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TEA1093T Scheda tecnica(PDF) 10 Page - NXP Semiconductors |
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TEA1093T Scheda tecnica(HTML) 10 Page - NXP Semiconductors |
10 / 28 page 1996 Feb 09 10 Philips Semiconductors Product specification Hands-free IC TEA1093 When the supply conditions drop below the required level, the gain of the loudspeaker amplifier is reduced in order to prevent the TEA1093 from malfunctioning. Only the gain of the loudspeaker amplifier is affected since it is considered to be the major power consuming part of the TEA1093. When the TEA1093 experiences a loss of current, the supply voltage VBB decreases. In this event, the gain of the loudspeaker amplifiers is slowly reduced (approximately a few seconds). When the supply voltage continues to decrease and drops below an internal voltage threshold of 2.75 V, the gain of the loudspeaker amplifier is rapidly reduced (approximately 1 ms). When normal supply conditions are resumed, the gain of the loudspeaker amplifier is increased again. This system ensures that in the event of large continuous signals, all current is used to power the loudspeaker while the voltage on pin VBB remains at its nominal value. By forcing a level lower than 0.2 V on pin DLC/MUTER, the loudspeaker amplifier is muted and the TEA1093 is automatically forced into the transmit mode. Duplex controller SIGNAL AND NOISE ENVELOPE DETECTORS: PINS TSEN, TENV, TNOI, RSEN, RENV AND RNOI The signal envelopes are used to monitor the signal level strength in both channels. The noise envelopes are used to monitor background noise in both channels. The signal and noise envelopes provide inputs for the decision logic. The signal and noise envelope detectors are shown in Fig.8. For the transmit channel, the input signal at MIC is 40 dB, amplified to TSEN. For the receive channel, the differential signal between RIN1 and RIN2 is 0 dB amplified to RSEN. The signals from TSEN and RSEN are logarithmically compressed and buffered to TENV and RENV respectively. The sensitivity of the envelope detectors is set with RTSEN and RRSEN. The capacitors connected in series with the two resistors block any DC component and form a first-order high-pass filter. In the basic application, see Fig.16, it is assumed that VMIC = 1 mV (RMS) and VRIN = 100 mV (RMS) nominal and both RTSEN and RRSEN have a value of 10 k Ω. With the value of CTSEN and CRSEN at 100 nF, the cut-off frequency is at 160 Hz. The buffer amplifiers leading the compressed signals to TENV and RENV have a maximum source current of 120 µA and a maximum sink current of 1 µA. Together with the capacitor CTENV and CRENV, the timing of the signal envelope monitors can be set. In the basic application, the value of both capacitors is 470 nF. Because of the logarithmic compression, each 6 dB signal increase means 18 mV increase of the voltage on the envelopes TENV or RENV at room temperature. Thus, timings can be expressed in dB/ms. At room temperature, the 120 µA sourced current corresponds to a maximum rise-slope of the signal envelope of 85 dB/ms. This is sufficient to track normal speech signals. The 1 µA current sunk by TENV or RENV corresponds to a maximum fall-slope of 0.7 dB/ms. This is sufficient for a smooth envelope and also eliminates the effect of echoes on switching behaviour. Fig.8 Signal and noise envelope detectors. handbook, full pagewidth MGD223 LOG 28 (24) 27 (23) 26 (22) 25 (21) 24 (20) 23 (19) LOG from microphone amplifier from loudspeaker amplifier DUPLEX CONTROLLER TSEN RTSEN CTSEN CTENV CTNOI RRSEN CRSEN CRENV CRNOI TENV TNOI RSEN RENV RNOI to logic to logic |
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