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Circuit Descriptions, Abbreviation List, and IC Data Sheets

Figure 9-12 Block diagram audio processing

9.5.2

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 9-13 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

disadvantag

e 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.

9.6

HDMI

9.6.1

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

8-bit) or 4:2:2 (up to 2

12-bit), where DVI

offers only RGB 4:4:4 (3

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).