D2-7XX83_14 Datasheet, PDF (21/33 Pages) Intersil Corporation – Intelligent Digital Amplifier and Sound Processor

D2-7xx83
DSD
The HDMI specification (version 1.2 and later) used in TV systems
supports streaming DSD encoded audio over HDMI. To support
this, the system can receive and process up to 6 DSD audio
streams. The DSD interface supports both standard and
phase-modulated data formats. A high-quality 16x decimator
engine converts all of the DSD data streams into 24-bit PCM
words with an FS of 176.4kHz using a 128-tap FIR filter. The DSD
decimation filter has a cutoff frequency of 50kHz and is
optimized for passband flatness.
SAI ports 2 and 3 support DSD format inputs. When the DSD
interface is enabled, all the pins of SAI 2 and the SC21 pin of
SAI3 become the DSD input signals. The 6 channels of DSD
audio are merged into 3 I²S PCM streams at a 176.4kHz sample
rate. These I²S streams are routed into both receivers on SAI 2
and the first receiver of SAI 3. The data is then passed to the
Sample Rate Converter (SRC). The SRC will rate-lock to the DSD
input clock and attenuate any jitter in the DSD input stream.
The DSD input processing clusters the DSD data into channel
pairs. This allows a flexible channel count of 2, 4, or all 6 DSD
data streams to be handled. Using 4-channel DSD frees the SAI 3
port for other uses. Similarly, using only 2-Channel DSD frees the
second SAI 2 port and the SAI 3 port for other uses.
The D2-7xx83 family of ICs also offers digital audio format
conversion support for DSD stereo format input to S/PDIF or I²S
format output, as well as DSD multichannel format input to
multiple I²S format output. This high-quality digital audio format
conversion path also offers the ability to reduce clock jitter in the
audio system introduced by certain transmission paths such as
HDMI.
This technique also enables consumer products to output a
downsampled and/or downmixed (if necessary) digital audio
output for audio that may not otherwise be made available to the
consumer in the original higher-bandwidth format due to certain
consumer electronic/content protection licensing restrictions.
The graphs in Figure 8 show the DSD decimation filter frequency
response at 2 different frequency zoom levels.
0
0.020
24 BITS
24 BITS
SPEC
0.015
SPEC
0.010
-50
0.005
0
-100
-0.005
-0.010
-0.015
-1500
2
4
6
8
10
12
14
FREQUENCY (Hz)
x10⁵
-0.020
0
0.5
1.0
1.5
2.0
2.5
3.0
FREQUENCY (Hz)
x 10⁴
FIGURE 8. DSD DECIMATOR FREQUENCY RESPONSE (128 TAPS DECIMATE BY 16)
21
FN7838.2
September 29, 2011