TEA1064A View Datasheet(PDF) - Philips Electronics
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TEA1064A Datasheet PDF : 36 Pages
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Philips Semiconductors
Low voltage versatile telephone transmission circuit
with dialler interface and transmit level dynamic limiting
Product specification
TEA1064A
Microphone inputs MIC+ and MIC− and gain pins
GAS1 and GAS2
The TEA1064A has symmetrical microphone inputs, its
input impedance is 64 kΩ (2 × 32 kΩ) and its voltage
amplification is typ. 52 dB with R7 = 68 kΩ. Either
dynamic, magnetic or piezo-electric microphones can be
used, or an electret microphone with a built-in FET buffer.
Arrangements for the microphone types are shown in
Fig.12.
The gain of the microphone amplifier is proportional to
external resistor R7 connected between GAS1 and GAS2
and with this it can be adjusted between 44 dB and 52 dB
to suit the sensitivity of the transducer.
An external 100 pF capacitor (C6) is required between
GAS1 and SLPE to ensure stability. A larger value of C6
may be chosen to obtain a first-order low-pass filter with a
cut-off frequency corresponding to the time constant
R7 × C6.
handbook, full pagewidth
MIC+
9
(1)
MIC−
8
(a)
VCC1
MIC−
16
8
MIC+
9
11
VEE
(b)
MIC+
9
MIC−
8
MGR067
(c)
Fig.12 Microphone arrangements: a) magnetic or dynamic microphone, the resistor (1) may be connected to
reduce the terminating impedance, or for sensitive types a resistive attenuator can be used to prevent
overloading the microphone inputs; b) electret microphone; c) piezo-electric microphone.
Dynamic limiter (microphone) pin DLS/MMUTE
A low level at the DLS/MMUTE pin inhibits the microphone
inputs MIC+ and MIC− but has no influence on the
receiving and DTMF amplifiers.
Removing the low level at the DLS/MMUTE pin provides
the normal function of the microphone amplifier after a
short time determined by the capacitor connected to
DLS/MMUTE pin. The microphone mute function can be
realised by a simple switch as shown in Fig.13.
To prevent distortion of the transmitted signal, the gain of
the sending amplifier is reduced rapidly when peaks of the
signal on the line exceed an internally-determined
threshold. The time in which gain reduction is effected
(attack time) is very short. The circuit stays in the
gain-reduced condition until the peaks of the sending
signal remain below the threshold level. The sending gain
then returns to normal after a time determined by the
capacitor connected to DLS/MMUTE (release time).
The internal threshold adapts automatically to the DC
voltage setting of the circuit (voltage VLN-SLPE). This
means that the maximum output swing on the line will be
higher if the DC voltage dropped across the circuit is
increased.
Fig.14 shows the maximum possible output swing on the
line as a function of the DC voltage drop (VLN-SLPE) with
Iline − Ip as a parameter.
handbook, halfpage
R17
3.3 kΩ
DLS/MMUTE
7
VEE
11
MGR068
Fig.13 Microphone-mute function.
March 1994
11
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