MC34118DWR2 Freescale Semiconductor, MC34118DWR2 Datasheet - Page 16

• Manufacturer Part Number: MC34118DWR2
• Description: IC VOICE SWITCH SPKPHONE 28-SOIC
• Manufacturer: Freescale Semiconductor

Specifications of MC34118DWR2

• 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: -
• Other names: MC34118DWTR

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
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:
where R
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.
input was measured at 0.833 V/V (-- 1.6 dB), the filter’s gain
MC34118
16
COUPLING
P
ACOUSTIC
The overall receive gain depends on the incoming signal
Referring to Figure 23, the gain from Tip/Ring to the filter
SPK
S
= 10
is the speaker impedance, and the dBm term is the
(G
dBm∕10 x 0.6
AC
V
)
M
R
S
RLI2
TLI2
I
MIKE
AMP
I
3
1
SPEAKER
R3
V
R1
V
AMP.
1
3
+
+
--
--
Figure 24. Basic Block Diagram for Design Purposes
(Equation 1)
C1
RXO
TXI
Tx ATTENUATOR
Rx ATTENUATOR
CONTROL
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
zero dB to obtain a stable circuit. This can be expressed as:
G
+ G
Using the typical numbers mentioned above, and knowing
that G
be determined:
G
+ 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
determined. Referring to Figure 24, with a receive signal V
applied to Tip/Ring, a current I
according to the following equation:
MA
AC
I 3 =
The total loop gain (of Figure 24) must add up to less than
To switch comparator C1, currents I
SA
TXO
RXI
< -- [31 + 20.1 + (-- 15) + 0 + (-- 40)
+ G
TX
+ G
V
R3
C2
TX
+ G
L
AC

+ G
RX
G
< 0
H
HA
= -- 40 dB, the required acoustic coupling can
R
+ G
x G
ST
FO
+ G
x G
FO
HYBRID
R4
3
+
RX
--
+
--
AMP
V
will flow through R3 into RLI2
4
+ G
R2
FILTER
x
RLI1
RX
G
G
I
TLI1
V
ST
4
SA
2
2
I
2
1

and I
HYBRID
G
G
MOTOROLA
HT
HR
3
(Equation 2)
(Equation 3)
(Equation 4)
need to be
TIP
RING
L