TLV320AIC3101 Datasheet, PDF (26/98 Pages) Texas Instruments – LOW-POWER STEREO AUDIO CODEC FOR PORTABLE AUDIO/TELEPHONY

TLV320AIC3101
SLAS520E – FEBRUARY 2007 – REVISED DECEMBER 2014
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The actual AGC decay time maximum is based on a counter length, so the maximum decay time scales with the
clock setup that is used. Table 2 shows the relationship of the NCODEC ratio to the maximum time available for
the AGC decay. In practice, these maximum times are extremely long for audio applications and should not limit
any practical AGC decay time that is needed by the system.
Table 2. AGC Decay Time Restriction
NCODEC RATIO
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
MAXIMUM DECAY TIME (SECONDS)
4
5.6
8
9.6
11.2
11.2
16
16
19.2
22.4
22.4
11.3.3.2.2.4 Noise Gate Threshold
The noise gate threshold determines the level below which if the input speech average value falls, AGC
considers it as a silence and hence brings down the gain to 0 dB in steps of 0.5 dB every sample period and sets
the noise threshold flag. The gain stays at 0 dB unless the input speech signal average rises above the noise
threshold setting. This ensures that noise does not get gained up in the absence of speech. Noise threshold level
in the AGC algorithm is programmable from –30 dB to –90 dB relative to full scale. A disable noise gate feature
is also available. This operation includes programmable debounce and hysteresis functionality to avoid the AGC
gain from cycling between high gain and 0 dB when signals are near the noise threshold level. When the noise
threshold flag is set, the status of gain applied by the AGC and the saturation flag should be ignored.
11.3.3.2.2.5 Maximum PGA Gain Applicable
The maximum PGA gain applicable allows the user to restrict the maximum PGA gain that can be applied by the
AGC algorithm. This can be used for limiting PGA gain in situations where environmental noise is greater than
programmed noise threshold. It can be programmed from 0 dB to 59.5 dB in steps of 0.5 dB.
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