Liquid crystal display device

• US 6,256,024 B1
• Filed: 09/02/1998
• Issued: 07/03/2001
• Est. Priority Date: 09/10/1997
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Maekawa, Toshikazu
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Laneau, Ronald
• Application Number:
  US09/144,880
• Time in Patent Office: 1,035 Days
• Field of Search: 345/205, 345/204, 345/87, 345/88, 345/90, 345/98, 345/100
• US Class Current: 345/205
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2310/0289 Details of voltage level shifters arranged for use in a driving circuit
• CPC Class Codes: G09G 2310/0294 Details of sampling or holding circuits arranged for use in a driver for data electrodes
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3688 suitable for active matrices only

Abstract

A driving circuit combined type LCD which employs sampling system of analog video signals can not be applied to a medium to large sized LCD. To solve this problem, in an active matrix type LCD having a driving circuit unit which is capable of accepting digital signals having the signal level lower than the power source voltage of a horizontal driving circuit system and pixel unit formed combinedly, level shift circuits for converting the level of sampled digital signals having a small amplitude to digital signals having a voltage of 0 to the power source voltage Vd (for example, 12 V) are provided between sampling switches and latch circuits, thus the structure is capable of accepting digital signals having a small signal amplitude from the outside.

Claims

1. A liquid crystal display device having a driving circuit unit and a pixel unit formed combinedly which is capable of accepting a digital signal input having a signal level lower than a power source voltage level of a horizontal driving circuit system, comprising:

pulse generation means for generating a sampling pulse which samples in time series an input digital signal correspondingly to a pixel;

sampling means for sampling said input digital signal in response to said sampling pulse;

level conversion means for converting a digital signal sampled by said sampling means to a signal having a signal level sufficient for subsequent processing;

latch means for means for holding a digital signal converted by said level conversion means, wherein said level conversion means and said latch means comprise a first switch that is connected to a digital data line, a second switch that is connected to said first switch and to a reference voltage, a capacitor that is connected to a connection middle point of said first switch and said second switch, a first inverter connected to the other end of said capacitor, a third switch provided between an input and output of said first inverter and controlled by said level shift pulse, a second inverter connected to the output of said first inverter, and a fourth switch connected in parallel to said first inverter and said second inverter and controlled by a latch pulse; and

D/A conversion means for generating an analog signal based on a digital signal which was level converted by said level conversion means.

2. The liquid crystal display device as claimed in claim 1, wherein said latch means holds a digital signal during one horizontal period.

3. The liquid crystal display device as claimed in claim 2, wherein said level conversion means and said latch means comprise a first switch that is connected to a digital data line, a second switch that is connected to said first switch and to a reference voltage, a capacitor that is connected to a connection middle point of said first switch and said second switch, a first inverter connected to said capacitor, a third switch provided between an input and output of said first inverter and controlled by said level shift pulse, a second inverter connected to the output of said first inverter, and a fourth switch connected in parallel to said first inverter and said second inverter and controlled by a latch pulse.

4. The liquid crystal display device as claimed in claim 3, wherein said level conversion means and said latch means further comprise a fifth switch provided between input and output of said second inverter and controlled by said level shift pulse additionally.

5. The liquid crystal display device as claimed in claim 3, wherein said reference voltage has an electric potential of approximately (VH−

VL)/2, in which VH stands for the high level of a input digital data and VL stands for the low level of the input digital data.

6. The liquid crystal display device as claimed in claim 4, wherein said reference voltage has an electric potential of approximately (VH−

VL)/2, in which VH stands for the high level of input digital data and VL stands for the low level of the input digital data.

7. The liquid crystal display device as claimed in claim 1, wherein said level conversion means and said latch means further comprise a fifth switch provided between input and output of said second inverter and controlled by said level shift pulse additionally.

8. The liquid crystal display device as claimed in claim 7, wherein said reference voltage has an electric potential of approximately (VH−

VL)/2, in which VH stands for the high level of input digital data and VL stands for the low level of the input digital data.

9. The liquid crystal display device as claimed in claim 1, wherein said reference voltage has an electric potential of approximately (VH−

VL)/2, in which VH stands for the high level of input digital data and the VL stands for the low level of the input digital data.

10. The liquid crystal display device as claimed in claim 1, wherein said level conversion means is a level shift circuit for shifting the level of the digital signal sampled by said sampling means to the power voltage level of said horizontal driving device.

11. The liquid crystal display device as claimed in claim 10, wherein said pulse generation means is a horizontal scanning circuit and generates also a level shift pulse to be supplied to said level shift circuit.

12. The liquid crystal display device as claimed in claim 1, wherein said sampling means is a switch element provided correspondingly to a column line.