ZL38001
Data Sheet
1.8 AGC
The AGC function is provided to limit the volume in the speaker path. The gain of the speaker path is automatically
reduced during the following conditions:
•
•
•
•
When clipping of the receive signal occurs
When initial convergence of the acoustic echo canceller detects unusually large echo return
When howling is detected
The AGC can be disabled by setting the AGC- bit to 1 in MC control register
1.9 18 dB Gain Pad at Sout
The purpose of the 18 dB gain pad is to improve the subjective quality in low ERL environments. The ZL38001 can
cancel echo with a ERL as low as 0 dB (attenuation from Rout to Sin). In many hand free applications, the ERL can
be low (or negative). This is due to both speaker and microphone gain setting. The speaker gain has to be set high
enough for the speaker to be heard properly and the microphone gain needs to be set high enough to ensure
sufficient signal is sent to the far end. If the ERL (Acoustic Attenuation - speaker gain - microphone gain) is greater
than 0 dB, then the echo canceller cannot cancel echo. To overcome this limitation, the ZL38001 has a 18 dB gain
pad at Sout. The microphone gain can be reduced by 18 dB to allow either the speaker gain and/or the acoustic
coupling to be increased by a total of 18 dB allowing more flexibility in the design.
1.10 Mute Function
A pcm mute function is provided for independent control of the Receive and Send audio paths. Setting the MUTE_R
or MUTE_S bit in the MC register, causes quiet code to be transmitted on the Rout or Sout paths respectively.
Quiet code is defined according to the following table.
LINEAR
16 bits
SIGN/
MAGNITUDE
µ-Law
CCITT (G.711)
µ-Law
A-Law
2’s complement
A-Law
+Zero
0000h
80h
FFh
D5h
(quiet code)
Table 1 - Quiet PCM Code Assignment
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Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
