Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2001-09-07
2003-01-28
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S403000, C315S383000, C348S244000, C348S255000, C348S655000
Reexamination Certificate
active
06512340
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the field of cathode ray tube (CRT)-based display technology. More specifically, the present invention relates to the field of thermal protection for a CRT-based display system using a current mode output temperature sensor.
BACKGROUND ART
The cathode ray tube (CRT) remains the dominant display technology for a wide range of application for both consumers and professionals. CRT-based display system has become an integral tool used in a wide variety of different display applications, such as in video display, computer terminal display, instrumentation (such as oscilloscope), radar, image recording, specialized military application, medical imaging, etc. As requirements for greater resolution and color purity have increased, improvements have also been made in the design and manufacture of CRT devices and their signal driving circuits. Within the last 10 years, improvements to the basic monochrome and color CRT have been pushed by the explosion of the personal computer industry and by the increased picture resolution demanded by end-users. Display size has also been a key element in CRT development. Furthermore, the acceptance of VGA (Video Graphics Adapter) computer monitors and high-definition television (HDTV) has accelerated this trend. For example, an HDTV, such as a Sony Trinitron, has 16:9 aspect ratio viewing area, horizontal resolution of over 1000 lines and vertical resolution of over 750 lines.
A typical CRT-based display system includes a CRT driver and a CRT display unit. The CRT display unit further includes a cathode ray tube (CRT) and a display screen. The CRT driver provides driving signals to the CRT display unit. As aspect ratio viewing area and resolution of the CRT-based display system increases, the amplitude and frequency of the signal input to the CRT driver also increase, causing significant power dissipation problems. For example, higher power dissipation shortens the lifetime of a CRT. Intuitively, the conventional heat sink does not solve the power dissipation problems because a heat sink for high power dissipation is bulky and costly. For example, placing a heat sink at the neck of a CRT display unit to reduce the temperature will add unwanted weight to a CRT-based display system such as television and VGA computer monitors. In addition, a bulky heat sink placed near the CRT display unit causes transportation problems because the CRT is a fragile and complicated tube. It is very difficult and expensive to manufacture a CRT. Materials used in an effective heat sink are very heavy, especially at high temperature. Therefore, it is undesirable to add a heavy and bulky heat sink in the vicinity of a CRT to dissipate heat.
Another approach to solve the temperature-associated problems for a CRT-based display system is to use automatic thermal shutdown. However, automatic shutdown for television or other CRT-based display systems is not preferable to the end-users. Another method to solve the temperature problems in a CRT-based display unit is to use low bandwidth and amplitude signals for the CRT driver. However, low bandwidth and amplitude equal low power. When less power is used, the picture becomes fuzzier because the brightness of a picture on a display screen is directly proportional to the power supplied to the electron gun of the CRT. In high-resolution display applications, wide bandwidth power amplifiers are used to enhance the picture quality. Therefore, reduced bandwidth and amplitude in the pre-amplifier does not solve the heat dissipation problems inside a CRT-based display system.
Yet another method used widely in the existing CRT-display system to reduce the temperature-associated problems is an Automatic Brightness Limiter (ABL) circuit. The ABL is a gain control circuit that controls the gain of a video pre-amplifier used in the CRT display unit. However, the ABL does not measure the temperature of the amplifier, but instead it measures the average DC current of the CRT. Therefore, an ABL can typically only monitor the temperature problems caused by a large amplitude current but not those caused by a high frequency of the video signals.
SUMMARY OF THE INVENTION
Accordingly, a need exists for achieving a low-cost, compact, and light-weight method and system for solving the power dissipation problems inherent in high-resolution CRT display applications so that the high temperature generated by amplitude and frequency signals is handled without having a thermal shutdown or sacrificing picture quality. The present invention provides a method and system which satisfies the above mentioned need.
For example, one embodiment of the present invention includes a temperature sensor with current mode output that is utilized within a cathode ray tube (CRT)-based display system for providing thermal protection to a CRT driver. Specifically, the current mode output temperature sensor of the present embodiment is implemented with the CRT driver of the CRT display system. Furthermore, the temperature sensor has a current sink output that is connected to an Automatic Brightness Limiter (ABL) circuit of the CRT display. The current sink of the temperature sensor operates in a manner similar to an “OR gate” with the CRT anode current. As such, when the CRT driver temperature rises above a threshold temperature, the current mode output temperature sensor sinks a current and activates the ABL circuit. As a result, the video amplitude of the CRT driver is reduced and its temperature is stabilized.
In another embodiment, the present invention provides a method for using a current mode output temperature sensor to provide thermal protection to a CRT driver. The method includes setting a temperature independent reference voltage. Additionally, the method includes setting a threshold temperature for the current mode output temperature sensor. Furthermore, the method includes coupling the current mode output temperature sensor to the CRT driver. The method also includes electrically coupling the current mode output temperature sensor to an Automatic Brightness Limiter (ABL) circuit. Moreover, the method includes determining if the temperature of the CRT driver exceeds the threshold temperature by utilizing the temperature independent reference voltage. In response to the temperature of the CRT driver exceeding the threshold temperature, the method includes the current mode output temperature sensor activating the ABL circuit and reducing the amplitude of a video signal received by the CRT driver in order to thermally protect the CRT driver.
In yet another embodiment, the present invention provides a current mode output temperature sensor for providing thermal protection to a CRT driver. The current mode output temperature sensor includes a comparator circuit coupled to a first current source. Additionally, the current mode output temperature sensor includes a voltage reference unit coupled to the comparator circuit and for providing a temperature independent voltage reference. Moreover, the current mode output temperature sensor includes a temperature sensing unit coupled to the comparator and for measuring temperature of the CRT driver. The current mode output temperature sensor includes also includes a temperature threshold setup unit coupled to the temperature sensing unit and for setting a threshold temperature. It should be understood that the current mode output temperature sensor thermally protects the CRT driver by reducing the amplitude of a video signal received by the CRT driver when the temperature of the CRT driver exceeds the temperature threshold.
These and other advantages of the present invention will become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the drawing figures.
REFERENCES:
patent: 4121252 (1978-10-01), Saiki et al.
patent: 5036387 (1991-07-01), Umezawa
patent: 5814953 (1998-09-01), George
patent: 6091397 (2000-07-01), Lee
patent: 6163314 (2000-12-01), Lin
National Semiconductor Corporation
Philogene Haissa
Wagner , Murabito & Hao LLP
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