This example shows how to configure the Specification parameter
GPZ Matrix of a CTLE in the SerDes Designer app to use zeros, poles, and gains output by the
zpk function, given poles and residues output by the
rational function. You can reformat the set of zeros, poles, and gains output by the
zpk function to use as a
GPZ matrix in a CTLE block.
Import a .csv file containing a transfer function using the
ctle_transfunc = readmatrix('ctle_transfer_function.csv','Range','A7:E775'); freq = ctle_transfunc(:,1); ri = ctle_transfunc(:,4:end);
To prepare data for use by the
rational function, convert the real numbers from the transfer function to complex numbers using the
data = complex(ri(:,1:2:end),ri(:,2:2:end));
You can use the
rational function to find the best fit to the transfer function. The
rational function performs iterations to identify a fit with the lowest error. It is important to set the argument
true to add a pole so that the fit tends to zero as S approaches infinity. This meets the requirement to have one more pole than the number of zeros in the GPZ matrix.
bestfit = rational(freq,data,'Tolerance',-40,'TendsToZero',true,'MaxPoles',8,'Display','on');
nSurrogate=1; reduced to 100.0% min achievable error=-Inf Region 1 of 1 init: np=0 errdb=0 Region 1 of 1: np=0 errdb=-3.04769 Region 1 of 1: np=2 errdb=-37.9389 Region 1 of 1: np=4 errdb=-122.215 final: np=4 errdb=-123.386
rational function returns poles and residues, but you need to convert these into zeros, poles and gains for a CTLE block. The CTLE can be configured to use Specification parameter
GPZ Matrix where the units for gains, poles and zeros are dB, Hz, and Hz, respectively.
[z,p,~,dcgain]=zpk(bestfit); gpz(1,1) = 20*log10(dcgain); % Convert to dB gpz(1,2:2:length(p)*2) = p/(2*pi); % Convert to Hz gpz(1,3:2:length(z)*2+1) = z/(2*pi); % Convert to Hz
Launch the SerDes Designer app. Place a CTLE block after the analog model of the receiver. Select the CTLE and from the Block Parameters pane, set the Specification parameter to
GPZ Matrix. Then copy the value of the
gpz variable and paste it to the Gain pole zero matrix parameter, or type the name of the variable
In the SerDes Designer app, plot the CTLE Transfer Function and Pulse Response from the Add Plots button.
Then click the Export > Make IBIS AMI Model for SerDes System button. The IBIS-AMI model may be loaded into an appropriate EDA tool to plot the Pulse Response from the model. For correlation purposes, you can compare the plots for Pulse Response from the SerDes Designer app and the EDA tool.