Light switching device with reset

• US 6,654,154 B2
• Filed: 01/08/2002
• Issued: 11/25/2003
• Est. Priority Date: 01/12/2001
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Johnson, Mark Thomas, Deane, Steven Charles, Hunter, Iain Mcintosh
• Primary Examiner(s): Ben, Loha
• Assistant Examiner(s): HASAN, MOHAMMED A
• Application Number:
  US10/042,448
• Publication Number:
  US 20020109900A1
• Time in Patent Office: 686 Days
• Field of Search: 359/245, 359/247, 359/291, 359/290, 359/298, 359/320, 359/315, 359/275, 359/267
• US Class Current: 359/275
• CPC Class Codes: G02F 1/163 Operation of electrochromic cells, e.g. electrodeposition cells; Circuit arrangements therefor
• CPC Class Codes: G02F 1/19 based on variable-reflection or variable-refraction elements not provided for in groups G02F1/015 - G02F1/169
• CPC Class Codes: G02F 2202/34 Metal hydrides materials
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 3/38 using electrochromic devices

Abstract

A reset driving scheme for addressing a switching mirror display enables current to flow in two directions through the switching elements. The display is forced into a predefined state and drives the display into the other optical states by using an addressable TFT providing a continous current.

Claims

1. Display device being operable in a reflective mode or in a transmissive mode and having pixel elements for modulating light, said pixel elements comprising:

a stack of layers including a switchable layer of an optically switchable material that switches the pixel elements from a first state to a second state, the second state being different from the first state, the first state and the second state being one of the following states;

a reflective state, a transmissive state, or an absorbing state;

means for modulating light in the reflective mode by switching from a reflective state to a non-reflective state, and for modulating light in the transmissive mode by switching from a transmissive state to a non-transmissive state, the non-reflective state being the transmissive state or the absorbing state and the non-transmissive state being the reflective state or the absorbing state,

the means for modulating light comprising for each pixel element a series connection of the pixel element and a current source to charge the pixel element (charge mode); and

means for resetting at least part of the pixel elements to a defined state (reset mode).

2. Display device according to claim 1 in which the optically switchable layer brings about switching by changing a concentration of hydrogen.

3. Display device according to claim 1 in which the common point of the pixel element and a current source is connected via a switch to a reset voltage.

4. Display device according to claim 1 in which the current source comprises a capacitor element connected to a control connection of a transistor.

5. Display device according to claim 1 in which the device comprises means for resetting all pixel elements to a defined state and further means to charge selected pixel elements.

6. Display device according to claim 5 in which the series connection of the pixel element and the current source is provided between power voltage connections and the means for resetting comprise means to switch one of the power voltage connections between at least two voltages having different signs or amplitudes with respect to the other power voltage connection.

7. Display device according to claim 1 in which a current sensor is provided in the current path common to both the charge mode and the reset mode of the display device.

8. Display device according to claim 1 in which the pixel elements are provided in a matrix structure and the further means comprise select switches controlled by select lines, to which data is presented via data lines.

9. Display device according to claim 8 in which power voltage connections for at least a group of pixel elements are provided as a mesh structure.

10. Display device according to claim 1 in which the switches comprise thin film transistors.