Philips 19PFL5522D Service Manual page 84

EN 84 9. LC7.2E LB
Principle
Figure 9-10 Principle Class-D Amplifier
The Class D amplifier works by varying the duty cycle of a
Pulse Width Modulated (PWM) signal.
By comparing the input voltage to a triangle wave, the amplifier
increases duty cycle to increase output voltage, and decreases
duty cycle to decrease output voltage.
The output transistors of a Class D amplifier switch from 'full off'
to 'full on' (saturated) and then back again, spending very little
time in the linear region in between. Therefore, very little power
is lost to heat. If the transistors have a low 'on' resistance
(RDS(ON)), little voltage is dropped across them, further
reducing losses.
A Low Pass Filter at the output passes only the average of the
output wave, which is an amplified version of the input signal.
In order to keep the distortion low, negative feedback is
applied.
The advantage of Class D is increased efficiency (= less heat
dissipation). Class D amplifiers can drive the same output
power as a Class AB amplifier using less supply current.
The disadvantage is the large output filter. The main reason
for this filter is that the switching waveform results in maximum
current flow. This causes more loss in the load, which causes
lower efficiency. An LC filter with a cut-off frequency less than
the Class D switching frequency, allows the switching current
to flow through the filter instead of the load, thus reducing the
overall loss and increasing the efficiency.
DC-protection
A DC-detection circuit is foreseen to protect the speakers. It is
built around three transistors (items 7A05 to 7A07) and
generates a protection signal (DC_PROT) to the
microprocessor in case of a DC failure in the Class D
amplifiers.
Circuit Descriptions, Abbreviation List, and IC Data Sheets
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9.9 HDMI
9.9.1 Introduction
Note: Text below is an excerpt from the "HDMI Specification"
that is issued by the HDMI founders (see http://www.hdmi.org).
The High-Definition Multimedia Interface is developed for
transmitting digital signals from audiovisual sources to
television sets, projectors and other video displays.
HDMI can carry high quality multi-channel audio data and can
carry all standard and high-definition consumer electronics
video formats. Content protection technology is available.
HDMI can also carry control and status information in both
directions.
HDMI is backward compatible with DVI (1.0). Compared with
DVI, HDMI offers extra:
• YUV 4:4:4 (3 x 8-bit) or 4:2:2 (up to 2 x 12-bit), where DVI
offers only RGB 4:4:4 (3 x 8 bit).
• Digital audio in CD quality (16-bit, 32/44.1/48 kHz), higher
quality available (8 channels, 192 kHz).
• Remote control via CEC bus (Consumer Electronics
Control): allows user to control all HDMI devices with the
TV's remote control and menus.
• Smaller connector (SCART successor).
• Less cables: e.g. from 10 audio/9 video cables to 3 HDMI
cables.
9.9.2 Implementation
The IC used is the Sil 9025 (Silicon Image) third generation
HDMI receiver (item 7817 on the SSB) with following features:
• Dual HDMI input connector.
• Two EEPROMS to support EDID.
• HDMI audio.
2
• I S output to DACs which operating freq. of 32 to 192 kHz.
• Integrated HDCP decryption engine.
• Built-in pre-programmed HDCP keys for copy protection.
• Colour space conversion RGB to YCbCr.
• "Hot Plug Reset" signal.
HDMI 1
DDC Reset
(Port 1)
HDMI
EDID
Receiver
Sil9025
(Port 2)
HDMI 2
EDID
COMP_AUDIO LR
for DVI audio input
only
Figure 9-11 HDMI implementation
HDMI connectors 1 and 2 are connected to resp. ports 1 and 2
of the HDMI receiver. The ports cannot be activated at the
same moment. Switching is controlled by software.
"Hot Plug Reset" and "DDC Reset" are controlled by the
microprocessor.
The HDMI receiver will convert all RGB or YCbCr 4:2:2 signals
to 24-bit YCbCr 4:4:4. When it receives a YCbCr 4:4:4 signal it
will just pass the signal directly to the Trident Video Processor.
Hot plug
HDMI_HOTPLUG_RESE T
Reset
DDC_RESET
Microprocessor
RST
I 2 C
Data Enable
Trident
HDMI CLK
24 bits YCbCr 4:4:4
CX32
H and V Sync
I 2 S
HDMI_Audio LR
I2S DAC
Audio Processor
Micronas MSP4450P
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