7

Multimedia ICs

BA7725S / BA7725FS

10

5

– 100

–50

0

Secondary echo

Sound source

Primary echo

0

LOOP GAIN CTRL pin voltage : (V)

Line output attenuation vs.

loop gain control pin voltage

Fig.7

0

– 50

– 100

05

10

Primary echo

Sound source

ECHO LEVEL CTRL pin voltage : (V)

Line output attenuation vs.

echo level control pin voltage

Fig.6

(2) LINE IN / LINE OUT gain

Line amplifier gain is fixed at +18dB.

+

+

+12dB

Fig.5

2

1

21

22

MIC AMP IN

R9

R10

SW

LINE OUT

LINE IN

After being amplified by the internal microphone amplifier, the audio signal is log-

arithmically compressed by 1 / 2 then input to the tertiary low pass filter, which

comprises an internal BF and attached capacitor and resistor.

(3) Echo level control

The DC voltage supplied to pin 4 (BA7725S) or pin 3 (BA7725FS) determines

when the microphone switch is turned on and off and controls the echo level.

Line input and level-controlled microphone input are mixed and output.

Mode

Threshold voltage

Operation

L (1.0V Max.)

Only line audio is output.

MIC OFF

H (2.0V Min.)

MIC ON

Microphone switch control

Echo level control

Attenuation of the primary echo signals from sound

source can be controlled by changing the DC voltage

impressed on pin 4 (BA7725S) or pin 3 (BA7725FS)

between 2V and 9V.

Attenuation of primary echo signals can be controlled

by changing the DC voltage impressed on pin 6

(BA7725S) or pin 5 (BA7725FS) .