gEDA/gaf RF Cascade Symbols and Netlister

by: Dan McMahill

This document is released under GFDL

December 3rd, 2003

Overview

This document describes the symbol library and gnetlist backend which support driving RF Cascade (http://rfcascade.sourceforge.net) simulations from the gEDA/gaf system. Cascade is a noise figure and distortion analysis tool geared towards radio receiver design.
The basic steps involved with using gEDA as the frontend for Cascade simulations are:

  1. Create schematics of the circuit.
  2. Extract the netlist.
  3. Run Cascade.

Requirements

You will need the following programs to be installed:

Creating Schematics

When creating a block diagram in the gschem schematic editor, use only the symbols from the cascade library. Every block diagram must have a \cascadesource” element. In addition, the block diagram must be a simple cascade. No parallel paths or branches are allowed.
All instances must have a unique reference designator. For a receiver block diagram, this is often times best achieved by manually entering them. The only restriction on reference designator names is that they contain no spaces. A descriptive name such as \RF Filter” or \First Mixer” is useful as it will show up in the cascade output report.

Extracting the Cascade Input File

To extract the Cascade input file, run:

gnetlist -g cascade -o test.cas file1.sch [file2.sch ...]

For the example file contained in this archive, you can run:

gnetlist -g cascade -o example.cas example.sch

The netlist will be left in example.cas.

Running Cascade

Cascade is exceptionally simple to run. Just run:

cascade example.cas > example.out

to run the analysis on the system contained in the file example.cas and write the results to the file example.out. Refer to the Cascade documentation for complete details.

Appendix A -- Symbols in the Library

Please note that all instances must have the refdes= attribute set.

Sources (cascade-source)

Source. Attributes:

Defaults (cascade-default)

This symbol sets the default impedance levels as well as the correlation coeffcient used for third order distortion calculations. There are two versions of this symbol. One is used to set the defaults at the beginnng of the definition. The other can be placed in series with the cascade to change the defaults part way through. This is useful if you wish to change impedance levels in the middle of the receiver chain. Attributes:

Elements

Cascade characterizes each block in a system by its gain and optionally noise figure and third order intercept point. As such, there is no distinction between various elements such as amplifiers, filters, and mixers. The gEDA/gaf RF Cascade symbol library contains different symbols for clarity in the diagram only. The currently available element symbols are: Attributes:

cascade-ampAmplifier
cascade-filterFilter
cascade-mixerMixer
cascade-transformerTransformer
Table 1: Element Types

Example

This appendix provides a simple example of the entire process of generating a schematic, producing a Cascade input file, running an analysis and looking at the result.

Example Schematics

Figure 1 shows the schematic of a simple receiver signal chain.
Figure 2 shows the contents of the example.cas file.

Netlist the Design

To netlist the design, run:

gnetlist -g cascade example.cas example.sch

Run the Analysis

Run the analysis with:

cascade example.cas

Document Revision History

December 3rd, 2003Created cascade.tex