EL5152, EL5153, EL5252, EL5455

FN7385 Rev 6.00

Page 11 of 16

March 2, 2009

Application Circuits

Sullen Key Low Pass Filter

A common and easy to implement filter taking advantage of the

wide bandwidth, low offset and low power demands of the

EL5152. A derivation of the transfer function is provided for

convenience. (See Figure 28.)

Sullen Key High Pass Filter

Again this useful filter benefits from the characteristics of the

EL5152. The transfer function is very similar to the low pass so

only the results are presented. (See Figure 29.)

FIGURE 28. SULLEN KEY LOW PASS FILTER

K

3

1

Q

RC

1

wo

K

Holp

C

R

C

R

C

R

C

R

C

R

C

R

)

K

1

(

1

Q

C

R

C

R

1

wo

K

Holp

)

C

R

C

R

C

R

)

K

1

((

jw

C

R

C

R

w

1

1

)

jw

(

H

1

s

)

C

R

C

R

C

R

)

K

1

((

s

C

R

C

R

K

)

s

(

H

0

s

C

1

Vi

Vo

R

V

K

Vo

1

R

Vi

V

V

1

s

C

R

1

K

Vo

R

R

1

K

1

1

2

2

1

2

2

1

2

2

1

1

2

2

1

1

2

2

2

1

1

1

2

2

1

1

2

2

21

2

1

1

1

2

2

2

1

1

1

2

1

1

1

1

2

2

A

B

































































Equations simplify if we let all

components be equal R = C

+

-

1n

5V

V2

C1

R1

R2

V1

1k

C2

RA

1k

1k

RB

5V

V3

R7

1k

1

3

2

V+

V-

4

U1A

1n

1n

1k

11

L1

10µH

C6

1n

C3

R5

1k

1n

C5

L3

10µH

1n

C4

R6

1k