ECE 3074
Experiment: Twin T Notch Filter
Name: ______________________
Date: _____________________
Analysis
The component values for the Twin T notch filter with feedback circuit are:
fo = 60 Hz
R1
R2
R3
Value

Value
C1
C2
C3
The calculations that demonstrate that the magnitudes of output resistance of each branch of the passive
Twin T notch, Zo1 and Zo2, are equal when the frequency is equal to the center frequency of the notch
filter are:
The calculations that demonstrate that the relationship between the output currents of the branches is io1 =
- io2 when the frequency f = fo are:
The voltage transfer characteristic of notch filters with feedback when VS = 1V:
Insert the MATLAB plots of the transfer function of the Twin T filter with feedback where a = 0.1, 0.5,
and 0.9
The bandwidth and Q of the Twin T notch filter with feedback, a, are:
feedback
a = 0.1
a = 0.5
B
Q


a = 0.9
The magnitude and phase of the output voltage as calculated using the voltage transfer characteristic are:
f = 55 Hz
Magnitude
f = 60 Hz
Phase
Magnitude
f = 65 Hz
Phase
Magnitude
Phase
a = 0.1
a = 0.5
a = 0.9
Modeling
The plots of the magnitude and phase angle of the output voltage of the Twin T notch filter with feedback
when a = 0.1, 0.5, and 0.9 are:
Insert PSpice plots of the magnitude and phase angle of the output voltage when a = 0.1. Include
appropriate figure captions.
Insert PSpice plots of the magnitude and phase angle of the output voltage when a = 0.5. Include
appropriate figure captions.
Insert PSpice plots of the magnitude and phase angle of the output voltage when a = 0.9. Include
appropriate figure captions.
The center frequency, bandwidth, and Q of the Twin T filters from the PSpice simulations and the percent
difference from the expected values calculated in the Analysis section are:
feedback
fo
%
difference
B
%
difference
Q
%
difference
a = 0.1
a = 0.5






a = 0.9
The magnitude and phase of the output voltage as calculated using the PSpice simulations and the percent
difference of these results from the expected results from the Analysis section are:
feedback
f = 55 Hz
f = 60 Hz
f = 65 Hz
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Phase
%
difference
Phase
%
difference
Phase
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Phase
%
difference
Phase
%
difference
Phase
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Phase
%
difference
Phase
%
difference
Phase
%
difference
a = 0.1
a = 0.5
a = 0.9
Measurements
The measured component values for the Twin T notch filter with feedback circuit are:
Value
R1
R2
R3

Value
C1
C2
C3
Insert plot from spectrum analyzer of function generator output using the waveform created using
MATLAB. Include appropriate figure captions.
Insert plot from spectrum analyzer of the output voltage from the Twin T filter when the feedback
a = 0.1. Include appropriate figure captions.
Insert plot from spectrum analyzer of the output voltage from the Twin T filter when the feedback
a = 0.5. Include appropriate figure captions.
Insert plot from spectrum analyzer of the output voltage from the Twin T filter when the feedback
a = 0.9. Include appropriate figure captions.
The magnitude of the voltage transfer characteristic as measured from the data collected from spectrum
analysis and the percent difference of these results from the expected results from the Analysis section
are:
feedback
a = 0.1
a = 0.5
a = 0.9
f = 55 Hz
f = 60 Hz
f = 65 Hz
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Insert Bode plot of the magnitude and phase of the output voltage from the Twin T filter when the
feedback a = 0.1. Include appropriate figure captions.
Insert Bode plot of the magnitude and phase of the voltage from the Twin T filter when the
feedback a = 0.5. Include appropriate figure captions.
Insert Bode plot of the magnitude and phase of the output voltage from the Twin T filter when the
feedback a = 0.9. Include appropriate figure captions.
The center frequency, bandwidth, and Q of the Twin T filters from the Bode plots and the percent
difference from the expected values obtained in the Analysis section are:
feedback
fo
%
difference
B
%
difference
Q
%
difference
a = 0.1
a = 0.5






a = 0.9
The magnitude and phase of the voltage transfer characteristic as calculated using the data from the Bode
plot and the percent difference of these results from the expected results from the Analysis section are:
feedback
f = 55 Hz
f = 60 Hz
f = 65 Hz
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Phase
%
difference
Phase
%
difference
Phase
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Phase
%
difference
Phase
%
difference
Phase
%
difference
Magnitude
%
difference
Magnitude
%
difference
Magnitude
%
difference
Phase
%
difference
Phase
%
difference
Phase
%
difference
a = 0.1
a = 0.5
a = 0.9
Conclusions
Given the information provided in the two application notes cited in the Preparation section of this
experiment, explain the deviations that you observed between the results obtained from your analysis,
modeling, and measurements.
What would you expect would happen if the value of R4 used is either too low or too high and what value
of R4 would you expect to be considered too low or too high?