LS404

8/11

In the circuit of figure 14, for fc = 3.4kHz and R

R1 = R2 = R3 = 10k

Ω, we obtain:

The attenuation of the filter is 30dB at 6.8kHz and

better than 60dB at 15kHz.

The same method, referring to table 2 and figure

15 is used to design high-pass filter. In this case

the damping factor is found by taking the recipro-

cal of the numbers in table 2. For fc = 5kHz and Ci

= C1 = C2 = C3 = 1nF we obtain:

Table 2 : Damping Factor for Low-pass Butterworth Filters

Figure 15 : 5th Order High-pass Filter (Butterworth) with Unity Gain configuration

Ci = 1.354

1

R

----

1

2

------------ = 6.33nF

C1 = 0.421

1

R

----

1

2

------------ = 1.97nF

C2 = 1.753

1

R

----

1

2

------------ = 8.20nF

C3 = 0.309

1

R

----

1

2

------------ = 1.45nF

C4 = 3.325

1

R

----

1

2

------------ = 15.14nF

Ri =

1

0.354

---------------

1

C

----

1

2

------------ = 25.5k

Ω

R1 =

1

0.421

---------------

1

C

----

1

2

------------ = 75.6k

Ω

R2 =

1

1.753

---------------

1

C

----

1

2

------------ = 18.2k

Ω

R3 =

1

0.309

---------------

1

C

----

1

2

------------ = 103k

Ω

R4 =

1

3.325

---------------

1

C

----

1

2

------------ = 9.6k

Ω

Order

Ci

C1

C2

C3

C4

C5

C6

C7

C8

2

0.707

1.41

3

1.392

0.202

3.54

4

0.92

1.08

0.38

2.61

5

1.354

0.421

1.75

0.309

3.235

6

0.966

1.035

0.707

1.414

0.259

3.86

7

1.336

0.488

1.53

0.623

1.604

0.222

4.49

8

0.98

1.02

0.83

1.20

0.556

1.80

0.195

5.125

R2

C2

C1

R1

Ri

Ci

R4

C3

R3

C4