M61520FP

Rev.1.0, Sep.19.2003, page 12 of 15

(5) Equivalent Circuit for the Bass-Boost Circuit

Input

Output

+

-

Switching-noise

reduction circuit

SEL

G0

f0

0dB

Q=4 (G=10dB)

Positive-feedback second-order high-pass filter circuit for the bass-boost module

VIN

VOUT

C1

C2

R2

+K

R1

Amplitude characteristics of the second-order high-pass filter

Q

G0

1

0 to 1dB

2

6dB

4

10dB

5

13dB

10

20dB

The transfer function is described by the following expressions:

VOUT

Q =

VIN

1

R2C1

R1C1

R1C2

R2C2

R2C2

R2C1

R1C1

R1C1

R2C2

+ (1-K)

+ (1-K)

+

++

11

R1R2C1C2

1

R1R2C1C2

1

1

=

The bass-boost module includes the above positive-feedback second-order high-pass filter.

In the above figure, when R1 = 1.2 k

Ω, R2 = 470 kΩ, and C1 = C2 = 0.1 µF (K = +1),

Fo = 70 Hz (f0 =

ωo/2π), Q = 10.