MSM7731-02 OKI [OKI electronic componets], MSM7731-02 Datasheet - Page 45

• Manufacturer Part Number: MSM7731-02
• Description: Dual Echo Canceler & Noise Canceler with Dual Codec for Hands-Free
• Manufacturer: OKI [OKI electronic componets]

GAIN ADJUSTMENT OF EXTERNAL SPEAKER AMPLIFIER
The overflow (clipping) of speaker amplifier output occurred in the echo path between the echo canceler output
(e.g. AVFRO) and the echo canceler input (e.g. AGSX) decreases the echo attenuation remarkably. In other words,
when an external speaker amplifier is used, do gain adjusting without overflow of speaker amplifier output.
Adjusting Method 1
Be careful of the following.
Adjusting Method 2
The speaker amplifier output can be adjusted appropriately by making the echo canceler input signal clipped
intentionally when the speaker amplifier output is small.
The following shows the circuit diagram.
1 Semiconductor
1. Echo canceler output pin (AVFRO/LVFRO)
2. External speaker amplifier output pin
1. External speaker amplifier gain
2. Speaker output adjustment
Adjust the AGSX/LGSX gain or RPAD/TPAD so as to set the output level to less than 1.3 V
level = -20 dBm0).
external speaker amplifier determine the speaker amplifier gain.
Adjust the gain so as to set the output level to less than the maximum output
The analog maximum output amplitude of the MSM7731 and the maximum output amplitude of
(Example)
Adjust the volume with the echo canceler input (RPAD).
RPAD
Canceler
MSM7731
Echo
AVFRO maximum output amplitude = 1.3 V
Gain of APWI and AOUT = 1
Maximum output amplitude of external speaker amplifier = 10 V
External speaker amplifier gain
= speaker amplifier maximum output amplitude/AVFRO maximum output
= 10/1.3
= less than 7.6
amplitude
CODEC
AVFRO
AOUT
APWI
20 k
20 k
C
10 k
pp
68 k
–
+
Amplifier
Speaker
amplitude.
FEDL7731-02-04
pp
MSM7731-02
Speaker
pp
(typical
45/53