SAA2501 Datasheet, PDF (18/52 Pages) NXP Semiconductors – Digital Audio Broadcast DAB decoder

Philips Semiconductors
Digital Audio Broadcast (DAB) decoder
Preliminary specification
SAA2501
ndbook, full pagewidth
transferred
input frame bits
slope: maximum
input bit rate
(1)
n
slope: CDSCL
frequency
B
B0
(2)
(3)
MGB498
B
B
slope: effective
input bit rate
t
time
(1) The actual transferring characteristics of all frames are restricted to this area.
(2) Effective transferring characteristic (example).
(3) Actual transferring characteristic of the first frame (example).
Fig.10 Slave input data transferring for the first frame.
The shaded area in Fig.10 represents the restrictions to
the actual transferring characteristic of all frames. The
actual transferring characteristic may not undercut the
effective transferring characteristic by more than B bits to
avoid an input underflow. On the other hand, the actual
transferring characteristic may not cross the shown upper
limit of the shaded area to prevent an input buffer overflow.
The slope of this upper limit is determined by the maximum
effective input bit rate (depending on the input data
format). Table 9 summarizes the slopes as determined by
the bit rates supported by ISO/MPEG and EU147.
Table 9 Slopes determined by bit rates supported by
ISO/MPEG and EU147
ISO/MPEG
AND EU147
LAYER
ISO/MPEG
layer I
ISO/MPEG
layer II
EFFECTIVE
INPUT BIT
RATE
(kbits/s)
±13.3⁽¹⁾ to ±448
TRANSFERRING
UPPER LIMIT
SLOPE
(kbits/s)
448
3.5⁽¹⁾ to 384
384
Note
1. Achieved using the free format option and the
minimum amount of the side information that must be
transmitted (this means using single channel mode, no
CRC and 32 kHz sample rate).
7.17.4 SLAVE INPUT TRANSFER SPEED OF SUBSEQUENT
FRAMES
The SAA2501 starts decoding as soon as enough data of
the first ISO/MPEG or EU147 input data frame has been
received. Thus the start moment of decoding depends on
the actual transferring characteristic of the first frame.
Decoding start times of subsequent input data frames are
also governed by this initial start time.
For this reason the transferring characteristic of all
subsequent frames must approximate the characteristic of
the first frame within the buffer margin ±B. For the example
shown in Fig.10, subsequent frames must be transferred
within the shaded area shown in Fig.11.
January 1995
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