Video display monitor

• US 6,243,073 B1
• Filed: 12/08/1997
• Issued: 06/05/2001
• Est. Priority Date: 12/06/1996
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Hirano, Takehisa, Nakai, Katsuhiro, Ohira, Kazuo, Kawamura, Hideaki, Kasahara, Mitsuhiro
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): NGUYEN, FRANCIS N
• Application Number:
  US08/986,504
• Time in Patent Office: 1,275 Days
• Field of Search: 345/148, 345/147, 345/213, 345/67-68, 345/60, 345/74-75, 345/63, 345/89, 345/212, 345/132, 348/797, 348/447
• US Class Current: 345/690
• CPC Class Codes: G09G 2310/0205 Simultaneous scanning of several lines in flat panels
• CPC Class Codes: G09G 2310/0216 Interleaved control phases for different scan lines in the same sub-field, e.g. initialization, addressing and sustaining in plasma displays that are not simultaneous for all scan lines
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/282 using DC panels

Abstract

A video display monitor, such as a plasma monitor, which uses a subfield method which overlaps weighted multiple binary video images in a time base for display. The stable driving of a plasma display panel may be assured and display in the 256 grey-level may be maintained although vertical synchronizing frequency of the input video signal changes. A vertical synchronizing measurement unit measures the vertical synchronizing frequency of the video signal, and a subfield number adjustment unit adjusts the number of subfields in accordance with a measured vertical synchronizing frequency. The stable driving of the plasma display panel and display in grey levels may be assured by selecting a ROM table with an output bit width equivalent to the number of subfields to be output from multiple ROM tables used for converting the number of bits in the input signal.

Claims

1. A video display monitor for use with a video signal having a vertical synchronizing frequency in which each field of the video signal is divided into a respective number of subfields, said subfields respectively weighted with one of a time width and a pulse value, and video images in said subfields are overlapped in a time base for displaying said video images as grey levels, said video display monitor comprising:

vertical synchronizing frequency measurement means for providing a measurement of the vertical synchronizing frequency of said video signal;

subfield number adjustment means for adjusting the number of said subfields in accordance with said measurement; and

subfield length adjustment means for adjusting one of i) the time width of said subfields and ii) the pulse value of said subfields in accordance with the measuring result of said vertical synchronizing frequency measurement means.

2. The video display monitor according to claim 1, wherein said subfield number adjustment means comprises at least one of the following functions:

i) the number of said subfields is decreased when the vertical synchronizing frequency is higher than a first specified frequency, wherein said first specified frequency is a frequency at which driving up to a predetermined subfield number within one-field period is prevented in order to maintain a predetermined resolution;

ii) the number of said subfields is increased when the vertical synchronizing frequency is lower than a second specified frequency, wherein said second specified frequency is a frequency at which it is possible to drive up to a higher subfield number than said predetermined sub-field number within a one-field period; and

iii) the number of said subfields is decreased when the vertical synchronizing frequency is higher than the first specified frequency, and the number of subfields is increased when the vertical synchronizing frequency is lower than the second specified frequency.

3. The video display monitor according to claim 2, further comprising comparison means for comparing the vertical synchronizing frequency and at least one of said first and second specified frequencies using hysteresis.

4. The video display monitor according to claim 1, further comprising a read only memory (ROM) table having different output bit widths corresponding to an input bit width, and one of the different output bit widths of said ROM table is selected in accordance with the number of said subfields determined by said subfield number adjustment means.

5. The video display monitor according to claim 4, wherein said subfield number adjustment means comprises at least one of the following functions:

i) the number of said subfields is decreased when the vertical synchronizing frequency is higher than a specified frequency, wherein at said specified frequency driving up to a predetermined subfield number within a one-field period is prevented in order to maintain a predetermined resolution;

ii) the number of said subfields is increased when the vertical synchronizing frequency is lower than another specified frequency, wherein at said another specified frequency a higher subfield number than said predetermined subfield number is driveable up to within a one-field period; and

iii) the number of said subfields is decreased when the vertical synchronizing frequency is higher than said specified frequency, and the number of subfields is increased when the vertical synchronizing frequency is lower than said another specified frequency.

6. The video display monitor according to claim 5, further comprising comparison means for comparing the vertical synchronizing frequency and at least one of said specified frequency and another specified frequency using hysteresis.

7. The video display monitor according to claim 4, further comprising subfield length adjustment means for adjusting one of i) the time width of said subfields and ii) the pulse value of said subfields.

8. The video display monitor according to claim 7, wherein said subfield number adjustment means decreases the number of said subfields when said vertical synchronizing frequency is higher than a specified frequency, and said subfield length adjustment means extends a length of said subfields when said vertical synchronizing frequency is lower than another specified frequency.

9. The video display monitor according to claim 8, further comprising comparison means for comparing the vertical synchronizing frequency and at least one of said specified frequency and another specified frequency using hysteresis.

10. The video display monitor according to claim 1, further comprising:

a random access memory (RAM) table for conducting a conversion of the video signal; and

RAM control means for writing table data having an output bit width equivalent to the number of subfields determined by said subfield number adjustment means to said RAM table.

11. The video display monitor according to claim 10, wherein said RAM control means writes the table data to said RAM table during a vertical retrace period of said video signal.

12. The video display monitor according to claim 11, wherein said subfield number adjustment means comprises at least one of the following functions:

i) the number of said subfields is decreased when the vertical synchronizing frequency is higher than a specified frequency, wherein at said specified frequency driving up to a predetermined subfield number within a one-field period is prevented in order to maintain a predetermined resolution;

ii) the number of said subfields is increased when the vertical synchronizing frequency is lower than a further specified frequency, wherein at said further specified frequency a higher subfield number than said predetermined subfield number is driveable to within a one-field period; and

iii) the number of said subfields is decreased when the vertical synchronizing frequency is higher than said specified frequency, and the number of subfields is increased when the vertical synchronizing frequency is lower than said further specified frequency.

13. The video display monitor according to claim 10, wherein said subfield number adjustment means comprises at least one of the following functions:

i) the number of said subfields is decreased when the vertical synchronizing frequency is higher than a specified frequency, wherein at said specified frequency driving up to a predetermined subfield number within a one-field period is prevented in order to maintain a predetermined resolution;

ii) the number of said subfields is increased when the vertical synchronizing frequency is lower than another specified frequency wherein at said another specified frequency a higher subfield number than said predetermined subfield number is driveable to within a one-field period; and

iii) the number of said subfields is decreased when the vertical synchronizing frequency is higher than said specified frequency, and the number of subfields is increased when the vertical synchronizing frequency is lower than said another specified frequency.

14. The video display monitor according to claim 10, further comprising subfield length adjustment means for adjusting one of i) the time width of said subfields and ii) the pulse value of said subfields.

15. A video display monitor for use with a video signal having a vertical synchronizing frequency in which each field of the video signal is divided into a respective number of subfields, said subfields respectively weighted with one of a time width and a pulse value, and video images in said subfields are overlapped in a time base for displaying said video images as grey levels, said video display monitor comprising:

vertical synchronizing frequency measurement means for providing a measurement of the vertical synchronizing frequency of said video signal;

subfield number adjustment means for adjusting the number of said subfields in accordance with said measurement and for decreasing the number of said subfields when said vertical synchronizing frequency is higher than a specified frequency wherein said specified frequency is a frequency at which driving up to a predetermined subfield number within a one-field period is prevented in order to maintain a predetermined resolution;

subfield length adjustment means for extending a length of said subfields when said vertical synchronizing frequency is lower than another specified frequency, wherein said another specified frequency is a frequency at which a longer subfield length than a predetermined subfield length is settable within a one-field period.

16. The video display monitor according to claim 15, further comprising comparison means for comparing the vertical synchronizing frequency and at least one of said specified frequency and said another specified frequency using hysteresis.