2.2.1.1. Broadcast Channel Timing
The incoming Broadcast Channel bitstream has a
framing with a period between Prime Rate Channel
Preambles (PRCP) of
prcpt = 432 ms
During one frame the transmission of the BC is inter-
rupted by a gap
prcpgap
of:
prcpgap = 2.5 ms
The data transmission is interrupted by a second gap
mfpgap
with a duration of
mfpgap = 1.2 ms
that is synchronous with the Master Frame Preamble
(MFP) cycle with a period of:
mfpt = 138 ms
Both cycles
mfpt
and
prcpt
have a least common multi-
ple at 9936 ms. These gaps are independent of the
number of Prime Rate Channels (PRC)
n
that create
the considered Broadcast Channel.
PRELIMINARY DATA SHEET
2.2.2. Broadcast Channel Demultiplexing
The Service Control Header that directly follows the
SCH-preamble in the BC bitstream is made accessible
to the controller after it has been detected. Its availabil-
ity is indicated by the BC-FRAME-SYNC signal. Infor-
mation about the content of the Broadcast Channel is
given in the Service Control Header data. The control-
ler may select the number of the Service Component
that is to be passed to the internal MPEG audio
decoder. By default, always Service Component “0” is
decoded by the MAS 3506D. An implemented
autoscan mode can be selected that skips non-audio
Service Components.
2.2.3. MPEG Audio Decoding
The MPEG 1/2/2.5 Layer 3 decoder performs the
audio decoding. The steps for decoding are:
– Synchronization
– Side information extraction
– Huffman decoding
– Synthesis filter bank
– Ancillary data extraction
The bit rates and sampling rates that are supported by
the MAS 3506D are listed in Table 2–1.
Table 2–1:
Sampling frequencies and bit rates
Sampling Freq. in kHz
48, 32, 24, 16, 12, 8
Bit rates in kBit/s
128, 112, 96, 80, 64, 56,
48, 40, 32, 24, 16, 8
2.2.1.2. Buffer-Controlled Loop
For the recovery of the audio sample clock, a buffer-
controlled loop is used that operates on the incoming
Broadcast Channel bit stream. The buffer control loop
characteristic suppresses the effects of these gaps on
the stability of the generated audio sample frequency
by more than 40 dB. Thus, no audible jitter is intro-
duced to the derived reference clock for the D/A con-
verter (see section 2.3. "Clock Management").
The step response of the buffer-controlled loop is plot-
ted in Figure 2–2 with respect to different number of
PRCs. The settling time for the buffer-controlled loop is
about 10 s.
0.12
0.1
0.08
0.06
0.04
0.02
4.3
8.6
13
17
21
Frame synchronization and decoding error signals are
provided at output pins of the MAS 3506D.
2.2.4. Baseband Processing
A digital volume control matrix is applied to the digital
stereo audio data. This matrix may also perform addi-
tional balance control and a simple kind of stereo
basewidth enhancement. The four factors LL, LR, RL,
and, RR are adjustable via the controller with 20 bit
resolution (see Fig. 3–2 on page 28).
t/s
Fig. 2–2:
buffer-controlled loop step response
8
Micronas
MICRONAS [ MICRONAS ]
