參數(shù)資料
型號(hào)： 933880320112
廠商： NXP SEMICONDUCTORS
元件分類： 無繩電話/電話
英文描述： TELEPHONE SPEECH CKT, PDSO20
封裝： PLASTIC, SOT-163, SO-20
文件頁(yè)數(shù)： 27/29頁(yè)
文件大小： 231K
代理商： 933880320112
June 1990
7
Philips Semiconductors
Product specication
Low voltage versatile telephone
transmission circuit with dialler interface
TEA1067
Automatic gain control input (AGC)
Automatic line loss compensation is achieved by
connecting a resistor (R6) between AGC and VEE. The
automatic gain control varies the gain of the microphone
amplifier and the receiving amplifier in accordance with the
DC line current. The control range is 5.9 dB. This
corresponds to a line length of 5 km for a 0.5 mm diameter
copper twisted-pair cable with a DC resistance of
176
/km and an average attenuation 1.2 dB/km. Resistor
R6 should be chosen in accordance with the exchange
supply voltage and its feeding bridge resistance (see
Fig.13 and Table 1). The ratio of start and stop currents of
the AGC curve is independent of the value of R6. If no
automatic line loss compensation is required the AGC may
be left open-circuit. The amplifiers, in this condition, will
give their maximum specified gain.
Power-down input (PD)
During pulse dialling or register recall (timed loop break)
the telephone line is interrupted. During these interruptions
the telephone line provides no power for the transmission
circuit or circuits supplied by VCC. The charge held on C1
will bridge these gaps. This bridging is made easier by a
HIGH level on the PD input which reduces the typical
supply current from 1 mA to 55
A and switches off the
voltage regulator preventing discharge through LN. When
PD is HIGH the capacitor at REG is disconnected with the
effect that the voltage stabilizer will have no switch-on
delay after line interruptions. This minimizes the
contribution of the IC to the current waveform during pulse
dialling or register recall. When this facility is not required
PD may be left open-circuit.
Side-tone suppression
The anti-sidetone network, R1//Zline, R2, R3, R9 and Zbal,
(see Fig.5) suppresses transmitted signal in the earpiece.
Compensation is maximum when the following conditions
are fulfilled:
(a) R9
× R2 = R1 (R3 + [R8//Zbal]);
(b) (Zbal / [Zbal + R8]) = (Zline / [Zline + R1])
If fixed values are chosen for R1, R2, R3, and R9 then
condition (a) will always be fulfilled when
R8//Zbal << R3.
To obtain optimum side-tone suppression condition (b)
has to be fulfilled resulting in:
Zbal = (R8/R1) Zline = k.Zline where k is a scale factor;
k = (R8/R1)
The scale factor (k), dependent on the value of R8, is
chosen to meet the following criteria:
(a) Compatibility with a standard capacitor from the E6 or
E12 range for Zbal
(b)
Zbal//R8 << R3 to fulfil condition (a) and thus
ensuring correct anti-sidetone bridge operation
(c)
Zbal + R8 >> R9 to avoid influencing the transmitter
gain
In practice Zline varies considerably with the line type and
length. The value chosen for Zbal should therefore be for
an average line length thus giving optimum setting for
short or long lines.
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