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RT5509 Arkusz danych(PDF) 22 Page - Richtek Technology Corporation |
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RT5509 Arkusz danych(HTML) 22 Page - Richtek Technology Corporation |
22 / 58 page RT5509 Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation www.richtek.com DS5509-00 August 2017 22 PWDN/SUSPD/Off/Fault/Mute mode. A register control bit can be configured to set if the pilot is also turned off in Silence mode. If yes, then the pilot should be turn off after signal power below threshold for SilenceResetTime. This bit also defines if the DC resistance is monitored or not in Silence mode. Except for Fault mode, the pilot always turned on or turned off at zero cross level. In worst case the pilot turn-off latency will be 11.6ms. Signal Detector The signal activity is detected when the input signal level is above a user defined threshold. The detection window can be specified to be 5ms/10ms/20ms. Another long time constant: SilenceRestTime is used to ensure the silence happen and set the ALC to its initial gain. Parameters : sThresAct : silence or active threshold (0 to 90dBFS, 6dB step) SilenceResetTime : the time to reset ALC gain to initial value (0 to 15 seconds) Peak Detector The peak detector monitors the peak of the signal magnitude and the estimated excursion. The algorithm is describe as following equation, with attack time can be specified as 0ms/1ms/2ms/4ms and release time can be specified by (1-RT) represented in 16- bit 2’s complement format. xPeak(n) = (1-AT) xPeak(n-1)+AT x(n) xPeak(n) = (1-RT) xPeak(n-1) for x(n) >xPeak(n-1) x(n) xPeak(n-1) Automatic Level Control (ALC) The core of ALC gain control is depicted in Figure 15. The gain is checked and adjusted every ALC_period, which is specified by UpDoubleTime and DnHalfTime registers. These two register bit fields has physical meaning which mapped to approximately ±6dB per second. They can be specified from 1/16 to 15.9375 seconds with resolution of 1/16s. The internal logic implements ALC_period by a counter expired every 16 * UpDoubleTime or 16 * DnHalfTime when the gain is going up/dn respectively. Depend on the clock base of I2S, the nominal of ±6dB per second for double/half the gain is actually approximately by : 44.1k : 20*log10((4097/4096)^(48000/16)) = 6.36dB; 20*log10((4095/4096)^(48000/16)) = 6.36dB 48k : 20*log10((4097/4096)^(44100/16)) = 5.84dB; 20*log10((4095/4096)^(44100/16)) = 5.84dB The Parameters for ALC Control : sThresALC[7:0] : Threshold of signal, specified by 0 to 1. 1 corresponds to the maximum allowable signal specified by clipper module. xThresALC[7:0] : Threshold of excursion, specified by 0 to 1. 1 corresponds to the maximum allowable excursion. sThresALC and xThresALC are 8-bit unsigned number representing the value 1/128 to 1, 0x80 is normalized to 1. UpDoubleTime[7:0] : gain double time = UpDoubleTime /16 (seconds) DnHalfTime[7:0] : gain half time = DnHalfTime /16 (seconds) InitUpDoubleTime[7:0] : gain double time used for signal just detected from silence mode. UpDoubleTime, DnHalfTime, InitUpDoubleTime and InitDnHalfTime are unsigned 8-bit number representing the value 1/16 to 15.9375, 0x10 is normalized to 1. ALCInitGain[2:0] : ALC initial gain when signal is detected from silence mode. 0 to 21dB, 3dB step. ALCMaxGain[2:0] : ALC maximum allowable gain. 0 to 21dB, 3dB step. |
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