TEA1112 データシートの表示（PDF） - Philips Electronics

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TEA1112

Low voltage versatile telephone transmission circuits with dialler interface

Philips Electronics 

Philips Semiconductors

Low voltage versatile telephone

transmission circuits with dialler interface

Product specification

TEA1112; TEA1112A

Receiving amplifier (pins IR, GAR and QR)

The receiving amplifier has one input (IR) and one output

(QR). The input impedance between pin IR and pin VEE is

20 kΩ. The voltage gain from pin IR to pin QR is set at

31.2 dB (typ). The gain can be decreased by connecting

an external resistor RGAR between pins GAR and QR; the

adjustment range is 12 dB. Two external capacitors CGAR

(connected between GAR and QR) and CGARS (connected

between GAR and VEE) ensure stability. The CGAR

capacitor provides a first-order low-pass filter. The cut-off

frequency corresponds to the time constant

CGAR × (RGARint // RGAR). RGARint is the internal resistor

which sets the gain with a typical value of 100 kΩ.

The relationship CGARS = 10 × CGAR must be fulfilled to

ensure stability.

The output voltage of the receiving amplifier is specified for

continuous wave drive. The maximum output swing

depends on the DC line voltage, the RCC resistor, the ICC

current consumption of the circuit, the Ip current

consumption of the peripheral circuits and the load

impedance.

Automatic gain control is provided on this amplifier for line

loss compensation.

Automatic gain control (pin AGC)

The TEA1112; TEA1112A perform automatic line loss

compensation. The automatic gain control varies the gain

of the microphone amplifier and the gain of the receiving

amplifier in accordance with the DC line current.

The control range is 5.8 dB (which corresponds

approximately to a line length of 5 km for a 0.5 mm

diameter twisted-pair copper cable with a DC resistance of

176 Ω/km and an average attenuation of 1.2 dB/km).

The ICs can be used with different configurations of

feeding bridge (supply voltage and bridge resistance) by

connecting an external resistor RAGC between pins AGC

and VEE. This resistor enables the Istart and Istop line

currents to be increased (the ratio between Istart and Istop is

not affected by the resistor). The AGC function is disabled

when pin AGC is left open-circuit.

Mute function (pin MUTE; TEA1112)

The mute function performs the switching action between

the speech mode and the dialling mode. When MUTE is

LOW or open-circuit, the microphone and receiving

amplifiers inputs are enabled while the DTMF input is

disabled, depending on the MMUTE level (see Table 1).

When MUTE is HIGH, the DTMF input is enabled and the

microphone and receiving amplifiers inputs are disabled.

Mute function (pin MUTE; TEA1112A)

The mute function performs the switching between the

speech mode and the dialling mode. When MUTE is LOW

or open-circuit, the DTMF input is enabled and the

microphone and receiving amplifiers inputs are disabled.

When MUTE is HIGH, the microphone and receiving

amplifiers inputs are enabled while the DTMF input is

disabled, depending on the MMUTE level (see Table 1).

DTMF amplifier (pin DTMF)

When the DTMF amplifier is enabled, dialling tones may

be sent on line. These tones can be heard in the earpiece

at a low level (confidence tone).

The TEA1112; TEA1112A have an asymmetrical DTMF

input. The input impedance between DTMF and VEE is

20 kΩ. The voltage gain from pin DTMF to pin LN is

25.5 dB. When an external resistor is connected between

pins REG and GAS to decrease the microphone gain, the

DTMF gain varies in the same way (the DTMF gain is

26.3 dB lower than the microphone gain with no AGC

control).

The automatic gain control has no effect on the DTMF

amplifier.

1997 Mar 26

7

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