HTN LCD - Ghosting Problem

Question

I am driving a large, complex HTN LCD with 3 Holtek HT1625 LCD drivers. There are over 700 segments. The data sheet for HT1625 LCD driver is here: http://www.holtek.com.tw/documents/10179/116706/ht1625v170.pdf

The problem is the ghosting effect, where the LCD segments are being partially on when they should be off.

All segments should be off in this picture.

This image shows OFF segments are affected by the ON segments. Some kind of crosswalks, I guess.

I measured the waveforms with a scope. This is one of the COMMON signal when the board is NOT connecting to the LCD glass:

This is the same COMMON signal when the board is connected to the LCD glass:

I am trying to figure out whether it is the driver or the LCD signal layout. Is there anything I can do to improve the display? I tried different LCD bias voltages but they seem to affect the view angles more than the ghosting effect.

Any pointers are appreciated.

Thank you.

Answer 1

I am a design engineer at Focus Displays and am providing the link below to support ghosting of segment displays. Please let me know if this is not allowed and I will remove supporting documents. Thank you

In some cases, ghosting can be a result of the internal traces giving cross talk. Some traces are too close and may need to be re-layed out. Here is an article that talks about cross talk and some of the causes.

Answer 2

I used get that when I messed up attaching the flex cable to the lcd display. Try a different assembly or put a different flex cable on the screen.