TEA1114AUH View Datasheet(PDF) - Philips Electronics

Part Name

Description

Manufacturer

TEA1114AUH

Low voltage telephone transmission circuit with dialler interface and regulated strong supply

Philips Electronics 

Philips Semiconductors

Low voltage telephone transmission circuit with

dialler interface and regulated strong supply

Product specification

TEA1114A

Automatic gain control (pin AGC)

The TEA1114A performs automatic line loss

compensation. The automatic gain control varies the gain

of the microphone amplifier and the gain of the receive

amplifier in accordance with the DC line current.

The control range is 6.0 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 IC 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)

The mute function performs the switching between the

speech mode and the dialling mode.

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

microphone and receive amplifier inputs are disabled.

In this mode, the DTMF tones are sent to the receive

output at a low level (confidence tone).

When MUTE is HIGH, the microphone and receiving

amplifiers inputs are enabled while the DTMF input is

disabled. The MUTE input is provided with an internal

pull-up current source to VCC.

Sidetone suppression

The TEA1114A anti-sidetone network comprising

RCC // Zline, Rast1, Rast2, Rast3, RSLPE and Zbal (see Fig.9)

suppresses the transmitted signal in the earpiece.

Maximum compensation is obtained when the following

conditions are fulfilled:

RSLPE × Rast1 = RCC × (Rast2 + Rast3 )

k = R-----a---s--t-2--R--×--a---s(--tR-1----a×--s---tR-3----S+---L--RP---E-S---L---P---E----)

Zbal = k × Zline

The scale factor k is chosen to meet the compatibility with

a standard capacitor from the E6 or E12 range for Zbal.

In practice, Zline varies considerably with the line type and

the line length. Therefore, the value of Zbal should be for an

average line length which gives satisfactory sidetone

suppression with short and long lines. The suppression

also depends on the accuracy of the match between Zbal

and the impedance of the average line.

The anti-sidetone network for the TEA1114A attenuates

the receiving signal from the line by 32 dB before it enters

the receiving amplifier. The attenuation is almost constant

over the whole audio frequency range.

A Wheatstone bridge configuration (see Fig.10) may also

be used.

More information on the balancing of an anti-sidetone

bridge can be obtained in our publication “Semiconductors

for Wired Telecom Systems; Application Handbook,

IC03b”. For ordering information please contact the Philips

Semiconductors sales office.

2000 Mar 21

10

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