Find Zeros, Poles, and Gains for CTLE from Transfer Function
This example shows how to use the ctlefitter
app to configure a CTLE block from SerDes Toolbox™ in the SerDes Designer™ app or in Simulink®. You will see how to use the ctlefitter
app to fit zeros, poles, and gains from a transfer function to create a GPZ Matrix
and export to your workspace. The ctlefitter
app finds the GPZ Matrix
by performing a fit comparison to a transfer function using the rational
function from RF Toolbox™.
Note: RF Toolbox is a distinctly separate product than RF PCB Toolbox™.
Using CTLE Fitter App
You can open the ctlefitter
app from SerDes Toolbox using any of three workflows:
Configure CTLE Block in the SerDes Designer App: This workflow creates a variable representing a GPZ Matrix
in the base workspace that is referenced by the CTLE block GPZ properties field in the Serdes Designer App. You can follow these steps:
Add a CTLE block and click on the button “Launch CTLE Fitter App”
Import a CTLE frequency response (there can also be multiple responses in your data file)
Adjust preprocess options for your transfer function data
Configure parameters of the
rational
function from RF Toolbox to optimize the fit to the transfer functionVisualize the fit response within the
ctlefitter
app using plots provided for Magnitude Response and Pulse ResponseClose the
ctlefitter
app and continue with your session in the Serdes Designer App
Simulink SerDes Model with a CTLE block: This workflow creates a variable representing a GPZ Matrix
in the model workspace and references this in the CTLE block mask GPZ field. You can follow these steps:
Open the CTLE block mask and click “Launch CTLE Fitter App”
Import a CTLE frequency response
Adjust preprocess options for your transfer function data
Configure parameters of the
rational
function from RF Toolbox to optimize the fit to the transfer functionVisualize the fit response within the
ctlefitter
app using plots provided for Magnitude Response and Pulse ResponseClose the
ctlefitter
app and continue with your session in Simulink
Standalone Mode: This workflow creates a variable in the base workspace representing a GPZ Matrix.
You can follow these steps:
Launch the app with the MATLAB command
ctlefitter
Import a CTLE frequency response
Adjust preprocess options for your transfer function data
Configure parameters of the
rational
function from RF Toolbox to optimize the fit to the transfer functionVisualize the fit response within the
ctlefitter
app using plots provided for Magnitude Response and Pulse ResponseThen you have the option to both export a script and save a
GPZ Matrix
to the base workspaceClose the
ctlefitter
app and continue with your session in MATLAB
Configure CTLE Block in the SerDes Designer App
Launch the SerDes Designer app. Place a CTLE block after the analog model of the receiver. Then in the Block Parameters section, you can click on the button to launch the CTLE Fitter App.
Import One or More CTLE Frequency Responses
The app will open with some default values shown. Follow these steps to import a file containing one or more CTLE frequency responses:
Click on the dropdown menu "Import CTLE frequency response from" and select the "CSV" option
Click the Browse button to open a .csv file containing a transfer function. Note: You can use the file attached to this example "CTLEdefault1RealImag.csv" to explore the features of the
ctlefitter
app. In the screenshots below, this file has been placed in the folder "D:\data" but may be in a different location on your system.You will see the app loads the file and automatically updates the figure shown on the Plot tab:
Adjust Preprocess Options
In the app, you can see many Preprocess Options are available. For example it is possible to truncate the data set from the transfer function used by the Fit. In the screenshot below you can see this is set to a cutoff frequency of 13 GHz:
You can also adjust:
Linearly resample with step size in MHz
Truncate response below a specified frequency in GHz
Truncate response above a specified frequency in GHz
Remove delay in picoseconds
Configure Rational Fitting Parameters
You can configure the way the MATLAB function rational
determines a fit by adjusting the following:
Error tolerance (dB)
Maximum number of poles
Use common poles for whole set
Enable or disable "tends to zero"
These parameters are explained in the documentation for the MATLAB function rational
, which is part of the RF Toolbox.
Report on Rational Fit Results
You can view the statistical parameters of the fit reported by the MATLAB function rational
on the "Report" tab:
Pulse Response
You can view the pulse response on the "Pulse Response" tab:
Export a GPZ Matrix for CTLE Block
You can export the GPZ Matrix
to the Workspace by clicking on the button "Save GPZ to Workspace."
Note: If you have previously exported a GPZ Matrix
, the name will automatically increment. For example, gpz01
is created in the figure below, but if gpz01
already exists in the workspace it would be automatically named gpz02
and added to your workspace.
Export Script from CTLE Fitter App to Base Workspace
You can also export a script from the ctlefitter
app to the base workspace by clicking on the button "Export to Script" and you can see example output below.
Note: The script contents you see may differ from the example below- depending on the data file being analyzed and your specific CTLE configuration options.
%Read in file: fn = 'CTLEdefault1RealImag.csv'; [f,H]=ctlefit.readcsv(fn); SymbolTime = 1e-10; %Initialize ctleit object obj = ctlefit(... 'f',f,... 'H',H,... 'SampleInterval',7.8125e-13,... 'MaxNumberOfPoles',2,... 'ErrorTolerance',-40,... 'TendsToZero',1,... 'UseCommonPoles',0,... 'PaddedPole',1e+11); %Preprocess transfer function waveform df = 1e+07; %resample(obj,df); fcut1 = 5e+08; %truncateBelow(obj,fcut1); fcut2 = 1.3e+10; truncateAbove(obj,fcut2); delay = 2.5e-12; %removeDelay(obj,delay); %Get GPZ matrix gpz = obj.GPZ; %Visualize and create report %TFView (Transfer function view) can be 'dB', 'Phase', 'Real/Imag', %'Phase Delay', 'Group Delay'. TFView = 'dB'; %ConfigSelect (CTLE Configuration Select) can be - 'All', 'Worst fit', 0 to %N-1, where N is the number of configurations. ConfigSelect = 'All'; %AxisStyle can be 'semilogx', 'plot', 'semilogy' or 'loglog'. AxisStyle = 'semilogx'; figure, plot(obj,TFView,ConfigSelect,AxisStyle)
figure, plotPulse(obj,ConfigSelect,SymbolTime)
figure, plotError(obj,ConfigSelect)
figure, plotFitMetric(obj)
figure, plotPoleZero(obj,ConfigSelect,SymbolTime)
report(obj,'All');
25-Mar-2022 15:4:1.966 CTLE with 1 Configurations Fit response with a maximum of 2 poles For ConfigSelect = 0 Fit error = -15.3406 dB Gain: -8.65231 V/V or 18.7426 dB Zeros: -1.39039 GHz = | -1.39039 + 0i |*1e9 Poles: -5.47276 GHz = | -3.83147 + 3.9078i |*1e9 -5.47276 GHz = | -3.83147 + -3.9078i |*1e9
Simulink SerDes Model with a CTLE block
You can configure a Simulink SerDes Model with a CTLE block by opening the CTLE block parameters and click the “Launch CTLE Fitter App" button. You can follow the same steps outlined above in the section Configure CTLE Block in the SerDes Designer App to configure the ctlefitter
app and export a GPZ Matrix
for use in a CTLE block.
In the Block Parameters of the CTLE, you can click the button to launch the ctlefitter
app:
After you close the ctlefitter
app, you will see the CTLE block is automatically configured to use the GPZ Matrix
it created:
You can confirm the transfer function represented by the GPZ Matrix
has a reasonable magnitude and phase response by clicking on "Visualize Response" button. These plots are also available in the SerDes Designer app workflow, and further detailed plots are provided as part of the exported script template.
Standalone Mode
Open the CTLE fitter app from the MATLAB command window:
ctlefitter;
You can follow the same steps outlined above in the section Configure CTLE Block in the SerDes Designer App to configure the ctlefitter
app and export a GPZ Matrix
to the base workspace in your MATLAB session.
Once you browse to and open a file containing one or more CTLE filter responses, you will see the app automatically updates the figure shown on the Plot tab:
This example has shown you how to configure a CTLE block using workflows in the SerDes Designer App, from within Simulink and Standalone Mode in MATLAB.
See Also
SerDes Designer | CTLE | serdes.CTLE
| rational
(RF Toolbox)