TSC2101-Audio Codec w/ Integrated Headphone Speaker Amp ...

SLAS392C− JUNE 2003 − REVISED SEPTEMBER 2004www.ti.comthat noise does not get gained up in the absence of speech. Noise threshold level in the AGC algorithm isprogrammable from −30dB to −90 dB for microphone input, and from −30 dB to −60 dB for cell-phone input.When AGC Noise Threshold is set to −70 dB, −80 dB, or −90 dB, the microphone input Max PGA applicablesetting must be greater than or equal to 11.5 dB, 21.5 dB, or 31.5 dB respectively. This operation includesdebounce and hysteresis to avoid the AGC gain from cycling between high gain and 0 dB when signals are nearthe noise threshold level. When noise threshold flag is set, status of gain applied by AGC and saturation flagshould be ignored.Max PGA applicable allows user to restrict maximum gain applied by AGC. This can be used for limiting PGAgain in situations where environment noise is greater than programmed noise threshold. Microphone input MaxPGA can be programmed from 0 dB to 59.5 dB in steps of 0.5 dB. Cell-phone input Max PGA can beprogrammed from −34.5 dB to −0.5 dB in steps of 0.5 dB, as well as +12 dB.See Table 1 for various AGC programming options. AGC can be used only if microphone input or Cell-phoneinput is routed to the ADC channel. When both microphone input and Cell-phone input are connected to theADC, AGC is automatically disabled.InputSignalOutputSignalTargetGainAGCGainDecay TimeAttackTimeFigure 19. AGC Characteristics24