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TEA1114AT Datasheet(PDF) 10 Page - NXP Semiconductors |
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TEA1114AT Datasheet(HTML) 10 Page - NXP Semiconductors |
10 / 28 page 2000 Mar 21 10 Philips Semiconductors Product specification Low voltage telephone transmission circuit with dialler interface and regulated strong supply 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: 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. R SLPE R ast1 × R CC R ast2 ( R ast3 ) + × = k R ast2 R ast3 R SLPE + () × R ast1 R SLPE × ----------------------------------------------------------- = Z bal kZ line × = |
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