TDA9874AHB View Datasheet(PDF) - NXP Semiconductors.
Part Name
Description
MFG CO.
'TDA9874AHB' PDF : 69 Pages View PDF
Philips Semiconductors
Digital TV sound demodulator/decoder
Product specification
TDA9874A
6.3 Description of the analog audio section
6.3.1 ANALOG CROSSBAR SWITCH AND ANALOG MATRIX
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 I2C-bus.
6.3.2 EXTERNAL AND MONO INPUTS
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 AUDIO DACS
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 AUDIO OUTPUT BUFFERS
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.
Table 5 Analog matrix functions
MODE
1
2
3
4
MATRIX OUTPUT
L OUTPUT
R OUTPUT
L input
R input
L input
R input
R input
L input
L input
R input
6.3.5 STANDBY MODE
The standby mode (see Section 7.3.3) 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.
handbook, full pagewidth
mono (AM)
EXTIL
EXTIR
source select
matrix
OUTL
2000 Aug 04
DACL
DACR
OUTR
DACM
OUTM
MHB589
Fig.6 Switch diagram for the analog audio section.
14
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