Circuit Descriptions, Abbreviation List, and IC Data Sheets
EN 110 LC03E9.
The video delay is significant, due to memory based
processing. For instance, the “frame rate conversion” cause a
delay of two frames, while the LCD panel response also cause
a delay.
The circuit is a (16 bit) FIFO based digital delay. The memory
size required for a 80 ms delay (with a data clock of 1.024 MHz)
can be calculated with: Memory size = delay time * f_clk.
This gives: 80 ms * 1.024 MHz = 81920 bits.
To calculate the memory size for a 16 bits mode I2S digital
audio stream we must use the following data:
• f_s = 32 kHz, 16 bits, stereo
• Data clock = 32 kHz * 16 * 2 = 1.024 MHz
• Memory size for 1 ms delay = 1 ms * 1.024 MHz = 1024 bits
= 1 kbit
So, the delay time of 80 ms can be built with five steps of 16
ms, which is close to the frame rate. Therefore, a 128 kbit
SRAM (16 x 8) is chosen.
9.9 Control
9.9.1 Painter
The microprocessor (SAA55xx, IC7064 called Painter)
provides:
• Control functions for the TV-set.
• On Screen Display (OSD).
• Teletext functions.
• P50 (Easylink) communication.
• I/O-ports for I2C, RC5, LED, and service modes.
• Error code generation.
Ten pages TXT-data can be stored internally. For 100 pages,
an external memory is used (IC7070).
The Non Volatile Memory IC7066 is a 4 kB version
M24C32W6.
All ICs in this part are supplied with 3V5 that is also present
during Standby. This voltage is supplied via voltage regulator
IC7920.
For stable OSD and TXT, the display is synchronised to the TV
signal processing device by way of horizontal and vertical sync
signals provided by external circuits (H-SYNC and V-SYNC).
From these signals, all display timings are derived.
The OSD/TXT RGB-outputs (46/47/48) and fast blanking (52)
are fed to the BOCMA (pins 35 - 38).
9.9.2 I2C-busses
In this chassis, two I2C-busses used:
• Hardware I2C-bus, used for all IC communication.
• Separate short bus for the Non Volatile Memory (NVM), to
avoid data corruption.
9.9.3 NVM
The Non Volatile Memory IC7066 contains all set related data
that must be kept permanently, such as:
• Software identification.
• Operational hours.
• Error-codes.
• Option codes.
• All factory alignments.
• Last Status items for the customer + a complete factory
recall.
9.9.4 Light Control
A pair of light sensors, at the Front Control panel, is used to
monitor the external ambient light condition and adjust the
brightness, contrast, and any relevant video parameters of the
display.
9.10 Inverter
1. Introduction
2. Control
3. Buck Converter
4. Royer Circuit
5. HV Circuit
6. Balance Circuit
7. Feedback Circuit
8. Protection Circuit
9.10.1 Introduction
Figure 9-6 Block diagram Inverter Circuit
This is a separate panel (separate from LCD) for the 15" and
17" models, but is built-in in the 23” LCD panel.
This circuit is a basic DC/AC inverter for driving Cold Cathode
Fluorescent Lamps (CCFL), who are located behind the LCD
panel.
9.10.2 Control
The “On/Off circuit” delivers an input signal to turn the AC
output voltage “on” or “off”:
• ON >= 2.5 V
• OFF <= 2.0 V
This signal switches transistor Q4 "on/off", resulting in "start/
stop" of the buck converter.
9.10.3 Buck Converter
This circuit uses the Power MOSFET (item Q8) to control the
input power for the Royer circuit. It is based on the "Buck
Converter" principle. The transistor switch (Q8) is the heart of
the buck converter, and it controls the power supplied to the
load. It is controlled via a PWM controller (U1, LM339).
The LM339 controls the lamp current and brightness. Its
functions include burst mode control, PWM control, and “soft
start”.
Note: this circuit needs a minimum load, in order to work
properly.
9.10.4 Royer Circuit
This is a standard Royer structure. It transfers the DC input
signal into an AC output signal.
AV4 AV4 (80 ms) AV4 (80 ms) RF (none) AV4 (80 ms)
RF RF (80 ms) RF (80 ms) RF (80 ms) RF (80 ms)
Input
Speaker
out(delay)
Monitor
out(delay)
SCART1
out(delay)
SCART2
out(delay)
CL 36532023_070.eps
140403
BUCK
CIRCUIT
ROYER
CIRCUIT
HV
CIRCUIT
BALANCE
CIRCUIT
Lamp 1 Lamp 2
Input Power
IC
ON/OFF
CIRCUIT
PROTECTION
CIRCUIT
FEEDBACK
CIRCUIT
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