Philips A02U AA Service Manual page 110

EN 110 9.
selected SSIF passes some anti-alias filtering, is amplified in
an AGC amplifier and is then converted from analog to digital
(SSIF AGC/ADC). Together with other signals, the digitized
SSIF is transferred via an I2D-Link to the ADOC IC.
The audio signal out of the AM demodulator is connected to the
analog X-bar in the MPIF IC. All other inputs to this multiplexer/
audio switch come from external, either from the PIP front end
(AMEXT/PIPMONO) or SCART/CINCH (AUDxin) or the DAC1,
DAC2 output signals from ADOC. The audio AD converters are
digitizing the audio signals foreseen for further digital
processing in ADOC. Three stereo outputs (AUDx out, LINE
out) are available for connections to SCART/CINCH sockets.
The sound part of ADOC consists of the demodulator/decoder
(DEMDEC), sample rate conversion (SRC), a digital input X-
bar, the digital audio processing for the loudspeaker,
headphone and DAC channels, the I2S processing and
interfacing as well as the DA conversion. This part will be
described in the next chapter.
9.7.3
ADOC Sound part
Introduction
The ADOC sound part contains two DSP cores as shown in the
block diagram. The first core called DEMDEC-DSP is
combined with DEMDEC (Demodulation/Decoding) hardware
and the second core is the AUDIO-DSP. The DEMDEC-DSP is
used for the decoder and demodulator tasks, plus the sample
rate conversion.
The AUDIO-DSP is used for the sound features, from the level
adjust unit up to the output cross bar. Audio DACs and I2S
hardware (optional) are converting the processed signals to
analog or digital audio.
All I2D data links carry sound signals. The data link processing
splits them from the other signals as video so that the DEMDEC
block receives the second sound IF (SSIF) and the audio
signals from the audio ADCs of the MPIF IC. The SSIF needs
some hardware processing before it enters the DEMDEC DSP.
The DEMDEC processing will be described in the next chapter.
The audio signals from the audio ADCs of the MPIF are
passing the DEMDEC DSP only for source selection and
sample rate conversion.
In this chassis, two of the DAC outputs are used to feed a
headphone. Two other DAC stereo outputs are provided for the
audio feedback to the MPIF IC. They are located to pins of the
ADOC that suit best for connection to MPIF.
7300-x
ADOC SOUND & AUDIO PROCESSING
Demodulation and Decoding DSP
Down
SSIF Preprocessing
Mix
B5
EXT. STEREO
Decimation
Filter
EXT. MONO
I/P
Level
Audio Processing DSP
X-
Adj.
Bar
I2SIN
7300-B N.C.
Figure 9-19 ADOC sound processing block diagram
DEMDEC DSP
The output signals of the above-mentioned hardware blocks,
plus four audio ADC channels are read in by the DEMDEC
DSP, processed, converted to the current audio sample rate,
A02U AA Circuit Descriptions, Abbreviation List, and IC Data Sheets
VDDCO
DDEP
Dematrix
SRC
and Select
AUD_SPK_R
AUD_SPK_L
AUD_SPK_SW
AUD_SPK_C
AUD_SPK_SL
O/P
X-
AUD_HP_R
Bar
DAC
WS PLL
AUD_HP_L
DSNDR2
I2SOUT
CL 36532058_077.eps
N.C.
"demultiplexed", and forwarded to the Audio DSP for further
processing (volume, tone control, effects etc.).
Down Mixer
The digitized SSIF input signal is fed to the mixers, which mix
one or both input sound carriers down to zero IF.
Pre-processing
This part contains the sound system identification and
demodulation circuitry.
Audio Sample Rate Conversion (SRC)
All input signals pass through a sample rate conversion to the
actual output sample rate (usually 48 kHz) such that the output
rate does not need to be synchronized with any of the input
rates. Up to five separate channels can be converted.
Audio Processing DSP
This block applies several filters, like down-sampling and de-
emphasis, noise reduction processing, performs a sample rate
conversion (SRC) to the current audio sample rate, and routes
the decoded signals to the output channels.
The generic processing controls are Volume, Bass, Treble,
Balance, Incredible Surround, Spatial (incredible mono), DBE,
Dynamic Ultra Bass II (for non-woofer sets only), AVL, Sub-
Woofer, and 5-band Graphic equalizer.
The Headphone volume can be separately controlled in the
Headphone menu without affecting the master volume (the
setting of the volume tables will be adapted after fine tuning).
For variable volume output for USA, the DAC1 output will
switch to the Main channel and therefore the same volume
curve for the Main Channel can be used.
9.7.4
Audio Amplifier
Speakers (diagram A6)
The audio output stage is built around IC7701, which is a
balanced amplifier, and is located on the LSP. It uses a
monolithic integrated power amplifier IC, the TDA7497. The
gain of the amplifier is constant. This means that volume
control is done via the ADOC.
The supply voltage is +28 V, generated by the power supply via
L5506 (or L5512). The TDA7497 delivers an output of 3 x 10
W_rms to two full range speakers and a (optional) subwoofer.
Muting
VDDE
There are three types of muting available: system mute,
headphone status mute, and user mute.
•
System mute. System muting is implemented for "special
events" such as channel/source change event, loss of
identification signal, "on/off" switching of the set, during
search and auto store/program, and/or sound mode
change. This muting is transparent to the user. Audio
output is muted before the above "special events"
occurred, to prevent problems such as audible plop. Muting
is done via the SOUND-ENABLE (software controlled) and/
or POR (hardware controlled) line connected (via TS7710
and 7711) to pin 10 of the amplifier-IC and coming from the
ADOC microprocessor.
•
Headphone status mute. A headphone status is available
to detect the presence of the headphone and mute the
DSNDL2
main speakers if the headphone is detected. The
DSNDR1
microprocessor will read the FRONT-DETECT status.
DSNDL1
•
User mute. This is a mute option available to the user. The
281003 user select the MUTE option on the remote control to
switch "off/on" the sound output to the main loudspeaker
and the (optional) subwoofer.
Headphone amplifier (diagram A7)
The headphone amplifier is built around IC7751 (NJM4556),
which is a high-gain, high output current dual operational
amplifier. The supply voltage is +5 V.