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參數(shù)資料
| 型號(hào)： | MC34118DW |
| 廠商： | Freescale Semiconductor |
| 文件頁數(shù)： | 9/22頁 |
| 文件大小： | 0K |
| 描述： | IC VOICE SWITCH SPKPHONE 28-SOIC |
| 標(biāo)準(zhǔn)包裝： | 26 |
| 功能： | 語音切換式揚(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)檢測器，驅(qū)動(dòng)器放大器，電平檢測器，麥克風(fēng)放大器，靜音 |
MC34118
MOTOROLA
17
where the terms in the brackets are the V/V gain terms. The
speaker amplifier gain is divided by two since GSA is the dif-
ferential gain of the amplifier, and V3 is obtained from one
side of that output. The current I1, coming from the micro-
phone circuit, is defined by:
(Equation 5)
I1 =
VM xGMA
R1
where VM is the microphone voltage. Since the switching
threshold occurs when I1 =I3, combining the above two
equations yields:
(Equation 6)
VM = VLx
R1
R3
GHRxGFOxGRXxGSA
GMA x2
This is the general equation defining the microphone voltage
necessary to switch comparator C1 when a receive signal VL
is present. The highest VM occurs when the receive attenua-
tor is at maximum gain (+ 6.0 dB). Using the typical numbers
for Equation 6 yields:
(Equation 7)
VM =0.52 VL
To switch comparator C2, currents I2 and I4 need to be de-
termined. With sound applied to the microphone, a voltage
VM is created by the microphone, resulting in a current I2 into
TLI1:
(Equation 8)
I2 =
VM
R2
G
MA xGTX x
GHA
2
Since GHA is the differential gain of the hybrid amplifiers, it is
divided by two to obtain the voltage V2 applied to R2.
Comparator C2 switches when I4 =I2.I4 is defined by:
(Equation 9)
I4 =
VL
R4
GHR xGFO
Setting I4 =I2, and combining the above equations results in:
(Equation 10)
VL = VM x
R4
R2
GMA xGTX xGHA
GHR xGFO x2
This equation defines the line voltage at Tip/Ring necessary
to switch comparator C2 in the presence of a microphone
voltage. The highest VL occurs when the circuit is in the
transmit mode (GTX = + 6.0 dB). Using the typical numbers
for Equation 10 yields:
(Equation 11)
VL = 840 VM (or VM = 0.0019 VL)
At idle, where the gain of the two attenuators is -- 20 dB
(0.1 V/V), Equations 6 and 10 yield the same result:
(Equation 12)
VM = 0.024 VL
Equations 7, 11, and 12 define the thresholds for switching,
and are represented in the following graph:
Figure 25. Switching Thresholds
VM
MRX
MI
MTX
VL
The “M” terms are the slopes of the lines (0.52, 0.024, and
0.0019) which are the coefficients of the three equations. The
MRX line represents the receive to transmit threshold in that it
defines the microphone signal level necessary to switch to
transmit in the presence of a given receive signal level. The
MTX line represents the transmit to receive threshold. The MI
line represents the idle condition, and defines the threshold
come noise on the other.
Some comments on the above graph:
— Acoustic coupling and sidetone coupling were not in-
cluded in Equations 7 and 12. Those couplings will affect the
actual performance of the final speakerphone due to their in-
teraction with speech at the microphone, and the receive sig-
nal coming in at Tip/Ring. The effects of those couplings are
difficult to predict due to their associated phase shifts and
frequency response. In some cases the coupling signal will
add, and other times subtract from the incoming signal. The
physical design of the speakerphone enclosure, as well as
the specific phone line to which it is connected, will affect the
acoustic and sidetone couplings, respectively.
—The MRX line helps define the maximum acoustic cou-
pling allowed in a system, which can be found from the fol-
lowing equation:
(Equation 13)
GAC–MAX =
R1
2xR3 x GMA
Equation 13 is independent of the volume control setting.
Conversely, the acoustic coupling of a designed system
helps determine the minimum slope of that line. Using the
component values of Figure 23 in Equation 13 yields a
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