# Voltage Controlled Switch

In this topic:

## Netlist Entry

Sxxxx nout1 nout2 vc+ vc- modelname IC=ic
 nout1 Switch node 1 nout2 Switch node 2 vc+ Positive control node vc- Negative control node modelname Name of model. Must begin with a letter but can contain any character except whitespace and period '.'. ic Initial condition. Hysteresis mode only. Defines initial state of switch if control voltage is between upper and lower thresholds. 0 for 'OFF' 1 for 'ON'

## Voltage Controlled Switch Model Syntax

.model modelname VSWITCH ( parameters )
OR
.model modelname SW ( parameters )

## Voltage Controlled Switch Model Parameters

 Name Description Units Default RON On resistance $\Omega$ 1 ROFF Off resistance $\Omega$ Hysteresis mode: 1.0E12. Continuous mode: 1.0E6 VON Voltage at which switch begins to turn on. (continuous mode) V 1 VOFF Voltage at which switch begins to turn off. (continuous mode) V 0 VT If present enables hysteresis mode. Sets threshold voltage V 0.5 VH Hysteresis voltage. (hysteresis mode) V 1.0 TON On time. (hysteresis mode) s 1ns TOFF Off time. (hysteresis mode) s 1n TD Delay time. (hysteresis mode) s 0 TD_ON On delay. (hysteresis mode) s TD TD_OFF Off delay. (hysteresis mode) s TD TIMETOL Time tolerance. (hysteresis mode) s 10p GIN Conductance at control terminals Siemens 0

GIN has a default value of zero unless the PSPICEGMIN option is set in which case it has a default value of GMIN. GMIN is set using ".OPTIONS GMIN=value" and has a default value of 1e-12.

## Voltage Controlled Switch Notes

The voltage controlled switch has two modes of operation:

1. Continuous mode: Behaves like a voltage controlled resistor. Between VON and VOFF the resistance varies gradually following a cubic law as described with the following equation:

where:

$R$ = $1/exp(-Lm - Lr*factor*(1.5 - 2*factor*factor) )$

$factor$ = $V_{control}-0.5$

$Lm$ = $-0.5*ln(g_{on}*g_{off})$

$Lr$ = $ln(g_{off}/g_{on})$

$g_{off}$ = $ROFF<>0: 1/ROFF, ROFF=0: GMIN$

$g_{on}$ = $RON<>0: 1/RON, RON=0: GMIN$

2. Hysteresis mode: Switches in a controlled time with a hysteresis characteristic. This mode is enabled if the VT parameter is defined. The switch transitions to the on state when:

$V_{control} > VT+VH$

and to the off state when:

$V_{control} < VT-VH$

The transition will be delayed by TD and the transition time will be TON when changing from OFF state to ON state and TOFF when changing from ON state to OFF state.

The transition will follow the same characteristic as continuous mode. That is, during the transition period the actual resistance of the switch will follow the continuous mode characteristic with the control voltage following a linear transition between VON and VOFF.

Hysteresis mode is similar and usually compatible with what is known as short-transition mode in PSpice. The difference is that in short-transition mode, the switching time is uncontrolled whereas in SIMetrix hysteresis mode the transition time is controlled by the TON and TOFF parameters.

GMIN is a simulation parameter which defaults to 10E-12 but which can changed using the .OPTIONS statement.

The SIMetrix voltage controlled switch is compatible with PSpice® but note that in hysteresis mode, the SIMetrix switches in a controlled time whereas the PSpice version switches abruptly.