEL 2 selects the Fowler Nordheim diode model LEVEL 3 selects the geometric junction diode model You can design Zener Schottky barrier and silicon diffused diodes by altering model parameters for both Level 1 and Level 3 Level 2 does not permit modeling of these effects For Zener diodes the BV parameter is set for an appropriate Zener breakdown voltage If you do not specify the LEVEL parameter in the MODEL statement the model defaults to the nongeometric junction diode model Level 1 Use control options with the diode model to scale model units select diffusion capacitance equations and change model parameters Control Options Control options related to the analysis of diode circuits as well as other models include DCAP DCCAP GMIN GMINDC SCALE and SCALM Specify these models using the OPTIONS statement Scaling Options Use the scale element option SCALE to scale Levels 2 and 3 diode element parameters Use the scale model option SCALM to scale Levels 2 and 3 diode model parameters Level 1 does not use SCALE or SCALM Include SCALM val in the MODEL statement to override global scaling that uses the OPTION SCALM val statement in a diode model Star Hspice Manual Release 1998 2 13 3 hspice book hspice ch13 4 Thu Jul 23 19 10 43 1998 Using Model and Element Statements Using Diodes Capacitor Equation Selector Option DCAP The DCAP option selects the equations used in calculating the depletion capacitance Level 1 and Level 3 The option DCCAP invokes calculation of capacitances in DC analysis Include the DCAP val in the diode s MODEL statement to override the global depletion capacitance equation selection with the OPTIONS DCAP val statement Convergence Diode convergence problems often occur at the breakdown voltage region when the diode is overdriven or in the OFF condition To achieve convergence in such cases include a nonzero value in the model for the series resistor parameter RS or increase GMIN the parallel conductance Hspice automatically places in the circuit You can specify GMIN and GMINDC in the OPTIONS statement The diode control options follow Capacitance DCAP DCCAP Conductance GMIN GMINDC Geometry SCALM SCALE 13 4 Star Hspice Manual Release 1998 2 hspice book hspice ch13 5 Thu Jul 23 19 10 43 1998 Using Diodes Specifying Junction Diodes Specifying Junction Diodes Use the diode element statement to specify the two types of junction diodes geometric and nongeometric Use a different element type format for the Fowler Nordheim model The diode element statement parameter fields define the connecting nodes initialization temperature geometric junction and capacitance parameters of the diode model selected in the diode MODEL statement Both Level 1 and Level 3 junction diode models share the same element parameter set Poly and metal capacitor parameters of LM LP WM and WP do not share the same element parameter Element parameters take precedence over model parameters if repeated in the MODEL statement as model parameters Parameters common to both element and model statements are AREA PJ M LM LP WM WP W and L Table 13 1 Junction Diode Element Parameters Function Parameters netlist Dxxx n n mname initialization IC OFF temperature DTEMP geometric junction AREA L M PJ W geometric capacitance Level 3 only LM LP WM WP Star Hspice Manual Release 1998 2 13 5 hspice book hspice ch13 6 Thu Jul 23 19 10 43 1998 Specifying Junction Diodes Using Diodes Diode Element General form Dxxx nplus nminus mname AREA val PJ val WP val LP val WM val LM val OFF IC vd M val DTEMP val or Dxxx nplus nminus mname area val periphery val OFF IC vd M val or Dxxx nplus nminus mname W val L val WP val LP val WM val LM val OFF IC vd M val DTEMP val AREA Area of the diode It modifies saturation currents capacitances and resistances Area factor for LEVEL 1 model is not affected by the option SCALE Default 1 0 Affects IK IKR JS CJO and RS For LEVEL 3 AREAeff AREA SHRINK2 or M AREAeff Weff Leff SCALE2 M The effective area overrides model parameter AREAeff calculated from model parameter AREA If unspecified AREA is calculated from W L 13 6 DTEMP The difference between element temperature and the circuit temperature Default 0 0 Dxxx Diode element name Must begin with a D which can be followed by a