TDA9875AH Philips Semiconductors, TDA9875AH Datasheet - Page 18

• Manufacturer Part Number: TDA9875AH
• 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 TDA9875A (see Figs 6 and 8). 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 TDA9875A 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
(see Fig.7).
The analog matrix provides the functions given in Table 6.
Table 6 Analog matrix functions
All switches and matrices are controlled via the I
1999 Dec 20
handbook, halfpage
1
2
3
4
Digital TV Sound Processor (DTVSP)
MODE
A
right input
NALOG CROSSBAR SWITCH AND ANALOG MATRIX
left input
Fig.7 Analog matrix.
left input
right input
left input
right input
LEFT OUTPUT
ANALOG
MATRIX
MATRIX OUTPUT
left output
right output
right input
left input
left input
right input
RIGHT OUTPUT
MGK110
2
C-bus.
18
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 TDA9875A, 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 a maximum
input of 1.4 V), there are 0/3 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.
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 or 0 dB via the I
The 3 dB position is needed to compensate for 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.
SCART
E
SCART
XTERNAL AND MONO INPUTS
INPUTS
OUTPUTS
Product specification
TDA9875A
2
C-bus.