of 38
7/29/2019 E9_sem_2_0506
1/38
ECE 2312 Sem 2 0506
Experiment # 9- Active Filters Low-Pass, High-Pass and Bandpass Filters
Venue : Electronic and Instrumentation Lab, E2
Aims
Identify the technique for synthesizing the voltage ratio H(s) = Vout / Vin Determine a network that can provide a desired transfer function Identify a single-pole filter and determine its gain and critical frequency Identify a two-pole filter and determine its gain and critical frequency Explain how a higher roll-off rate is achieved by cascading low-pass filters
Materials Required
Resistance Capacitance A741 op-amp Function generator DC supplies Traning kit PSpice programme
Procedure
1. Measure the components values for three types of filters (single-pole activelow pass filter, two-pole active low-pass filter and single-pole active high-pass
filter) and fill in the Table 9.1. The nominal values are R10=14.8k,
R11=15.0k, R12=3.9k, R13=6.8k, R15=10.0k, C6=2.4nF, C7=1.2nF,
C8=1.2nF, C9=5.4nF.
R10 R11 R12 R13 R15 C6 C7 C8 C9
Table 9.1 : Measured values of components used
Active Low-Pass Filter
2. Construct a single pole low-pass filter as shown in Figure 9.1.Notethat thetrainers op amp is A741 as indicated in the schematic.
7/29/2019 E9_sem_2_0506
2/38
ECE 2312 Sem 2 0506
Figure 9.1 : Single-pole active low-pass filter
3. Using the measured component values, calculate the theoretical cutofffrequency, fc = 1/2RC
4. With a fixed input voltage Vi = 5Vrms, vary the frequency over the rangef=100Hz to f=100kHz and record down the corresponding output voltage
taken at point 6 with respect to ground as given in Table 9.2. Turn OFF the
supplies.
Freq. Vin Vout1
pole
Vout2
poles
Voltage ratio(dB)
1 pole(exp.)
Voltage ratio(dB)
1 pole(PSpice)
%error
Voltage ratio(dB)
2 poles(exp.)
Voltage ratio(dB)
1 pole(PSpice)
%error
100 Hz 5Vrms
1 kHz 5Vrms
20 kHz 5Vrms
50 kHz 5Vrms
80 kHz 5Vrms
100 kHz 5Vrms
1 pole - fc (calculated) =_____ ; fc(experimental)=______ , % error = ______; fc (PSpice) =_____ ;
2 pole - fc (calculated) =_____ ; fc(experimental)=______ ; % error = ______; fc (PSpice) =_____ ;
Table 9.2 : Response of a single-pole and a two-poles active low-pass active filter
5. On a separate graph using semilog scale, manually plot the voltage gain in dBvs. frequency and indicate the experimental cutoff (3 dB) frequency. Discuss
the frequency response.
6. Construct a two-pole active low-pass filter as shown in Figure 9.2.7. Repeat steps 3, 4 and 5.
7/29/2019 E9_sem_2_0506
3/38
ECE 2312 Sem 2 0506
8. By means of measured components values, use Pspice to simulate theoreticalresults by plotting voltage gain in dB over frequency curves in semilog scales
for both cases. Mark points of interest at each step of frequency for closed-
loop voltage gain and critical frequency in the PSpice extrapolated curve. Find
some sample error for gain and cutoff frequency and complete Table 9.2. Give
the numerical expression of the transfer function H(s) = Vo/Vi for the circuit
considering passive realization.
Figure 9.2 : Two-pole active low-pass filter
Active High-Pass Filter
9. Construct a high-pass filter as shown in Figure 9.3.
7/29/2019 E9_sem_2_0506
4/38
7/29/2019 E9_sem_2_0506
5/38
Assignment # 9
PSpice Families of Curves, The Parametric Mode
1. Study the example given in the accompanying notes given earlier for Families ofCurves, The Parametric ModeusingAC analysis infrequency domain. Students
are advised to have other MicroSim Pspice and for windows related reference.
2. Draw the circuit in Figure 9.4 given below.
Figure 9.4 : Multiple feedback narrow bandpass filter
Frequency
0.1KHz 0.2KHz 0.3KHz 0.4KHz 0.5KHz 0.6KHz 0.7KHz 0.8KHz 0.9KHz 1.0KHz
V(Vin:+) V(R5:2)
0V
2.0V
4.0V
6.0V
Use this command for cursor search
sb#1#(200,400)1:le(0.871,p)
sf#1#(200,400)1:le(0.871,p)
(371.480,871.000m)
(252.114,871.000m)
(198.238,2.5580)
(157.540,2.5580)
(149.965,4.1720)
(124.962,4.1720)
(305.611,1.2321) R2=25 kiloohm; fr=306Hz
(177.555,3.6179) R2=75 kiloohm; fr=178Hz
(136.072,5.9008) R2=125 kiloohm; fr=136Hz; BW=fh-fl
Figure 9.5 : Narrowband filter response for various values of feedback resistance R2
7/29/2019 E9_sem_2_0506
6/38
ECE 2312 Sem 2 0506
3. Study the PSPICE program in the appended notes for parameter values andanalysis setup. Note the addition of R5 = 1.
4. Simulate the circuit and find the resonant frequency by using cursor to acquirethe peak values. Label the peak values as illustrated in Figure 9.5 above.Write proper titles for schematic (.sch) and graphs (.dat) for submission. Find
the bandwidth and quality factor and complete Table 9.4 below.
Resistor
(k)
Resonant frequency
(Hz)
Bandwidth
(Hz)
Q-factor
25
75
125
Table 9.4 : Center frequency, bandwidth, and Q factor for a narrow bandpass
filter for various values of feedback R2
Marking scheme
1. Report Tabulated results (1x 3pts. = 3pts.) 6 Plots experimental & theoretical (6 x 0.5pt. = 3pts.) Discussion & Conclusion, and derivation of H(s) as in notes (2pts. + 2pts. = 4pts.)Total points = 10
2. Assignment #9PSpice simulation; schematic, plot and table (2pts. + 4pts.+ 4pts =10 pts.)
7/29/2019 E9_sem_2_0506
7/38
7/29/2019 E9_sem_2_0506
8/38
7/29/2019 E9_sem_2_0506
9/38
7/29/2019 E9_sem_2_0506
10/38
7/29/2019 E9_sem_2_0506
11/38
7/29/2019 E9_sem_2_0506
12/38
7/29/2019 E9_sem_2_0506
13/38
7/29/2019 E9_sem_2_0506
14/38
7/29/2019 E9_sem_2_0506
15/38
7/29/2019 E9_sem_2_0506
16/38
7/29/2019 E9_sem_2_0506
17/38
7/29/2019 E9_sem_2_0506
18/38
7/29/2019 E9_sem_2_0506
19/38
7/29/2019 E9_sem_2_0506
20/38
7/29/2019 E9_sem_2_0506
21/38
7/29/2019 E9_sem_2_0506
22/38
7/29/2019 E9_sem_2_0506
23/38
7/29/2019 E9_sem_2_0506
24/38
7/29/2019 E9_sem_2_0506
25/38
7/29/2019 E9_sem_2_0506
26/38
7/29/2019 E9_sem_2_0506
27/38
7/29/2019 E9_sem_2_0506
28/38
7/29/2019 E9_sem_2_0506
29/38
7/29/2019 E9_sem_2_0506
30/38
7/29/2019 E9_sem_2_0506
31/38
7/29/2019 E9_sem_2_0506
32/38
7/29/2019 E9_sem_2_0506
33/38
7/29/2019 E9_sem_2_0506
34/38
7/29/2019 E9_sem_2_0506
35/38
7/29/2019 E9_sem_2_0506
36/38
7/29/2019 E9_sem_2_0506
37/38
7/29/2019 E9_sem_2_0506
38/38
