Philips 28PW9618, Service Manual

Page: 139 / 172

Circuit Descriptions, Abbreviation List, and IC Data Sheets
EN 139 EM6E 9.
Both channels contain an "automatic carrier mute" function,
which automatically mutes the output of the analogue section
when no carrier is detected.
After demodulation, the FM-signals are subjected to a de-
emphasis operation. After that, the matrix of the stereo system
is applied.
9.7.3
Audio: Processing
Figure 9-10 Audio processing block diagram
The sound processing is performed completely by the MSP:
•
The user performs volume control via the SOUND menu.
•
Tone control in "Stereo" sets is performed via the BASS/
TREBLE control.
•
Headphone control: the MSP has a separate Headphone
output so separate sound control is possible.
The Micronas Dolby Digital System
The Micronas Dolby Digital system solution consists of three
dedicated integrated circuits:
•
The MSP 44x0G is the interface for all TV-sound and
analogue input signals. It performs the TV-audio
demodulation including analogue stereo, NICAM, and
Wegener Panda decompression. It has four pairs of audio
D/A-converters, two of them including sound control
facilities, and one additional subwoofer D/A converter.
•
The DPL 4519G adds the Dolby Surround Sound features
and has three pairs of audio D/A-converters, two of them
including sound control facilities, and one additional
subwoofer D/A converter.
•
The MAS 3528E performs the Dolby Digital or MPEG
decoding and has additional functions that are necessary
for the Dolby Digital system.
While the MSP 44x0G is a stand-alone TV-sound solution, the
combination with a DPL 4519G results in a high-end TV with
Dolby Pro Logic functionality. With the addition of the MAS
3528E, the TV provides full Dolby Digital/MPEG-1 capabilities.
Micronas DPL 4519G
The DPL 4519G receives its incoming data via an I2S interface.
The synchronisation is performed by means of an adaptive
high-quality sample rate converter.
In an application together with the Dolby Digital decoder MAS
3528E, eight channels (left, right, surround left, surround right,
centre, subwoofer, Pro Logic encoded left, Pro Logic encoded
right) are fed in and processed in the DPL 4519G.
Similar to the multichannel I2S input interface, the DPL is
provided with an 8-channel I2S output interface, which is
connected to the MSP 44x0G. Therefore, all eight channels
can be routed to each output in both ICs.
The base band processing including e.g. balance, bass, treble,
and loudness is performed at a fixed sample rate of 48 kHz.
Micronas MAS 3528E
The MAS 3528E receives S/PDIF or serial data streams, and
decodes the Dolby Digital (AC-3), MPEG or PCM-encoded
audio formats.
Due to the automatic format detection, no controller interaction
is needed for the standard operation. On the other hand, the
controller has full access to all vital information contained in the
Dolby Digital bit stream.
The choice of different output formats, as defined by Dolby,
guarantees good adaptation to various listening environments.
The hardware of the MAS 3528E consists of a high
performance RISC Digital Signal Processor (DSP) and
appropriate interfaces.
The MAS 3528E is driven by a single clock at a frequency of
18.432 MHz. The clock is provided from an external source
(SYS-CLK1 from the DPL 4519G) to pin XTI.
9.7.4
Audio: Amplifier
The audio amplifier is an integrated "class-D" power amplifier
IC, the TDA7490. It delivers an output of 2 x 15 W_rms to two
full range speakers. For the higher specified sets, a subwoofer
and centre speaker are easy to implement, by adding a second
amplifier. This circuit is described in the EM5 manual.
9.7.5
Audio: Headphone Amplifier
The headphone amplifier is a straightforward OpAmp amplifier
(ICA07-A, MC33178D). It is supplied with +11V_AUD.
9.8
Wireless Surround Loudspeaker System
9.8.1
Introduction
With the Wireless Surround Loudspeaker System, it is possible
to connect rear speakers wireless with the main set. The
system consists of:
•
Transmitter part (TX): a transmitter board (click-on
module).
•
Receiver part (RX): a receiver board, an amplifier board,
and a power supply part.
•
Loudspeaker boxes for Left and Right rear.
The wireless system is intended for stereo sound in the range
from 20 Hz to 20 kHz.
It can be used for normal L/R stereo sound or for the surround
channels in Dolby systems.
The system has an analogue sound processing system
(compressing - expanding) and uses synthesised tuning at
both the transmitter and receiver side. There are frequency
executions available in different frequency bands:
•
433 MHz (some EU countries).
•
864 MHz (EU).
In each particular frequency band, there is a choice between
four different channels or frequencies.
System Considerations
The Wireless system uses a very high performance audio
processing that allows up to 100 dB dynamic range to be
transmitted over a classic analogue link, through the
compressing effect at the transmitter (reducing the dynamic
range by a factor of 2 in dB) and the expanding effect in the
receiver (increasing the dynamic range by a factor of 2 in dB).
In addition, the system has the possibility to maintain the high
S/N up to low RX field strengths by applying sliding stereo (this
means reducing the stereo effect at low signal field strengths).
Pre-emphasis (at TX) / de-emphasis (at RX) technique is
with15 us time constance.
Since the signal processing is analogue, there is a low latency
in the system of < 15 us between input TX and output RX.
The receiver part has a power save mode that will be initiated
automatically when no signal to reduce power consumption.
MSP
SW
L
R
Headphone or C/S
SC1
SC2 Monitor
QSS
7A02
7A63
7A30
I
2
C DPL
I
2
S MSP
Sys-CLK0
DDD
17
Sys-CLK1
DPL
Decoder
Sys-CLK
AM-PIP
SND_4R
(optional)
Main in
Center in
I
2
S DD
SPDIF 1/2 IN SPDIF OUT
Subw
Center
Sur-L
Sur-R
CL 36532008_137.eps
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