GB2335562A - Video input level control circuit - Google Patents
Video input level control circuit Download PDFInfo
- Publication number
- GB2335562A GB2335562A GB9912188A GB9912188A GB2335562A GB 2335562 A GB2335562 A GB 2335562A GB 9912188 A GB9912188 A GB 9912188A GB 9912188 A GB9912188 A GB 9912188A GB 2335562 A GB2335562 A GB 2335562A
- Authority
- GB
- United Kingdom
- Prior art keywords
- video
- section
- level
- signal
- input
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000001514 detection method Methods 0.000 claims 1
- 239000000872 buffer Substances 0.000 description 6
- 238000010586 diagram Methods 0.000 description 4
- 239000003990 capacitor Substances 0.000 description 3
- 230000003321 amplification Effects 0.000 description 2
- 238000003199 nucleic acid amplification method Methods 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000009738 saturating Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
- H04N5/57—Control of contrast or brightness
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
- G09G5/10—Intensity circuits
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/06—Adjustment of display parameters
- G09G2320/0606—Manual adjustment
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/06—Adjustment of display parameters
- G09G2320/0626—Adjustment of display parameters for control of overall brightness
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/06—Adjustment of display parameters
- G09G2320/066—Adjustment of display parameters for control of contrast
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/66—Transforming electric information into light information
- H04N5/68—Circuit details for cathode-ray display tubes
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/64—Circuits for processing colour signals
- H04N9/641—Multi-purpose receivers, e.g. for auxiliary information
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- General Physics & Mathematics (AREA)
- Theoretical Computer Science (AREA)
- Processing Of Color Television Signals (AREA)
Abstract
A video input level control circuit in a video display device includes a contrast control section (6) connected to an input of an amplifier (8) for controlling the contrast voltage level to adjust brightness of a screen of the video display device (9); a signal comparing section (11) for comparing each of the RGB video signals outputted from a video signal output section (7) with preset standard voltages; a level detecting section (12) for detecting excessive saturation of the RGB video signals based on the signals outputted from the signal comparing section (11); and a level control section (13) having an input connected to the level detecting section (12) and an output connected to the contrast control section (6), the level control section (13) controlling the contrast control section (6) according to an input gain level of the RGB video signals detected by the level detecting section (12).
Description
2335562 VIDEO INPUT LEVEL CONTROL CIRCUIT IN A VIDEO APPLIANCE The present
invention relates to a video input level control circuit in a video appliance. More particularly the invention relates to a video input level control circuit which can improve picture quality of the video appliance by selectively controlling input levels of the video signals inputted in different manners from the different-type video cards of a personal computer (PC).
A conventional video input level control circuit is shown in FIG. 1. Referring to FIG. 1, the conventional circuit comprises a video input circuit 71 for amplifying a video signal inputted from a video card mounted on a PC 70 to a predetermined level; a Video output amplifying section 73 for amplifying the video signal outputted from the video input circuit 71 to a predetermined output level, and outputting the amplified signal to a cathode ray tube (CRT) 72; and a video input level control section 74 for controlling an input level of the video signal inputted from the video output amplifying section 73 to the CRT 72.
The video output amplifying section 73 comprises a buffer transistor Q1 for buffening the video signal inputted ftorn the video input circuit 71, and amplifying transistors Q2, Q3 for cascode-amplifying the video signal outputted from the buffer twsistor Q 1.
A base terminal of the anpliffin Umsistor Q2 is connected to an emitter terminal of the buffer transistor Q1, and the emitter terminal of the amplifying transistor Q2 is connected to the collector terminal of the amplifying transistor Q3. Bias voltages Wcl, Wc3 are connected to the collector terminal of the transistors Q1, Q2 via resistors RI, R3. A bias voltage Wc2 is connected to the base terminal of the amplifying transistor Q2, and CRT 72 is connected to the collector terminal of the amplifiring transistor Q3. Resistors 1 voltage level at the base terminal becomes higher than the standard voltage level Vb=0.7+Ve. The bias voltage Vcc4 flowing to the base terminal of the switching transistor Q5 subsequently changes its flow to the detecting transistor Q4. Ile switching transistor Q5 is turned on as a consequence.
If the switching Istor Q5 is turned on, the collector voltage level at the switching transistor Q5 becomes higher, and the emitter voltage level at the collector terminal of the switching istor Q5 subsequently becomes higher. As a consequence, the amplification ability of the amplifying transistors Q2, Q3 deteriorates and the video input level applied to the CRT 72 can be automatically controlled.
If the switching transistor Q5 is turned on, the transistor Q6 is subsequently turned on, and controls operation of the detecting transistor Q4. As shown in FIG. 2A, the detecting transistor Q4 recognizes the video signal which is as high as the base voltage as a starting signal, and operates imperfectly during the interval T I, as shown in FIG. 2B. 7he transistor Q6 is turned on only while the capacitor Cl, which is discharged through the resistor R 11 having a great resistance value, is charged. While the transistor Q6 is turned on, the voltage at the emitter of the detecting transistor Q4 flows to the transistor Q6, thereby lowering the voltage level of the emitter of the detecting transistor Q4. 71crefore, the detecting transistor Q4 operates only while the transistor Q6 is turned on. Ibus, the tuming-on interval of the detecting transistor Q4 is determined by the interval of the capacitor Cl. 71e interval of the capacitor Cl is short as shown to be TI in FIG. 2C. Accordingly, the video output level inputted to the CRT 72 rapidly becomes lower, and brightness of the screen can be controlled to be minimal.
The conventional video input level control circuit constituted above is thermally stable and can compensate the varied portion if the video input level becomes higher than a 4 the base terminal of the buffer transistor QI of the video output amplifying section. Subsequently, the buffer transistor QI buffers the inputted video signal and inputs the buffered video signal to the base terminal of the arnplifing transistor Q3. lle amplifying transistor Q3 is then turned on, and the amplifying transistor Q2 is subsequently turned on. -Me video signal is cascode-amplifled by these two transistors Q2, Q3, and inputted to the CRT 72. CRT 72 then displays an image according to the inputted video signal.
The video signal of the video input circuit 71 is also inputted to the base terminal of the detecting transistor Q4. Since the emitter standard voltage Ve of the detecting transistor Q4 is set to be bias voltage Wc4 by the resistor RIO, the base voltage Vb=0.7+Ve. llerefore, the detecting transistor Q4 is turned on only at the voltage higher than the base voltage. In other words, if the video signal input level is applied to the CRT 72 as a normal voltage level, e.g., 0.7V, the detecting transistor Q4 is not turned on. Accordingly, neither the switching transistor Q5 nor the transistor Q6 is turned on, thereby never affecting the emitter voltage level of the amplifying transistor Q3.
However, if the video signal input level is applied to the CRT 72 at an abnormal level, e.g., high, or if an internal temperature of the product increases, the voltage level at the base terminal of the detecting istor Q4 becomes higher than Vb=0.7+Ve. In other words, if the internal of the product affecting the video input level increases, the internal resistance of the thermistor THI becomes greater, and consequently, the bias voltage Wc4 at the base te of the detecting transistor Q4 becomes higher than Vb=0.7+Ve after passing through the thermistor THI. In another case, if the video signal input level inputted through the video input circuit 71 is higher than the normal level, the video signal is applied to the base terminal at a voltage higher than the base voltage of the detecting transistor Q4. Accordingly, the detecting transistor Q4 is turned on since the 3 present invention; and FIGs. 4A to 4C are waveform diagrams illustrating input gain control waveforms applied to the circuit in FIG. 3.
FIG. 3 shows an automatic video input level control circuit according to an embodiment of the present invention.
Referring to FIG. 3, the present invention comprises a video signal output section 7 for R, CT, B signal-processing the video signal inputted from the PC 2; a pre-amplifying section 8 for amplifying the color video signals inputted from the video signal output section 7 by a predetermied amplification factor; a video output ampliffing section 10 for outputarnpWng the color video signal inputted to the pre-amplifying section 8, and displaying the amplified video signal on the CRT 9; a contrast control section 6 connected to the V-CW terminal for controlling the con voltage level to control brightness of the screen of the monitor (not illustrated in the drawing); a signal comparing section 11 for each of the k G, B color video signals outputted from the video signal output section 7 with preset standard voltages, and outputting the compared signals; a level detecting section 12 for detecting excessive saturation of the video signals by means of the compared signals outputted from the signal comparing section 11; and a level control section 13 for controlling the con control section 8 according to the input gain level of the R, G, B color video signals detected by the level detecting section 12 to control the input levels of the video signals.
7Me signal comparing section 11 comprises a first comparator 14 connected to the R color video output terminal of the video signal output section 7 for comparatively outputting the R video color signal according to a standard voltage Vref 1; a second comparator 15 connected to the G color video output terminal of the video signal output 6 predetermined level. If the video input level becomes lower than the standard input level due to different types of video cards of the PC 70, the varied portion cannot be compensated, thereby excessively saturating the video signal and deteriorating quality of the screen.
In order to resolve the above problem, an object of the present Invention is therefore to provide a video input level control circuit in a Video appliance which can notably improve quality of the screen of the video appliance by selectively controlling the video signal input level, which is inputted in difibrent manners according to the different types of video cards of a PC, to be minimal.
Another object of the present invention is to provide a video input level control circuit in a video appliance which can automatically control video input level without a separate manipulation by the user by detecting an excessive input of the video signals of red (R), green (0) and blue (B) colors which are inputted in different manners from the PC, and adjusting the video signal input level and displaying an image on a monitor screen.
The present invention is defined in the accompanying independent claim. Some preferred features are recited in the dependent claims.
The above objects, other feat and advantages of the present invention wflil become more apparent with reference to the preferred embodiments accompanying the drawings in which:
FIG. 1 is a block diagram illustrating the conventional video input level control circuit; FIGs. 2A to 2C are waveform diagrams illustrating waveforms of the detecting transistor of the circuit in FIG. 1; FIG. 3 is a block diagram illug a circuit according to an embodiment of the subsequently compares the inputted G color video signal with the standard voltage Vref 2 divided by the resistors R13 and R14. If the inputted G color video signal is lower than the standard voltage Vref 2 as a result of comparison by the second comparator 15, a signal 'high' is outputted. If higher than the standard voltage Vref 2, a signal low' is inputted to the level detecting section 12.
Simultaneously, the B color video signal of the video signal output section 7 is inputted to the inverting terminal of the third comparator 16, and the third comparator 16 compares the inputted B color video signal with the standard voltage Vref 3 divided by the resistors R15 and R16. If the inputted B color video signal is proved to be lower than the standard voltage Vref 3 as a result of comparison by the third comparator 16, a signal high' is outputted. If the inputted B color video signal is proved to be higher than the standard voltage Vref 3, a signal 'low' is inputted to the level detecting section 12.
Thus, the level detecting section 12 detects logic signals according to the input level of the R, G, B video signals inputted from the first to the third comparators 14, 15, 16, and detects whether the video input level currently outputted to the CRT 9 is excessively saturated. If the level detecting section 12 detects that the video signals outputted by the first to the third comparators 14, 15, 16 are all high', this means that the video signal input level is inputted in normal state. llerefore, a waveform illustrated in FIG. 4C, which does not require a gain control, is inputted to the contrast control secfion 6. If the level detecting section 12 detects that any video signal(s) outputted by the first to the third comparators 14, 15, 16 is (are) low', this means that the video signal input level is excessive as illustrated in FIG. 4A. Then, the level detecting section 12 ffliputs the detected video signals to the level control section 13. lle level control section 13 subsequently Inputs an adjustment width W of the video signal to be adjusted according to 8 section 7 for comparatively outputting the 0 color video signal according to a standard voltage Vref 2; and a third comparator 16 connected to the B color video output terminal of the video signal output section 7 for comparatively outputting the B color video signal according to a standard voltage Vref 3.
The standard voltage Vref 1 divided by the resistors RI 1 and R12 is connected to the non-inveffing terminal of the first comparator 14, and the standard voltage Vref 2 divided by the resistors R13 and R14 is connected to the non-inverting terminal of the third comparator 16. Bias voltages Vccl, Vec2, Wc3 are connected to the other terminals of the resistors R 12, R 14, RI 6, respectively.
The present invention according to the above embodiment operates as follows.
If a video signal is inputted to the video signal output section 7 from a video card of the PC 2, the video signal output section 7 R, G, B signalprocesses the inputted video signal, and inputs the signal-processed video signal to the pre-amplifying section 8.
Ibe R, G, B color signals of the video signal output section 7 are inputted to the comparators 14, 15, 16, respecti of the signal comparing section 11. In other words, the R color video signal of the video signal output section 7 is inputted to the inverting terminal of the first comparator 14. The firm comparator subsequently compares the inputted R color video signal with the standard voltage Vref 1 divided by the resistors R 11 and R12. If the inputted R color video signal is compared to be lower than the standard voltage Vref 1 as a result of comparison by the first comparator 14, a signal 'high' is outputted. If compared to be higher than the standard voltage Vref 1, a signal 'loW is inputted to the level detecting section 12.
Simultaneously, the G color video signal of the video signal output section 7 is inputted to the inverting terminal of the second comparator 15. The second comparator 7
Claims (6)
1. A video input level control circuit In a video display device including an amplifying section for amplifying RGB video signals containing red green and blue signals and being inputted from a video signal output section, the circuit comprising: a contrast control section connected to an input of the amplifier for controlling the cont" voltage level to adjust brightness of a screen of the video display device; a signal comparing section for comparing each of the RGB video signals outputted from the video signal output section with preset standard voltages, and outputting the compared signals. a level detecting section for detecting excessive saturation of the RGB video signals based on the compared signals outputted from the signal comparing section; and a level control section having an input connected to the level detecting section and an output connected to the con control section, the level control section controlling the contrast control section according to an input gain level of the RGB video signals detected by the level detecting section.
2. A video input level control circuit of claim 1, wherein the signal comparing section compnses: a first comparator connected to the R video output terminal of the video signal output section for outputting the R color video signal after comparison with a standard voltage Vref 1; a second comparator connected to the G video output terminal of the video signal 1 ideo signal after comparison ith a standard output section for outputting the G color V1 1 wl voltage Vref 2; and a third comparator connected to the B video output terminal of the video signal the control signal detected by the level detecting section 12, i.e., an input gain level adjustment control signal of the waveforms of the brightness and excessive saturation, to the con control section 6. Then, the con control section 6 automatically varies and adjusts the contrast voltage level set at the pre-amplifring section 8 according to the input gain level adjustment control signal inputted through the V-CW terminal of the preamplifying section 8. The pre-amplifying section 8 subsequently R, 0, B signal-amplifies the video signal, the con voltage level of which has been adjusted, as illustrated in FIG. 4B, and displays the amplified signals on the CRT 9 through the video output amplifying section 10.
According to the preferred embodiment of the present invention as described above, picture quality of a video appliance can be notably improved by selectively controlling the video signal input levels inputted in different manners according to the different types of video cards in a PC to be optimum input levels. The present invention therefore enables an automatic control of the video input levels without a separate manipulation by the user through comparators which can produce excessive saturation of the R, G, B color video signals inputted in different manners from the PC and adjust the video signal input gain level as a result of detection to display a resultant image on a monitor screen.
9 output section for outputting the B color video signal after comparison with a standard voltage Vref3.
3. A video input level control circuit as claimed in claim 2, wherein the standard voltage Vrefl is provided by dividing a first supply voltage over two resistors.
4. A video input level control circuit as claimed in claim 2 or claim 3, wherein the standard voltage Vref2 is provided by dividing a second supply voltage over two resistors.
5. A video input level control circuit as claimed in claim 2 or claim 3 or claim 4, wherein the standard voltage VreS is provided by dividing a third supply voltage over two resistors.
6. A video input level control circuit substantially as specifically described herebefore with reference to the accompanying drawings and as shown in FIG 3.
11
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1019960076827A KR100254766B1 (en) | 1996-12-30 | 1996-12-30 | Circuit for selecting video input level by using micom |
| KR1019970031282A KR100262366B1 (en) | 1997-07-07 | 1997-07-07 | Video input level automatic selection circuit |
| GB9727412A GB2321155B (en) | 1996-12-30 | 1997-12-29 | Video input level control circuit in a video appliance |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9912188D0 GB9912188D0 (en) | 1999-07-28 |
| GB2335562A true GB2335562A (en) | 1999-09-22 |
| GB2335562B GB2335562B (en) | 1999-11-03 |
Family
ID=27269161
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9912188A Expired - Fee Related GB2335562B (en) | 1996-12-30 | 1997-12-29 | Video input level control circuit in a video appliance |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2335562B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103680469A (en) * | 2013-12-23 | 2014-03-26 | 深圳市华星光电技术有限公司 | Liquid crystal display and adjusting method for brightness and contrast degree of liquid crystal display |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5550556A (en) * | 1993-11-01 | 1996-08-27 | Multivideo Labs, Inc. | Transmitting data and commands to display monitors |
-
1997
- 1997-12-29 GB GB9912188A patent/GB2335562B/en not_active Expired - Fee Related
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5550556A (en) * | 1993-11-01 | 1996-08-27 | Multivideo Labs, Inc. | Transmitting data and commands to display monitors |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103680469A (en) * | 2013-12-23 | 2014-03-26 | 深圳市华星光电技术有限公司 | Liquid crystal display and adjusting method for brightness and contrast degree of liquid crystal display |
| CN103680469B (en) * | 2013-12-23 | 2015-12-30 | 深圳市华星光电技术有限公司 | The method of adjustment of the brightness and contrast of a kind of liquid crystal display and liquid crystal display thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2335562B (en) | 1999-11-03 |
| GB9912188D0 (en) | 1999-07-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20101229 |