Lab 5 Report
– Bandpass Filter

Bill
Chun Wai Hung

18 July 2004

A. Describe the Set-up

The
setup is shown in figure 1.

Figure 1

With a
source file of

V_V1
IN 0 DC 0Vdc AC 1Vac

R_R2
0 OUT  8k

R_R1
IN N00142
8k

X_U5
N01107 N00142 N09163 N08709 N01107 uA741

C_C1
0 N00142
1n

C_C2
OUT N01107
1u

V_V2
N09163 N08709 16Vdc

B. Desbribe Inputs

The
values of the inputs are set as

R1=8k
ohm

R2=8k
ohm

C1=1n
farad

C2=1u
farad

AC
Voltage source = 1V

f0=1/(2pi*R1C1) = 20kHz

f1=1/(2pi*R2C2) = 20Hz

The Op
Amp used is LMC64, the kind of op amp that is used in the previous labs.

Stimuli:
The Voltage is 1V in amplitude, and the value equals to 2 V peak-to-peak voltage.

With a
stimulation of pSpice, the ideal result should be
close to the one shown in Figure 2.

Figure 2

C. Describe What you Observe

The
circuit generated an experimental voltage values shown in Table 1 and Figure 3.

Table 1.

Frequency
(Hz)

P-P
voltage (mV)

5

500

10

922

15

1220

20

1440

25

1578

50

1891

75

1953

100

1984

150

2000

200

2000

400

2016

600

2016

800

2016

1500

2016

2000

2000

2500

1984

3000

1969

3500

1953

4000

1953

4500

1938

5000

1922

5500

1906

6000

1891

6500

1872

7000

1859

7500

1844

8000

1812

8500

1797

9000

1781

9500

1766

10000

1734

20000

1344

30000

1031

40000

828

50000

671

60000

578

70000

515

80000

453

90000

406

100000

391

200000

187

300000

156

400000

125

500000

109

600000

93

700000

78

800000

78

900000

78

1000000

78

Figure 3

D. What you can deduce

The
result of the experiment is that. The Experimental Plot of the voltage value
resembles the ideal voltage values shown in Figure 2.

The
cutoff frequencies (20kHz and 20Hz) are not as obvious
in the experimental plot. In other words, the voltage change around the cutoff frequencies  (20kHz
and 20Hz)  are not as rapid as shown
in the ideal plot. This is because the resistors used during the lab are not
ideal. A small difference of the resistance from the ideal value changes the
frequency response a lot. This is why the voltage rise and drop around the
cutoff frequencies are not as rapid as the ideal plot.

What I
am planning to do in order to claim my circuit works:

If the
input voltage is changed from 1V to 2V, the output voltage would change
accordingly. However, the cutoff frequencies will not be change. In other
words, the shape of the voltage against frequency plot will still be the same
except the whole graph is scaled upward.

This
experiment shows the differences between ideal case and the real case. Further
more, the experiment explore how to construct a bandpass
filter to filter out a desired range of frequencies.