Texas Instruments TLV320AIC26EVM, Руководство пользователя

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Program Description
3-17 Operation
3.5.3.1 Codec Section
By checking Power Up Codec in the codec section, the audio codec is powered
up.
In this EVM, the audio codec samples at 44.1 kHz in 16-bit I
2
S mode. Also, the
AIC26 codec functions as a slave in the interface. Although the AIC26 device
has much more flexibility, this EVM has these values fixed.
3.5.3.2 ADC Section
By checking Power Up ADC, audio ADC power is enabled.
The audio ADC also has a high-pass filter which is a submultiple of the sample
rate, to remove dc or low frequency components from the input signal.
The input signal to the audio ADC can come from: 1) the pin MICIN, a
single-ended input; 2) the pin AUX, also a single-ended input; or 3) the pin
MIC2IN and AUX, a differential input, selectable through the Input Select box.
Figure 3−6 shows the single-ended input from MICIN (if selected).
A microphone bias voltage of either 2.5 V or 2.0 V can also be generated by
the AIC26 (refer to Figure 3−6). Note that to use the microphone bias voltage,
jumper JMP2 should be set to position 2 to 3 (refer to Table 3−1 of this
document for jumper settings).
If the differential microphone inputs to the EVM (through the microphone jack
J5) the JMP1 should be installed, and the input select should be set to DIFF
(MIC/AUX) in this section.
In the ADC input path, there is a programmable EVM amplifier (ADC PGA),
allowing analog input gain control from 0 dB to 59 dB. When not using
automatic gain control (AGC OFF), moving the volume slide adjusts the PGA
and checking the Mute box mutes the ADC signal.
When the gain changes from the current value to the programmed value, it
changes in steps of 0.5 dB. Also, the change rate can be controlled if the PGA
Soft Stepping box is checked, where the PGA changes 0.5 dB at either 1 step
per sample or 1 step per 2 samples.
Automatic gain control (AGC) is another more sophisticated way to control the
ADC gain. When the box by AGC ON is checked, AGC is enabled, as shown
in Figure 3−7. Refer to the AIC26 data sheet for setting and using the AGC.