6.3.1 Overview

This document describes the symbol library and lepton-netlist backend which support driving RF Cascade (http://rfcascade.sourceforge.net) simulations from the Lepton system. Cascade is a noise figure and distortion analysis tool geared towards radio receiver design.

The basic steps involved with using Lepton as the frontend for Cascade simulations are:

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

6.3.2 Requirements

You will need the following programs to be installed:

• lepton-eda A version of Lepton package.
• RF Cascade The executable is usually called cascade. If you do not have Cascade available on your system, you will need to get a copy from http://rfcascade.sourceforge.net.

6.3.3 Creating Schematics

When creating a block diagram in the lepton-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.

6.3.4 Extracting the Cascade Input File

To extract the Cascade input file, run:

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

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

lepton-netlist -g cascade -o example.cas example.sch

The netlist will be left in example.cas.

6.3.5 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.

6.3.6 Appendix A – Symbols in the Library

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

• Sources (cascade-source)
• Defaults (cascade-default)
• Elements

6.3.7 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
• Netlist the Design
• Run the Analysis

6.3.7.1 Example Schematics

Figure 6.1 shows the schematic of a simple receiver signal chain.

Figure 6.1: Simple receiver signal chain block diagram

Figure 6.2 shows the contents of the example.cas file.

# Cascade (http://rfcascade.sourceforge.net)
# Created with Lepton EDA netlister

# Initial global defaults
defaults RIN=75 ROUT=75 RHO=0 

# Source definition
source C=-35 CN0=78 CN=0 BW=1

# Cascaded system
RF_FILTER1 G=-2.5 NF=2.5
LNA G=12 NF=2.7 IIP3=0
RF_FILTER2 G=-2.5 NF=2.5
MIXER G=-7 NF=7 IIP3=-3
IF_FILTER G=-6 NF=6
T1 G=0 NF=0 RIN=75 ROUT=50
defaults  RIN=75 ROUT=50 RHO=0
IF_AMP G=12 NF=6 IIP3=7

# End of netlist created by Lepton EDA netlister

Figure 6.2: Example RF Cascade input file, example.cas

lepton-netlist -g cascade example.cas example.sch

cascade example.cas

6.3.8 Document Revision History

December 3rd, 2003

Created cascade.tex