Television – Image signal processing circuitry specific to television – Color balance or temperature
Reexamination Certificate
2002-06-04
2003-03-04
Kostak, Victor R. (Department: 2614)
Television
Image signal processing circuitry specific to television
Color balance or temperature
C348S656000
Reexamination Certificate
active
06529247
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an automatic white balance adjusting circuit for automatically adjusting a white balance in a television receiver or a monitor apparatus.
In a television receiver or a monitor apparatus, when a white color reference signal is inputted, a predetermined color temperature must be reproduced at a cathode-ray tube (hereinafter, referred to as CRT). In general, the rate of each of output lights R (red), G (green), and B (blue) of the CRT is determined depending on the rate of each cathode current. However, characteristics of the cathode current to a cathode voltage differs with the CRT. Therefore, in order to reproduce a predetermined color temperature, it is required to adjust the rate of the cathode current among R, G, and B, by the CRT.
Conventionally, the CRT screen has been monitored on a television camera or the like to detect a white balance state, the detected value has been fed back to a computer system or service personnel for process adjustment to compare it with a predetermined reference value, and the DC voltage level and gain of each of the outputs R, G, and B has been adjusted according to the comparison results. In addition, during this adjustment, variable resistors provided at a DC voltage level adjusting circuit and a gain adjusting circuit has been manually adjusted or adjustment data stored in a storage circuit has been rewritten through a data bus.
However, in the above mentioned conventional method, an industrial television camera, a computer system for process adjustment, or service personnel is required at an adjustment site. Therefore, there is a problem that the white balance characteristics cannot be self-adjusted following an change of CRT with an elapse of time after shipment of the television receiver or monitor apparatus.
In recent years, an Automatic Kine Bias (AKB) circuit for automatically perform such adjustment is available in use. In this circuit, a reference signal is inputted during a vertical blanking period of a video signal, a cathode current of the CRT at this time is detected, and a white balance is automatically adjusted using the detected value.
FIG. 1
shows an example of a conventional circuit of such AKB circuit. A while balance is adjusted by setting a drive gain (AC amplitude) and a cutoff level (DC voltage level) on each of the R, G, and B axes. Specifically, during a certain period, the cutoff level is adjusted using a reference signal
1
(black level) substituted for a video signal, and similarly, during a period free of being superimposed on the reference signal
1
, the drive gain is adjusted using a reference signal
2
(white level) substituted for the video signal. These two black and white levels are adjusted, thereby equally setting a ratio of the respective input signal and cathode current of each of the R, G, and B axes.
Now, the AKB circuit of
FIG. 1
will be specifically described.
Switch circuits
1
,
2
,
3
each select and output respective one among R, G, and B signals and the reference signal
1
(black level) and the reference signal
2
(white level). A period for selecting the reference signals
1
and
2
is a period that is a vertical blanking period, but is not a vertical feedback period, i.e., a part of a period that is generally over-scanned and not visualized by a user. The level of the reference signal
1
corresponding to a reference black level is about 3 to 5 IRE, for example (a peak of the white signal is 100IRE), and the level of the reference signal
2
corresponding to a reference white level is about 30 to 50 IRE, for example.
In addition, the above R, G, and B signals are primary color signals of each of the R, G, and B axes in a three-primary color drive, and the brightness, tint or the like of these primary signals are controlled in advance.
Drive gain adjusting circuits
4
,
5
, and
6
respectively consisting of gain control amplifiers perform adjustment of drive gain to signals outputted respectively from switch circuits
1
,
2
, and
3
, i.e., adjustment of an AC amplitude. In addition, cutoff adjusting circuits
7
,
8
,
9
respectively consisting of clamp circuits, for example, performs adjustment (for example, clamping) of the DC level of signals output respectively from the drive gain adjusting circuits
4
,
5
, and
6
. Outputs of the cutoff adjusting circuits
7
,
8
, and
9
are supplied to bases of output transistors (PNP transistors)
13
,
14
, and
15
each via respective one of drive circuits
10
,
11
, and
12
. Emitters of these transistors
13
,
14
, and
15
are connected respectively to the cathode electrodes of the R, G, and B axes of the CRT
16
. These transistors
13
,
14
, and
15
are driven by outputs from the drive circuits
10
,
11
, and
12
, whereby a current flow the cathode electrode of each of the R, G, and B axes of CRT
16
, and CRT
16
are driven to be displayed.
To collectors of the above transistors
13
,
14
, and
15
each, resistors
17
,
18
, and
19
for converting the current flowing through each cathode electrode into a voltage are connected. Drop voltages in these resistors
17
,
18
, and
19
are sampled respectively at a sample hold circuit (S/H)
20
,
21
and
22
. These sample hold circuits
20
,
21
, and
22
samples voltages proportional to a cathode current during a certain period, for example 1H (1 horizontal period). The sampled voltages are held by capacitors
23
,
24
, and
25
for holding a black level respectively and by capacitors
26
,
27
, and
28
for holding a white level.
The voltages held by the above capacitors
23
,
24
, and
25
are compared respectively with a reference voltage corresponding to the reference black level in comparator circuits
29
,
30
, and
31
. The reference voltage is outputted from a reference voltage source
32
. The comparison results of these comparator circuits
29
,
30
, and
31
are supplied respectively to the cutoff adjusting circuits
7
,
8
, and
9
, and the DC level is adjusted by each of the R, G, and B axes.
The voltages held by the above capacitors
26
,
27
, and
28
are compared respectively with a reference voltage corresponding to the reference white level in the comparator circuits
33
,
34
and
35
. The reference voltage is outputted from a reference voltage source
36
. The comparison results of these comparator circuits
33
,
34
, and
35
are supplied respectively to drive gain adjusting circuits
4
,
5
, and
6
, and the AC amplitude is adjusted by each of the R, G, and B axes.
In the AKB circuit shown in
FIG. 1
, by each of the R, G, and B axes, adjusting operation of an AC amplitude and an adjusting operation of a DC level are controlled respectively by each negative feedback loop consisting of drive gain adjusting circuits
4
,
5
and
6
; cutoff adjusting circuits
7
,
8
and
9
; drive circuits
10
,
11
, and
12
; transistors
13
,
14
, and
15
; sample hold circuits
20
,
21
, and
22
; and comparator circuits
29
to
35
. At a time when voltages of both input terminals of each of comparator circuits
29
to
31
and
33
to
35
are equal to each other, the above operation of each negative feedback loop becomes stable. At a time when operation of each feedback loop becomes stable, a rate of the cathode current among each of the R, G, and B axes to a reference signal is set to be equal.
In the meantime, in the conventional AKB circuit shown in
FIG. 1
, in order to hold a voltage obtained by converting a cathode current during a keyline period, sample hold circuits
20
to
22
require capacitors
23
to
28
. Since this keyline period is b
1
V (1 vertical period, about 17 mS), these capacitors require a relatively large capacitance, and use about several &mgr;F to 10 &mgr;F.
As a result, an integrated AKB circuit can not incorporate these capacitors in an integrated circuit, and is required to be provided outside of the integrated circuit. In addition, the integrated circuit is required to provide a dedicated external terminal for providing these capacitors outside the circ
Hara Kenji
Sumiyoshi Hajime
Tagomori Reiji
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