U4080B Datasheet, PDF (10/15 Pages) TEMIC Semiconductors – Voice-Switched Circuit for Handsfree Operation

U4080B
Input Signal MIC
[ ^{CP 2 ( Pin 12 )}
DV₁ 200 mV
+ ^ǒ[ ń ^{Ǔ dV 10 mA}
dt
C
2 V sec
2.7 x DV₁
[ Slope 0.5 V / sec
CP 1 ( Pin 11 )
Non inverting
input of transmit
36 mV _{detector comp}
TDO ( Pin 23 ) 4 V
94 7828 e
t
Figure 11. Transmit detector operation
Microphone Amplifier
The microphone amplifier is non-inverting, has an inter-
x ^{nal gain of 34 dB and a nominal input impedance of}
10 kΩ. The output impedance is typically 15 Ω. The
maximum voltage swing available is approximately 2 V
less than V_CC, which is substantially more than what is
required in most applications. The input at Pin 9 (MIC)
should be ac coupled to the microphone so as not to upset
the bias voltage. Generally, microphone sensitivity may
be adjusted by varying the two microphone bias resistors
rather than an attempting to vary the gain of the amplifier.
Power Supply (V+)
The voltage for the supply at Pin 16 should be in the range
of 6.0 to 11V, although the circuit will operate down to
4.0 V. The voltage can be supplied either from Tip and
Ring or from a separate supply. The required supply cur-
rent, with no signal to the speaker, is shown in figure 12
The upper curve indicates the normal operating current
when Chip Select (Pin 18) is a logic O. Figure 13 indicates
the average dc current required when supplying various
power levels to a 25 Ω speaker. Figure 13 also shows the
minimum supply voltage required to provide the indi-
cated power levels. The peak in the power supply current
at 5.0 to 5.4 V occurs as the V_CC circuit comes into regula-
tion.
For stability reasons, supply should be grounded properly
against ac noise. If this pin is not well filtered (by a
1000 µF capacitor), any variation at V+ caused by the re-
quired speaker current flowing through this pin can cause
a low frequency oscillation. The result is usually that the
circuit will cut the speaker signal on and off at the rate of
a few hertz. Experiments have shown that only a few in-
ches of wire between the supply and the IC can cause the
problem if the filter capacitor is not physically adjacent
to the IC. It is equally imperative that both ground pins
(Pins 14 and 22) have a loss connection to the power
supply ground.
8
CS = 0
6
4
Select input
T_amb = 25 °C
2
0
4
94 7877 e
CS = 1
6
8
10
12
V₁₆ ( V )
Figure 12.
10 (15)
TELEFUNKEN Semiconductors
Preliminary Information
Rev. A1, 20-May-96