LCD Display Drivers

Over the past year I have pulled apart several old phones. I thought it would be interesting to look at a selection of the LCD display drivers and how they have progressed.LCD DisplaysI am going to look at three LCD displays, the first from the Nortel Meridian office phone from 1994 with a 2-line 24 character LCD.  Secondly from a Panasonic cordless phone from 2005 also with a 2-line backlit LCD.  And the last is the display from a Blackberry 8830 from 2007. This one is more advanced with a 2.5″ (Diagonal) 320 x 240 pixel colour display.

Nortel Meridian LCD Display

Made circa 1994/1995 the display uses a conventional daughter board PCB connected to the LCD panel with a 94 pin flex connector.Meridian LCD On the front of the board the LCD display driver is split into two chips. Conventionally bonded and placed on the board, however the die are not in normal plastic packages.  Instead they have a thin rough plastic coating. They also do not have any package marks, which is typical of display drivers.  I don’t know why they do not label/brand the parts, perhaps it is related to the supply chain of the display module.  Maybe the LCD module makers control the IP and make it harder for new entrants in the space.  In nearly all the other chip applications package branding is the norm.


A single sided board with nothing of interest on the back




Meridian Large Die

Looking first at the large die which is 5.56 mm x 6.02 mm (33.5mm2)  a fairly large piece of silicon for 1994Larger Display Driverclick on image for higher resolution version

The only die mark 3C7985-8733 is an internal code number and there are no manufacturers logo. Thus the die will have to remain anonymous forever.

The part is made in a 3μm CMOS process, which is consistent with the Nortel and Motorola  parts I previously looked at in this phone. Here is a section of CMOS logic. What is neat is that you can see the polysilicon layer clearly has two colors. The green and brown sections are differentiating the PMOS and NMOS gate regions. The different doping the polysilicon receives during the process sequences for NMOS and PMOS transistors results in the different appearance.Also in this image the metal layer definition is not the greatest, notice how the track in the middle of the image is notched where it runs parallel to the polysilicon edge. Several contacts also seem to have only partial metal coverage on one side.


There are two RAM areas at the top of the die, which I think is 6T SRAM, here is the RAM at high magnificationAnd the memory array at the bottom of the chip is I believe a ROM array programmed with metal links (Notice the gaps in metal in places)

Meridian Small Die

The smaller die 3.31 mm x 3.15 mm (10.4 mm2) and looks to have been made on the same processSmall Display Driverclick on image for higher resolution version

A lot simpler than the larger die, the bulk of the die consists of 40 repeated elements.  These each contain a very small logic area with large driver transistors.


Panasonic Cordless Phone Display

Front and back of the display module

By 2005 the technology for small LCD displays had advanced.  Mounting the display driver chips directly onto the LCD glass using a a new bonding technology “Chip on Glass”.

I peeled away the soft black coating to reveal the display driver chip hereThe COG technology is quite fascinating, here is a white paper from NXP describing the technology. The die has gold bumps bonded to Indium Tin Oxide (ITO) tracks on the glass by means of an Anisotropic Conductive Film (ACF)

From NXP: COG for LCD modules white paper

This Anisotropic Conducting Film is interesting stuff. A solution of conductive beads cured at low temperature. Anisotropic as it conducts only vertically ie. not horizontally between pads! The surface tensions of the glue on the conductive beads is apparently the key to this magic.

I released the die from the glass with some heat, and cleaned it up in hot sulphuric acid. The die is now classic rectangle of a display driver measuring 7 mm x 1.6 mm (11.2  mm2).  You can clearly see the gold electroplated pads

KS0093 Die PhotoSamsung KS0093click on image for higher resolution version

The die marks are KS0093 and searching for that I was surprised to find a datasheet. The Samsung KS0093 “26 COM/80 SEG Driver and Controller for STN LCD”.  There are no Samsung logos on the die, but it is clearly our chip matching the size and description perfectly.

With 180 pins it is quite a complex chip.  This is the block diagram from the datasheetThis is made on a much more sophisticated process, its using Copper metallization and I think is a 3 or 4 metal 180nm process.  Here you can see the electroplated Gold contacts on a 90μm pitchAnd here is a higher mag image of a logic area (80x objective focus stacked), you can barely make out the transistor layers

Blackberry 8830 LCD Display

From 2007 this is only a couple of years younger than the Panasonic display, but being one of the first Smartphones this display is really in a different league with 65000 colours, and 320 x 240 pixels (It really is quite remarkable how rapidly the resolution of smartphone screens progressed in the past 10 years).Peeling off the frame reveals the die that is also using COG bonding.



It’s a really long die measuring a whopping 23.5 mm x 1.5 mm (35.25 mm2)It was difficult to remove the driver chip from the glass, I tried lots of hot air with no success and it eventually took two hot acid baths to finally separate the die from the glass. With the huge aspect ratio getting a reasonable looking die photo image proved a challenge. The only way I could make the die photo practical to view was to split it into three parts


CentreRightclick on images for higher resolution versions

Made about two years after the Samsung KS0093. Fabricated on a more advanced process, likely 6 levels of Copper 130 nm CMOS (Or even 90 nm).

Finally we have an LCD driver with a manufacturer marking/logo. Searching for “Renesas R63401” also yielded a datasheet which indicates this is customized driver for Sharp who manufacture the LCD module.

Nothing worth exploring in the optical microscope for a part that is this advanced.

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LTC3789 High Efficiency Buck-Boost Regulator


The Linear Technology High Efficiency, Synchronous, 4 -Switch Buck-Boost Controller is a very sophisticated voltage regulator capable of regulating an output voltage to 1% from an input voltage range of 4V to 38V that can be above or below the output voltage. LTC3789 buck-boost regulatorMine has a week 25 2011 date code.

Die Photo

The die size is 2.17 mm x 1.82 mm  (Just 3.95 mm2). The die is very colourful and interesting to look at with lots of distinctive functional blocksLTC3789 Die Photo(click on image for higher resolution version)

As an aside, I originally create significantly higher resolution images than what I am able to post. I cannot post images above ~10MB without getting an upload error. This seems to be a limitation related to WordPress and my web host.  I have tried all sorts of work arounds to no avail.

The part is made on a two metal fairly modern Bipolar process. Designed in 2009, here is a link to the datasheet and the block diagram for the partIts a pretty complex circuit and well above my level of electronics skill to try and decipher, so I did not try.

I will finish with an image of an interesting pair of transistors

And once again thank you to Jeremy for sending me the part.

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Rohm BA6860FS 3-phase Motor Driver


From 1994 another chip from the JVC Camcorder.  This one was located on an area of the board labeled “SERVO” so I guessed it was a motor driver.Rohm BA6860 Motor DriverI was somewhat surprised to manage to find a datasheet.  Turns out it is a 3-phase motor driver for the capstan motor (The motor that drives the tape movement spindle) in the Camcorder.

Die Photo

The die photo is quite good looking. The die is 2.97 mm x 2.83 mm (8.4 mm2) and is made on a 2 metal (Aluminum) Bipolar process.Rohm BA6860FS die photo(click on image for higher resolution image)

The driver transistors for the 3-phases are clearly seen in the top right. This is the block diagram from the datasheet The pinout is quite strange (Even though pin 1 is annotated on the die) and I was not able to figure out the pinouts so can not make out the block functions.

Still a nice looking die though.

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Motorola MC6802

A few months ago I looked at a Motorola MC6800 bought on eBay that was branded with a Freescale logo, contained an Hitachi fabricated die (probably from late 80’s or early 90’s) and had a 2016 assembly date code.  Reader Jeremy wanted to compare a real vintage 6800 and kindly ordered this MC6802 for me.

I can make out from the very worn and faded markings

MC6802L  P1H852

Which I believe is a week 52 1978 assembly date code. Released in 1977 as an upgrade to the MC6800, offering an internal oscillator and 128 Bytes of RAM.


Thus assembled almost exactly 39 years ago prior to the date of this this post. It is a truly vintage part, packaged in a ceramic DIP.  I popped the lid off using a blowtorch to melt the solder. I also used a strong magnet to pull the lid off (To avoid damaging the die.)The die is soldered to the lead frame, one interesting feature the ground wire has two bond wires, one going to the die, another to the lead frame, but rather than bonding directly to the gold plated lead frame it is bonded to very small piece of silicon or metal – I can’t see why they did that.As it is in the package I am able to take a die photo with the bond wires intact.  The package depth limits me to the 10x objective for the die photo.  The working distance of my high magnification objectives is too small to focus on the die in-situ. To zoom in on the features I had to remove the die from the package.

MC6802 Die PhotoMC6802 Die Photo

(click on image for high resolution version)

Back in 1978 3″ silicon wafers was state of the art.  With a die size of 5.55mm x 4.96mm I calculate they would have had 99 candidate die per wafer.  They were probably doing well to yield 25-30 die per wafer at the time. The datasheet also mentions an MC6808 which was identical to the 6802 but without the 128 Byte RAM, so they obviously recovered some failed parts where just the RAM was defective to gross more parts per wafer.

The die has a distinctive and unusual monochrome look to it.  I removed the die (By heating the package on a hotplate and carefully sliding the die off of the solder. Which proved tricky to do with a very hot die and without a jig holding the die still.

You can see the pitted/mottled texture of the oxide layers which is obscuring the poly and active areas. The latter can be tricky to see in some structures.Normally the oxides are transparent (It is effectively glass), since this was sealed in a ceramic package, it must have come out of the wafer fab looking like this.  I have seen this once before on another old Motorola part.  So clearly it is a characteristic of the process Motorola used. It’s unfortunate for us as it makes viewing the structures quite difficult.

The main die logo is very visible confirming this is pucker Motorola MC6802MC6802 Die Logo

Not so visible, hidden under the mottled dielectrics there is another die mark R1H.  Could that be Ray Hirt sneaking his initials onto the chip (He is one of the designers referred to on the MC6800 Wiki page) or is R1H for something else?

MC6802 Layout

One aspect of taking the die photo in-situ is that it makes identifying the pin-out much easier.  Here is the die photo with pin-out labelled.MC6802 pin-outYou can see the internal oscillator pins on the the top left side.  T he ROM that contains the instruction set on the left, the data input pins at the top, and the output pins bottom and right sides.

MC6802 Memory


There’s a 2kBytes (16kb) large ROM on the chip. A NOR type ROM programmed with a masked (depletion) implant.  Comparing this image to a reference I found online and it is clear

(Attribution unsure found in lecture published on-line, original maybe slide set “Digital Integrated Circuits” by Rabaey et al ©2003)

(Static) RAM


The 128 Byte (1kb) RAM is also interesting. The datasheet mentions that 32 Bytes of RAM are retainable and this is clearly the smaller section on the left. I can trace the Vcc line of that section to the Vcc/Standby pin. (The larger right side goes to the main Vcc pin.)



















Counting out the bits, (the small retainable section in one half is 16Bytes or 128bits, so this image contains 4 bits (Or 4 SRAM cells)In part because it is difficult to see the active area and use of buried contacts I cannot figure out the circuit used.  Given this is an NMOS process I suspect it is a resistive load SRAM cell like this one, but I am unable to reverse engineer it from the layout (Without removing the metal).

MC6802 Process

I mentioned buried contacts, or more correctly buried poly contacts.  These are contacts between polysilicon and substrate, used extensively on this part. In a CMOS process you would not find them.  Here is an example of two such contacts on the die

Some commentary about the process quality you can  observe. In 1978 the metal lines would have been wet etched (Likely in a buffered phosphoric acid mixture). Given that the etch quality of the Aluminum tracks appears very good to meYou can see a tiny amount of notching sometimes where the metal line crosses a poly line, and there is slight mis-alignment of metal to contacts, and the metal lines look a little small for the size of the contacts.  But overall though this looks like a good quality process for 1978.

Finally many thanks again to Jeremy for supplying the part, and merry christmas to all of you who celebrate it.

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