Data processing: measuring – calibrating – or testing – Calibration or correction system – Circuit tuning
Reexamination Certificate
2001-05-09
2003-07-15
Bui, Bryan (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Circuit tuning
C702S117000, C702S125000, C702S196000, C345S055000, C345S082000, C345S205000
Reexamination Certificate
active
06594606
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to electrical drivers for a matrix of current driven devices, and more particularly to methods and apparatus for determining and providing a precharge for such devices.
BACKGROUND OF THE INVENTION
There is a great deal of interest in “flat panel” displays, particularly for small to midsized displays, such as may be used in laptop computers, cell phones, and personal digital assistants. Liquid crystal displays (LCDs) are a well-known example of such flat panel video displays, and employ a matrix of “pixels” which selectably block or transmit light. LCDs do not provide their own light; rather, the light is provided from an independent source. Moreover, LCDs are operated by an applied voltage, rather than by current. Luminescent displays are an alternative to LCD displays. Luminescent displays produce their own light, and hence do not require an independent light source. They typically include a matrix of elements which luminesce when excited by current flow. A common luminescent device for such displays is a light emitting diode (LED).
LED arrays produce their own light in response to current flowing through the individual elements of the array. The current flow may be induced by either a voltage source or a current source. A variety of different LED-like luminescent sources have been used for such displays. The embodiments described herein utilize organic electroluminescent materials in OLEDs (organic light emitting diodes), which include polymer OLEDs (PLEDs) and small-molecule OLEDs, each of which is distinguished by the molecular structure of their color and light producing material as well as by their manufacturing processes. Electrically, these devices look like diodes with forward “on” voltage drops ranging from 2 volts (V) to 20 V depending on the type of OLED material used, the OLED aging, the magnitude of current flowing through the device, temperature, and other parameters. Unlike LCDs, OLEDs are current driven devices; however, they may be similarly arranged in a 2 dimensional array (matrix) of elements to form a display.
OLED displays can be either passive-matrix or active-matrix. Active-matrix OLED displays use current control circuits integrated with the display itself, with one control circuit corresponding to each individual element on the substrate, to create high-resolution color graphics with a high refresh rate. Passive-matrix OLED displays are easier to build than active-matrix displays, because their current control circuitry is implemented external to the display. This allows the display manufacturing process to be significantly simplified.
FIG. 1A
is an exploded view of a typical physical structure of such a passive-matrix display
100
of OLEDs. A layer
110
having a representative series of rows, such as parallel conductors
111
-
118
, is disposed on one side of a sheet of light emitting polymer, or other emissive material,
120
. A representative series of columns are shown as parallel transparent conductors
131
-
138
, which are disposed on the other side of sheet
120
, adjacent to a glass plate
140
.
FIG. 1B
is a cross-section of the display
100
, and shows a drive voltage V applied between a row
111
and a column
134
. A portion of the sheet
120
disposed between the row
111
the column
134
forms an element
150
which behaves like an LED. The potential developed across this LED causes current flow, so the LED emits light
170
. Since the emitted light
170
must pass through the column conductor
134
, such column conductors are transparent. Most such transparent conductors have relatively high resistance compared with the row conductors
111
-
118
, which may be formed from opaque materials, such as copper, having a low resistivity.
This structure results in a matrix of devices, one device formed at each point where a row overlies a column. There will generally be M×N devices in a matrix having M rows and N columns. Typical devices function like light emitting diodes (LEDs), which conduct current and luminesce when voltage of one polarity is imposed across them, and block current when voltage of the opposite polarity is applied. Exactly one device is common to both a particular row and a particular column, so to control these individual LED devices located at the matrix junctions it is useful to have two distinct driver circuits, one to drive the columns and one to drive the rows. It is conventional to sequentially scan the rows (conventionally connected to device cathodes) with a driver switch to a known voltage such as ground, and to provide another driver, which may be a current source, to drive the columns (which are conventionally connected to device anodes).
FIG. 2
represents such a conventional arrangement for driving a display having M rows and N columns. A column driver device
260
includes one column drive circuit (e.g.
262
,
264
,
266
) for each column. The column driver circuit
264
shows some of the details which are typically provided in each column driver, including a current source
270
and a switch
272
which enables a column connection
274
to be connected to either the current source
270
to illuminate the selected diode, or to ground to turn off the selected diode. A scan circuit
250
includes representations of row driver switches (
208
,
218
,
228
,
238
and
248
). A luminescent display
280
represents a display having M rows and N columns, though only five representative rows and three representative columns are drawn.
The rows of
FIG. 2
are typically a series of parallel connection lines traversing the back of a polymer, organic or other luminescent sheet, and the columns are a second series of connection lines perpendicular to the rows and traversing the front of such sheet, as shown in FIG.
1
A. Luminescent elements are established at each region where a row and a column overlie each other so as to form connections on either side of the element.
FIG. 2
represents each element as including both an LED aspect (indicated by a diode schematic symbol) and a parasitic capacitor aspect (indicated by a capacitor symbol labeled “CP”).
In operation, information is transferred to the matrix display by scanning each row in sequence. During each row scan period, each column connected to an element intended to emit light is also driven. For example, in
FIG. 2
a row switch
228
grounds the row to which the cathodes of elements
222
,
224
and
226
are connected during a scan of Row K. The column driver switch
272
connects the column connection
274
to the current source
270
, such that the element
224
is provided with current. Each of the other columns
1
to N may also be providing current to the respective elements connected to Row K at this time, such as the elements
222
or
226
. All current sources are typically at the same amplitude. OLED element light output is controlled by controlling the amount of time the current source for the particular column is on. When an OLED element has completed outputting light, its anode is pulled to ground to turn off the element. At the end of the scan period for Row K, the row switch
228
will typically disconnect Row K from ground and apply Vdd instead. Then, the scan of the next row will begin, with row switch
238
connecting the row to ground, and the appropriate column drivers supplying current to the desired elements, e.g.
232
,
234
and/or
236
.
Only one element (e.g. element
224
) of a particular column (e.g. column J) is connected to each row (e.g. Row K), and hence only that element may be “exposed,” or connected to both the particular column drive (
264
) and row drive (
228
) so as to conduct current and luminesce during the scan of that row. However, each of the other devices on that particular column (elements
204
,
214
,
234
and
244
as shown, but actually including typically 63 other devices) are connected by the driver for their respective row (
208
,
218
,
238
and
248
respectively) to a voltage source, Vdd. Therefore, the parasitic capacitance of each o
Bui Bryan
Clare Micronix Integrated Systems, Inc.
Knobbe Martens Olson & Bear LLP
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