Data driver

Details Data driver Data driver

2003-06-12

2004-09-07

JeanPierre, Peguy (Department: 2819)

Coded data generation or conversion

Analog to or from digital conversion

With particular solid state devices

C341S144000

Reexamination Certificate

active

06788231

ABSTRACT:

This Application claims priority to Taiwan Patent Application No. 092103685 filed on Feb. 21, 2003.
FIELD OF INVENTION
The present invention relates to a data driver for an active matrix organic light emitting display (AMOLED), which is configured to convert digital voltage signals into analog current signals to drive pixels in the display to emit light.
BACKGROUND OF THE INVENTION
Pixels in an AMOLED are driven by analog current signals; however, the signals that control the pixels to emit light are digital voltage signals. Therefore, each AMOLED needs a data driver (or source driver) to convert digital control voltage signals into analog current signals.
FIG. 1
illustrates a data driver
1
of the prior art. As it shows, the data driver
1
includes a first shift register
101
, a data register
103
, a voltage latch
105
, a converter
107
, a current latch
109
, a current source
111
, and a second shift register
113
. The converter
107
is configured to receive the digital voltage signals
110
, which will later drive pixels to emit light, from the voltage latch
105
, and to convert the digital voltage signals
110
into analog current signals
112
based on the reference currents provided by the current source
111
. The second shift register
113
is configured to switch on or off each cell in the current latch
109
in order to store the analog current signals
112
sent by the converter
107
. After a proper period of time, an enabling signal
108
enables the current latch
109
so that all the analog current signals
114
, identical to the analog current signals
112
, are able to reach all pixels of the AMOLED to present a transient frame.
The framework of the converter
107
is basically a current mirror.
FIG. 2
illustrates one kind of current mirror of the prior art. With reference to
FIG. 2
, a reference current I
s
, generated by the current source
111
shown in
FIG. 1
, mirrors I
p1
, I
p2
, I
p3
, etc. through a transistor MP
1
. It is noted that the values of the mirrored currents, e.g. I
p1
, I
p2
, I
p3
, etc., are associated with the characteristics, i.e. aspect ratio, threshold voltage, and mobility, of MP
2
, MP
3
, MP
4
, etc. Once any deviation from the theoretical characteristics of the transistors is induced during fabricating, the practical values of the mirrored current I
p1
, I
p2
, I
p3
etc. will bring error as well. The error, even if it is tiny, might still influence the gray level that an analog current signal actually sets in due to the narrow band of each gray level and, therefore, pixels might emit unexpected illumination.
SUMMARY OF THE INVENTION
The present invention discloses a data driver for an active matrix organic light emitting display (AMOLED), which converts digital voltage signals into analog current signals in order to drive all pixels in the display to emit light.
The data driver includes a first shift register, a data register, a data latch, a second shift register, and N converters The first shift register is configured to provide an N-bit first control signal The data register is configured to store N M-bit digital voltage signals by switching on the cells in it in turn in response to the first control signal, and to send the N digital voltage signals to the data latch. The data latch is configured to receive the N digital voltage signals and respectively transmit them to the N converters in response to an enabling signal. The second shift register is configured to provide an (M+1)-bit second control signal to control the procedure of converting the digital voltage signals into analog current signals.
Each converter of the data driver of the present invention is a digital-voltage-to-analog-current converter with M units regarded as current sources. Each current source (or each unit) includes two control signals to enable or disable the transistors within so as to control the generation timing of mirrored currents. The current source can overcome the drawbacks of the prior art and, therefore, the mirrored current does not deviate even if the characteristics of the transistors within have been changed during fabricating.


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patent: 6154160 (2000-11-01), Meyer et al.
patent: 6166670 (2000-12-01), O'Shaughnessy
patent: 6538591 (2003-03-01), Sato et al.
patent: 6608577 (2003-08-01), Nishimura
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Article entitled 36.4L: Late-News Paper:4.0-in. TFT-OLED Displays and a Novel Digital Driving Method by Kazutaka Inukai et al., pp. 924-927, published in SID 00 DIGEST, publication ISSN0000-0966X100/3101-0924-$1.00+.00 copyright. 2000 SID.
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Article entitled “The Impact of the Transient Response of Organic Light Emitting dioes on the Design of Active Matrix OLED Displays” by R.M.A. Dawson et al. publication No. 0-7803-4774-9/98/$10.00 copyright 1998 IEEE, pp. 32.6.1-32.6.4.
Article entitled “Low-Temperature Poly-Si TFT Driven Light-Emitting-Polymer Displays and Digital Gray Scale for Uniformith by M. Kimura, et al. pp. 171-174, publication IDW”99.

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