LEFT
RIGHT
LEFT
RIGHT
LEFT
RIGHT
DIG_MIC_CLK
DIG_MIC_IN
Digital Microphone Input/Decimation Filter
Figure 2-7. Timing Diagram for Digital Microphone Interface
The digital-microphone mode can be selectively enabled for only-left, only-right, or stereo channels. The
AOSR value for the ADC channel must be configured to select the desired decimation ratio to be achieved
based on the external digital microphone properties.
2.3.2 Digital Volume Control
The TLV320DAC3203 also has a digital volume-control block with a range from -12dB to +20dB in steps
of 0.5dB. It is set by programming Page 0, Register 83 and 84 respectively for left and right channels.
Table 2-4. Digital Volume Control for ADC
Desired Gain
Left / Right Channel
dB
Page 1, Register 83/84,
D(6:0)
–12.0
110 1000
–11.5
110 1001
–11.0
110 1010
..
–0.5
111 1111
0.0
000 0000 (Default)
+0.5
000 0001
..
+19.5
010 0111
+20.0
010 1000
During volume control changes, the soft-stepping feature is used to avoid audible artifacts. The soft-
stepping rate can be set to either 1 or 2 gain steps per sample. Soft-stepping can also be entirely
disabled. This soft-stepping is configured via Page 1, Register 81, D(1:0), and is common to soft-stepping
control for the analog PGA. During power-down of an ADC channel, this volume control soft-steps down to
-12.0dB before powering down. Due to the soft-stepping control, soon after changing the volume control
setting or powering down the ADC channel, the actual applied gain may be different from the one
programmed through the control register. The TLV320DAC3203 gives feedback to the user, through read-
only flags Page 1, Reg 36, D(7) for Left Channel and Page 1, Reg 36, D(3) for the right channel.
2.3.2.1
Fine Digital Gain Adjustment
Additionally, the gains in each of the channels is finely adjustable in steps of 0.1dB. This is useful when
trying to match the gain between channels. By programming Page 0, Register 82 the gain can be adjusted
from 0dB to -0.4dB in steps of 0.1dB. This feature, in combination with the regular digital volume control
allows the gains through the left and right channels be matched in the range of -0.5dB to +0.5dB with a
resolution of 0.1dB.
2.3.3 Digital Microphone Decimation Filtering and Signal Processing Overview
The TLV320DAC3203 includes a built-in digital decimation filter to process the oversampled data from the
PDM input to generate digital data at Nyquist sampling rate with high dynamic range. The decimation filter
can be chosen from three different types, depending on the required frequency response, group delay and
sampling rate.
22
TLV320DAC3203 Application
SLAU434 – May 2012
Copyright © 2012, Texas Instruments Incorporated