MC34118DW Freescale Semiconductor, MC34118DW Datasheet - Page 18

• 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: -

G
an acoustic coupling loss of > 40 dB is desirable.
pling (G
the following equation:
Using the component values of Figure 23 in Equation 14
yields a maximum sidetone of 0 dB. Experience has shown,
however, that a minimum of 6.0 dB loss is preferable.
tor values for the level detector inputs. Equation 6 can be
used to determine the R1/R3 ratio, and Equation 10 can be
used to determine the R4/R2 ratio. In Figure 24, R1 -- R4
each represent the combined impedance of the resistor and
coupling capacitor at each level detector input. The magni-
tude of each RC’s impedance should be kept within the
range of 2.0 k -- 15 kΩ in the voiceband (due to the typical
signal levels present) to obtain the best performance from
the level detectors. The specific R and C at each location will
determine the frequency response of that level detector.
DIAL TONE DETECTOR
15 mV (10 mVrms) below V
can be reduced by connecting a resistor from RXI to ground.
The resistor value is calculated from:
where V
threshold reduction. By connecting a resistor from V
RXI, the threshold can be increased. The resistor value is
calculated from:
where ∆V is the amount of the threshold increase.
BACKGROUND NOISE MONITORS
ceive attenuators can be set to the “on” position, by disabling
the background noise monitors, and applying a signal so as
to activate the level detectors. Grounding the CPR pin will
disable the receive background noise monitor, thereby indi-
cating the “presence of speech” to the attenuator control
block. Grounding CPT does the same for the transmit path.
matically disabled by the dial tone detector whenever the re-
ceive signal exceeds the detector’s threshold.
TRANSMIT/RECEIVE DETECTION PRIORITY
such that the attenuators are halfway between their full on
and full off positions, the idle mode can be biased towards
the transmit or the receive side. With this done, gaining con-
MC34118
18
G
R = 10 k
R = 10 k
AC--MAX
— The M
The above equations can be used to determine the resis-
The threshold for the dial tone detector is internally set at
For testing or circuit analysis purposes, the transmit or re-
Additionally, the receive background noise monitor is auto-
Although the MC34118 was designed to have an idle mode
ST
=
ST
B
of -- 37 dB. Experience has shown, however, that
2 x R2 x G
) allowed in the system, which can be found from
is the voltage at Pin 15, and ∆V is the amount of
TX


APPLICATION INFORMATION
V
∆V
V
line helps define the maximum sidetone cou-
B
CC
R4
∆V
– 1
– V

FO
B
– 1

B
(see Figure 5). That threshold
(Equation 14)
CC
to
trol of the circuit from idle will be easier for that side towards
which it is biased since that path will have less attenuation at
idle.
circuit will be biased towards the transmit side. The resistor
value is calculated from:
where R is the added resistor, R
tween Pins 14 and 15 (typically 120 kΩ), and ∆V is the differ-
ence between V
Figure 10).
cuit will be biased towards the receive side. The resistor val-
ue is calculated from:
R, R
somewhat affected in each case due to the different voltage
excursions required to get to transmit and receive from idle.
For practical considerations, the ∆V shift should not exceed
100 mV.
VOLUME CONTROL
the volume control, the graph of Figure 14 indicates that the
receive gain will not vary in a linear manner with respect to
the pot’s position. In situations where this may be objection-
able, a potentiometer with an audio taper (commonly used in
radio volume controls) will provide a more linear relationship
as indicated in Figure 26. The slight non--linearity at each
end of the graph is due to the physical construction of the
potentiometer, and will vary among different manufacturers.
APPLICATION CIRCUIT
used in parallel with any other telephone which contains the
R = R
R = R
By connecting a resistor from C
By connecting a resistor from C
If a potentiometer with a standard linear taper is used for
The circuit of Figure 23 is a basic speakerphone, to be
-- 40
+10
--10
--20
--30
T
, and ∆V are the same as above. Switching time will be
0
0
Figure 26. Receive Attenuator Gain versus
Potentiometer Position Using Audio Taper
T
T


V
∆V
V
40
B
CC
∆V
– 1
B
– V

80
and the voltage at C
B
DEGREES OF ROTATION
– 1
120

160
T
is the resistor normally be-
T
T
(Pin 14) to V
(Pin 14) to ground, the
200
T
at idle (refer to
240
MOTOROLA
CC
280
, the cir-
320