TDA9875 Philips Semiconductors, TDA9875 Datasheet - Page 17

• Manufacturer Part Number: TDA9875
• Description: Digital TV Sound Processor DTVSP
• Manufacturer: Philips Semiconductors

Philips Semiconductors
6.3.1
There are a number of analog input and output ports with
the TDA9875. Analog source selector switches are
employed to provide the desired analog signal routing
capability. The analog signal routing is performed by the
analog crossbar switch section. A dual audio ADC
provides the connection to the DSP section and a dual
audio DAC provides the connection from the DSP section
to the analog crossbar switch. The digital signal routing is
performed by a digital crossbar switch.
The basic signal routing philosophy of the TDA9875 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.
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 6
(see also Fig.5).
Table 6 Analog matrix functions
All switches and matrices are controlled via the I
There is one restriction for switching signals at inputs and
outputs for SCART 1 and SCART 2. At these ports, an
input signal cannot be copied to its own output, i.e. it is not
possible to make a copy from SCART 1 input to SCART 1
output.
1998 Feb 13
handbook, halfpage
Digital TV Sound Processor (DTVSP)
MODE
A
(see also Fig.6)
1
2
3
4
right input
NALOG CROSSBAR SWITCH AND ANALOG MATRIX
left input
Fig.5 Analog matrix.
LEFT OUTPUT
right input
right input
left input
left input
ANALOG
MATRIX
MATRIX OUTPUT
left output
right output
RIGHT OUTPUT
MGK110
right input
right input
left input
left input
2
C-bus.
17
6.3.2
The SCART specification allows for a signal level of up to
2 V (RMS). Because of signal handling limitations, due to
the 5 V supply voltage of the TDA9875, it is necessary to
have fixed 3 dB attenuators at the SCART inputs to obtain
a 2 V input. This results in a 3 dB SCART-to-SCART
copy gain. If 0 dB copy gain is preferred (with maximum
1.4 V input), there are +3 dB/0 dB amplifiers at the outputs
of SCART 1 and SCART 2 and at the line output.
The input attenuator is realized by an external series
resistor in combination with the input impedance, both of
which form a voltage divider. With this voltage divider the
maximum SCART signal level of 2 V (RMS) is scaled
down to 1.4 V (RMS) at the input pin. If it is known for
certain applications that the input signal level is always
below 1.4 V (RMS), the SCART inputs can be used
without external resistors.
6.3.3
The 3 dB input attenuators are not required for the external
and mono inputs, because those signal levels are under
control of the TV designer. The maximum allowed input
level is 1.4 V (RMS). By adding external series resistors,
the external inputs can be used as an additional SCART
input.
6.3.4
The SCART outputs employ amplifiers with two gain
settings. The gain can be set to +3 dB or to 0 dB via the
I
the 3 dB attenuation at the SCART inputs should
SCART-to-SCART copies with 0 dB gain be preferred
[under the condition of 1.4 V (RMS) maximum input level].
The 0 dB position is needed, for example, for an
external-to-SCART copy with 0 dB gain.
6.3.5
The line output can provide an unprocessed copy of the
audio signal in the loudspeaker channels. This can be
either an external signal that comes from the dual audio
ADC, or a signal from an internal digital audio source that
comes from the dual audio DAC. The line output employs
amplifiers with two gain settings. The +3 dB position is
needed to compensate for the attenuation at the
SCART inputs, while the 0 dB position is needed, for
example, for non-attenuated external or internal digital
signals (see Section 6.3.4).
2
C-bus. The +3 dB position is needed to compensate for
SCART
E
SCART
L
INE OUTPUT
XTERNAL AND MONO INPUTS
INPUTS
OUTPUTS
Preliminary specification
TDA9875