Datasheet

687
32142D–06/2013
ATUC64/128/256L3/4U
28. Audio Bit Stream DAC (ABDACB)
Rev.: 1.0.0.0
28.1 Features
• 16 bit digital stereo DAC
• Oversampling D/A conversion architecture
– Adjustable oversampling ratio
– 3rd order Sigma-Delta D/A converters
• Digital bitstream output
• Parallel interface
• Connects to DMA for background transfer without CPU intervention
• Supported sampling frequencies
– 8000Hz, 11025Hz, 12000Hz, 16000Hz, 22050Hz, 24000Hz, 32000Hz, 44100Hz, and 48000Hz
• Supported data formats
– 32-, 24-, 20-, 18-, 16-, and 8-bit stereo format
– 16- and 8-bit compact stereo format, with left and right sample packed in the same word to
reduce data transfers
• Common mode offset control
• Volume control
28.2 Overview
The Audio Bitstream DAC (ABDACB) converts a 16-bit sample value to a digital bitstream with
an average value proportional to the sample value. Two channels are supported making the
Audio Bitstream DAC particularly suitable for stereo audio. Each channel has a pair of comple-
mentary digital outputs, DAC and DACN, which can be connected to an external high input
impedance amplifier.
The Audio Bitstream DAC is made up of several signal processing blocks and a 3rd order Sigma
Delta D/A converter for each channel. The Sigma Delta modulator converts the parallel data to a
bitstream, while the signal processing blocks perform volume control, offset control, upsampling,
and filtering to compensate for the upsampling process. The upsampling is performed by a Cas-
caded Integrator-Comb (CIC) filter, and the compensation filter is a Finite Impulse Response
(FIR) CIC compensation filter.
28.3 Block Diagram
Figure 28-1. ABDACB Block Diagram
U
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I
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f
a
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Synchronizer
Volume control
Offset control
CIC Compensation
filter (FIR)
CIC
Comb
Section
CIC Integrator
section
Clock
divider
Sigma Delta
Modulator
Sigma Delta
Modulator
clk_abdacb gclk
Signal processing
(before up-sampling)
CLK
DAC[0]
DACN[0]
DAC[1]
DACN[1]
PB