LS404ID Datasheet LS404ID, LS404IDT, LS404CDT | P7-P9

LS404

7/11

Fixed R = R1 = R2, we have (see figure 13)

Figure 13 : Filter Configuration

Three parameters are needed to characterize the

frequency and phase response of a 2nd order ac-

tive filter: the gain (Gv), the damping factio (ξ) or

the Q factor (Q = 2 ξ)

1

), and the cuttoff frequency

(fc).

The higher order response are obtained with a se-

ries of 2nd order sections. A simple RC section is

introduced when an odd filter is required.

The choice of ’ξ' (or Q factor) determines the filter

response (see table 1).

Table 1

EXAMPLE

Figure 14 : 5th Order Low-pass Filter (Butterworth) with Unity Gain configuration

C

1 =

1

R

----

ζ

ω

c

-------

C

2 =

1

R

----

1

ξω

c

-----------

C2

R2R1

Vin

C1

Vout

Filter Response

ξ

Q Cuttoff Frequency fc

Bessel

Frequency at which Phase Shift is -90°C

Butterworth Frequency at which Gv = -3dB

Chebyschev

Frequency at which the amplitude response

passes through specified max. ripple band and

enters the stop bank.

3

2

-------

1

3

-------

2

-------

1

2

-------

2

-------

1

2

-------

C2

R2R1

C1

Ri

Ci

C4

R4R3

C3

LS404

8/11

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

i

=

R1 = R2 = R3 = 10kΩ, 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 π

fc

------------ = 6.33 n F

C1 = 0.421

1

R

----

1

2 π

fc

------------ = 1.97 n F

C2 = 1.753

1

R

----

1

2 π

fc

------------ = 8.20 n F

C3 = 0.309

1

R

----

1

2 π

fc

------------ = 1.45 n F

C4 = 3.325

1

R

----

1

2 π

fc

------------ = 15 . 14nF

Ri =

1

0.354

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

1

C

----

1

2π

fc

------------ = 2 5.5 k Ω

R1 =

1

0.421

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

1

C

----

1

2π

fc

------------ = 7 5.6k Ω

R2 =

1

1.753

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

1

C

----

1

2π

fc

------------ = 1 8.2k Ω

R3 =

1

0.309

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

1

C

----

1

2π

fc

------------ = 103kΩ

R4 =

1

3.325

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

1

C

----

1

2π

fc

------------ = 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

LS404

9/11

Figure 16 : Multiple Feedback 8-pole Bandpass Filter

Figure 17 : Six pole 355Hz Low-pass Filter (chebychev type)

This is a - pole Chebychev type with ±0.25dB ripple in the passband. A decoupling stage is used to avoid

the influence of the input impedance on the filter’s characteristics. The attenuation is about 55dB at 710Hz

and reaches 80dB at 1065Hz. the in band attenuation is limited in practise to the ±0.25dB ripple and does

not exceed 0.5dB at 0.9fc.

Figure 18 : Subsonic Filter (Gv = 0dB)

Figure 19 : High Cut filter (Gv = 0dB)

IN

C1

0.1 Fm

R1

C2

R4

Vcc

R2

R3

22kW

1

2

3

4

R5

C3

C4

0.1 Fm

¼

LS404

¼

LS404

¼

LS404

¼

LS404

R6

R7

C5

C6

R8

R9

R10

C7

220 Fm

C8

C9

R11

7

11

5

6

8

9

10

R12

R13

C10

C11

R14

14

13

12

Out

C12

0.1 Fm

C13

0.22 Fm

56kΩ

0.47 Fµ

10kΩ

86.1nF

161nF

10kΩ

220nF

16.3nF

10kΩ

60nF

3.54nF

10kΩ

C

22kΩ

Vout

Fc (Hz)

15

22

30

55

100

C ( F)

0.68

0.47

0.33

0.22

0.10

µ

C2

10kΩ

Vin

C1

Vout

10kΩ

3

2

1

Fc (Hz)

3

5

10

15

C1 (nF)

3.9

2.2

1.2

0.68

C2 (nF)

6.8

4.7

2.2

1.5

LS404ID

LS404ID

Products related to this Datasheet