how to plot transfer function exported from LTSpice

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francesco baldi on 26 Dec 2021

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Commented: Star Strider on 26 Dec 2021

Draft3.txt

hi there, i used the following code to plot the bode diagram of a trasnfer function exported from LTSpice:

filename = 'nameofthefile.txt';

fidi = fopen(filename, 'rt');

Dc = textscan(fidi, '%f(%fdB,%f°)', 'CollectOutput',1);

D = cell2mat(Dc);

figure

subplot(2,1,1)

semilogx(D(:,1), D(:,2))

title('Amplitude (dB)')

grid

subplot(2,1,2)

semilogx(D(:,1), D(:,3))

title('Phase (°)')

grid

xlabel('Frequency')

the fact is that it works well if i export the data from Spice in polar coordinates (dB and deg). Now i'd like to obtain the same result by exporting the data in cartesian coordinates (real and imm), and i don't know what to modify in this code. i attach the data set i'd like to plot.

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Answer 1

Star Strider on 26 Dec 2021

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https://au.mathworks.com/matlabcentral/answers/1617580-how-to-plot-transfer-function-exported-from-ltspice#answer_862095

Edited: Star Strider on 26 Dec 2021

Open in MATLAB Online

I have no idea what would be necessary for LTSPice to export in Cartesian coordiantes, however to convert them to Cartesian in MATLAB is straightforward, by extracting the real and imag components of the ‘Rsp’ vector as the ‘Real’ and ‘Imag’ vectors (this also identifies the system, since I had that code ready to go) —

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/844455/Draft3.txt';

T1 = readtable(filename, 'VariableNamingRule','preserve')

T1 = 401×2 table

Var1 Var2 _______________________________________________ ___________ {'1.00000000000000e+001→4.99999950651983e-001'} -0.00015708 {'1.02329299228075e+001→4.99999948326283e-001'} -0.00016074 {'1.04712854805090e+001→4.99999945890976e-001'} -0.00016448 {'1.07151930523761e+001→4.99999943340896e-001'} -0.00016831 {'1.09647819614319e+001→4.99999940670635e-001'} -0.00017223 {'1.12201845430196e+001→4.99999937874529e-001'} -0.00017625 {'1.14815362149688e+001→4.99999934946646e-001'} -0.00018035 {'1.17489755493953e+001→4.99999931880776e-001'} -0.00018455 {'1.20226443461741e+001→4.99999928670417e-001'} -0.00018885 {'1.23026877081238e+001→4.99999925308757e-001'} -0.00019325 {'1.25892541179417e+001→4.99999921788668e-001'} -0.00019775 {'1.28824955169313e+001→4.99999918102682e-001'} -0.00020236 {'1.31825673855641e+001→4.99999914242981e-001'} -0.00020707 {'1.34896288259165e+001→4.99999910201378e-001'} -0.00021189 {'1.38038426460288e+001→4.99999905969300e-001'} -0.00021683 {'1.41253754462275e+001→4.99999901537771e-001'} -0.00022188

V2c = cellfun(@(x)sscanf(x, '%f\t%f'), T1.Var1, 'Unif',0);

V2m = [cell2mat(V2c')' T1.Var2]

V2m = 401×3

10.0000 0.5000 -0.0002 10.2329 0.5000 -0.0002 10.4713 0.5000 -0.0002 10.7152 0.5000 -0.0002 10.9648 0.5000 -0.0002 11.2202 0.5000 -0.0002 11.4815 0.5000 -0.0002 11.7490 0.5000 -0.0002 12.0226 0.5000 -0.0002 12.3027 0.5000 -0.0002

T2 = table('Size',[size(T1.Var1,1) 3],'VariableTypes',{'double','double','double'}, 'VariableNames',{'FreqHz','MagndB','PhasDg'});

T2.FreqHz = V2m(:,1);

T2.MagndB = V2m(:,2);

T2.PhasDg = V2m(:,3)

T2 = 401×3 table

FreqHz MagndB PhasDg ______ ______ ___________ 10 0.5 -0.00015708 10.233 0.5 -0.00016074 10.471 0.5 -0.00016448 10.715 0.5 -0.00016831 10.965 0.5 -0.00017223 11.22 0.5 -0.00017625 11.482 0.5 -0.00018035 11.749 0.5 -0.00018455 12.023 0.5 -0.00018885 12.303 0.5 -0.00019325 12.589 0.5 -0.00019775 12.882 0.5 -0.00020236 13.183 0.5 -0.00020707 13.49 0.5 -0.00021189 13.804 0.5 -0.00021683 14.125 0.5 -0.00022188

D = table2array(T2)

D = 401×3

10.0000 0.5000 -0.0002 10.2329 0.5000 -0.0002 10.4713 0.5000 -0.0002 10.7152 0.5000 -0.0002 10.9648 0.5000 -0.0002 11.2202 0.5000 -0.0002 11.4815 0.5000 -0.0002 11.7490 0.5000 -0.0002 12.0226 0.5000 -0.0002 12.3027 0.5000 -0.0002

Mag = db2mag(T2.MagndB); % Absolute MAgnitude (Not Decibels)

Phs = deg2rad(T2.PhasDg); % Radian Phase Angle

Rsp = Mag.*exp(1j*Phs)

Rsp =

1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0004i 1.0592 - 0.0004i 1.0592 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0590 - 0.0005i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0588 - 0.0008i 1.0588 - 0.0008i 1.0588 - 0.0008i 1.0588 - 0.0008i 1.0588 - 0.0008i 1.0587 - 0.0008i 1.0587 - 0.0009i 1.0587 - 0.0009i 1.0587 - 0.0009i 1.0586 - 0.0009i 1.0586 - 0.0010i 1.0586 - 0.0010i 1.0585 - 0.0010i 1.0585 - 0.0010i 1.0585 - 0.0010i 1.0584 - 0.0011i 1.0584 - 0.0011i 1.0584 - 0.0011i 1.0583 - 0.0011i 1.0583 - 0.0012i 1.0582 - 0.0012i 1.0582 - 0.0012i 1.0581 - 0.0012i 1.0581 - 0.0013i 1.0580 - 0.0013i 1.0580 - 0.0013i 1.0579 - 0.0014i 1.0578 - 0.0014i 1.0578 - 0.0014i 1.0577 - 0.0014i 1.0576 - 0.0015i 1.0576 - 0.0015i 1.0575 - 0.0015i 1.0574 - 0.0016i 1.0573 - 0.0016i 1.0572 - 0.0017i 1.0571 - 0.0017i 1.0570 - 0.0017i 1.0569 - 0.0018i 1.0568 - 0.0018i 1.0567 - 0.0018i 1.0566 - 0.0019i 1.0565 - 0.0019i 1.0564 - 0.0020i 1.0563 - 0.0020i 1.0561 - 0.0020i 1.0560 - 0.0021i 1.0558 - 0.0021i 1.0557 - 0.0022i 1.0555 - 0.0022i 1.0554 - 0.0023i 1.0552 - 0.0023i 1.0550 - 0.0023i 1.0548 - 0.0024i 1.0546 - 0.0024i 1.0544 - 0.0025i 1.0542 - 0.0025i 1.0540 - 0.0026i 1.0538 - 0.0026i 1.0536 - 0.0027i 1.0533 - 0.0027i 1.0531 - 0.0028i 1.0528 - 0.0028i 1.0525 - 0.0029i 1.0523 - 0.0029i 1.0520 - 0.0030i 1.0517 - 0.0030i 1.0514 - 0.0031i 1.0510 - 0.0031i 1.0507 - 0.0032i 1.0504 - 0.0032i 1.0500 - 0.0033i 1.0496 - 0.0033i 1.0493 - 0.0034i 1.0489 - 0.0034i 1.0485 - 0.0035i 1.0481 - 0.0035i 1.0476 - 0.0036i 1.0472 - 0.0036i 1.0468 - 0.0037i 1.0463 - 0.0037i 1.0458 - 0.0038i 1.0453 - 0.0038i 1.0448 - 0.0039i 1.0443 - 0.0039i 1.0438 - 0.0040i 1.0433 - 0.0040i 1.0427 - 0.0041i 1.0422 - 0.0041i 1.0416 - 0.0041i 1.0410 - 0.0042i 1.0405 - 0.0042i 1.0399 - 0.0042i 1.0393 - 0.0043i 1.0386 - 0.0043i 1.0380 - 0.0043i 1.0374 - 0.0044i 1.0367 - 0.0044i 1.0361 - 0.0044i 1.0354 - 0.0044i 1.0348 - 0.0044i 1.0341 - 0.0044i 1.0335 - 0.0045i 1.0328 - 0.0045i 1.0321 - 0.0045i 1.0314 - 0.0045i 1.0307 - 0.0045i 1.0301 - 0.0045i 1.0294 - 0.0045i 1.0287 - 0.0045i 1.0280 - 0.0045i 1.0273 - 0.0045i 1.0267 - 0.0045i 1.0260 - 0.0045i 1.0253 - 0.0044i 1.0247 - 0.0044i 1.0240 - 0.0044i 1.0233 - 0.0044i 1.0227 - 0.0044i 1.0221 - 0.0043i 1.0214 - 0.0043i 1.0208 - 0.0043i 1.0202 - 0.0042i 1.0196 - 0.0042i 1.0190 - 0.0042i 1.0184 - 0.0041i 1.0178 - 0.0041i 1.0172 - 0.0041i 1.0167 - 0.0040i 1.0161 - 0.0040i 1.0156 - 0.0039i 1.0151 - 0.0039i 1.0146 - 0.0038i 1.0141 - 0.0038i 1.0136 - 0.0037i 1.0131 - 0.0037i 1.0126 - 0.0036i 1.0122 - 0.0036i 1.0117 - 0.0036i 1.0113 - 0.0035i 1.0109 - 0.0034i 1.0105 - 0.0034i 1.0101 - 0.0033i 1.0097 - 0.0033i 1.0094 - 0.0032i 1.0090 - 0.0032i 1.0087 - 0.0031i 1.0083 - 0.0031i 1.0080 - 0.0030i 1.0077 - 0.0030i 1.0074 - 0.0029i 1.0071 - 0.0029i 1.0068 - 0.0028i 1.0065 - 0.0028i 1.0063 - 0.0027i 1.0060 - 0.0027i 1.0058 - 0.0026i 1.0055 - 0.0026i 1.0053 - 0.0025i

Real = real(Rsp) % REAL Part Of Complex Response Vector

Real = 401×1

1.0593 1.0593 1.0593 1.0593 1.0593 1.0593 1.0593 1.0593 1.0593 1.0593

Imag = imag(Rsp) % IMAG Part Of Complex Response Vector

Imag = 401×1

1.0e+00 * -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000

Sizes = [size(T2.FreqHz); size(Rsp)]

Sizes = 2×2

401 1 401 1

sysfr = idfrd(Rsp,T2.FreqHz,0,'FrequencyUnit','Hz') % Create System Response Data Object

sysfr = IDFRD model. Contains Frequency Response Data for 1 output(s) and 1 input(s). Response data is available at 401 frequency points, ranging from 10 Hz to 1e+05 Hz. Status: Created by direct construction or transformation. Not estimated.

sys_ss = ssest(sysfr, 3) % State Space Realisation

sys_ss = Continuous-time identified state-space model: dx/dt = A x(t) + B u(t) + K e(t) y(t) = C x(t) + D u(t) + e(t) A = x1 x2 x3 x1 -1.967e+05 4.001e+05 1.656e+08 x2 2.268e-07 1.976e+05 1.66e+08 x3 -8.426e-11 -8.339e-11 5.911e+11 B = u1 x1 1.475e-10 x2 -1.957e-10 x3 1.049e+06 C = x1 x2 x3 y1 1359 -1362 -5.638e+05 D = u1 y1 0 K = y1 x1 0 x2 0 x3 0 Parameterization: FREE form (all coefficients in A, B, C free). Feedthrough: none Disturbance component: none Number of free coefficients: 15 Use "idssdata", "getpvec", "getcov" for parameters and their uncertainties. Status: Estimated using SSEST on frequency response data "sysfr". Fit to estimation data: 100% FPE: 4.055e-14, MSE: 3.935e-14

figure

compare(sysfr, sys_ss)

sys_tf = tfest(sysfr, 2, 2) % Transfer Function Realisation

sys_tf = s^2 + 885.4 s - 4.117e10 ------------------------ s^2 - 860.3 s - 3.887e10 Continuous-time identified transfer function. Parameterization: Number of poles: 2 Number of zeros: 2 Number of free coefficients: 5 Use "tfdata", "getpvec", "getcov" for parameters and their uncertainties. Status: Estimated using TFEST on frequency response data "sysfr". Fit to estimation data: 100% FPE: 4.796e-14, MSE: 4.678e-14

figure

compare(sysfr, sys_tf)

figure

pzmap(sys_ss)

grid on

format long E

Poles = pole(sys_ss)

Poles = 3×1

1.0e+00 * -1.967237778489041e+05 1.975767036132812e+05 5.911429745307852e+11

Zeros = zero(sys_ss)

Zeros = 2×1

1.0e+00 * -2.033539159391936e+05 2.024607634016894e+05

figure

subplot(2,1,1)

semilogx(D(:,1), D(:,2))

title('Amplitude (dB)')

grid

subplot(2,1,2)

semilogx(D(:,1), D(:,3))

title('Phase (°)')

grid

xlabel('Frequency')

EDIT — (26 Dec 2021 at 13:24)

Corrected name provided to readtable, and provided subsequent correct parsing of the resulting table.

With those changes, my code runs without error and produces the correct results.

.

9 Comments
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Star Strider on 26 Dec 2021

Open in MATLAB Online

I copied tther correct file to ‘filename’ however forgot to substitute ‘filename’ in the readtable call. Also, the textscan format string no longer works with this file, as the data are significantly different.

My cellfun call:

V2c = cellfun(@(x)sscanf(x, '%f\t%f'), T1.Var1, 'Unif',0);

converts it correctly.

This is significantly different in format from the previous files, so it required a different way to parse them.

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/844455/Draft3.txt';

T1 = readtable(filename, 'VariableNamingRule','preserve')

T1 = 401×2 table

Var1 Var2 _______________________________________________ ___________ {'1.00000000000000e+001→4.99999950651983e-001'} -0.00015708 {'1.02329299228075e+001→4.99999948326283e-001'} -0.00016074 {'1.04712854805090e+001→4.99999945890976e-001'} -0.00016448 {'1.07151930523761e+001→4.99999943340896e-001'} -0.00016831 {'1.09647819614319e+001→4.99999940670635e-001'} -0.00017223 {'1.12201845430196e+001→4.99999937874529e-001'} -0.00017625 {'1.14815362149688e+001→4.99999934946646e-001'} -0.00018035 {'1.17489755493953e+001→4.99999931880776e-001'} -0.00018455 {'1.20226443461741e+001→4.99999928670417e-001'} -0.00018885 {'1.23026877081238e+001→4.99999925308757e-001'} -0.00019325 {'1.25892541179417e+001→4.99999921788668e-001'} -0.00019775 {'1.28824955169313e+001→4.99999918102682e-001'} -0.00020236 {'1.31825673855641e+001→4.99999914242981e-001'} -0.00020707 {'1.34896288259165e+001→4.99999910201378e-001'} -0.00021189 {'1.38038426460288e+001→4.99999905969300e-001'} -0.00021683 {'1.41253754462275e+001→4.99999901537771e-001'} -0.00022188

V2c = cellfun(@(x)sscanf(x, '%f\t%f'), T1.Var1, 'Unif',0);

V2m = [cell2mat(V2c')' T1.Var2]

V2m = 401×3

10.0000 0.5000 -0.0002 10.2329 0.5000 -0.0002 10.4713 0.5000 -0.0002 10.7152 0.5000 -0.0002 10.9648 0.5000 -0.0002 11.2202 0.5000 -0.0002 11.4815 0.5000 -0.0002 11.7490 0.5000 -0.0002 12.0226 0.5000 -0.0002 12.3027 0.5000 -0.0002

T2 = table('Size',[size(T1.Var1,1) 3],'VariableTypes',{'double','double','double'}, 'VariableNames',{'FreqHz','MagndB','PhasDg'});

T2.FreqHz = V2m(:,1);

T2.MagndB = V2m(:,2);

T2.PhasDg = V2m(:,3)

T2 = 401×3 table

FreqHz MagndB PhasDg ______ ______ ___________ 10 0.5 -0.00015708 10.233 0.5 -0.00016074 10.471 0.5 -0.00016448 10.715 0.5 -0.00016831 10.965 0.5 -0.00017223 11.22 0.5 -0.00017625 11.482 0.5 -0.00018035 11.749 0.5 -0.00018455 12.023 0.5 -0.00018885 12.303 0.5 -0.00019325 12.589 0.5 -0.00019775 12.882 0.5 -0.00020236 13.183 0.5 -0.00020707 13.49 0.5 -0.00021189 13.804 0.5 -0.00021683 14.125 0.5 -0.00022188

D = table2array(T2)

D = 401×3

10.0000 0.5000 -0.0002 10.2329 0.5000 -0.0002 10.4713 0.5000 -0.0002 10.7152 0.5000 -0.0002 10.9648 0.5000 -0.0002 11.2202 0.5000 -0.0002 11.4815 0.5000 -0.0002 11.7490 0.5000 -0.0002 12.0226 0.5000 -0.0002 12.3027 0.5000 -0.0002

Mag = db2mag(T2.MagndB); % Absolute MAgnitude (Not Decibels)

Phs = deg2rad(T2.PhasDg); % Radian Phase Angle

Rsp = Mag.*exp(1j*Phs)

Rsp =

1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0000i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0593 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0001i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0002i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0003i 1.0592 - 0.0004i 1.0592 - 0.0004i 1.0592 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0004i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0591 - 0.0005i 1.0590 - 0.0005i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0590 - 0.0006i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0589 - 0.0007i 1.0588 - 0.0008i 1.0588 - 0.0008i 1.0588 - 0.0008i 1.0588 - 0.0008i 1.0588 - 0.0008i 1.0587 - 0.0008i 1.0587 - 0.0009i 1.0587 - 0.0009i 1.0587 - 0.0009i 1.0586 - 0.0009i 1.0586 - 0.0010i 1.0586 - 0.0010i 1.0585 - 0.0010i 1.0585 - 0.0010i 1.0585 - 0.0010i 1.0584 - 0.0011i 1.0584 - 0.0011i 1.0584 - 0.0011i 1.0583 - 0.0011i 1.0583 - 0.0012i 1.0582 - 0.0012i 1.0582 - 0.0012i 1.0581 - 0.0012i 1.0581 - 0.0013i 1.0580 - 0.0013i 1.0580 - 0.0013i 1.0579 - 0.0014i 1.0578 - 0.0014i 1.0578 - 0.0014i 1.0577 - 0.0014i 1.0576 - 0.0015i 1.0576 - 0.0015i 1.0575 - 0.0015i 1.0574 - 0.0016i 1.0573 - 0.0016i 1.0572 - 0.0017i 1.0571 - 0.0017i 1.0570 - 0.0017i 1.0569 - 0.0018i 1.0568 - 0.0018i 1.0567 - 0.0018i 1.0566 - 0.0019i 1.0565 - 0.0019i 1.0564 - 0.0020i 1.0563 - 0.0020i 1.0561 - 0.0020i 1.0560 - 0.0021i 1.0558 - 0.0021i 1.0557 - 0.0022i 1.0555 - 0.0022i 1.0554 - 0.0023i 1.0552 - 0.0023i 1.0550 - 0.0023i 1.0548 - 0.0024i 1.0546 - 0.0024i 1.0544 - 0.0025i 1.0542 - 0.0025i 1.0540 - 0.0026i 1.0538 - 0.0026i 1.0536 - 0.0027i 1.0533 - 0.0027i 1.0531 - 0.0028i 1.0528 - 0.0028i 1.0525 - 0.0029i 1.0523 - 0.0029i 1.0520 - 0.0030i 1.0517 - 0.0030i 1.0514 - 0.0031i 1.0510 - 0.0031i 1.0507 - 0.0032i 1.0504 - 0.0032i 1.0500 - 0.0033i 1.0496 - 0.0033i 1.0493 - 0.0034i 1.0489 - 0.0034i 1.0485 - 0.0035i 1.0481 - 0.0035i 1.0476 - 0.0036i 1.0472 - 0.0036i 1.0468 - 0.0037i 1.0463 - 0.0037i 1.0458 - 0.0038i 1.0453 - 0.0038i 1.0448 - 0.0039i 1.0443 - 0.0039i 1.0438 - 0.0040i 1.0433 - 0.0040i 1.0427 - 0.0041i 1.0422 - 0.0041i 1.0416 - 0.0041i 1.0410 - 0.0042i 1.0405 - 0.0042i 1.0399 - 0.0042i 1.0393 - 0.0043i 1.0386 - 0.0043i 1.0380 - 0.0043i 1.0374 - 0.0044i 1.0367 - 0.0044i 1.0361 - 0.0044i 1.0354 - 0.0044i 1.0348 - 0.0044i 1.0341 - 0.0044i 1.0335 - 0.0045i 1.0328 - 0.0045i 1.0321 - 0.0045i 1.0314 - 0.0045i 1.0307 - 0.0045i 1.0301 - 0.0045i 1.0294 - 0.0045i 1.0287 - 0.0045i 1.0280 - 0.0045i 1.0273 - 0.0045i 1.0267 - 0.0045i 1.0260 - 0.0045i 1.0253 - 0.0044i 1.0247 - 0.0044i 1.0240 - 0.0044i 1.0233 - 0.0044i 1.0227 - 0.0044i 1.0221 - 0.0043i 1.0214 - 0.0043i 1.0208 - 0.0043i 1.0202 - 0.0042i 1.0196 - 0.0042i 1.0190 - 0.0042i 1.0184 - 0.0041i 1.0178 - 0.0041i 1.0172 - 0.0041i 1.0167 - 0.0040i 1.0161 - 0.0040i 1.0156 - 0.0039i 1.0151 - 0.0039i 1.0146 - 0.0038i 1.0141 - 0.0038i 1.0136 - 0.0037i 1.0131 - 0.0037i 1.0126 - 0.0036i 1.0122 - 0.0036i 1.0117 - 0.0036i 1.0113 - 0.0035i 1.0109 - 0.0034i 1.0105 - 0.0034i 1.0101 - 0.0033i 1.0097 - 0.0033i 1.0094 - 0.0032i 1.0090 - 0.0032i 1.0087 - 0.0031i 1.0083 - 0.0031i 1.0080 - 0.0030i 1.0077 - 0.0030i 1.0074 - 0.0029i 1.0071 - 0.0029i 1.0068 - 0.0028i 1.0065 - 0.0028i 1.0063 - 0.0027i 1.0060 - 0.0027i 1.0058 - 0.0026i 1.0055 - 0.0026i 1.0053 - 0.0025i

Real = real(Rsp) % REAL Part Of Complex Response Vector

Real = 401×1

1.0593 1.0593 1.0593 1.0593 1.0593 1.0593 1.0593 1.0593 1.0593 1.0593

Imag = imag(Rsp) % IMAG Part Of Complex Response Vector

Imag = 401×1

1.0e+00 * -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000 -0.0000

Sizes = [size(T2.FreqHz); size(Rsp)]

Sizes = 2×2

401 1 401 1

sysfr = idfrd(Rsp,T2.FreqHz,0,'FrequencyUnit','Hz') % Create System Response Data Object

sysfr = IDFRD model. Contains Frequency Response Data for 1 output(s) and 1 input(s). Response data is available at 401 frequency points, ranging from 10 Hz to 1e+05 Hz. Status: Created by direct construction or transformation. Not estimated.

sys_ss = ssest(sysfr, 3) % State Space Realisation

sys_ss = Continuous-time identified state-space model: dx/dt = A x(t) + B u(t) + K e(t) y(t) = C x(t) + D u(t) + e(t) A = x1 x2 x3 x1 -1.967e+05 4.001e+05 1.656e+08 x2 2.268e-07 1.976e+05 1.66e+08 x3 -8.426e-11 -8.339e-11 5.911e+11 B = u1 x1 1.475e-10 x2 -1.957e-10 x3 1.049e+06 C = x1 x2 x3 y1 1359 -1362 -5.638e+05 D = u1 y1 0 K = y1 x1 0 x2 0 x3 0 Parameterization: FREE form (all coefficients in A, B, C free). Feedthrough: none Disturbance component: none Number of free coefficients: 15 Use "idssdata", "getpvec", "getcov" for parameters and their uncertainties. Status: Estimated using SSEST on frequency response data "sysfr". Fit to estimation data: 100% FPE: 4.055e-14, MSE: 3.935e-14

figure

compare(sysfr, sys_ss)

sys_tf = tfest(sysfr, 2,2) % Transfer Function Realisation

sys_tf = s^2 + 885.4 s - 4.117e10 ------------------------ s^2 - 860.3 s - 3.887e10 Continuous-time identified transfer function. Parameterization: Number of poles: 2 Number of zeros: 2 Number of free coefficients: 5 Use "tfdata", "getpvec", "getcov" for parameters and their uncertainties. Status: Estimated using TFEST on frequency response data "sysfr". Fit to estimation data: 100% FPE: 4.796e-14, MSE: 4.678e-14

figure

compare(sysfr, sys_tf)

figure

pzmap(sys_ss)

grid on

format long E

Poles = pole(sys_ss)

Poles = 3×1

1.0e+00 * -1.967237778489041e+05 1.975767036132812e+05 5.911429745307852e+11

Zeros = zero(sys_ss)

Zeros = 2×1

1.0e+00 * -2.033539159391936e+05 2.024607634016894e+05

figure

subplot(2,1,1)

semilogx(D(:,1), D(:,2))

title('Amplitude (dB)')

grid

subplot(2,1,2)

semilogx(D(:,1), D(:,3))

title('Phase (°)')

grid

xlabel('Frequency')

Everything now runs without error and the system is correctly identified. It took a few experiments to determine what the variables were, and where they were.

With the file correctly parsed, ‘Real’ and ‘Imag’ are correct, and the system is correctly identified

.

Star Strider on 26 Dec 2021

I have no idea what is in the file, since the columns are not labeled. The code posted in the Question shed no light on this, and the textscan format string is completely inappropriate for this file, since there are no ‘dB’ or ‘°’ characters in it. The delimiters are also inconsistent.

The first 3 rows of the file (that has no header lines) are —

1.00000000000000e+001 4.99999950651983e-001,-1.57079617176353e-004

1.02329299228075e+001 4.99999948326283e-001,-1.60738470739046e-004

1.04712854805090e+001 4.99999945890976e-001,-1.64482549896060e-004

The first column appears to be frequency, the second column magnitude, and the third, phase. (It required some effort to parse the file correctly.) That asssumption works with respect to the identification part of the code as well.

My code appears to parse the data correctly and identify the systems correctly.

If I did not guess correctly what the file contained, it is because I had no reliable information to work with.

I will do my best to help, however I need to know what information is provided in the file so I can work with it correctly.

Star Strider on 26 Dec 2021

Edited: Star Strider on 26 Dec 2021

Open in MATLAB Online

In that instance, only a few changes in my code are necessary, those being to construct the response vector ‘Rsp’ using the real and imaginary parts of the signal —

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/844455/Draft3.txt';

T1 = readtable(filename, 'VariableNamingRule','preserve')

T1 = 401×2 table

Var1 Var2 _______________________________________________ ___________ {'1.00000000000000e+001→4.99999950651983e-001'} -0.00015708 {'1.02329299228075e+001→4.99999948326283e-001'} -0.00016074 {'1.04712854805090e+001→4.99999945890976e-001'} -0.00016448 {'1.07151930523761e+001→4.99999943340896e-001'} -0.00016831 {'1.09647819614319e+001→4.99999940670635e-001'} -0.00017223 {'1.12201845430196e+001→4.99999937874529e-001'} -0.00017625 {'1.14815362149688e+001→4.99999934946646e-001'} -0.00018035 {'1.17489755493953e+001→4.99999931880776e-001'} -0.00018455 {'1.20226443461741e+001→4.99999928670417e-001'} -0.00018885 {'1.23026877081238e+001→4.99999925308757e-001'} -0.00019325 {'1.25892541179417e+001→4.99999921788668e-001'} -0.00019775 {'1.28824955169313e+001→4.99999918102682e-001'} -0.00020236 {'1.31825673855641e+001→4.99999914242981e-001'} -0.00020707 {'1.34896288259165e+001→4.99999910201378e-001'} -0.00021189 {'1.38038426460288e+001→4.99999905969300e-001'} -0.00021683 {'1.41253754462275e+001→4.99999901537771e-001'} -0.00022188

V2c = cellfun(@(x)sscanf(x, '%f\t%f'), T1.Var1, 'Unif',0);

V2m = [cell2mat(V2c')' T1.Var2]

V2m = 401×3

10.0000 0.5000 -0.0002 10.2329 0.5000 -0.0002 10.4713 0.5000 -0.0002 10.7152 0.5000 -0.0002 10.9648 0.5000 -0.0002 11.2202 0.5000 -0.0002 11.4815 0.5000 -0.0002 11.7490 0.5000 -0.0002 12.0226 0.5000 -0.0002 12.3027 0.5000 -0.0002

T2 = table('Size',[size(T1.Var1,1) 3],'VariableTypes',{'double','double','double'}, 'VariableNames',{'FreqHz','Real','Imag'});

T2.FreqHz = V2m(:,1);

T2.Real = V2m(:,2);

T2.Imag = V2m(:,3)

T2 = 401×3 table

FreqHz Real Imag ______ ____ ___________ 10 0.5 -0.00015708 10.233 0.5 -0.00016074 10.471 0.5 -0.00016448 10.715 0.5 -0.00016831 10.965 0.5 -0.00017223 11.22 0.5 -0.00017625 11.482 0.5 -0.00018035 11.749 0.5 -0.00018455 12.023 0.5 -0.00018885 12.303 0.5 -0.00019325 12.589 0.5 -0.00019775 12.882 0.5 -0.00020236 13.183 0.5 -0.00020707 13.49 0.5 -0.00021189 13.804 0.5 -0.00021683 14.125 0.5 -0.00022188

D = table2array(T2)

D = 401×3

10.0000 0.5000 -0.0002 10.2329 0.5000 -0.0002 10.4713 0.5000 -0.0002 10.7152 0.5000 -0.0002 10.9648 0.5000 -0.0002 11.2202 0.5000 -0.0002 11.4815 0.5000 -0.0002 11.7490 0.5000 -0.0002 12.0226 0.5000 -0.0002 12.3027 0.5000 -0.0002

Rsp = hypot(T2.Imag,T2.Real).*exp(1j*atan2(T2.Imag,T2.Real)) % Create Complex Response Vector

Rsp =

0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0002i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0003i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0004i 0.5000 - 0.0005i 0.5000 - 0.0005i 0.5000 - 0.0005i 0.5000 - 0.0005i 0.5000 - 0.0005i 0.5000 - 0.0005i 0.5000 - 0.0005i 0.5000 - 0.0005i 0.5000 - 0.0005i 0.5000 - 0.0006i 0.5000 - 0.0006i 0.5000 - 0.0006i 0.5000 - 0.0006i 0.5000 - 0.0006i 0.5000 - 0.0006i 0.5000 - 0.0006i 0.5000 - 0.0007i 0.5000 - 0.0007i 0.5000 - 0.0007i 0.5000 - 0.0007i 0.5000 - 0.0007i 0.5000 - 0.0007i 0.5000 - 0.0008i 0.5000 - 0.0008i 0.5000 - 0.0008i 0.5000 - 0.0008i 0.5000 - 0.0008i 0.5000 - 0.0008i 0.5000 - 0.0009i 0.5000 - 0.0009i 0.5000 - 0.0009i 0.5000 - 0.0009i 0.5000 - 0.0009i 0.5000 - 0.0010i 0.5000 - 0.0010i 0.5000 - 0.0010i 0.5000 - 0.0010i 0.5000 - 0.0011i 0.5000 - 0.0011i 0.5000 - 0.0011i 0.5000 - 0.0011i 0.5000 - 0.0012i 0.5000 - 0.0012i 0.5000 - 0.0012i 0.5000 - 0.0012i 0.5000 - 0.0013i 0.5000 - 0.0013i 0.5000 - 0.0013i 0.5000 - 0.0014i 0.5000 - 0.0014i 0.5000 - 0.0014i 0.5000 - 0.0015i 0.5000 - 0.0015i 0.5000 - 0.0015i 0.5000 - 0.0016i 0.5000 - 0.0016i 0.5000 - 0.0016i 0.5000 - 0.0017i 0.5000 - 0.0017i 0.5000 - 0.0018i 0.5000 - 0.0018i 0.5000 - 0.0018i 0.5000 - 0.0019i 0.5000 - 0.0019i 0.5000 - 0.0020i 0.5000 - 0.0020i 0.5000 - 0.0021i 0.5000 - 0.0021i 0.5000 - 0.0022i 0.5000 - 0.0022i 0.5000 - 0.0023i 0.5000 - 0.0023i 0.5000 - 0.0024i 0.5000 - 0.0024i 0.5000 - 0.0025i 0.5000 - 0.0025i 0.5000 - 0.0026i 0.5000 - 0.0027i 0.5000 - 0.0027i 0.5000 - 0.0028i 0.5000 - 0.0029i 0.5000 - 0.0029i 0.5000 - 0.0030i 0.5000 - 0.0031i 0.5000 - 0.0031i 0.5000 - 0.0032i 0.5000 - 0.0033i 0.5000 - 0.0034i 0.5000 - 0.0034i 0.5000 - 0.0035i 0.5000 - 0.0036i 0.5000 - 0.0037i 0.5000 - 0.0038i 0.5000 - 0.0039i 0.5000 - 0.0039i 0.5000 - 0.0040i 0.5000 - 0.0041i 0.5000 - 0.0042i 0.5000 - 0.0043i 0.5000 - 0.0044i 0.5000 - 0.0045i 0.5000 - 0.0046i 0.5000 - 0.0047i 0.5000 - 0.0049i 0.5000 - 0.0050i 0.4999 - 0.0051i 0.4999 - 0.0052i 0.4999 - 0.0053i 0.4999 - 0.0054i 0.4999 - 0.0056i 0.4999 - 0.0057i 0.4999 - 0.0058i 0.4999 - 0.0060i 0.4999 - 0.0061i 0.4999 - 0.0063i 0.4999 - 0.0064i 0.4999 - 0.0065i 0.4999 - 0.0067i 0.4999 - 0.0069i 0.4999 - 0.0070i 0.4999 - 0.0072i 0.4999 - 0.0073i 0.4999 - 0.0075i 0.4999 - 0.0077i 0.4999 - 0.0079i 0.4999 - 0.0081i 0.4999 - 0.0082i 0.4999 - 0.0084i 0.4999 - 0.0086i 0.4998 - 0.0088i 0.4998 - 0.0090i 0.4998 - 0.0092i 0.4998 - 0.0095i 0.4998 - 0.0097i 0.4998 - 0.0099i 0.4998 - 0.0101i 0.4998 - 0.0104i 0.4998 - 0.0106i 0.4998 - 0.0109i 0.4998 - 0.0111i 0.4997 - 0.0114i 0.4997 - 0.0116i 0.4997 - 0.0119i 0.4997 - 0.0122i 0.4997 - 0.0125i 0.4997 - 0.0128i 0.4997 - 0.0131i 0.4996 - 0.0134i 0.4996 - 0.0137i 0.4996 - 0.0140i 0.4996 - 0.0143i 0.4996 - 0.0146i 0.4996 - 0.0150i 0.4995 - 0.0153i 0.4995 - 0.0157i 0.4995 - 0.0161i 0.4995 - 0.0164i 0.4994 - 0.0168i 0.4994 - 0.0172i 0.4994 - 0.0176i 0.4994 - 0.0180i 0.4993 - 0.0184i 0.4993 - 0.0189i 0.4993 - 0.0193i 0.4992 - 0.0197i 0.4992 - 0.0202i 0.4991 - 0.0207i 0.4991 - 0.0212i 0.4991 - 0.0216i 0.4990 - 0.0221i 0.4990 - 0.0227i 0.4989 - 0.0232i 0.4989 - 0.0237i 0.4988 - 0.0243i 0.4988 - 0.0248i 0.4987 - 0.0254i 0.4986 - 0.0260i 0.4986 - 0.0266i 0.4985 - 0.0272i 0.4984 - 0.0278i 0.4984 - 0.0285i 0.4983 - 0.0291i 0.4982 - 0.0298i 0.4981 - 0.0305i 0.4980 - 0.0312i 0.4980 - 0.0319i 0.4979 - 0.0327i 0.4978 - 0.0334i 0.4976 - 0.0342i 0.4975 - 0.0350i 0.4974 - 0.0358i 0.4973 - 0.0366i 0.4972 - 0.0375i 0.4970 - 0.0383i 0.4969 - 0.0392i 0.4968 - 0.0401i 0.4966 - 0.0410i 0.4965 - 0.0420i 0.4963 - 0.0429i 0.4961 - 0.0439i 0.4959 - 0.0449i 0.4957 - 0.0460i 0.4955 - 0.0470i 0.4953 - 0.0481i 0.4951 - 0.0492i 0.4949 - 0.0503i 0.4946 - 0.0515i 0.4944 - 0.0526i 0.4941 - 0.0538i 0.4939 - 0.0550i 0.4936 - 0.0563i 0.4933 - 0.0576i 0.4930 - 0.0589i 0.4926 - 0.0602i 0.4923 - 0.0616i 0.4919 - 0.0630i 0.4916 - 0.0644i 0.4912 - 0.0658i 0.4908 - 0.0673i 0.4903 - 0.0688i 0.4899 - 0.0703i 0.4894 - 0.0719i 0.4889 - 0.0735i 0.4884 - 0.0752i 0.4879 - 0.0768i 0.4873 - 0.0785i 0.4868 - 0.0803i 0.4862 - 0.0820i 0.4855 - 0.0838i 0.4849 - 0.0857i 0.4842 - 0.0875i 0.4835 - 0.0894i 0.4827 - 0.0914i 0.4819 - 0.0934i 0.4811 - 0.0954i 0.4802 - 0.0974i 0.4793 - 0.0995i 0.4784 - 0.1016i 0.4774 - 0.1038i 0.4764 - 0.1060i 0.4754 - 0.1082i 0.4743 - 0.1105i 0.4731 - 0.1128i 0.4719 - 0.1151i 0.4707 - 0.1175i 0.4694 - 0.1199i 0.4680 - 0.1223i 0.4666 - 0.1248i 0.4652 - 0.1273i 0.4637 - 0.1298i 0.4621 - 0.1324i 0.4604 - 0.1350i 0.4587 - 0.1376i 0.4569 - 0.1403i 0.4551 - 0.1430i 0.4532 - 0.1457i 0.4512 - 0.1484i 0.4491 - 0.1512i 0.4470 - 0.1540i 0.4447 - 0.1568i 0.4424 - 0.1596i 0.4400 - 0.1624i 0.4376 - 0.1653i 0.4350 - 0.1681i 0.4324 - 0.1710i 0.4296 - 0.1739i 0.4268 - 0.1768i 0.4239 - 0.1796i 0.4209 - 0.1825i 0.4177 - 0.1854i 0.4145 - 0.1882i 0.4112 - 0.1911i 0.4078 - 0.1939i 0.4043 - 0.1967i 0.4007 - 0.1995i 0.3970 - 0.2022i 0.3931 - 0.2050i 0.3892 - 0.2077i 0.3852 - 0.2103i 0.3811 - 0.2129i 0.3768 - 0.2154i 0.3725 - 0.2179i 0.3681 - 0.2203i 0.3636 - 0.2227i 0.3590 - 0.2250i 0.3542 - 0.2272i 0.3494 - 0.2294i 0.3446 - 0.2314i 0.3396 - 0.2334i 0.3345 - 0.2353i 0.3294 - 0.2371i 0.3242 - 0.2387i 0.3189 - 0.2403i 0.3135 - 0.2418i 0.3081 - 0.2431i 0.3026 - 0.2444i 0.2971 - 0.2455i 0.2915 - 0.2465i 0.2859 - 0.2474i 0.2803 - 0.2482i 0.2746 - 0.2488i 0.2689 - 0.2493i 0.2631 - 0.2497i 0.2574 - 0.2499i 0.2516 - 0.2500i 0.2459 - 0.2500i 0.2401 - 0.2498i 0.2344 - 0.2495i 0.2287 - 0.2491i 0.2230 - 0.2485i 0.2173 - 0.2479i 0.2117 - 0.2470i 0.2061 - 0.2461i 0.2005 - 0.2450i 0.1950 - 0.2439i 0.1895 - 0.2426i 0.1842 - 0.2412i 0.1788 - 0.2397i 0.1736 - 0.2380i 0.1684 - 0.2363i 0.1633 - 0.2345i 0.1583 - 0.2326i 0.1533 - 0.2306i 0.1485 - 0.2285i 0.1437 - 0.2263i 0.1390 - 0.2240i 0.1345 - 0.2217i 0.1300 - 0.2193i 0.1256 - 0.2169i 0.1213 - 0.2143i 0.1171 - 0.2118i 0.1131 - 0.2092i 0.1091 - 0.2065i 0.1052 - 0.2038i 0.1014 - 0.2011i 0.0978 - 0.1983i 0.0942 - 0.1955i 0.0907 - 0.1927i 0.0874 - 0.1899i 0.0841 - 0.1870i 0.0809 - 0.1841i 0.0778 - 0.1813i 0.0749 - 0.1784i 0.0720 - 0.1755i 0.0692 - 0.1726i 0.0665 - 0.1698i 0.0639 - 0.1669i 0.0614 - 0.1640i 0.0589 - 0.1612i 0.0566 - 0.1584i 0.0543 - 0.1556i 0.0521 - 0.1528i 0.0500 - 0.1500i 0.0480 - 0.1472i 0.0460 - 0.1445i

Sizes = [size(T2.FreqHz); size(Rsp)]

Sizes = 2×2

401 1 401 1

sysfr = idfrd(Rsp,T2.FreqHz,0,'FrequencyUnit','Hz') % Create System Response Data Object

sysfr = IDFRD model. Contains Frequency Response Data for 1 output(s) and 1 input(s). Response data is available at 401 frequency points, ranging from 10 Hz to 1e+05 Hz. Status: Created by direct construction or transformation. Not estimated.

sys_ss = ssest(sysfr, 1) % State Space Realisation

sys_ss = Continuous-time identified state-space model: dx/dt = A x(t) + B u(t) + K e(t) y(t) = C x(t) + D u(t) + e(t) A = x1 x1 -2e+05 B = u1 x1 256 C = x1 y1 390.6 D = u1 y1 0 K = y1 x1 0 Parameterization: FREE form (all coefficients in A, B, C free). Feedthrough: none Disturbance component: none Number of free coefficients: 3 Use "idssdata", "getpvec", "getcov" for parameters and their uncertainties. Status: Estimated using SSEST on frequency response data "sysfr". Fit to estimation data: 100% FPE: 1.281e-31, MSE: 1.268e-31

figure

compare(sysfr, sys_ss)

sys_tf = tfest(sysfr, 1,1) % Transfer Function Realisation

sys_tf = 1e05 -------- s + 2e05 Continuous-time identified transfer function. Parameterization: Number of poles: 1 Number of zeros: 1 Number of free coefficients: 3 Use "tfdata", "getpvec", "getcov" for parameters and their uncertainties. Status: Estimated using TFEST on frequency response data "sysfr". Fit to estimation data: 100% FPE: 2.133e-31, MSE: 2.101e-31

figure

compare(sysfr, sys_tf)

figure

pzmap(sys_ss)

grid on

format long E

Poles = pole(sys_ss)

Poles =

-200000

Zeros = zero(sys_ss)

Zeros = 0×1 empty double column vector

figure

subplot(2,1,1)

semilogx(D(:,1), mag2db(abs(Rsp))) % Changed

title('Amplitude (dB)')

grid

subplot(2,1,2)

semilogx(D(:,1), angle(Rsp)) % Changed

title('Phase (°)')

grid

xlabel('Frequency')

This is now revealed to be a simple, first-order system.

EDIT — (26 Dec 2021 at 17:42)

Changed magnitude plot call to —

semilogx(D(:,1), mag2db(abs(Rsp)))

.

francesco baldi on 26 Dec 2021

the figure is correct, i don't understand why the scale on the y axis is different. The amplitude should go from -6dB to approximately -16dB, and the phase from 0 to approximately -77° in that range of frequencies.

Star Strider on 26 Dec 2021

In the last plot, I did not initially plot it in dB so I went back and edited the magnitude plot call to do that.

Now, all the plots agree.

.

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how to plot transfer function exported from LTSpice

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how to plot transfer function exported from LTSpice

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