Integrated Injection Logic SmartSpice Behavioral Model

The SmartSpice Analog Behavioral Device is used to model the integrated ingection logic gate. The model schematic is shown in figure 1. In behavioral modeling, the terminal characteristics of the circuit are described without the details of the internal workings.

Model Description

The i2l subcircuit code contains three SmartSpice analog behavioral elements, the diode AD, the delay, ADELAY, and the output transistor, AOUT. Actually, there are 4 output transistors for this gate.
Figure 1

The statement:

 AD      INPUT   0       I =  IF V(INPUT) >  0.7 V(INPUT)-0.7 ELSE 0
describes the input diode AD, shown in figure 1. The diode current is V - 0.7 if V is greater than 0.7 Volts. Otherwise it is zero. This is a diode that turns on at 0.7 Volts with an incremental resistance of one ohm.

The gate delay is implemented by the statement: 

 ADELAY  INPUT   OUTB    DELAY = {DeltaT}
The voltage at node OUTB is equal to the voltage at node INPUT delayed by DeltaT seconds.

The output circuit is modeled by the following behavioral statement; 

 AOUT1   OUT1    0       I = IF V(OUTB) > 0.5 THEN V(OUT1)/{RSAT} ELSE 0
This represents a transistor that is either cut off or saturated. If the voltage at node OUTB (node C in figure 1) is greater than 0.5 volts then the current flowing into node OUT1 is the output voltage divided by RSAT. If the voltage at node OUTB is less than 0.5 volts the output current is zero. That is, the output circuit is either an open circiut or Rsat depending on the delayed input voltage.

The time delay, DeltaT, is calculated from the injection current using the formula; 

.PARAM DeltaT = '5E-8 + 5E-13/IINJECTOR'
There are two model parameters; the injector current for each gate, IINJECTOR, and the output transistor saturation resistance, RSAT. Default values for these parameters are 1 uA and 100 Ohms, respectively. A .PARAM statement in the calling deck will override these values.

Model Operation

Injector current flowing in Rin produces a voltage at the input node. When this voltage reaches 0.7 volts the diode, AD, turns on. If the injector current is being sunk by a signal source attached to the input, the voltage at the input node will not rise to the level of 0.5 Volts required to turn on the output transistors. When the input voltage rises above 0.5 volts the output transistors turn on after a delay introduced by the delay element ADELAY.

A sample circuit using this model has been run.