Datasheet

Digital AudioDataSerialInterface
ADC
+
+
DIN
DOUT BCLK
WCLK
DINL
DINR DOUTL DOUTR
ADC
AGC
AGC
RecordPath
RecordPath
Effects
Effects
SW-D1
SW-D2
SW-D4
SW-D3
Left-Channel
AnalogInputs
Right-Channel
AnalogInputs
PGA
0dB–59.5dB,
0.5-dBSteps
PGA
0dB–59.5dB,
0.5-dBSteps
Volume
Control
Volume
Control
DAC
Powered
Down
DAC
Powered
Down
DAC
L
DAC
R
B0173-01
AUTOMATIC GAIN CONTROL (AGC)
TLV320AIC3101
www.ti.com ........................................................................................................................................ SLAS520D – FEBRUARY 2007 – REVISED DECEMBER 2008
Figure 25. Record- Only Mode With Digital Processing Path Enabled
An automatic gain control (AGC) circuit is included with the ADC and can be used to maintain nominally constant
output signal amplitude when recording speech signals (it can be fully disabled if not desired). This circuitry
automatically adjusts the PGA gain as the input signal becomes overly loud or very weak, such as when a
person speaking into a microphone moves closer or farther from the microphone. The AGC algorithm has several
programmable settings, including target gain, attack and decay time constants, noise threshold, and maximum
PGA gain applicable that allow the algorithm to be fine-tuned for any particular application. The algorithm uses
the absolute average of the signal (which is the average of the absolute value of the signal) as a measure of the
nominal amplitude of the output signal.
Note that completely independent AGC circuitry is included with each ADC channel with entirely independent
control over the algorithm from one channel to the next. This is attractive in cases where two microphones are
used in a system, but may have different placement in the end equipment and require different dynamic
performance for optimal system operation.
Target level represents the nominal output level at which the AGC attempts to hold the ADC output signal level.
The TLV320AIC3101 allows programming of eight different target levels, which can be programmed from – 5.5
dB to – 24 dB relative to a full-scale signal. Because the device reacts to the signal absolute average and not to
peak levels, it is recommended that the target level 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 7 ms to 1,408 ms. The extended right-channel attack time can be programmed by writing to
page 0, register 103, and the left channel is programmed by writing to page 0, register 105.
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