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參數(shù)資料
| 型號： | MT92303 |
| 廠商： | Mitel Networks Corporation |
| 元件分類： | Codec |
| 英文描述： | 3.3V Quad Interface, Dual Codec(3.3V 四接口雙編解碼器（提供音頻到PCM的接口）) |
| 中文描述： | 3.3四種接口，雙編解碼器（3.3四接口雙編解碼器（提供音頻到的PCM的接口）） |
| 文件頁數(shù)： | 8/34頁 |
| 文件大?。?/td> | 166K |
| 代理商： | MT92303 |
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MT92303
Preliminary Information
8
Microphone Presence Detect
When an electret microphone is connected as shown
in Figures 8 and 9, it draws a bias current from the
MICBIAS pin. The voltage across the ‘bottom’ bias
resistor is monitored by the MICDETECT input and is
used to set a ‘presence’ flag in the MT92303’s Status
Register. This allows the external controller to
determine whether or not the handset and headset
are plugged-in. The internal workings of the
MT92303 are not affected by the state of the
‘presence’ flag.
Figure 9 - Mic Presence and Mute Detect
Microphone Mute Detect
Any of the 4 Microphone inputs can be ‘muted’ under
direct software control via the ‘Mode Control’
register.
In addition, the MICDETECT inputs may also be
used to mute the microphone paths of the 2
associated
Audio
Interfaces.
instantaneous blanking of the microphone path, and
consequently the sidetone path, and allows the ‘pop’
associated with electret muting to be avoided.
This
allows
As shown in Figure 9, the internal ‘Mic Mute Detect’
signal is activated whenever the voltage across the
‘bottom’ bias resistor (R2) exceeds 40% of the
MICBIAS voltage. A small amount of hysteresis is
implemented such that the voltage needs to fall
below 35% of the MICBIAS voltage before the
internal ‘Mic Mute Detect’ signal is deactivated.
In addition to internally muting the microphone
channel, the ‘Mic Mute Detect’ signal is passed to the
MT92303’s Status Register.
The behaviour of the mute function can be
programmed to operate in four different ways.
It is important to note that in the third mode
(MUTEMODE=10) described in table 2, it is the
designer’s responsibility to re-enable the microphone
path after it has been muted by the MICDETECT pin.
This allows the designer to re-establish the signal
path after a time sufficient for the settling of any
microphone bias circuitry.
The on-chip ‘Status’ register provides access to the
internal ‘Mic Mute Detect’ signal, and also the
acknowledged version ‘Mute’ which denotes whether
or not the microphone channel is actually muted.
These two bits of information are expected to be
used by the external controller to determine when
the channel needs to be re-enabled. This will be
when ‘Mute’ is high, and ‘Mic Mute Detect’ has fallen
low, but the external controller may introduce a delay
before re-establishing the microphone path. The path
should be re-enabled by momentarily switching to
MUTEMODE=00.
Bandgap Voltage Reference
The MT92303 has its own internal bandgap voltage
reference which determines the absolute gains of the
TX & RX paths. The bandgap voltage is brought out
to the VREF pin for external decoupling with a
capacitor (100nF to GNDA) that should be located as
MICBIAS
0 to 2.52V
in 15 steps
GND
40%
35%
4%
3%
Mic
Presence
Detect
Mic
Mute
Detect
MICDETECT
R1
R2
MUTE
MODE
Mute Operation (see Figure 9)
00
Microphone path enabled (normal
operation). ‘Mic Mute Detect’ signal
ignored.
01
Microphone path disabled (muted) while
‘Mic Mute Detect’ signal is high, and
enabled while low.
10
Microphone path disabled (muted) while
‘Mic Mute Detect’ signal is high,
but must
be re-enabled by the external
controller
.
11
Microphone path disabled (muted). ‘Mic
Mute Detect’ signal ignored.
Table 2. Microphone Mute Detection
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