Switched amplifier drive circuit for liquid crystal displays

• US 20040027321A1
• Filed: 05/30/2003
• Published: 02/12/2004
• Est. Priority Date: 11/29/2001
• Status: Abandoned Application

• Current Assignee: Thomson Licensing SA (Vantiva SA)
• Original Assignee: Thomson Licensing SA (Vantiva SA)
• Inventors: OʼDonnell, Eugene Murphy
• Application Number:
  US10/433,163
• Publication Number:
  US 20040027321A1
• Time in Patent Office: Days
• US Class Current: 345/87
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0823 used to establish symmetry in driving, e.g. with polarity inversion
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2310/0224 Details of interlacing
• CPC Class Codes: G09G 2310/04 Partial updating of the display screen
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 3/3614 Control of polarity reversal in general
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A cell driver (70) for a display unit (50) having a memory element and a liquid crystal cell among a plurality of liquid crystal cells includes a first storage capacitor (14) and a first differential amplifier (16) selectively coupled between the first storage capacitor and the liquid crystal cell forming a first drive circuit. The cell driver also includes a second storage capacitor (14′) and a second differential amplifier (16′) coupled between the second storage capacitor and the liquid crystal cell forming a second drive circuit A switching mechanism (72 and 74) is used for switching the liquid crystal cell between the first and second drive circuits.

Claims

1. A display unit having an array of liquid crystal cells, comprising:

an array of display drivers, a given display driver being associated with a given liquid crystal cell and including;

a first storage capacitance and a first amplifier selectively coupled between the first storage capacitance and the given liquid crystal cell forming a first drive circuit;

a second storage capacitance and a second amplifier coupled between the second storage capacitance and the given liquid crystal cell forming a second drive circuit; and

a switching arrangement for switching the first and second drive circuits to the given liquid crystal cell.

2. The display driver of claim 1, wherein the first amplifier and the second amplifier are both differential amplifiers.

3. The display driver of claim 2, wherein the differential amplifier comprises a pair of N-Channel transistors having respective drain electrodes coupled and serving as an output to the liquid crystal cell.

4. The display driver of claim 1, wherein the each of said first and second drive circuits further comprises a global switch element coupled between the respective storage capacitance and the amplifier, wherein the global switch element transfers data from the storage capacitance to one of the first and second drive circuits.

5. The display driver of claim 1, wherein the switching mechanism comprises a first transistor driven by a first global switching voltage and a second transistor driven by a second global switching voltage.

6. A display driver for a given liquid crystal cell of an array of liquid crystal cells, comprising:

a first drive circuit coupled to a first memory element of the given liquid crystal cell;

at least a second drive circuit coupled to a second memory element of the given liquid crystal cell, wherein at least one of the first drive circuit and at least the second drives circuit includes an amplifier; and

a switching arrangement for repeatedly switching the liquid crystal cell between the first and at least the second drive circuits.

7. The display driver of claim 6, wherein each of the first and the second drive circuits comprise differential amplifiers comprising a pair of N-Channel transistors having respective source electrodes coupled to a current source and serving as an isolation amplifier to the liquid crystal cell.

8. The display driver of claim 6, wherein each of the first and the second drive circuits comprise differential amplifier comprising a pair of N-Channel transistors having respective sources coupled to a current source.

9. The display driver of claim 6, wherein the switching mechanism comprises a first transistor driven by a first global switching voltage and a second transistor driven by a second global switching voltage.

10. The display driver of claim 6, wherein the display driver further comprises a global switching element which is coupled between a storage capacitor and a differential amplifier and used for reducing image retention and flicker.

11. The display driver of claim 6, wherein the display driver updates an entire array of liquid crystal arrays elements simultaneously.

12. The display driver of claim 6, wherein the display driver updates only a memory cell that has changed from a previous frame.