Display device and control circuit for a light modulator
View Patent ↗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.
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 of 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,
and 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 and 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 3 , wherein the modulators and the first and second control switches are components fabricated in thin-film polysilicon or thin-film amorphous silicon.
6. Image display device according to claim 5 , 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.
7. 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.
8. 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.
9. Image display device according to claim 1 , wherein each emitter is an organic light-emitting diode.