Unformatted text preview: lter whose
impulse response is
h[ n ] = δ [ n ] − 0.2(0.8) u[ n ] Solutions 6-38 M. J. Roberts - 8/16/04 and display the image on the screen using the imagesc command in MATLAB. Notice how this highpass spatial filter empahsize the edges and de-emphasizes the
constant regions between the edges. A highpass filter does allow fast transitions to
44. In the system of Figure E0 let the CTFT of the the excitation be X( f ) = tri . This fc system is sometimes called a scrambler because it moves the frequency components of a
signal to new locations making it unintelligible.
(a) Using only an analog multiplier and an ideal filter, design a “descrambler” which
would recover the original signal.
(b) Sketch the magnitude spectrum of each of the signals in the scrambler-descrambler
ys (t) x(t)
cos(2πfct) Figure E0 A “scrambler”
No help here. Left as a challenge for the student.
45. Electronic amplifiers that handle very-low-frequency signals are difficult to design
because thermal drifts of offset voltages cannot be distinguished from the signals. For
this reason a popular technique for designing low-frequency amplifiers is the so called
“chopper-stabilized” amplifier (Figure E45). Solutions 6-39 M. J. Roberts - 8/16/04 Typical Amplifier
Chopper-Stabilized Amplifier +
- BPF LPF +
- Figure E45 A chopper-stabilized amplifier
A chopper-stabilized amplifier “chops” the excitation signal by switching it on and off
periodically. This action is equivalent to a pulse amplitude modulation in which the pulse
train being modulated by the excitation is a 50% duty-cycle square wave which alternates
between zero and one. Then the “chopped” signal is bandpass filtered to remove any slow
thermal drift signals from the first amplifier. Then the amplified signal is “chopped” again
at exactly the same rate and in phase with the chopping signal used at the input of the first
amplifier. Then this signal may be further amplified. The last step is to lowpass filter the
signal out of the last amplifier to recover an amplified versi...
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- Spring '09