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MT9122AP Datasheet(PDF) 7 Page - Mitel Networks Corporation |
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MT9122AP Datasheet(HTML) 7 Page - Mitel Networks Corporation |
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7 / 32 page  Preliminary Information MT9122 8-23 where 0 < NLPTHR(dec) < 1 The comfort noise injection can be disabled by setting the INJDis bit to 1 in Control Register 1. It should be noted that the NLPTHR is valid and the comfort noise injection is active only when the NLP is enabled. Disable Tone Detector G.165 recommendation defines the disable tone as having the following characteristics: 2100 Hz ( ± 21Hz) sinewave, a power level between -6 to -31dBm0, and a phase reversal of 180 degrees ( ± 25 degrees) every 450ms ( ± 24ms). If the disable tone is present for a minimum of one second with at least one phase reversal, the Tone Detector will trigger. G.164 recommendation defines the disable tone as a 2100 Hz ( ±21Hz) sinewave with a power level between -6 to -31dBm0. If the disable tone is present for a minimum of one second, with or without phase reversal, the Tone Detector will trigger. The MT9122 has four Tone Detectors in order to monitor the occurrence of a valid disable tone on channels A and B on both Rin and Sin. Upon detection of a disable tone, output pins TD1 or TD2 will go low as illustrated in Figure 4. Figure 4 - Disable Tone Detection Once a Tone Detector has been triggered, the MT9122 no longer needs a valid disable tone (G.164 or G.165) to maintain Tone Detector status (e.g. TD1, TD2 pins low). The Tone Detector status will only release (e.g. TD1, TD2 pins high) if the signals Rin and Sin fall below -30dBm0, in the frequency range of 390Hz to 700Hz, and below -34dBm0, in the frequency range of 700Hz to 3400Hz, for at least 400ms. Controllerless Mode The selection between G.165 and G.164 tone disable is controlled by the REV pin. When the REV pin is connected to Vss, G.164 is selected. This applies to all four Tone Detectors. In response to a valid disable tone, the MT9122 must be switched from the Enable Adaptation state to the Bypass state. In an application, the Tone Detect outputs, TD1 and TD2, may be used to switch the echo cancellers between these two states. This is achieved by connecting S1 and S3 pins to Vdd and by connecting the TD1 and TD2 outputs to the S2 and S4 input pins respectively. Controller Mode The selection between G.165 and G.164 tone disable is controlled by the PHDis bit in Control Register 2. When the PHDis bit is set to 1, G.164 tone disable requirements are selected. This applies to all four Tone Detectors. In response to a valid disable tone, the MT9122 must be switched from the Enable Adaptation state to the Bypass state. This can be done in two ways, automatically or externally. In automatic mode, the Tone Detectors internally control the switching between Enable Adaptation and Bypass states. The automatic mode can be activated by setting the AutoTD bit in Control Register 2 to high. In external mode, an external controller is needed to poll the TD bit in Status Register A or B. Following the detection of a disable tone (TD bit high), the external controller should switch the echo canceller from Enable Adaptation to Bypass state. The TD1 and TD2 output pins remain active, as in Controllerless mode, and they can be used as an interrupt to an external controller. Narrow Band Signal Detector (NBSD) Single or dual frequency tones (e.g. DTMF tones) present in the reference input (Rin) of the echo canceller for a prolonged period of time may cause the adaptive filter to diverge. The Narrow Band Signal Detector (NBSD) is designed to prevent this divergence by detecting single or dual tones of arbitrary frequency, phase, and amplitude. When narrow band signals are detected, the adaptation process is halted but the echo canceller continues to cancel echo. TD1 Rin Sin Echo Canceller A Tone Detector Tone Detector Echo Canceller B TD2 Rin Sin Tone Detector Tone Detector |
Similar Part No. - MT9122AP |
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Similar Description - MT9122AP |
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