Matrix element precharge voltage adjusting apparatus and method

• US 6,943,500 B2
• Filed: 10/17/2002
• Issued: 09/13/2005
• Est. Priority Date: 10/19/2001
• Status: Active Grant

• Current Assignee: Clare Micronix Integrated Systems, Inc.
• Original Assignee: Clare Micronix Integrated Systems, Inc.
• Inventors: LeChevalier, Robert
• Primary Examiner(s): Vo, Tuyet Thi
• Application Number:
  US10/274,489
• Publication Number:
  US 20030173904A1
• Time in Patent Office: 1,062 Days
• Field of Search: 3151691-1694, 345 74- 77, 345 90- 92, 345/55, 345/63, 345/84
• US Class Current: 315/169.3
• CPC Class Codes: G09G 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0259 with use of an analog or digital ramp generator in the column driver or in the pixel circuit
• CPC Class Codes: G09G 2320/0223 Compensation for problems related to R-C delay and attenuation in electrodes of matrix panels, e.g. in gate electrodes or on-substrate video signal electrodes
• 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 3/3216 using a passive matrix
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements

Abstract

An apparatus for establishing and applying a voltage to precharge current-driven elements in a matrix. During ordinary scan cycles, a conduction voltage is sensed while the elements conduct a selected current. One or more such sensed conduction voltages are combined to provide a basis for a precharge voltage. Conduction and transient errors are determined, and are compensated for by offsetting the final precharge voltage from the conduction voltage basis. The final precharge voltage is provided to one or more columns during a precharge period of the scan cycle.

Claims

1. An apparatus for providing a precharge for display elements, comprising:

a current source configured to provide a controlled current to a selected display element;

a sample circuit configured to obtain a display conduction voltage sample which substantially reflects an output voltage caused by conduction of the controlled current at least partly through the selected display element;

a storage device to hold a representation of a reference voltage which is based on the display conduction voltage; and

a precharge voltage source configured to output a voltage reflecting the reference representation of output voltage as offset by a quantity selected to compensate for expected transient voltage effects.

2. The apparatus of claim 1, further comprising:

a converter configured to produce a digital representation of the sampled display conduction voltage; and

a digital controller configured to store such digital representation, to add thereto a digital value reflecting the selected offset, and to store the reference voltage represented thereby.

3. The apparatus of claim 1, wherein the precharge voltage source is configured to provide an output controllably offset from the input accepting the stored reference voltage.

4. The apparatus of claim 1, further comprising a digitally controllable offset circuit for the precharge voltage.

5. The apparatus of claim 4, wherein the offset circuit is included in the precharge voltage source.

6. The apparatus of claim 4, wherein the offset circuit includes a plurality of digitally enabled current sources connected to drive current to one side of a differential amplifier circuit.

7. An apparatus for driving conduction lines connected to matrix elements to a precharge voltage level, the apparatus comprising:

a current source switchably connected to a conduction line during a conduction period of a matrix element;

a voltage sampling circuit configured to sample a voltage of the conduction line during the conduction period;

a combining circuit configured to determine a conduction line voltage level from a combination of one or more conduction line voltage samples;

a precharge basis storage circuit configured to obtain a precharge basis which is based upon the determined conduction line voltage level, and to store a representation of the precharge basis;

a precharge voltage source configured to provide a precharge voltage based upon the stored representation of precharge basis;

an offset circuit configured to offset the precharge voltage from the determined conduction line voltage level; and

a switch controllable to connect the provided precharge voltage to an element conduction line during a precharge period.

8. The apparatus of claim 7, wherein the conduction cycle of the element is preceded by a precharge period and is part of an operational scan cycle.

9. The apparatus of claim 8, wherein the offset circuit includes a digital control input.

10. The apparatus of claim 9, wherein the precharge voltage source further comprises a differential amplifier with a binary data offset control input.

11. The apparatus of claim 10, wherein the precharge voltage source further comprises a plurality of current sources enabled by binary data.

12. A device for providing a precharge for elements in a matrix, comprising:

a plurality of controlled level current sources which are switchably connectable to a corresponding plurality of column connections;

a sample circuit configured to obtain a column connection voltage sample while the corresponding current source is connected to the column connection;

a storage device configured to store a reference voltage based at least in part on the column connection voltage sample; and

a precharge voltage source connectable during a precharge period to at least one column connection to provide a precharge voltage which is offset from the reference voltage by a predetermined compensation voltage.

13. The device of claim 12, further comprising a circuit to selectably vary the compensation voltage.

14. The device of claim 12, further comprising a circuit configured to vary the compensation voltage in accordance with one or more digital bits.

15. The device of claim 12, wherein the precharge voltage source further includes a differential amplifier.

16. The device of claim 15, further comprising a circuit configured to provide controllable current to one side of the differential amplifier.

17. The device of claim 12, further comprising a circuit to prevent sampling a column voltage during a predetermined minimum time after a beginning of a conduction drive period for the column connection.

18. An apparatus for providing a precharge for display elements, comprising:

means for providing a known current to a selected display element;

means for obtaining a display conduction voltage which is caused by conduction of the known current at least partly by the selected display element;

means for storing a reference voltage which is based on the display conduction voltage; and

means for outputting a precharge voltage substantially equal to the reference voltage as offset by an amount which is selected to compensate for differences between the output precharge voltage and the display conduction voltage which are expected due to connection changes associated with changing from a precharge state to a conduction state.

19. The apparatus of claim 18, wherein the means for outputting a precharge voltage includes a buffer amplifier circuit having means for selectably varying an offset voltage between a reference input to the buffer amplifier circuit and an output from the buffer amplifier circuit.

20. The apparatus of claim 19, wherein the means for selectably varying an offset voltage includes means for control in accordance with a plurality of data bits.

21. The apparatus of claim 19, wherein the means for selectably varying an offset voltage includes means for selectably controlling current into one of two differential sides of the buffer amplifier.

22. The apparatus of claim 18, further comprising means for controlling durations for the provision of the known current to the selected display element so as to substantially control a quantity of charge conducted by the selected display element during a row scan cycle.

23. The apparatus of claim 18, further comprising means for sampling a plurality of matrix conduction voltages.

24. The apparatus of claim 23, further comprising means for combining the plurality of matrix conduction voltages to forma a basis for the reference voltage.

25. A method for establishing a precharge voltage for current-driven device elements in a matrix, the method comprising:

selecting an element for sampling;

driving a controlled current from a current source into a connection to the selected element via a current drive path;

producing a conduction voltage sample by sampling a voltage which substantially reflects a voltage caused by the selected element conducting at least part of the controlled current;

generating an offset voltage to compensate for perturbations to a delivered voltage which are expected for a subsequently driven element;

combining the offset voltage with one or more conduction voltage samples to obtain an adjusted precharge voltage level;

generating a precharge voltage source output substantially at the adjusted precharge voltage level; and

precharging the subsequently driven element from the precharge voltage source during a precharge period.

26. The method of claim 25, wherein the step of generating an offset voltage includes selecting the offset from within a controllable range of offset voltages.

27. The method of claim 26, further comprising selecting the offset voltage by setting binary data bits which control an amount of the offset voltage.

28. The method of claim 25, wherein the selected current is driven through the selected element during an exposure period of a normal scan cycle.

29. The method of claim 25, further comprising:

deriving a previous conduction voltage reference from the one or more conduction voltage samples; and

offsetting the previous conduction voltage reference with the offset voltage to obtain the adjusted precharge voltage level.

30. The method of claim 29, further comprising:

sampling conduction voltages for selected elements during ordinary scan periods; and

combining conduction voltage samples from a plurality of different scan cycles to derive the previous conduction voltage reference.

31. The method of claim 29, further comprising:

selecting a plurality of different elements;

sampling a conduction voltage of each of the plurality of different elements during one scan cycle to obtain a plurality of conduction voltage samples; and

averaging the plurality of conduction voltage samples to form a scan conduction voltage value.

32. The method of claim 29, wherein generating the precharge voltage source output includes providing the previous conduction voltage reference as an input to a voltage buffer having a differential amplifier circuit to control an output of the buffer.

33. The method of claim 32, further comprising switching an offset current source to provide current to one side of the differential circuit whereby the buffer output voltage is offset from the previous conduction voltage reference input to the buffer.

34. The method of claim 33, wherein switching the offset current source further comprises

switching each of a plurality of switchable current sources with a corresponding binary data bit, and

summing current from the plurality of switchable current sources to form the offset current.

35. A method for adjusting a precharge voltage for current-driven device elements in a matrix, the method comprising:

selecting an element for sampling;

applying the precharge voltage to a connection to the element during a precharge period of a scan cycle;

driving a selected current from a current source to the connection to the element during a current conduction period of the scan cycle;

sampling a conduction voltage during the current conduction period of the scan cycle;

adjusting the precharge voltage based at least in part on the sampled conduction voltage.

36. The method of claim 35, further comprising:

selecting an offset voltage to compensate for expected differences between sampled conduction voltages and a precharge voltage needed to cause a correct voltage to be developed on a subsequently driven element at a beginning of a conduction period therefor; and

combining the selected offset voltage with one or more sampled conduction voltages to control an adjusted precharge voltage.

37. The method of claim 36, further comprising setting a plurality of binary data bits to select the offset voltage.

38. The method of claim 37, further comprising:

deriving a reference voltage from a plurality of sampled conduction voltages, and

offsetting the reference voltage with the selected offset to determine the voltage output from a precharge buffer.

39. A method of manufacturing an electronic display device, comprising:

obtaining a matrix device column driver configured to sample a voltage of a column drive output during a conduction period

of an exposure cycle to obtain an exposure conduction sample voltage, and provide, to a column drive output, a precharge voltage which is offset

from a precharge voltage basis derived in part from the exposure conduction sample voltage, the offset being selected to compensate for expected deviations between a delivered precharge voltage and a voltage of a column drive output following termination of the precharge voltage provision;

connecting a plurality of column drive outputs of the matrix device column driver to corresponding column connections of a luminescent display; and

connecting a plurality of row connections of the luminescent display to a corresponding plurality of row drive outputs of an electronic row driver device which is configured to selectively connect one of the plurality of row drive outputs to a row drive voltage during the exposure time of the matrix device column driver.

40. The method of making of claim 39, wherein the row driver and the column driver are fabricated on different semiconductor substrates.

41. The method of making of claim 39, wherein:

the matrix device column driver further includes a converter configured to produce a digital representation of the exposure conduction sample voltage; and

the method of making the electronic display device further includes incorporating a digital controller configured to store the digital representation of the exposure conduction voltage, to add thereto a digital value reflecting the selected offset to create a reference voltage, and to store the reference voltage.

42. The method of making of claim 39, wherein the precharge voltage source of the matrix device column driver further includes an output which is controllably offset from an input which accepts a stored reference voltage.

43. The method of making of claim 42, wherein the precharge voltage source output offset from the input is controlled by a digitally controllable offset circuit.

44. The method of making of claim 43, wherein the offset circuit is included in a precharge voltage source buffer.

45. The method of making of claim 44, wherein the offset circuit includes a plurality of digitally enabled current sources connected so as to drive current to one side of a differential amplifier circuit.

46. A method of manufacturing a device for driving a multiplicity of output conduction lines when they are connected to matrix display elements, the method comprising:

switchably connecting a corresponding electronic current source to each of the output conduction lines;

emplacing control logic devices to selectably connect one of the current sources to its corresponding output conduction line during a conduction period;

disposing a voltage sampling circuit in the device which is configured to sample a voltage of the conduction line during the conduction period;

connecting a combining circuit to the device configured to determine a basis for a precharge voltage from a combination of one or more conduction line voltage samples;

incorporating a controllable offset circuit in the device; and

providing a precharge voltage source buffer in the device configured to produce a precharge voltage which is offset from the precharge voltage basis in accordance with an offset from the offset circuit.

47. The method of making of claim 46, further comprising incorporating timing control elements, and configuring the timing control elements to control the outputs of the device throughout a sequence of operational scan cycles, such that

during each scan cycle the precharge voltage is applied to active outputs during a precharge period, and

a current from the corresponding current source is applied to the active outputs for a controllable portion of an exposure period following the precharge period.

48. The method of claim 46, further comprising including a digital control input to the offset circuit.

49. The method of claim 46, further comprising incorporating a differential amplifier with a binary data offset control input within the precharge voltage source buffer.

50. The method of claim 49, wherein the binary data offset control input is configured to control a plurality of current sources within the precharge voltage source buffer.

51. A method for establishing a precharge voltage for current-driven device elements in a matrix, the method comprising:

driving a selected current from a current source to a selected matrix element via a current drive path;

generating a conduction voltage reference value reflecting a conduction voltage of the current drive path;

offsetting the conduction voltage reference value with a selected voltage offset value to compensate for expected differences between a delivered precharge voltage and a voltage occurring during subsequent conduction by the device element; and

outputting a precharge voltage substantially at the offset conduction voltage reference value during a precharge period.