hspice book hspice ch14 1 Thu Jul 23 19 10 43 1998 Chapter 14 BJT Models IThe bipolar junction transistor BJT model in HSPICE is an adaptation of the integral charge control model of Gummel and Poon The HSPICE model extends the original Gummel Poon model to include several effects at high bias levels This model automatically simplifies to the Ebers Moll model when certain parameters VAF VAR IKF and IKR are not specified This chapter covers the following topics Using the BJT Model Using the BJT Element Understanding the BJT Model Statement Using the BJT Models NPN and PNP Understanding BJT Capacitances Modeling Various Types of Noise Using the BJT Quasi Saturation Model Using Temperature Compensation Equations Converting National Semiconductor Models Star Hspice Manual Release 1998 2 14 1 hspice book hspice ch14 2 Thu Jul 23 19 10 43 1998 Using the BJT Model BJT Models Using the BJT Model The BJT model is used to develop BiCMOS TTL and ECL circuits For BiCMOS devices use the high current Beta degradation parameters IKF and IKR to modify high injection effects The model parameter SUBS facilitates the modeling of both vertical and lateral geometrics Model Selection To select a BJT device use a BJT element and model statement The element statement references the model statement by the reference model name The reference name is given as MOD1 in the following example In this case an NPN model type is used to describe an NPN transistor Example Q3 3 2 5 MOD1 parameters MODEL MOD1 NPN parameters Parameters can be specified in both element and model statements The element parameter always overrides the model parameter when a parameter is specified as both The model statement specifies the type of BJT for example NPN or PNP 14 2 Star Hspice Manual Release 1998 2 hspice book hspice ch14 3 Thu Jul 23 19 10 43 1998 BJT Models Using the BJT Model Control Options Control options affecting the BJT model are DCAP GRAMP GMIN and GMINDC DCAP selects the equation which determines the BJT capacitances GRAMP GMIN and GMINDC place a conductance in parallel with both the base emitter and base collector pn junctions DCCAP invokes capacitance calculations in DC analysis Table 14 1 BJT Options capacitance DCAP DCCAP conductance GMIN GMINDC GRAMP Override global depletion capacitance equation selection that uses the OPTION DCAP val statement in a BJT model by including DCAP val in the BJT s MODEL statement Convergence Adding a base collector and emitter resistance to the BJT model improves its convergence The resistors limit the current in the device so that the forwardbiased pn junctions are not overdriven Star Hspice Manual Release 1998 2 14 3 hspice book hspice ch14 4 Thu Jul 23 19 10 43 1998 Using the BJT Element BJT Models Using the BJT Element The BJT element parameters specify the connectivity of the BJT normalized geometric specifications initialization and temperature parameters Table 14 2 BJT Element Parameters Type Parameters netlist Qxxx mname nb nc ne ns geometric AREA AREAB AREAC M initialization IC VBE VCE OFF temperature DTEMP General form Qxxx nc nb ne ns mname aval OFF IC vbeval vceval M val DTEMP val or Qxxx nc nb ne ns mname AREA val AREAB val AREAC val OFF VBE val VCE val M val DTEMP val 14 4 Qxxx BJT element name Must begin with a Q which can be followed by up to 15 alphanumeric characters nc collector terminal node name nb base terminal node name ne emitter terminal node name ns substrate terminal node name optional Can be set in the model with BULK Node name mname model name reference aval value for AREA Star Hspice Manual Release 1998 2 hspice book hspice ch14 5 Thu Jul 23 19 10 43 1998 BJT Models Using the BJT Element OFF sets initial condition to OFF for this element in DC analysis Default ON IC vbeval initial internal base to emitter voltage vbeval or initial internal collector to vceval emitter voltage vceval Overridden by the IC statement M multiplier factor to simulate multiple BJTs All currents capacitances and resistances are affected by M DTEMP the difference between element and circuit temperature default 0 0 AREA emitter area multiplying factor that affects resistors capacitors and currents default 1 0 AREAB base area multiplying factor that affects resistors capacitors and currents default AREA AREAC collector area multiplying factor that affects resistors capacitors and currents default AREA Examples Q100 CX BX EX QPNP AREA 1 5 AREAB 2 5 AREAC 3 0 Q23 10 24 13 QMOD IC 0 6 5 0 Q50A 11 265 4 20 MOD1 Scaling Scaling is controlled by the element parameters AREA AREAB AREAC and M The AREA parameter the normalized emitter area divides all resistors and multiplies all currents and capacitors AREAB and AREAC scale the size of the base area and collector area Either AREAB or AREAC is used for scaling depending on whether vertical or lateral geometry is selected using the SUBS model parameter For vertical geometry AREAB is the scaling factor for IBC ISC and CJC For lateral geometry AREAC is the scaling factor The scaling factor is AREA for all other parameters Star Hspice Manual Release 1998 2 14 5 hspice book hspice ch14 6 Thu Jul 23 19 10 43 1998 Using the BJT Element BJT Models The scaling of the DC model parameters IBE IS ISE IKF IKR and IRB for both vertical and lateral BJT transistors is determined by the following formula Ieff AREA M I where I is either IBE IS ISE IKF IKR or IRB For both the vertical and lateral the resistor model parameters RB RBM RE and RC are scaled by the following equation R Reff AREA M where R is either RB RBM RE or RC BJT Current Convention The direction of current flow through the BJT is assumed for example purposes in Figure 13 1 Use either I Q1 or I1 Q1 syntax to print the collector current I2 Q1 refers to the base current I3 Q1 refers to the emitter current and I4 Q1 refers to the substrate current nb base node I2 Q1 nc collector node I1 Q1 ns substrate node I4 Q1 ne emitter node I3 Q1 Figure 13 1 BJT Current Convention 14 6 Star Hspice Manual Release 1998 2 hspice book hspice ch14 7 Thu Jul 23 19 10 43 1998 BJT Models Using the BJT Element BJT Equivalent Circuits HSPICE uses four equivalent circuits in the analysis of BJTs DC transient AC and AC noise circuits The components of these circuits form the basis for all element and model equations Since these circuits represent the entire BJT in HSPICE every effort has been made to demonstrate the relationship between the equivalent circuit and the element model parameters The fundamental
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