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Circuit Descriptions, Abbreviation List, and IC Data Sheets
2
•
Three I
S-inputs for signals ("DATA", "CLK" and "WS")
coming from the HDMI interface
•
Five analogue inputs: for CVI1, CVI2, AV1, AV2, DTV
(China) and PC audio
•
Loudspeaker output path
•
Headphone output path
•
Monitor output path (WYSIWYG).
Digital audio signals coming from HDMI sources are directly
fed to the MSP via the I2S_DA_IN3, I2S_WS3 and I2S_CL3
lines. This ensures a "true digital path".
In case of reception of digital TV signals, a multiplexer is used
to switch between China DTV or DVI2 audio. In China sets, the
audio signal coming from the DTV module is in analogue
format. The output from the multiplexer is fed to the MSP via
the SC5-input.
In both applications, the microprocessor (item 7311) controls
the audio part with the following control lines:
•
MUTEn: used to mute the Class D amplifiers
•
ANTI_PLOP: used to detect any DC failure in the Class D
amplifiers
•
DC_PROT: used to detect any DC failure in the Class D
amplifiers.
9.7.2
Audio Amplifier
The audio amplifier is an integrated class-D amplifier
(TDA8932T, item 7A01). It combines a good performance with
a high efficiency, resulting in a big reduction in heat generation.
Principle
Figure 9-11 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.
+V
-V
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LC7.1E LA
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.
9.8
HDMI
9.8.1
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 DVD players, set-top boxes
and other 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.
9.8.2
Implementation
The IC used is the Sil 9025 (Silicon Image) third generation
HDMI receiver, item 7817 on the SSB.
It has the following features:
•
Dual HDMI input connector
•
Two EEPROMS to support EDID
•
HDMI audio
2
•
I
S output to low-cost DACs which operate at a frequency
of 32 to 192 kHz
•
Integrated HDCP decryption engine
•
Built-in pre-programmed HDCP keys for highest level of
copy-protection security
•
Colour space conversion RGB to YCbCr
•
"Hot Plug Reset" signal.
Figure "HDMI implementation" shows the HDMI configuration
in this chassis.
9.
EN 79
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