* gnucap:manual:examples

gnucap:manual:examples:experimentally_finding_model_parameters

Sometimes you need to determine model parameters, based on having no real information. In this example, we find the parameter “IS” of a diode, based on its forward voltage. We would like to have a diode... D2 (a k) 1n4004 Now you need a model statement ...

gnucap:manual:examples:fm_spectrum_analysis

In this demo, we will look at the spectrum of a frequency modulated signal, with the intent of exploring the effect of overmodulation on bandwidth. The circuit is simple, just a voltage source, with a Spice-style “SFFM” waveform. We will use parameters to tinker with the signal, and the Fourier command to display the spectrum. You could calculate the spectrum using Bessel functions, but we will look at it with simulation.

gnucap:manual:examples:hello_world

Copyright 1999 Telford Tendys (with mods by Albert Davis) This is not an alternative to reading the manual. The manual is very nicely presented in LaTeX and you should print it out and keep it handy when working. This document is organised starting from easy and working towards difficult and presumes that you have some idea of what electrical circuits are but don't know much about simulators. The manual is organised in alphabetical order and in groups of concepts and it presumes that you know S…

gnucap:manual:examples:multiplying_two_voltages_using_diode_nonlinearity

The above example shows diode voltage drop behaviour but the diode can also be used as an exponential function. In this example, a group of diodes are used to construct a voltage multiplier. Most circuit components add and subtract voltages and currents but multiplication is a bit special. What is done in this circuit is to use the exponential behaviour of the diodes to take the logarithm of two input voltages, then add those up and use another diode to find the exponential of the sum. This work…

gnucap:manual:examples:noise_syntax

Noise Syntax This section contains descriptions which are not implemented yet in simualtor. Work is in progress. Spice .noise command syntax is implemented: .noise V([,]) * , - output node numbers, if N2 is omited ground is implied; * - input AC source at which noise power will be calculated; * - gnucap AC simulation statement.

gnucap:manual:examples:nonlinear_devices_--_diodes

All of the previous circuits have been linear. This is to say that all the devices (voltage sources, current sources, dependent source and resistors) are linear devices and the overall “shape” of the problem does not change as the values of the system are scaled up or down. For example, if a circuit is solved once, then after that all of the voltage sources in the circuit are doubled, the circuit doesn't need to be solved a second time because all the node voltages will merely be double those of…

gnucap:manual:examples:paramset_recursive

A paramset permits the recursive definition of component models. In this example we analyse a chain of RC lowpass filters whithout having to type it out explicitly. some typing. First, define two modules as follows. module tln0(a, b); parameter r; parameter c; resistor #(.r(r)) r(a b); capacitor #(.c(c)) c(b, 0); endmodule module tln1(a, b); parameter length parameter r; parameter c; resistor #(.r(r)) r(a i); capacitor #(.c(c)) c(i, 0); tln #(.length(length - 1) .c(c) .r…

gnucap:manual:examples:phase_shift_oscillator

Getting started In this example, we will analyze a phase shift oscillator. It was designed in a hurry, so the specs are not expected to be very good. We will see. It uses a single BJT, plus an emitter follower, and runs on a single-ended 12 volt supply.

gnucap:manual:examples:polyglot

In some situations it may be desirable to share circuit and analysis across multiple backends. Examples are cross verification, benchmarking, pointing out differences, or demonstrate problems. Gnucap provides a mechanism that can be used to share batch files with other spice implementations more easily. Consider the following spice input.

gnucap:manual:examples:resistors_and_sources

The previous example covers enough concepts to model arbitrarily complex networks of resistors and sources. These are essentially linear circuits that have no relation to time. A more elaborate example is presented below: eg2.ckt NETWORK OF RESISTORS AND VOLTAGE SOURCES V1 2 1 10 V2 4 3 5 V3 0 3 3 R1 1 2 220 R2 2 3 4.7k R3 4 5 3.3k R4 3 5 10k R5 0 1 22k R6 0 5 15k

gnucap:manual:examples:simple_power_supply

Getting started In this example, we will analyze a simple power supply. The power supply consists of a “lump” power transformer with fairly loose coupling for short circuit protection, a full wave bridge rectifier, and a filter capacitor. The desired output is about 50 volts at .5 amps (100 Ohm load), with less than 1 volt of ripple. The power supply should be able to handle a short with no damage, with no fuse.

gnucap:manual:examples:spice_to_verilog

Transition from SPICE to Verilog In the not so distant past, people migrated from Fortran to C. But, as rewriting Fortran code does not always pay off, there are means to intergrate Fortran libraries into modern systems. Now close to everyone is running Fortran code, most without even noticing. We are in a very similar situation with SPICE and Verilog. Here are some examples that show how to connect the worlds. These build on verilog_basics.

gnucap:manual:examples:things_that_can_go_wrong

Voltage sources in parallel eg4.ckt VOLTAGE SOURCES IN PARALLEL V1 1 0 10.0 V2 1 0 10.2 .print dc v(1) i(V1) i(V2) .dc .end Here we have V1 and V2 both driving the same node at about 10 volts. Actually, V2 is very slightly higher than 10 volts so there will be some argument between V1 and V2 as to exactly what the final voltage at node 1 really is. You should see that huge currents are flowing through the supplies (10,000 amps) just due to this small voltage difference. Also note that gnuc…

gnucap:manual:examples:verilog_basics

getting started, device and testbench Lets look at spice first. An RC lowpass (1 ohm, 1 farad)... The stanza gnucap> spice spice> .subckt rclp in out ref spice> R1 in out 1 spice> C1 out ref 1 spice> .ends declares a subcircuit (macro) with 3 ordered ports and no parameters. It could model a PCB with a 3 pin connector (or so), and some oversimplification.