参数资料
型号: TLV320AIC32IRHBG4
厂商: TEXAS INSTRUMENTS INC
元件分类: 消费家电
英文描述: SPECIALTY CONSUMER CIRCUIT, PQCC32
封装: 5 X 5 MM, GREEN, PLASTIC, QFN-32
文件页数: 19/72页
文件大小: 4594K
代理商: TLV320AIC32IRHBG4
www.ti.com
Decay Time
Target
Gain
Input
Signal
Output
Signal
AGC
Gain
Attack
Time
TLV320AIC32
SLAS479A – AUGUST 2005 – REVISED SEPTEMBER 2005
Target gain represents the nominal output level at which the AGC attempts to hold the ADC output signal level.
The TLV320AIC32 allows programming of eight different target gains, which can be programmed from –5.5 dB to
–24 dB relative to a full-scale signal. Since the device reacts to the signal absolute average and not to peak
levels, it is recommended that the larger gain be set with enough margin to avoid clipping at the occurrence of
loud sounds.
Attack time determines how quickly the AGC circuitry reduces the PGA gain when the input signal is too loud. It
can be varied from 8 ms to 20 ms.
Decay time determines how quickly the PGA gain is increased when the input signal is too low. It can be varied
in the range from 100 ms to 500 ms.
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 FS 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.
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.
Figure 25. Typical Operation of the AGC Algorithm During Speech Recording
Note that the time constants here are correct when the ADC is not in double-rate audio mode. The time
constants are achieved using the Fsref value programmed in the control registers. However, if the Fsref is set in
the registers to, for example, 48 kHz, but the actual audio clock or PLL programming actually results in a different
Fsref in practice, then the time constants would not be correct.
26
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