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参数资料
| 型号： | MC34118DW |
| 厂商： | Freescale Semiconductor |
| 文件页数： | 8/22页 |
| 文件大小： | 0K |
| 描述： | IC VOICE SWITCH SPKPHONE 28-SOIC |
| 标准包装： | 26 |
| 功能： | 语音切换式扬声电话 |
| 电路数： | 1 |
| 电源电压： | 3.5 V ~ 6.5 V |
| 电流 - 电源： | 5.5mA |
| 工作温度： | -20°C ~ 60°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.295"，7.50mm 宽） |
| 供应商设备封装： | 28-SOIC W |
| 包装： | 管件 |
| 包括： | 背景噪声监视器，芯片禁用，拨号音调检测器，驱动器放大器，电平检测器，麦克风放大器，静音 |
MC34118
MOTOROLA
16
TIP
(GAC)
ACOUSTIC
COUPLING
+
--
+
--
+
Tx ATTENUATOR
HYBRID
AMP
TXI
TXO
VM
MIKE
AMP
I1
V1
R1
TLI2
RLI2
I3
V3
CONTROL
V2
R2
I2
RLI1
HYBRID
GST
GHT
GHR
I4
V4
FILTER
R4
TLI1
Figure 24. Basic Block Diagram for Design Purposes
C1
R3
Rx ATTENUATOR
RXO
RXI
C2
SPEAKER
AMP.
RING
amplified as soon as possible to minimize signal/noise prob-
lems; 2) to provide a reasonable signal level to the TLI2 level
detector; and 3) to minimize any gain applied to broadband
noise generated within the attenuator. However, to cover the
normal voiceband, the microphone amplifier’s gain should
not exceed 48 dB (see Figure 16). For the circuit of Fig-
ure 23, the gain of the microphone amplifier was set at
35 V/V (31 dB), and the differential gain of the hybrid amplifi-
ers was set at 10.2 V/V (20.1 dB).
II) Receive Gain
The overall receive gain depends on the incoming signal
level, and the desired output power at the speaker. Nominal
receive levels (independent of the peaks) at Tip/Ring can be
35 mVrms (-- 27 dBm), although on long lines that level can
be down to 8.0 mVrms (-- 40 dBm). The speaker power is:
PSPK =
10dBm∕10 x0.6
RS
(Equation 1)
where RS is the speaker impedance, and the dBm term is the
incoming signal level increased by the gain of the receive
path. Experience has shown that ≈30 dB gain is a satisfac-
tory amount for the majority of applications. Using the above
numbers and Equation 1, it would appear that the resulting
power to the speaker is extremely low. However, Equation 1
does not consider the peaks in normal speech, which can be
10 to 15 times the rms value. Considering the peaks, the
overall average power approaches 20 -- 30 mW on long
lines, and much more on short lines.
Referring to Figure 23, the gain from Tip/Ring to the filter
input was measured at 0.833 V/V (-- 1.6 dB), the filter’s gain
is unity, and the receive attenuator’s gain is 2.0 V/V
(+ 6.0 dB) at maximum volume. The speaker amplifier’s gain
is set at 22 V/V (26.8 dB), which puts the overall gain at
≈31.2 dB.
III) Loop Gain
The total loop gain (of Figure 24) must add up to less than
zero dB to obtain a stable circuit. This can be expressed as:
(Equation 2)
GMA +GTX +GHA +GST +GFO +GRX
+GSA +GAC < 0
Using the typical numbers mentioned above, and knowing
that GTX +GRX = -- 40 dB, the required acoustic coupling can
be determined:
(Equation 3)
GAC < -- [31 + 20.1 + (-- 15) + 0 + (-- 40)
+ 26.8] = -- 22.9 dB.
An acoustic loss of at least 23 dB is necessary to prevent in-
stability and oscillations, commonly referred to as “singing.”
However, the following equations show that greater acoustic
loss is necessary to obtain proper level detection and switch-
ing.
IV) Switching Thresholds
To switch comparator C1, currents I1 and I3 need to be
determined. Referring to Figure 24, with a receive signal VL
applied to Tip/Ring, a current I3 will flow through R3 into RLI2
according to the following equation:
I3 =
VL
R3
G
H
R xGFO xGRX x
GSA
2
(Equation4)
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相关代理商/技术参数 |
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| MC34118-E28-T | 制造商:UTC-IC 制造商全称:UTC-IC 功能描述:VOICE SWITCHED SPEAKER-PHONE CIRCUIT |
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