MATLAB: Can a complete 4-port S-parameter (including differential and common mode) simulation of a RF broadband system be done using the RF Toolbox 2.5 (R2009a)

RF Toolbox

I have the following requirements:

a) Sources are broad band – DC to ~30GHz frequency content (they are not narrow band RF signals). 4 port S pars are typically touchstone files.

b) Zs1, Zs2, ZL1, ZL2 are frequency dependent impedances.

c) V2 is not necessarily equal to –V1, i.e., it will contain a common mode signal component

d) The aim is to find the differential signal and the common mode signal at the loads.

Can a complete 4 port simulation be done which takes mode conversions into account?

Best Answer

This can be done using the RF Toolbox 2.5 (R2009a). The following functions can be used to realize this application.

S2MM - Convert 4N-port single-ended S-parameters to 4 2N-port mixed-mode S-parameters.

SMM2s - Convert 4 2N-port mixed-mode S-parameters to single-ended S-parameters.

S2DD - Convert 4-port S-parameters to differential 2-port S-parameters Sdd.

S2DC - Convert 4-port S-parameters to cross mode 2-port S-parameters Sdc.

S2SCD - Convert 4-port S-parameters to cross mode 2-port S-parameters Scd.

S2SCC - Convert 4-port S-parameters to common mode 2-port S-parameters Scc.

S2TF - Calculate transfer function from 2-port S-parameters.

In order to model mixed-mode simulation, there might be multiple approaches to go about it.

The RF Toolbox documentation includes an example "Modeling a High-Speed Backplane (Part 2: 4-Port S-Parameters to a Rational Function Model)" showing a differential-model application.

If you replace S2SDD with S2SCC, you will get the common-mode. Please note that when using S2TF, the impedances are different for differential-mod and common-mode:

 Zs(common-mode) = (Zs1 * Zs2)/(Zs1 + Zs2)
 Zl(common-mode) = (Zl1 * Zl2)/(Zl1 + Zl2)
 Z0(common-mode) = Z0/2

vs.

 Zs(differential-mode) = Zs1 + Zs2
 Zl(differential -mode) = Zl1 + Zl2
 Z0(differential -mode) = 2*Z0

Related Solutions

MATLAB: How to cascade a four port device with a two port device using rfckt objects in RF Toolbox

Unlike RF Blockset which has a 'Coupler' block for Simulink, there is no four port device rfckt object. In RF Toolbox, rfckt circuit objects are designed for chain of objects, i.e. we are limited to two port networks. As a workaround, if you could represent the Coupler as a 2 port network touchstone file, it will be possible to read the file and create a 'rfckt.passive' element with it. And then we can continue do the RF analysis on that network.

Please refer to the sample scripts below demonstrating this using two approaches -

1. Use the 'nport' object which reads both S-parameters and noise data from a Touchstone file. Then cascade them using an 'rfbudget' object. This sample script is the recommended and approach and it uses some functions which were released in MATLAB R2017a.

%%Using NEW nport objects (Recommended)/Approach 1
%%Read in a 3 Port coupler 

S3 = sparameters('default.s3p');

Coupler to to 2-port nport

S2 = snp2smp(S3);
rfwrite(S2, 'coupler2port.s2p')
% Creating a nport object
Coupler2port = nport('coupler2port.s2p');
% Note that coupler does not have noise of its own.
ckt1 = nport('default.s2p'); % Other 2 port sparameter device

% Noise Data can be viewed by doing ckt1.NoiseData
%%CASCADE

ckt_cascade = rfbudget([Coupler2port ckt1],[2e9:1e9:10e9],-30,10);
show(ckt_cascade);

To export the network into Simulink, i.e. RF Blockset please uncomment and execute the command below

% exportRFBlockset(ckt_cascade)

2. Use the 'rfckt.amplifier' object which contains both S-parameter and noise data. Then cascade them using 'rfckt.cascade'. This approach is not recommended, as it might be not available in future releases.

%%Using OLD rfckt objects /Approach 2
%%Read in a 3 Port coupler 
ckt = read(rfckt.passive,'default.s3p'); % This only works for passive data
s3p = ckt.NetworkData.Data;
Z0 = ckt.NetworkData.Z0;

Coupler to to 2-port rfckt.amplifier

s2p = snp2smp(s3p,Z0);
% Creating a rfckt object
rfwrite(s2p,ckt.NetworkData.Freq,'coupler2port_ckt.s2p')
Coupler2port = read(rfckt.amplifier,'coupler2port_ckt.s2p');
ckt1 = read(rfckt.amplifier,'default.s2p'); % Other 2 port sparameter device
%%CASCADE
ckt_cascade = rfckt.cascade('Ckts', {Coupler2port, ckt1});
analyze(ckt_cascade, 2.9e9)

MATLAB: How to cascade N-port S-parameters using the RF Toolbox

This enhancement has been incorporated in Release 2007b (R2007b). For previous product releases, read below for any possible workarounds:

The ability to cascade N-port S-parameters is not available in RF Toolbox. RF Toolbox only supports cascading of two port networks only.

However, RF Toolbox does allow reading and writing of N-port data files, but any analysis routines of this data must be provided by the user.

The following is an example of writing and reading N-port S-parameter files.

nports=42;
h=rfckt.passive
h.NetworkData.Freq = [1;2]*1e9
h.NetworkData.Data = cat(3,rand(nports,nports)+j*rand(nports,nports),rand(nports,nports)+j*rand(nports,nports))
analyze(h,h.NetworkData.Freq)
write(h,['test.s' num2str(nports) 'p'])
h2=read(rfckt.passive, ['test.s' num2str(nports) 'p'])

Best Answer

Related Solutions

MATLAB: How to cascade a four port device with a two port device using rfckt objects in RF Toolbox

MATLAB: How to cascade N-port S-parameters using the RF Toolbox

Related Question