MC34118DW Freescale Semiconductor, MC34118DW Datasheet - Page 17

• Manufacturer Part Number: MC34118DW
• Description: IC VOICE SWITCH SPKPHONE 28-SOIC
• Manufacturer: Freescale Semiconductor

Specifications of MC34118DW

• Function: Voice-Switched Speakerphone
• Number Of Circuits: 1
• Voltage - Supply: 3.5 V ~ 6.5 V
• Current - Supply: 5.5mA
• Operating Temperature: -20°C ~ 60°C
• Mounting Type: Surface Mount
• Package / Case: *
• Includes: Background Noise Monitor, Chip Disable, Dial Tone Detector, Driver Amplifiers, Level Detectors, Microphone Amplifier, MUTE
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power (watts): -
• Interface: -

where the terms in the brackets are the V/V gain terms. The
speaker amplifier gain is divided by two since G
ferential gain of the amplifier, and V
side of that output. The current I
phone circuit, is defined by:
where V
threshold occurs when I
equations yields:
This is the general equation defining the microphone voltage
necessary to switch comparator C1 when a receive signal V
is present. The highest V
tor is at maximum gain (+ 6.0 dB). Using the typical numbers
for Equation 6 yields:
termined. With sound applied to the microphone, a voltage
V
TLI1:
Since G
divided by two to obtain the voltage V
Comparator C2 switches when I
Setting I
This equation defines the line voltage at Tip/Ring necessary
to switch comparator C2 in the presence of a microphone
voltage. The highest V
transmit mode (G
for Equation 10 yields:
(0.1 V/V), Equations 6 and 10 yield the same result:
MOTOROLA
V
V
V
V
M
I 1 =
I 2 =
I 4 =
V
M
To switch comparator C2, currents I
L
At idle, where the gain of the two attenuators is -- 20 dB
M
M
L
is created by the microphone, resulting in a current I
= 840 V
= 0.52 V
= 0.024 V
= V
= V
V
V
V
R4
R2
HA
4
M
M
M
L
L
M
= I
x R1
is the differential gain of the hybrid amplifiers, it is

x G
R1
is the microphone voltage. Since the switching

M
G
x R4
2
L
R3
G
, and combining the above equations results in:
HR
R2
L
MA
MA
(or V

x G
TX
G

x G
G
HR

M
G
= + 6.0 dB). Using the typical numbers
MA
FO
= 0.0019 V
TX
HR
x G
L

M
x G
1
occurs when the circuit is in the
G
x
FO
x G
occurs when the receive attenua-
= I
MA
G
TX
x G
HA
2
FO
3
, combining the above two
4
x 2
x G
RX

1
= I
L
x 2
)
, coming from the micro-
HA
2
x G
3

. I
2
is obtained from one

and I
4
SA
is defined by:
2

4
applied to R2.
need to be de-
(Equation 10)
(Equation 12)
(Equation 11)
(Equation 5)
(Equation 6)
(Equation 7)
(Equation 8)
(Equation 9)
SA
is the dif-
2
into
L
Equations 7, 11, and 12 define the thresholds for switching,
and are represented in the following graph:
0.0019) which are the coefficients of the three equations. The
M
defines the microphone signal level necessary to switch to
transmit in the presence of a given receive signal level. The
M
line represents the idle condition, and defines the threshold
level on one side (transmit or receive) necessary to over-
come noise on the other.
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.
pling allowed in a system, which can be found from the fol-
lowing equation:
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
G
RX
TX
The “M” terms are the slopes of the lines (0.52, 0.024, and
Some comments on the above graph:
— Acoustic coupling and sidetone coupling were not in-
— The M
V
AC–MAX
M
line represents the transmit to receive threshold. The M
line represents the receive to transmit threshold in that it
RX
Figure 25. Switching Thresholds
=
line helps define the maximum acoustic cou-
2 x R3 x G
M
RX
R1
MA
M
I
M
TX
(Equation 13)
MC34118
V
L
17
I