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Compensating Drive Method and Thin Film Transistor Structure to Reduce Photo Leak in Thin Film Transistor Liquid Crystal Display

IP.com Disclosure Number: IPCOM000117216D
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Kimura, Y: AUTHOR [+3]

Abstract

Disclosed is a compensating drive method and Thin Film Transistor (TFT) structure to reduce photo leak in Liquid Crystal Display (LCD). The a-Si TFT has photo leak at gate off state which increases in high luminance condition. The photo leak causes degradation of the image such as low contrast, dot defect and bad luminance uniformity. Fig. 1 shows an example of the block diagram of a driving circuit which has a photo sense TFT in the liquid crystal cell. Fig. 2 shows an example of the liquid crystal cell which has photo sense TFT array. The photo sense array is placed at upper left of the screen. The sensor should placed near the active area to minimize the measurement error. Structure of the photo sense TFT array is shown in Fig. 3. The value of the leak current is depend on the TFT structure.

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Compensating Drive Method and Thin Film Transistor Structure to Reduce
Photo Leak in Thin Film Transistor Liquid Crystal Display

      Disclosed is a compensating drive method and Thin Film
Transistor (TFT) structure to reduce photo leak in Liquid Crystal
Display (LCD).  The a-Si TFT has photo leak at gate off state which
increases in high luminance condition.  The photo leak causes
degradation of the image such as low contrast, dot defect and bad
luminance uniformity.  Fig. 1 shows an example of the block diagram
of a driving circuit which has a photo sense TFT in the liquid
crystal cell.  Fig. 2 shows an example of the liquid crystal cell
which has photo sense TFT array.  The photo sense array is placed at
upper left of the screen.  The sensor should placed near the active
area to minimize the measurement error.  Structure of the photo sense
TFT array is shown in Fig. 3.  The value of the leak current is
depend on the TFT structure.  So, the structure of the photo sense
TFT should be the same as the TFT of each pixel.  In addition, the
leak current of a single TFT is too small for accurate measurement.
This case, the photo-sense TFT may connected parallel to magnify the
photo leakage current.  Fig. 4 shows the circuit diagram of photo
sense amplifier.  OP1 is current voltage convertor circuit.  Output
voltage(V1) of OP1 is given by
  V1= -(I x R1)
  where the leakage current is I and feedback resistor is R1.
  OP2 is voltage amplifier.  Output voltage...