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Chapter 2 Linear System Representation
© National Instruments Corporation 2-17 Xmath Control Design Module
gain_z = 20*log10(abs(freq(Hd_z,F)));
gain_e = 20*log10(abs(freq(Hd_e,F)));
and plot it (as shown in Figure 2-1).
plot ([gainc,gain_f,gain_b,gain_t,gain_z,gain_e],
{legend = ["Continuous", "Forward",
"Backward", "Tustins", "Pole Zero",
"Exponential"], x_log,
xlab="Frequency (Hz)",ylab="Magnitude (dB)"})
Figure 2-1. Comparison of Different Frequency Response Techniques
Although most of the discretizations used would give acceptable
approximations to the continuous-time response, notice that most of them
diverge greatly at higher frequencies. You may find it illustrative to run this
example with larger and smaller sampling intervals to see how the choice
of sampling rate, as well as the choice of method, affects the accuracy of
the discretized frequency response.
makecontinuous( )
Sys=makecontinuous(SysD,{exponential, forward,
backward,tustins, ztransform})