參數(shù)資料
型號(hào)： MC34118DW
廠商： Freescale Semiconductor
文件頁(yè)數(shù)： 22/22頁(yè)
文件大?。?/td> 0K
描述： IC VOICE SWITCH SPKPHONE 28-SOIC
標(biāo)準(zhǔn)包裝： 26
功能： 語(yǔ)音切換式揚(yáng)聲電話
電路數(shù)： 1
電源電壓： 3.5 V ~ 6.5 V
電流 - 電源： 5.5mA
工作溫度： -20°C ~ 60°C
安裝類型： 表面貼裝
封裝/外殼： 28-SOIC（0.295"，7.50mm 寬）
供應(yīng)商設(shè)備封裝： 28-SOIC W
包裝： 管件
包括： 背景噪聲監(jiān)視器，芯片禁用，撥號(hào)音調(diào)檢測(cè)器，驅(qū)動(dòng)器放大器，電平檢測(cè)器，麥克風(fēng)放大器，靜音
MC34118
MOTOROLA
9
(which would be considered as continuous noise) from fad-
ing away as the circuit would have the tendency to switch to
the idle mode. By disabling the receive idle mode, the dial
tone remains at the normally expected full level.
Figure 5. Dial Tone Detector
TO
ATTENUATOR
CONTROL
BLOCK
TO Rx
ATTENUATOR
15 mV
C4
RXI
VB
+
--
AGC
The AGC circuit affects the circuit only in the receive
mode, and only when the supply voltage (VCC) is less than
3.5 volts. As VCC falls below 3.5 volts, the gain of the receive
attenuator is reduced according to the graph of Figure 15.
The transmit path attenuation changes such that the sum of
the transmit and receive gains remains constant.
The purpose of this feature is to reduce the power (and
current) used by the speaker when a line--powered speaker-
phone is connected to a long line, where the available power
is limited. By reducing the speaker power, the voltage sag at
VCC is controlled, preventing possible erratic operation.
ATTENUATOR CONTROL BLOCK
The Attenuator Control Block has the seven inputs de-
scribed above:
— The output of the comparator operated by RLO2 and
TLO2 (microphone/speaker side) — designated C1.
— The output of the comparator operated by RLO1 and
TLO1 (Tip/Ring side) — designated C2.
— The output of the transmit background noise monitor —
designated C3.
— The output of the receive background noise monitor —
designated C4.
— The volume control.
— The dial tone detector.
— The AGC circuit.
The single output of the Control Block controls the two atten-
uators. The effect of C1 -- C4 is as follows:
Inputs
Output
C1
C2
C3
C4
Output
Mode
Tx
Rx
Tx
Rx
Tx
Rx
Tx
Rx
Tx
Rx
Tx
Rx
1
y
X
0
X
y
1
X
0
Transmit
Fast Idle
Receive
Slow Idle
X = Don’t Care; y = C3 and C4 are not both 0.
A definition of the above terms:
1) “Transmit” means the transmit attenuator is fully on (+ 6.0 dB),
and the receive attenuator is at max. attenuation (-- 46 dB).
2) “Receive” means both attenuators are controlled by the volume
control. At max. volume, the receive attenuator is fully on
(+ 6.0 dB), and the transmit attenuator is at max. attenuation
(-- 46 dB).
3) “Fast Idle” means both transmit and receive speech are present
in approximately equal levels. The attenuators are quickly
switched (30 ms) to idle until one speech level dominates the
other.
4) “Slow Idle” means speech has ceased in both transmit and re-
ceive paths. The attenuators are then slowly switched (1 se-
cond) to the idle mode.
5) Switching to the full transmit or receive modes from any other
mode is at the fast rate (≈30 ms).
A summary of the truth table is as follows:
1) The circuit will switch to transmit if: a) both transmit
level detectors sense higher signal levels relative to the re-
spective receive level detectors (TLI1 versus RLI1, TLI2
versus RLI2), and b) the transmit background noise monitor
indicates the presence of speech.
2) The circuit will switch to receive if: a) both receive level
detectors sense higher signal levels relative to the respective
transmit level detectors, and b) the receive background noise
monitor indicates the presence of speech.
3) The circuit will switch to the fast idle mode if the level
detectors disagree on the relative strengths of the signal lev-
els, and at least one of the background noise monitors indi-
cates speech. For example, referring to the Block Diagram
(Figure 2), if there is sufficient signal at the microphone amp
output (TLI2) and there is sufficient signal at the receive input
(RLI1) to override the signal at the hybrid output (TLI1), and
either or both background monitors indicate speech, then the
circuit will be in the fast idle mode. Two conditions which can
cause the fast idle mode to occur are a) when both talkers
are attempting to gain control of the system by talking at the
same time, and b) when one talker is in a very noisy environ-
ment, forcing the other talker to continually override that
noise level. In general, the fast idle mode will occur infre-
quently.
4) The circuit will switch to the slow idle mode when
a) both talkers are quiet (no speech present), or b) when one
talker’s speech level is continuously overriden by noise at
the other speaker’s location.
The time required to switch the circuit between transmit,
receive, fast idle and slow idle is determined in part by the
components at the CT pin (Pin 14). (See the section on
Switching Times for a more complete explanation of the
switching time components.) A schematic of the CT circuitry
is shown in Figure 6, and operates as follows:
—RT is typically 120 k, and CT is typically 5.0 F.
— To switch to the receive mode, I1 is turned on (I2 is off),
charging the external capacitor to + 240 mV above VB.
(An internal clamp prevents further charging of the ca-
pacitor.)
— To switch to the transmit mode, I2 is turned on (I1 is off)
bringing down the voltage on the capacitor to -- 240 mV
with respect to VB.
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