AK4345_10 Datasheet, PDF (14/27 Pages) Asahi Kasei Microsystems – 100dB 96kHz 24-Bit Stereo 3.3V ΔΣ DAC with DIT

[AK4345]
■ Data Transmission Format
Data transmitted on the TX outputs is formatted in blocks as shown in Figure 14. Each block consists of 192 frames. A
frame of data contains two sub-frames. A sub-frame consists of 32 bits of information. Each received data bit is coded
using a bi-phase mark encoding as a two binary state symbol. The preambles violate bi-phase encoding so they may be
differentiated from data. In bi-phase encoding, the first state of an input symbol is always the inverse of the last state of
the previous data symbol. For a logic 0, the second state of the symbol is the same as the first state. For a logic 1, the
second state is the opposite of the first. Figure 15 illustrates a sample stream of 8 data bits encoded in 16 symbol states.
M Channel 1 W Channel 2 B Channel 1 W Channel 2 M Channel 1 W Channel 2
Sub-frame Sub-frame
Frame 191
Frame 0
Frame 1
Figure 14. Block format
0 11 00 0 10
Figure 15. A biphase-encoded bit stream
The sub-frame is defined in Figure 16 below. Bits 0-3 of the sub-frame represent a preamble for synchronization. There
are three preambles. The block preamble, B, is contained in the first sub-frame of Frame 0. The channel 1 preamble, M, is
contained in the first sub-frame of all other frames. The channel 2 preamble, W, is contained in all of the second
sub-frames.
Table 4 below defines the symbol encoding for each of the preambles. Bits 4-27 of the sub-frame contain the 24 bit audio
sample in 2’s complement format with bit 27 as the most significant bit. For 16 bit mode, Bits 4-11 are all 0. Bit 28 is the
validity flag. This is “H” if the audio sample is unreliable. Bit 29 is a user data bit. Frame 0 contains the first bit of a 192
bit user data word. Frame 191 contains the last bit of the user data word. Bit 30 is a channel status bit. Again frame 0
contains the first bit of the 192 bit word with the last bit in frame 191. Bit 31 is an even parity bit for bits 4-31 of the
sub-frame.
0
34
L
Sync S
B
Audio sample
Figure 16. Sub-frame format
27 28 29 30 31
M
SV UC P
B
The block of data contains consecutive frames transmitted at a state-bit rate of 64 times the sample frequency, fs. For
stereophonic audio, the left or A channel data is in channel 1 while the right or B data is in channel 2. For monophonic
audio, channel 1 contains the audio data.
Preamble
B
M
W
Preceding state = 0
11101000
11100010
11100100
Preceding state = 1
00010111
00011101
00011011
Table 4. Sub-frame preamble encoding
■ Channel Status bit
In the consumer mode (bit0 = “0”), bits20-23(audio channel) must be controlled by the CS20 bit. When the CS20 bit is
“1”, the AK4345 corresponds to “stereo mode”, bits20-23 are set to “1000”(left channel) in sub-frame 1, and is set to
“0100”(right channel) in sub-frame 2. When the CS20 bit is “0”, bits20-23 is set to “0000” in both sub-frame 1 and
sub-frame 2.
MS0635-E-01
- 14 -
2010/09