SPICE

In the experiments we have done till now we have designed gates by arranging transistors in various fashions. The simulation of these designs gave graphs of output voltages and we analyzed how these graph changes with varying different parameters of the transistor. Now when you place a transistor on screen there is a back end code which tells a simulator what are the points to which the transistor's substrate, gate, drain, source are connected. The language in which this information is conveyed is spice.

INTRODUCTION TO SPICE

SPICE (Simulation Program with Integrated Circuit Emphasis) is a powerful program that is used in integrated circuit and board-level design to check the integrity of circuit designs and to predict circuit behavior. SPICE was originally developed at the Electronics Research Laboratory of the University of California, Berkeley (1975). Simulating the circuit with SPICE is the industry-standard way to verify circuit operation at the transistor level before committing to manufacturing an integrated circuit. In spice program, circuit elements (transistors, resistors, capacitors, etc) and their connections being translated into a text net list.

Several types of circuit analyses can be done using SPICE program. Here are the most important ones-

• DC analysis: calculates the DC transfer curve.
• Transient analysis: calculates the voltage and current as a function of time when a large signal is applied.
• AC Analysis: calculates the output as a function of frequency. A bode plot is generated.
• Noise analysis.
• Sensitivity analysis.
• Distortion analysis.
• Fourier analysis: calculates and plots the frequency spectrum.
• Monte Carlo Analysis

All analyses can be done at different temperatures. The default temperature is 300K.

XOR, XNOR GATES

XOR (exclusive OR)

For a 2 input XOR, the output of the gate is low when both the inputs are same (either both low or both high). The output is high if one and only one of the inputs is high. The function is addition modulo 2 and hence the gate is used in half adder. The schematic and truth table for 2 inputs A and B for XOR gate :-

SCHEMATIC OF XOR GATE

XNOR (exclusive NOR)

For a 2 input XNOR, the output of the gate is high when both the inputs are same(either both low or both high). The output is low if one and only one of the inputs is high. The schematic and truth table for 2 input A and B for XOR gate :-

SCHEMATIC OF XNOR GATE