An LCD monitor

This is an approx. 10 years old 15" LCD monitor, from the era when LCD monitors just started to be more widely available, and replacing the bulky and quirky CRT monitors at the desks of those who could afford them. I am not going to show the mechanical disassembly - these monitors are all alike, so here just the backside is shown, with the bezel and back cover removed.

The LCD panel itself is not shown here, too. Basically, it consists of two glasses with a mesh of transparent electrodes and a pattern of color filters, spaced a fraction of millimeter apart, filled with the liquid crystal material. The panel also contains the first set of integrated circuits - the row and column drivers. These are in fact only a set of shift registers with an unusually high number of outputs, which can be either driven to one of the relatively unusual supply voltages (such as -6V or +18V), or be left floating.

LCD monitor with back cover off

What we see here is the bulk of electronics in the monitor. In those times, videocards with digital output were very unusual, rare and expensive, so the standard VGA signal/connector (F) was the norm. That signal had to be converted into the serial stream for the panel, this task (among others) was accomplished by the main electronics board (A), which is connected to the LCD panel through two flexible conductor foils (B). The monitor has a non-negligible power consumption of around 30W (which is still maybe an order of magnitude less than a typical CRT monitor's consumption), and is powered from the mains (E) using a switching mode power supply (D). The backlight is provided by fluorescent tubes, which are powered from an inverter (C), covered for reduced electromagnetic interference. The main electronics board (A) was covered by a metal cover, too, which has been removed so that this picture could be taken.

Let's have a closer look at the main electronics board.

main logic board of LCD monitor

The VGA signal enters through connector (A) and after some analog trimming the RGB signals are converted into digital form by a specialized circuit AD9883A of Analog Devices (B). This circuit not contains three blazing fast (140 million samples per second (MSPS)) 8-bit analog-to-digital converter (ADC), but also contains a phase-locked loop (PLL) which enables precise sampling of the analog signal to recover individual pixels.

The digital color data together with the sync signals are then fed to the "fattest" IC on the board, the Trumpion's Zipro (C), which is a specialized circuit (ASIC) for scaling the input picture to the display's native resolution. This circuit also provides the data serialization as required by the panel's row/column drivers, and outputs the serial data/clock/sync mixture onto the panel's connectors (G) and (H).

As both the ADC and the ASIC are overtly complex circuits which have a wide range of settings, depending on the parameters of input signal and the properties of the attached panel, these settings have to be provided to these circuits every time the monitor is powered up. This task is accomplished by a microcontroller (D), here, of W78E62 type, a FLASH-based 8051 derivative by Winbond. This microcontroller provides also the user interface, using a couple of buttons and a two-color LED on a subboard connected through connector (K), storing the user-chosen values into a standard serial EEPROM of 24C16 type (E). The microcontroller displays the on-screen (OSD) menu using a specialized circuit also by Trumpion (F), which outputs the OSD signal to the ASIC, which in turn mixes it into the signal from the VGA input.

There is also a small, relatively independent circuit based on a serial EEPROM 24C21 (M), which through connector (L) provides into the VGA cable a couple of signals according to the DDC standard. This allows the PC to "enquire" the monitor about its type and capabilities.

As the panel requires almost half a dozen of different supply voltages, which have to be switched on and off in a given sequence, and have to be precisely stabilized to prevent flickering and other artefacts in the picture, there is a relatively complex power supply built around a switching converter IC (I), which is supplied from the main power supply through connector (N), and provides also power for the backlighting inverter (J).


LCD monitors are a commonplace by now, but are still a marvellous piece of advanced technology, electronics design and manufacturing.