TDA9874A Philips Semiconductors, TDA9874A Datasheet - Page 14

• Manufacturer Part Number: TDA9874A
• Description: Digital TV sound demodulator/decoder
• Manufacturer: Philips Semiconductors

Philips Semiconductors
6.3
6.3.1
The TDA9874A has one external analog stereo input, one
mono input, one 2-channel and one single-channel output
port. Analog source selector switches are employed to
provide the desired analog signal routing capability, which
is done by the analog crossbar switch section.
The basic signal routing philosophy of the TDA9874A is
that each switch handles two signal channels at the same
time (e.g. left and right, language A and B) directly at the
source. For an overview of the signal flow see Fig.7.
Each source selector switch is followed by an analog
matrix to perform further selection tasks, such as putting a
signal from one input channel, say language A, to both
output channels or for swapping left and right channels.
The analog matrix provides the functions given in Table 5.
Automatic matrixing for TV applications is also supported.
All switches and matrices are controlled via the I
Table 5 Analog matrix functions
1999 Dec 03
handbook, full pagewidth
Digital TV sound demodulator/decoder
MODE
Description of the analog audio section
A
1
2
3
4
NALOG CROSSBAR SWITCH AND ANALOG MATRIX
mono (AM)
L OUTPUT
R input
R input
EXTIR
DACM
L input
L input
DACR
EXTIL
DACL
MATRIX OUTPUT
Fig.6 Switch diagram for the analog audio section.
R OUTPUT
R input
R input
L input
L input
2
C-bus.
source select
14
6.3.2
The external and mono inputs accept signal levels of up to
1.4 V (RMS). By adding external series resistors to
provide suitable attenuation, the external input could be
used as a SCART input. Whenever the external or mono
input is selected, the output of the DAC is muted to
improve the crosstalk performance.
6.3.3
The TDA9874A comprises a 2-channel audio DAC and an
additional single-channel audio DAC for feeding signals
from the DSP section to the analog crossbar switch. These
DACs have a resolution of 15 bits and employ four-times
oversampling and noise shaping.
6.3.4
The output buffers provide a gain of 0 dB and offer a
muting possibility. The post filter capacitors of the audio
DACs are connected to the buffer outputs.
6.3.5
The standby mode (see Section 10.3.3) disables most
functions and reduces power dissipation of the
TDA9874A. It provides no other function.
Internal registers may lose their information in standby
mode. Therefore, the device needs to be initialized on
returning to normal operation. This can be accomplished in
the same way as after a Power-on reset.
E
A
A
S
matrix
XTERNAL AND MONO INPUTS
UDIO
UDIO OUTPUT BUFFERS
TANDBY MODE
DAC
S
OUTL
OUTR
OUTM
MHB589
Preliminary specification
TDA9874A