Hitachi, Ltd. (NYSE:HIT) today announced a low-power-consumption liquid crystal driver 
chip-set, comprising the HD66136 and HD66137, which is ideal for use with liquid crystal 
displays in portable information devices such as PDAs (personal digital assistants).  Sample 
shipments will begin in December 1998 in Japan.

LCDs, with their features of lightness, thinness, and low power consumption, are widely 
used as display systems in portable information devices such as PDAs.  With the increasing 
popularity of portable telephones and the Internet, there is a demand for higher quality 
displays in portable information devices, including larger screen size and color capability, as 
well as ultra-low power consumption allowing use of these devices for periods exceeding 20 
hours.

With a conventional LCD panel configuration, improving picture quality by increasing the 
display area, providing color capability, and so forth, means increasing the number of drive 
elements, and thus also the power consumption.  While various techniques have already been 
devised to reduce the power consumption of the logic circuits within LSIs, it also became 
necessary to devise a drive method that reduces the charge/discharge power of the liquid 
crystal panel, which is driven at a high voltage.

With the conventional liquid crystal drive method, liquid crystal elements are charged and 
discharged using the same high voltage (of around 20 V or so) for both segment and 
common drivers.  Usually, the segment drivers switch the output potential at high speed, and 
a large number are used to provide color capability. The common drivers, on the other hand, 
operate at low speed, performing only line scanning pulse drive, and only one or two are 
used in the system configuration.

By using a new drive method that employs a low drive voltage of 3 to 6 V for the large 
number of high-speed segment drivers, it is possible to reduce the liquid crystal panel 
charge/discharge power and greatly decrease the overall power consumption of large, color 
LCDs, something that has previously been difficult to achieve.

In developing the HD66136/HD66137 liquid crystal chip-set for medium-sized color LCDs 
of 320×240 to 640×240 dots, ideal for color PDA use, Hitachi has employed a new liquid 
crystal drive method to achieve lower power consumption.

In addition to cutting power consumption, the new liquid crystal drive method used in this 
chip-set also provides improved image quality by reducing the amplitude of the liquid crystal 
drive waveform, thus minimizing drive waveform distortion and preventing a decrease in 
contrast.

The HD66136/HD66137 chip-set is of the simple driver type, and has the same drivers and 
interface as the conventional drive method, allowing a conventional liquid crystal module to 
be directly replaced by a module using this chip-set.  This alone will result in an 
approximately 50% reduction in overall display system power consumption (in the case of a 
640×240-dot color display).

The HD66136 segment driver chip can switch between 400 and 384 liquid crystal drive 
outputs, for compatibility with a wide variety of liquid crystal panels, and when used in 
combination with the HD66137 common driver chip, can implement a 640×240-dot color 
display with a 5-chip/1-chip configuration, enabling the number of parts to be significantly 
reduced.

The HD66137 common driver chip incorporates part of the liquid crystal drive power supply 
circuitry, enabling a conventional power supply circuit to be used with the new drive 
method.  In addition, signals for liquid crystal drive output alternation can be set for any 
number of lines, to suit the frequency characteristics of the liquid crystal used.

The packages used are TCPs (tape carrier packages), for lightweight, compact liquid crystal 
displays with a small mounting area.  Future development plans include models offering an 
even greater reduction in power consumption.

< Applications >
PDAs
Sub-notebook PCs

< Prices in Japan >

< Features >
1. Low power consumption
Use of a new low-voltage liquid crystal drive method has enabled the segment driver liquid 
crystal drive voltage to be reduced to 3 to 6 V, reducing power consumption to 50% that of 
the conventional method.
2. Improved display quality
Use of a low-voltage liquid crystal drive method has improved the display quality by 
reducing crosstalk, etc.
3. Large number of outputs
An increased number of outputs enables the number of parts to be reduced.
4. Part of power supply circuitry provided on-chip (HD66137)
A conventional power supply circuit can be used with the new liquid crystal drive method.

< Specifications >
HD66136 (segment driver chip)

HD66137 (common driver chip)