Matrix display device and its method of operation

• US 5,892,504 A
• Filed: 01/26/1994
• Issued: 04/06/1999
• Est. Priority Date: 07/17/1991
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Knapp, Alan G.
• Primary Examiner(s): LAO, LUNYI
• Application Number:
  US08/187,364
• Time in Patent Office: 1,896 Days
• Field of Search: 345/204, 345/205, 345/206, 345/87, 345/90, 345/91, 345/92, 345/100, 345/904, 359/55, 359/59, 178/18, 178/19, 349/41-54
• US Class Current: 345/204
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 3/367 with a nonlinear element in series with the liquid crystal cell, e.g. a diode, or M.I.M. element
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

A matrix display device comprising a row and column array of display elements (14), e.g. LC display elements, each of which is connected in series with a two terminal non-linear device (15), such as a MIM, between associated row and column address conductors (16,17) and drive means (20,22,25) for applying drive voltages to the picture elements comprising a scanning signal circuit (20) and a data signal circuit (22) for applying selection signals and data signals respectively to the sets of address conductors, in which a sensing circuit (40) provides a control signal (V₁) indicative of current flowing in one, or more, address conductor (16) of one set during the application of selection signals to that conductor which determines the drive voltages applied to the picture elements, preferably by adjustment of the selection signal level, so as to compensate for changes over time in the threshold characteristics of the non-linear devices. Four or five level scanning signal drive schemes may be used. Such compensation may be effected periodically or continually in operation of the display device.

Claims

1. A matrix display device comprising sets of row and column address conductors, a row and column array of picture elements operable to produce a display, each of which comprises an electro-optic display element connected in series with a two terminal non-linear device exhibiting a threshold characteristic between a row conductor and a column conductor, and picture element drive means connected to the sets of address conductors for applying drive voltages to the picture elements comprising a scanning signal drive circuit for applying selection signals to the conductors of one set and a data signal drive circuit for applying data signals to the conductors of the other set, characterised in that the drive means includes a sensing circuit which is arranged to provide a control signal indicative of electrical current flowing in at least one address conductor of the one set in response to the application of selection signals to that address conductor, and a voltage control circuit to which the control signal is supplied for determining the drive voltages applied by the drive means to the picture elements in accordance with the value of the control signal.

2. A matrix display device according to claim 1, characterised in that the voltage control circuit provides an output which determines the level of the selection signals in accordance with the control signal.

3. A matrix display device according to claim 2, characterised in that the level of the selection signals is adjusted in accordance with the difference between the control signal and a reference level.

4. A matrix display device according to claim 2, characterised in that the scanning signal drive circuit applies a scanning signal waveform which comprises reset signals in addition to the selection signals and in that the output of the voltage control circuit also determines the level of the reset signals.

5. A matrix display device according to claim 2, characterised in that the scanning signal circuit is electrically connected to a supply line to which a potential determining the level of the selection signal is supplied and in that the sensing circuit is arranged to sense electrical current flowing in that supply line.

6. A matrix display device according to claim 1, characterised in that the sensing circuit provides a voltage signal which varies in accordance with electrical current sensed thereby and in that the control signal is obtained by correcting the voltage signal in accordance with the level of data signals applied to address conductors of the other set.

7. A matrix display device according to claim 6, characterised in that the control signal is obtained from a subtractor circuit to which the voltage signal from the sensing circuit and a data signal supplied to the data signal drive circuit are applied.

8. A matrix display device according to claim 7, characterised in that said signals are applied to the substractor circuit respectively via matched low pass filters.

9. A matrix display device according to claim 1, characterised in that the sensing circuit is arranged to provide said control signal at selected periods and in that the data signal drive circuit is operable to supply a predetermined potential level to the address conductors of the other set during said periods.

10. A matrix display device according to claim 9, characterised in that the control signal is indicative of electrical current in an address conductor associated with a row of picture elements to which a predetermined data signal is applied each time a selection signal is applied to that address conductor.

11. A matrix display device according to claim 1, characterised in that the non-linear devices comprise MIMs.

12. A matrix display device according to claim 1, characterised in that the electro-optic display element of each picture element comprises a liquid crystal display element.

13. A method of operating a matrix display device comprising sets of row and column address conductors, a row and column array of picture elements operable to produce a display, each of which comprises an electro-optic display element connected in series with a two terminal non-linear device exhibiting a threshold characteristic between a row conductor and a column conductor, and picture element drive means connected to the sets of address conductors for applying drive voltages to the picture elements comprising a scanning signal drive circuit for applying selection signals to the conductors of one set and a data signal drive circuit for applying data signals to the conductors of the other set, characterised by the steps of deriving a control signal indicative of the electrical current flowing in at least one address conductor of the one set in response to the application of selection signals to that address conductor and controlling the level of the drive voltages applied to the picture elements in accordance with the value of the control signal.

14. A method according to claim 13, characterised in that the level of the selection signals is controlled in accordance with the value of the control signal.

15. A method according to claim 13, characterised in that the step of deriving a control signal comprises generating a voltage signal which varies in accordance with the level of said electrical current and adjusting said voltage signal according to the data signal level.

16. A method according to claim 13, characterised in that the step of controlling the drive voltages applied to the picture elements is carried out periodically in operation of the display device.