EE145M Spring 92 Final
College of Engineering
Electrical Engineering and Computer Science
Berkeley
Problem 1 (total 36 points):
Define the following terms (30 words or less)
a. (6 points) Glitch (of a D/A converter)
b. (6 points) Transition Voltages (of an A/D converter)
c. (6 points) Frequency Aliasing
d. (6 points) Sample and Hold Amplifier
e. (6 points). Flash A/D Converter
f. (6 points) Successive Approximation A/D Converter
Problem 2 (41 points)
You have a data-acquisition system that can sample an analog waveform, digitize it and transfer the resulting
digital number into computer memory every 10 micro(s) .(Note: This system has no analog filtering before
digitizing).
a. (5 points) What is the sampling frequency?
b. (18 points) You sample a sine wave with frequency f=25kHz, look at the resulting data, and observe that
there are four samples per sinewave period. How many samples per apparent sinewave period would you
expect to observe if the input frequency were 10, 50, 75 and 100 kHz?
c. (18 points). You acquire 1024 samples of a 9766-Hz sine wave oscillating between 0 and 2V, and take the
fast Fourier transorm of the resulting data. List the location (frequency indices) of all non-zero Fourier
amplitudes. (Hint : 1024 x 0.9766 = 1.0000.)
Problem 3 (total 45 points):
You have been using the system described in Problem 2 for input frequencies below 20kHz for some time nad
with great success until a colleague in the next room turns on a pure 1,000-Mhz ( +/-1Hz) sine-wave oscillator
and some of the unwanted signal gets into the analog input of your system.
a. (15 points) What would be the effect of the 1Mhz signal on your digitized data? Explain.
b. (15 points). If you took several 1024 point data sets, where the start time was determined at random push of
a button), would be the effecgt of the 1 Mhz signal be the same for each data set? Give a reason for your
answer.
c. (15 points) How could you most easily eliminate the effect of the unwanted 1 Mhz signal in you digitized
data?
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