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TEA1085AT Scheda tecnica(PDF) 6 Page - NXP Semiconductors |
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TEA1085AT Scheda tecnica(HTML) 6 Page - NXP Semiconductors |
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6 / 32 page  March 1992 6 Philips Semiconductors Preliminary specification Listening-in circuit for line-powered telephone sets TEA1085; TEA1085A FUNCTIONAL DESCRIPTION Figure 1 illustrates a block diagram of the TEA1085/TEA1085A with external components and connections to the transmission IC. The TEA1085/TEA1085A are bipolar ICs which have been designed for use in line-powered telephone sets and provide a listening-in facility for the received line signal via a loudspeaker. Nearly all the line current can be used for powering the loudspeaker. The loudspeaker amplifier consists of a preamplifier, to amplify the earpiece signal from the transmission circuit and, a double push-pull output stage to drive the loudspeaker in the BTL (bridge tied load) or SE (single ended) configuration. The gain of the preamplifier is controlled by a dynamic limiter which prevents high distortion of the loudspeaker signal. This is achieved by preventing clipping of the loudspeaker signal, with respect to the supply voltage, and at too low supply current. Two logic inputs can be used to reduce the gain in 3 steps. Because of acoustic feedback from the loudspeaker to the microphone, howling signals (Larsen effect) can occur on the telephone line and in the loudspeaker. When the Larsen signal exceeds a voltage and time duration threshold the Larsen level limiter (LLL) will reduce the Larsen signal to a low level within a short period of time by reducing the gain of the receiving preamplifier. This is achieved by using the microphone signal as an input signal which is processed in the LLL via a preamplifier and 3rd-order filter. The MUTE input can be used to enable or disable the loudspeaker amplifier. The MUTE function of the TEA1085 has a toggle input to permit the use of a simple push-button switch. The MUTE function of the TEA1085A has a logic input to operate with a microcontroller. By activating the power-down input the current consumption of the circuit will be reduced, this enables pulse dialling or flash (register recall). An internal start circuit ensures normal start-up of the transmission IC and start-up of the listening-in IC in the standby mode. The TEA1085/TEA1085A are intended for use in conjunction with a member of the TEA1060 family and should be connected between LINE and SLPE of the transmission IC. The transmission characteristics (impedance, gain settings, for example) are not affected. The interconnection between the two ICs is illustrated in Fig.3. Fig.3 Interconnection of the TEA1085/TEA1085A with the TEA1060. handbook, full pagewidth MGR033 TEA1060 VCC LN VEE SLPE QR MIC + MIC − LAI + LAI − TEA1085 TEA1085A SREF SUP VSS LSI1 LSI2 QLS LINE to TEA1060 (SLPE) |
Codice articolo simile - TEA1085AT |
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Descrizione simile - TEA1085AT |
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