AReS

PART9Active Filter Circuit

Experiment 3 :Band-Pass Filter

Theory

fig9-9

Fig. 9-9Multiple Feedback Band Pass Filter

As in fig.9-9, about under 10 is proper for the Q for basic multiple feedback band pass filter. This is called multiple feedback because on more feedback path is added. In other words, the input of OP-Amp is connected to the inverting terminal. The center frequency for this circuit is determined in the formula below.

f_o=1/2πC∙√(1/R3∙(R1+R2)/R1R2)

However, three resistances can be determined simply by the formulae below.

R1=Q/(2πf_o G_o C),R2=Q/(2πf_o (2Q^2-G_o ) ),R3=1/(πf_o C)

When the formulae above are combined, G₀ can be calculated as below.

G_o=R3/2R1

Also, the relationship between Q and G₀ can be induced.

Q>√(G_o/2)

Generally, after selecting proper value for C, calculate systemically the value needed for 3 resistances which are based on the necessary condition for Q, G₀ and f₀.

State Variable(Universal) Filter

By combining 3 OP-Amps properly, the outputs of secondary low pass and high pass and band pass filters can be obtained at the same time. This filter is as in fig. 9-10 and is called state variable filter, or universal filter. As seen in the circuit, it is basically composed of one difference amplifier (A1) and two same integrators (A2, A3). The center frequency and cutoff frequency for this filter can be as the formula below.

f_o=f_c=1/2πRC

The Q of the filter is determined by the resistance R_A and R_B.

R_A=(3Q-1)

The band pass gain to low pass output and high pass output is “1”. The gain of center frequency to band pass output is same as the value of Q.

fig9-10

Fig. 9-10State Variable(Universal) Filter

When this circuit has secondary response to low pass output and high pas output, this circuit does not have optimal performance which can get all three outputs at the same time. To one response among low pass butter worth or high pass butter worth response, the Q should be same as 0.707. Eventually, the band pass response does not come out properly. That is, to the response of the secondary 3dB Chevychev filter, Q is 1.3, which is not a proper response. One among secondary butter worth low pass response, high pass response(Q=0.707) or band pass response of high Q should be designed.

Notch Filter

One advantage of the state variable filter in fig. 9-11 is that it can get low pass output and high pass output at the same time. Therefore, notch filter can be made. This filter is very useful to minimize the existence of Hum of 60Hz in the acoustic signal. What is needed is two input adder circuit that have same gains.

fig9-11

Fig. 9-11State Variable Notch Filter

Experiment Process

fig9-12

Fig. 9-12BPF Circuit(a)

fig9-13

Fig. 9-13BPF Circuit(b)

1. In Circuit-3 of M-09, connect between the both ends of 3d-3e, 3h-3i and compose a circuit as in fig. 9-12

2. Make the input voltage as 1V(rms) and change the frequency as given in table 9-3 and measure the output voltage and record it in the relevant column.

3. Next, Connect the low pass filter of fig.9-4 and high pass filter of fig. 9-8 in series and compose a band pass filter as in fig. 9-13.

4. Make the input voltage as 1V(rms) and change the frequency as given in table 9-3 and measure the output voltage and record it in the relevant column.

tab1

Experiment 9-3.1 Band Pass Filter Experiment
(In circuit-3, 4 of M09, compose circuits as in fig. 9-12(a), fig. 9-13(b), and fig. 9-14(c).)

1.Connection(Circuit-3 of M09), Fig. 9-12 BPF Circuit(a) 1

1.Circuit Connection

Capacitor C1, C3 Connection; Connect between 3d terminal and 3e terminal, between 3h terminal and 3i terminal of Circuit-3 with yellow lines.

2.Power Connection

It is connected internally

3.Measuring Instrument Connection

Function Generator Connection

Plug in BNC cable to BNC terminal of Signal Output on front panel and connect red line to 3a terminal of Circuit-3, and black line to 3b terminal.

Voltmeter Connection

Input Voltage Measurement Connection: - Connect between 3a terminal of Circuit-3 and A+ terminal of Signal Input CH A on the front panel of Multimeter with red line, and between 3b terminal and A- terminal with black line.

Output Voltage Measurement Connection: Connect between 3m terminal of Circuit-3 and B+ terminal of Signal Input CH B on the front panel of Multimeter with red line, and between 3n terminal and B- terminal with black line.

2.Wiring Diagram

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3.Measurement

1Choose analog output at Touch LCD panel, click Function Generator and set up Amplitude Range as 20vpp, and click arrow bottom of Amplitude and set up as amplitude 15% .
Set up Signal as sine, and choose 100 at Frequency and click arrow to set up as 200hz .
Click on and apply the output of Function Generator to input of Circuit-2.

Changing 1V(rms) as Vpp can be done by the formula below. V_PP=V_rms×2√2=1V×2×1.414=2.83V_PP The 15% of 20Vpp set up above is 3.0Vpp so it is set up as the approximation of 1V(rms).
2Measurement
Choose analog input at front panel, choose Volt & Ampere Meter tab and click voltage, ac , rms at CH A, CH B and record the output voltage measured at CH B in the Fig. 9-12-1 column of table 9-3.

Choose quick launch on the left bottom of the screen, click Analog Output and click arrow right of Frequency at Function to change the frequency as in table 9-3. Record the measured output voltage in the Fig. 9-12-2 column of table 9-3.

After the measurement, click on red at quick launch screen and cut off the output.
3Fig. 9-12 BPF Circuit(a) Experiment 2
Capacitor C2, C4 Connection: Change the connection between C1 and C3 to between 3d terminal and 3g terminal, and between 3j terminal and 3i terminal of Circuit-3 and connect with yellow lines.

Wiring Diagram

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Execute as the process 2) above and record the result in the Fig.9-12-3 column of table 9-3.
4Fig. 9-13 BPF Circuit(b) Experiment
Compose Circuit-1(LPF Circuit) and Circuit-2(HPF Circuit) of M09 as in fig. 9-13(b).

a) Circuit Connection

Capacitor C1, C3 Connection; Connect between 1c terminal and 1d terminal, between 1f terminal and 1g terminal of Circuit-1 with yellow lines.

Resistance R2, R4 Connection: Connect between 2c terminal and 2e terminal, between 2f terminal and 2h terminal of Circuit-2 with yellow lines.

Connection between Output Terminal of Circuit-1 and Input Terminal of Circuit-2: Connect between 1i terminal of Circuit-1 and 2a terminal of Circuit-2 with red line, and between 1j terminal of Circuit-1 and 2b of Circuit-2 with black line.

b) Measuring Instrument Connection

Function Generator Connection

Input Connection: Plug in BNC cable to BNC terminal of Signal Output on front panel and connect red line to 1a terminal of Circuit-1, and black line to 1b terminal.

Voltmeter Connection

Input Voltage Measurement Connection: - Connect between 1a terminal of Circuit-1 and A+ terminal of Signal Input CH A on the front panel of Multimeter with red line, and between 1b terminal and A- terminal with black line.

Input Voltage Measurement Connection: - Connect between 1a terminal of Circuit-1 and A+ terminal of Signal Input CH A on the front panel of Multimeter with red line, and between 1b terminal and A- terminal with black line.

c) Wiring Diagram

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d) Measurement

Execute as the process 2) above and record the result in the Fig.9-13 column of table 9-3.

After the measurement, click on red at quick launch screen and cut off the output.
5Fig. 9-14 BPF Circuit(c)
Compose Circuit-4 of M09 as in fig. 9-14(c).

Fig. 9-14BPF Circuit(c)

a) Measuring Instrument Connection

Function Generator Connection

Input Connection: Plug in BNC cable to BNC terminal of Signal Output on front panel and connect red line to 4a terminal of Circuit-4, and black line to 4b terminal.

Voltmeter Connection

Input Voltage Measurement Connection: - Connect between 4a terminal of Circuit-4 and A+ terminal of Signal Input CH A on the front panel of Multimeter with red line, and between 4b terminal and A- terminal with black line.

Output Voltage Measurement Connection: Connect between 4h terminal of Circuit-4 and B+ terminal of Signal Input CH B on the front panel of Multimeter with red line, and between 4i terminal and B- terminal with black line.

b) Wiring Diagram

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c) Measurement

Choose analog output at Touch LCD panel, click Function Generator and set up Amplitude Range as 20vpp , and click arrow bottom of Amplitude and set up as amplitude 100 .
Set up Signal as sine , and choose 100 at Frequency and click arrow to set up as frequency 200hz.

Click on and apply the output of Function Generator to input of Circuit-4.

Execute as the process 2) above and record the result in the Fig.9-14 column of table 9-3.

After the measurement, click on red at quick launch screen and cut off the output.

Experiment Result Report

result
Title	Band-Pass Filter	Date
Department		Id Number		Name

1. Experiment Result Table

Table 9-3

result_table
Input Frequency [㎐]		200	400	600	800	1k	1.2k	1.4k	1.6k	1.8k	2k	3k
Out put	Fig. 9-12.1
	Fig. 9-12.2
	Fig. 9-13
	Fig. 9-14

2. Review and Explanation

1) Using the measured result in table 9-3, draw the characteristic curve in the graph.

section paper Characteristic of Active Filter(HPF)

2) Using the figure and formula below, calculate the amplification degree Av, Q,and center frequency of circuit 9-12, 9-13.

A_v=〖-R〗_2/〖2R〗_1 ,Q=0.5√(R_2/(R_1∥R_3 )),f_0=1/(2πC√((R_1∥R_3 ) R_2 ))

fig03

3) Calculate center frequency, bandwidth and Q in the circuit below.
(Calculate using the 3dB frequency calculation result in LPF experiment result report and HPF experiment result report.)

Center Frequency f₀ = √(f₁ f₂)
Bandwidth BW = f₂ - f₁
Q = f₀ / BW

fig04

	Amplification Degree A_v	Q	Center Frequency f₀
Circuit 9-12
Circuit 9-13

PART9Active Filter Circuit

Experiment 3 :Band-Pass Filter

Theory

State Variable(Universal) Filter

Notch Filter

Experiment Process

Experiment 9-3.1 Band Pass Filter Experiment
(In circuit-3, 4 of M09, compose circuits as in fig. 9-12(a), fig. 9-13(b), and fig. 9-14(c).)

1.Connection(Circuit-3 of M09), Fig. 9-12 BPF Circuit(a) 1

1.Circuit Connection

2.Power Connection

3.Measuring Instrument Connection

2.Wiring Diagram

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3.Measurement

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Experiment Result Report

1. Experiment Result Table

2. Review and Explanation

1) Using the measured result in table 9-3, draw the characteristic curve in the graph.

2) Using the figure and formula below, calculate the amplification degree Av, Q,and center frequency of circuit 9-12, 9-13.

3) Calculate center frequency, bandwidth and Q in the circuit below.
(Calculate using the 3dB frequency calculation result in LPF experiment result report and HPF experiment result report.)

4) With the experiment result of fig. 9-14, explain the difference between this circuit and other filter circuits

3. Discuss the experiment result.

PART9Active Filter Circuit

Experiment 3 :Band-Pass Filter

Theory

State Variable(Universal) Filter

Notch Filter

Experiment Process

Experiment 9-3.1 Band Pass Filter Experiment (In circuit-3, 4 of M09, compose circuits as in fig. 9-12(a), fig. 9-13(b), and fig. 9-14(c).)

1.Connection(Circuit-3 of M09), Fig. 9-12 BPF Circuit(a) 1

1.Circuit Connection

2.Power Connection

3.Measuring Instrument Connection

2.Wiring Diagram

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3.Measurement

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Experiment Result Report

1. Experiment Result Table

2. Review and Explanation

1) Using the measured result in table 9-3, draw the characteristic curve in the graph.

2) Using the figure and formula below, calculate the amplification degree Av, Q,and center frequency of circuit 9-12, 9-13.

3) Calculate center frequency, bandwidth and Q in the circuit below. (Calculate using the 3dB frequency calculation result in LPF experiment result report and HPF experiment result report.)

4) With the experiment result of fig. 9-14, explain the difference between this circuit and other filter circuits

3. Discuss the experiment result.

Experiment 9-3.1 Band Pass Filter Experiment
(In circuit-3, 4 of M09, compose circuits as in fig. 9-12(a), fig. 9-13(b), and fig. 9-14(c).)

3) Calculate center frequency, bandwidth and Q in the circuit below.
(Calculate using the 3dB frequency calculation result in LPF experiment result report and HPF experiment result report.)