electronics simulation using spice software


introduction to spice

introduction to spice

SPICE: Electronic circuit design requires accurate methods for evaluating circuit performance. Because of enormous complexity of modern integrated circuits, Computer Aided circuit analysis is essential and can provide information about circuit performance that is almost impossible to obtain with laboratory prototype measurements.
Computer aided analysis permits:
1.Evaluating the effects of variations in elements, such as resistors, transistors, transformers and so on.
2.The assessment of performance (of circuit improvements or degradations.
3.Evaluaing the effects of noise and signal distortion without the need of expensive measuring instruments.
4.Sensitivity analysis to determine the permissible bounds due totolorances on each and every element value or parameters of active elements.
5.It also permits the Fourier analysis, without expensive wave analysers.
6.Evaluating the effects of non-linear elements on the circuit performance.
7.Optimising the design of electronic circuits in terms of circuit parameters.
SPICE is such type of computer-Aided circuit analyser. It is a general purpose circuit program that simulates electronic circuits. SPICE was developed in university of California, Berkeley and is the de-facto world standard for analog circuit simulation. There is a lot we can do with a circuit simulator that corresponds to what we might do on the lab-bench as well as simulated measurements that go beyond what is possible with laboratory experiments.

SPICE helps us to simulate our electronic circuit designs before to build these in laboratories. This lets one to decide if changes are needed, without touching any hardware. Also, it is possible through the help of SPICE to check the circuit design after we think that the design of circuit is complete. SPICE also let’s us decide if the circuit will work correctly, that is will provide god production yield or not. So we can say that spice is a simulated lab-bench on which we create test circuits and make measurements but it will not design the circuit for us, rather we have to design the circuit and verifies whether the circuit performance is good or not. If the circuit performance is not so good, then we have to change the circuit parameters so as to give good result by the help of spice and without doing the lab-work. Before the development of spice the circuit performance could only be checked when the circuit is built up practically. So, it took much time, if the circuit does not have good performance. But this problem is now solved after the development of SPICE. Now we have two ways to build an electrical circuit. Those are:
1.The circuit had to be either physically built which is expensive and time consuming.
2.Carefully simulated using a computer program. That is by the help of SPICE.
Naturally one will prefer the second one due to time saving and simplicity. That’s why, the acronym, SPICE stands for Simulation Program with Integrated Circuit Emphasis.
TYPES OF SPICE: Spice has many versions like spice-1, spice-2 and so on. Again the commercially supported versions of SPICE-2 can be divided into two types.:
1.Mainframe versions.
2. PC- based versions.
Their methods of computation may differ but their features are almost identical to SPICE-2.However some may include such additions as a pre-processor or shell program to manage input and provide interactive control as well as a post-processor for refining the normal SPICE output.
Mainframe versions are; H-SPICE, RAD-SPICE, IG-SPICE, I-SPICE, PSPICE, Cadence SPICE, SPICE Plus etc.

DIFFERENT TYPES OF ANALYSIS USING SPICE: The important analysis of the circuits by any version of spice are the same. Each analysis is invoked by including its command statement. The main analyses are:
1. DC Analysis: It is used for circuits with time in-variant sources, (steady state Dc sources). It calculates all node voltages and branch currents over a range of values, and their quiscent (DC) values are the outputs.
2.DC Operating point: DC analysis for given source values.
3.TRANSIENT Analysis: It is used for circuits with time- variant sources (ac sources and switched dc sources). It calculates all node voltages and branch currents over a time interval and their instantaneous values are the outputs.
4. AC Analysis: It is used for small signal analysis of circuits with sources of variable frequencies. It calculates all the node voltages and branch currents over a range of frequencies and their magnitude and phase angles are the outputs.
5. Distortion Analysis:
6. Noise Analysis: Analysis of the device generated noise in the circuit.
7. Small signal sensitivity Analysis:
8. Pole-Zero Analysis: It locates poles and zeros in the small signal transfer function.
9. Transfer Function Analysis: It calculates the DC small signal transfer functions, input and output resistances.