Download m4.4 Signal Processing Circuits: (a) Design a two

m4.4 Signal Processing Circuits:
(a) Design a two-stage signal processor to serve as a “distortion box” for an electric
guitar. The first-stage amplifier applies a variable gain magnitude in the range
13.3 to 23.3 while the second-stage amplifier attenuates the signal by 13.3,
i.e., the second-stage amplifier has a fixed gain of 1/13.3. Note that when
the first-stage amplifier gain is 13.3 the overall distortion box gain is unity.
The distortion effect relies on intentionally driving the first-stage amplifier
into saturation (also called “clipping”) when its gain is higher than 13.3. Use
a 10-kΩ potentiometer and standard-value resistors in the range 1.0 kΩ and
100 kΩ; see the resistor parts list in Appendix A of the myDAQ tutorial on
the . You may combine two standard-value resistors in series to achieve the
required amplifier gains.
(b) Derive a general formula for percent clipping of a unit-amplitude sinusoidal
test signal; this is the percent of time during one period in which the signal is
clipped. The formula includes the peak sinusoidal voltage Vp that would appear
at the output of the first-stage amplifier with saturation ignored and the actual
maximum value Vs due to saturation.
(c) Apply your general formula to calculate percent clipping of a 1-V peak
amplitude sinusoidal signal for the potentiometer dial in three positions: fully
counter-clockwise (no distortion), midscale (moderate distortion), and fully
clockwise (maximum distortion). Assume the op-amp outputs saturate at
±13.5 V.
(d) Apply a 1-V peak amplitude sinusoidal signal with 100-Hz frequency to the
distortion box input and plot its output for the potentiometer dial in the same
three positions as above. State the maximum and minimum values of the
distortion box output.
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Solution: (begins on next page)
m4.4 – Signal Processing Circuits
Summary Comparison:
Results:
Analysis
Simulation
Measurement
Relative Differences:
Simulation -- Analysis
Measurement -- Analysis
Analytical Solution:
% clipping, beta=0.5 % clipping, beta=1.0 vo (max) vo (min)
47.2
60.7
1.00
-1.00
50.0
60.4
1.02
-1.02
49.2
60.4
1.00
-1.04
5.9%
4.2%
-0.5%
-0.5%
2.0%
0.0%
2.0%
4.0%
Multisim Results:
Potentiometer 0% (no distortion):
Clipping time = 0; percent clipped = 0%
Potentiometer at 50% (medium distortion):
Clipping time = 2.50ms, percent clipped = 50.0%
Potentiometer at 100% (maximum distortion):
Clipping time = 3.02ms, percent clipped = 60.4%
Max and min values of second-stage output:
Positive saturation voltage: 1.02 V
Negative saturation voltage: -1.02 V
myDAQ Results:
Function Generator setup:
Potentiometer full counter-clockwise (no distortion):
Clipping time = 0; percent clipped = 0%
Potentiometer at 12:00 (medium distortion):
Clipping time = 2.46ms, percent clipped = 49.2%
Potentiometer full clockwise (maximum distortion):
Clipping time = 3.02ms, percent clipped = 60.4%
Max and min saturation voltage of second-stage output:
Min voltage = -1.04V, max voltage = 1.00V