MC34118DW Freescale Semiconductor, MC34118DW Datasheet - Page 9

• 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: -

(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.
AGC
mode, and only when the supply voltage (V
3.5 volts. As V
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.
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
V
ATTENUATOR CONTROL BLOCK
scribed above:
— The output of the comparator operated by RLO2 and
— The output of the comparator operated by RLO1 and
— The output of the transmit background noise monitor —
— The output of the receive background noise monitor —
— 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:
MOTOROLA
CC
The AGC circuit affects the circuit only in the receive
The purpose of this feature is to reduce the power (and
The Attenuator Control Block has the seven inputs de-
X = Don’t Care; y = C3 and C4 are not both 0.
TLO2 (microphone/speaker side) — designated C1.
TLO1 (Tip/Ring side) — designated C2.
designated C3.
designated C4.
is controlled, preventing possible erratic operation.
C1
Rx
Rx
Rx
Rx
Tx
Tx
Tx
Tx
RXI
CC
Figure 5. Dial Tone Detector
V
C2
Rx
Rx
Rx
Rx
Tx
Tx
Tx
Tx
B
falls below 3.5 volts, the gain of the receive
Inputs
15 mV
TO Rx
ATTENUATOR
--
+
C3
X
X
1
y
y
0
0
0
C4
C4
X
1
X
0
0
0
y
y
TO
ATTENUATOR
CONTROL
BLOCK
Slow Idle
Slow Idle
Slow Idle
Slow Idle
Transmit
Fast Idle
Fast Idle
CC
Receive
Output
Output
Mode
) is less than
A definition of the above terms:
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.
detectors sense higher signal levels relative to the respective
transmit level detectors, and b) the receive background noise
monitor indicates the presence of speech.
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.
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.
receive, fast idle and slow idle is determined in part by the
components at the C
Switching Times for a more complete explanation of the
switching time components.) A schematic of the C
is shown in Figure 6, and operates as follows:
— R
— To switch to the receive mode, I
— To switch to the transmit mode, I
A summary of the truth table is as follows:
1) The circuit will switch to transmit if: a) both transmit
2) The circuit will switch to receive if: a) both receive level
3) The circuit will switch to the fast idle mode if the level
4) The circuit will switch to the slow idle mode when
The time required to switch the circuit between transmit,
1) “Transmit” means the transmit attenuator is fully on (+ 6.0 dB),
2) “Receive” means both attenuators are controlled by the volume
3) “Fast Idle” means both transmit and receive speech are present
4) “Slow Idle” means speech has ceased in both transmit and re-
5) Switching to the full transmit or receive modes from any other
charging the external capacitor to + 240 mV above V
(An internal clamp prevents further charging of the ca-
pacitor.)
bringing down the voltage on the capacitor to -- 240 mV
with respect to V
and the receive attenuator is at max. attenuation (-- 46 dB).
control. At max. volume, the receive attenuator is fully on
(+ 6.0 dB), and the transmit attenuator is at max. attenuation
(-- 46 dB).
in approximately equal levels. The attenuators are quickly
switched (30 ms) to idle until one speech level dominates the
other.
ceive paths. The attenuators are then slowly switched (1 se-
cond) to the idle mode.
mode is at the fast rate (≈30 ms).
T
is typically 120 kΩ, and C
B
.
T
pin (Pin 14). (See the section on
T
is typically 5.0 µF.
1
2
is turned on (I
is turned on (I
MC34118
T
2
circuitry
1
is off),
is off)
B
9
.