Display device and control circuit for a light modulator

• US 20070057874A1
• Filed: 06/25/2004
• Published: 03/15/2007
• Est. Priority Date: 07/03/2003
• Status: Active Grant

• Current Assignee: InterDigital CE Patent Holdings SAS (InterDigital, Inc.)
• Original Assignee: Thomson Licensing SA (Vantiva SA)
• Inventors: Fery, Christophe, Prat, Christophe, Le Roy, Philippe
• Granted Patent: US 7,557,778 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0833 forming a linear amplifier or follower
• 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 2300/0876 Supplementary capacities in pixels having special driving circuits and electrodes instead of being connected to common electrode or ground; Use of additional capacitively coupled compensation electrodes
• CPC Class Codes: G09G 2300/088 using a non-linear two-terminal element
• CPC Class Codes: G09G 2320/02 Improving the quality of display appearance
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

The invention relates to an active-matrix image display device that comprises an array of light emitters. Each light emitter is controlled by a current modulator having a particular trip threshold voltage. The device also includes compensation means for compensating for the trip threshold voltage of the modulators. These compensation means comprise at least one operational amplifier connected between the gate electrode and the source electrode of the modulator. The feedback of this operational amplifier compensates for the trip threshold voltage of at least one modulator whatever the value of the said voltage.

Claims

1. Active-matrix image display device comprising:

several light emitters forming an array of emitters distributed in rows and in columns,

means for controlling the emission of the light emitters of the array, comprising;

for each light emitter the array, a current modulator capable of controlling the said emitter, and comprising a source electrode, a drain electrode, a gate electrode and a trip threshold voltage,

column address means capable of addressing the emitters of each column of emitters by applying a data voltage to the gate electrode of their modulators in order to control them,

row select means capable of selecting the emitters of each row of emitters by applying a select voltage,

compensation means for compensating for the trip threshold voltage of each modulator,

wherein;

the compensation means comprise at least one operational amplifier, having an inverting input, a non-inverting input and an output terminal,

wherein;

the non-inverting input of the operational amplifier is connected to a column address means controlling the said modulator, and

the inverting input of the operational amplifier is connected to the source electrode of the said modulator, and

the output of the operational amplifier being connected to the gate electrode of the said modulator,

the said connections of the inverting input and of the output of this operational amplifier thus forming a feedback capable of compensating for the trip threshold voltage of the said modulator

2. Image display device according to claim 1, wherein the control means comprise, for the said modulator associated with an emitter, at least a first control switch connected between the output of the operational amplifier the gate electrode of the said modulator, the first switch having a gate electrode capable of receiving the row select voltage for this emitter.

3. Image display device according to claim 2, wherein the control means comprise, for the said modulator associated with an emitter, a second control switch connected between the inverting terminal of the operational amplifier and the source electrode of the modulator, the second switch having a gate electrode connected to the gate electrode of the said first switch in order to receive, synchronously, the select voltage.

4. Image display device according to claim 2, wherein the row select means are capable of supplying a gate electrode of at least one of the said first switches in order to select at least one emitter in this row.

5. Image display device according to claim 1, wherein the operational amplifier is capable of compensating for the trip threshold voltage of all of the modulators controlling the emitters of a column.

6. Image display device according to claim 3, wherein the modulators and the first (I1) and second control switches are components fabricated in thin-film polysilicon or thin-film amorphous silicon.

7. Image display device according to claim 1, wherein the modulators are n-type transistors and in that their drain is supplied by a supply means.

8. Image display device according to claim 6, wherein the modulators are p-type transistors and wherein the control means furthermore include a passive component placed between the source and a supply electrode of the modulator.

9. Image display device according to claim 1, wherein each emitter is an organic light-emitting diode.

10. Circuit for controlling a current modulator having a source electrode, a drain electrode, a gat electrode and an undefined trip threshold voltage the circuit including trip threshold voltage compensation means,

wherein the trip threshold voltage compensation means comprise at least one operational amplifier, having an inverting input, a non-inverting input and an output terminal, in which the output terminal is capable of being connected to the gate electrode of the said modulator and in which the inverting input is capable of being connected to the source electrode of the said modulator, the said connections thus forming a feedback capable of compensating for the trip threshold voltage of the modulator so that the intensity of the drain current flowing through the modulator is independent of the trip threshold voltage of the modulator.

11. Circuit according to claim 10, wherein it includes a storage capacitor connected to the gate electrode of the modulator and capable of storing the voltage applied to the gate electrode of the modulator.