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TEA1094 Scheda tecnica(PDF) 11 Page - NXP Semiconductors |
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TEA1094 Scheda tecnica(HTML) 11 Page - NXP Semiconductors |
11 / 28 page 1996 Jul 15 11 Philips Semiconductors Product specification Hands free IC TEA1094; TEA1094A DECISION LOGIC: PINS IDT AND SWT Fig.9 Decision logic. The pin numbers given in parenthesis refer to the TEA1094A. (1) When MUTET = HIGH, +10 µA is forced. When DLC/MUTER < 0.2 V, −10 µA is forced. handbook, full pagewidth MGD224 13 mV 13 mV TENV TNOI RENV MUTET from dynamic limiter RNOI Vdt XX 1 1 − 10 µA + 10 µA + 10 µA X1 0 X 1X 0 X XX 1 0 0 00 0 X 0 Vref RIDT CSWT SWT 16 (12) 14 (11) 27 (23) 26 (22) 24 (20) 23 (19) 19 (15) IDT DUPLEX CONTROLLER LOGIC(1) ATTENUATOR The TEA1094 and TEA1094A select their modes of operation (transmit, receive or idle mode) by comparing the signal and the noise envelopes of both channels. This is executed by the decision logic. The resulting voltage on pin SWT is the input for the voice-switch. To facilitate the distinction between signal and noise, the signal is considered as speech when its envelope is more than 4.3 dB above the noise envelope. At room temperature, this is equal to a voltage difference VENV − VNOI = 13 mV. This so called speech/noise threshold is implemented in both channels. The signal on MIC contains both speech and the signal coming from the loudspeaker (acoustic coupling). When receiving, the contribution from the loudspeaker overrules the speech. As a result, the signal envelope on TENV is formed mainly by the loudspeaker signal. To correct this, an attenuator is connected between TENV and the TENV/RENV comparator. Its attenuation equals that applied to the microphone amplifier. When a dial tone is present on the line, without monitoring, the tone would be recognized as noise because it is a signal with a constant amplitude. This would cause the TEA1094 (TEA1094A) to go into the idle mode and the user of the set would hear the dial tone fade away. To prevent this, a dial tone detector is incorporated which, in standard applications, does not consider input signals between RIN1 and RIN2 as noise when they have a level greater than 127 mV (RMS). This level is proportional to RRSEN. |
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