2009年山东大学信号考试试卷.doc

Signal and system test paper 2008-11-20For Electrical Engineering Department 2007PART 1 CHOOSING THE BEST ANSWER 1. The following signals are shown below, the _is periodic signal.A. x(t)=costu(t) B. xn=cos(1/4)nC. X()=The Fourier transform of xn2. The Fourier transform of periodic signal xT(t) is_ .A. discrete values ckB. impulse train（冲激序列）C. continuous function3. The frequency transfer function of the ideal filter is given by H()=0 for -BB, H()=1 for Bthe ideal filter is_. A. a high-pass filter B. a band-stop filter C. a low-pass filter 4. The input/output relationship of the discrete-time system in time domain is _.A. The Fourier transform representation and the convolution model.B. The input/output differential equation and the convolution model.C. The input/output difference equation and the convolution model.5. The rectangular pulse train is periodic signal with fundamental period T. The amplitude spectrum is |Ck|. When T becomes large, Then_A. |Ck| becomes larger and the line spectrum interval (谱线间隔) becomes largerB. |Ck| becomes smaller and the line spectrum interval becomes larger C. |Ck| becomes smaller and the line spectrum interval becomes smaller6. Suppose that x(t) is given by x(t)=x1(t) t1tt2 and x2(t) tt2.The signal x(t) can be expressed _.A. x(t)=x1(t)u(t-t1)- u(t-t2)+ x2(t)u(t-t1)- u(t-t2) B. x(t)=x1(t)u(t-t1)- u(t-t2)+ x2(t)u(t-t2)C. x(t)=x1(t) + x2(t)u(t-t1)- u(t-t2)7. The discrete-time system hes the relationship with the input and the output .yn= nxn.To determined the system are _.A. linear,causal,time varying , memorylessB. nonlinear,causal,time varying, memoryC. linear,causal, time invariant, memoryless8 The relationship between the DTFT and DFT is _.A. DTFT=DFTB.C. , k=0,1N-19The magnitude function of the ideal lowpass filter is 1 for |B, the time delay is td for all frequency. The input signal to the ideal lowpass filter is (t), the Fourier transform Y() of the response y(t) is _.A. 1, for all.B. ,for |BC. 1, for |2B.01X()-BB6. Given a linear time-invariant continuous-time system.The input X(t) and output Y(t) shown the following figure a) and figure b).Plot the Y(t) with input X(t-3) and 1/2X(t). X(t)t11Y(t)t-1 1 2 321-1 figure a) figure b)7To indicate the class of the following signals according to class method by continuous-time or discrecte-time, periodic or non-periodic, digital or analog. 8A linear time-invariant discrete-time system has the unit pulse response .A. Compute the step response gn for n0.B. Compute the output response yn for n0 when input xn=un-un-5, no initial conditions.PART 3 COMPUTE AND ANSWER THE FOLLOWING QUESTIONS1Given an input of x(t)=4+2cos(10t+/4)+3 cos(30t+/2) .find the output y(t) to each of the following filters. H() H() 2 1 -20 0 20 -2 0 2(a) (b)2Given a bandlimited signal x(t) ,the Fourier transform X() is shown in Fig. A. The system is shown in Fig. B.H()X() x(t) a(t) b(t) y(t) H() -10 0 10 cos30t cos30t 1 -15 0 15 Fig A Fig BPlot the A(),B() and Y(). Note: x(t)cos0t1/2 X(+0)+ X(-0) 3.Given two signals x1(t)=x2(t) = compute the convolution y(t)=x1(t)*x2(t) and the Fourier transform Y(), plot the waveform of y(t) and |Y()|.4Given the frequency response function of the ideal lowpass filter H()= 1, |c .the input signal x(t)=sinat/t. Compute and analyse the following questions.(a).if a c,the filter output y(t).(c).which case come into being the output distortion.(where x(t)=sinat/t-取样函数)5. Given the system is shown following the figure.The