Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific voltage responsive fault sensor
Reexamination Certificate
2001-06-14
2003-07-29
Nelms, David (Department: 2818)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific voltage responsive fault sensor
C361S092000, C361S018000
Reexamination Certificate
active
06600639
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of integrated circuit design. More particularly, the present invention relates to a precision low voltage supply system and method with undervoltage lockout capabilities.
BACKGROUND OF THE INVENTION
Electronic systems and circuits have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems have facilitated increased productivity and reduced costs in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. Frequently, it is desirable for an electronic system to operate at a relatively low voltage. Low voltage electronic systems typically provide significant benefits such as reduced power consumption, minimized heat dissipation problems, etc. However, electronic systems often depend upon accurate and reliable voltage sources and it is difficult to accurately determine if voltages are at a desired level in low voltage electronic systems. Voltages are often required to reach an appropriate level and be accurately defined for a system to operate properly, especially for a low voltage electronic system in which many tolerance ranges are very narrow.
A number of electronic components require voltage power supply rails to power up and reach a predetermined voltage level for the system to operate properly. For example, in the case of a switching regulator the reference circuit usually does not come up right away. In many systems a determination should be made if a voltage level on a rail is sufficient and if the circuit should turn on at all. If the circuit attempts to operate before the voltage reaches a desired level components may be damaged and unreliable results are likely. Inadequate voltage levels on power supply rails often have detrimental impacts on a number of circuits, including low voltage systems.
Low voltage electronic systems typically offer significant advantages over high voltage systems. Low voltage electronic systems usually have lower power consumption characteristics than higher voltage electronic systems. Power consumption is a critical concern in a variety of devices, particularly those with limited power supplies such as portable devices. The convenience advantages of mobile devices are very desirable and there is an increasing demand for advanced mobile devices that provide greater functionality. Advanced devices typically require a greater number of components (e.g., transistors) to achieve the enhanced functionality and the increased number of components put increased demands on the limited power supplies. By operating the components at lower voltages this increased demand on the limited power supplies is significantly less than components operating at higher voltages. However, operating at lower voltages typically means tolerances are much tighter and a number of features such as reference voltages are required to be very precise.
Integrated circuits typically utilize reference voltages to perform a number of operations and are often utilized in the performance of critical tasks. It is usually very important for a reference voltage level to be accurate and reliable. Components of many electronic systems are very sensitive and voltage references that do not dependably provide a voltage supply at a sufficiently precise level often have a detrimental impact on the performance and functionality of an electronic circuit. For example, numerous devices utilize comparators to perform a comparison to a reference voltage and a reference voltage that is not reliable and relatively precise usually has a detrimental impact on the accuracy of the comparison. The acceptable tolerance range for variations in a reference voltage is usually very narrow. The tolerance ranges for low voltage electronic systems are particularly small since a small absolute change in a low voltage system is usually a significant relative voltage change since the total range from zero to the maximum voltage is very limited.
Reliable low voltage references are not easily produced and reliably providing a precise voltage reference is often a difficult task. For example, low voltage avalanche devices often have difficulty providing a precise reference voltage. Most avalanche or zener diode devices have high doping concentrations making precise operations at low voltage very difficult if not impossible to achieve. Zener devices usually generate a lot of noise due to the basic noise of the breakdown mechanism and the load currents typically are restricted to less than the driving current. Zener devices also often include adverse breakdown characteristics and require temperature coefficient compensation measures. A temperature compensated zener reference is limited in terms of initial accuracy and loading, usually the best TC for the diode current must be carefully controlled.
What is required is an integrated circuit system and method that provides a reliable low voltage reference.
SUMMARY OF THE INVENTION
The present invention is an integrated circuit system and method that provides a reliable and precise identification of a desired voltage level. The reference voltage identification system and method of the present invention includes undervoltage lockout capabilities that prevent a premature or false response. In one embodiment of the present invention, a physical constant trigger circuit initiates a response based upon a physical constant. In one exemplary implementation, the physical constant is a stable point associated with a voltage summation in a transistor circuit (e.g., a delta VBE generator) with components configured to produce equal and opposite temperature coefficients. The physical constant trigger circuit includes response signals (e.g., the collector signals of transistors) with polarities that change at a predetermined inflection point (e.g., a voltage level associated with the stable point of the physical constant trigger circuit). A comparator compares the signals from the physical constant trigger circuit and determines when a change occurs in the response signals. An input signal port conveys an input signal to the physical constant trigger circuit and output port conveys an indication of the response (e.g., a desired reference voltage is available).
The present invention is easily adaptable to a variety of embodiments. In one exemplary implementation of the present invention, a voltage divider provides a varying voltage to the physical constant trigger and when a swept up voltage level corresponds to the physical constant it is utilized as the reference voltage. In one embodiment of the present invention, a lockout circuit ensures a supply rail reaches an appropriate voltage level and the reference voltage identification system and method does not provide a false indication that a particular voltage level is available.
REFERENCES:
patent: 4857823 (1989-08-01), Bitting
patent: 4928056 (1990-05-01), Pease
patent: 5122920 (1992-06-01), Pease
patent: 5196833 (1993-03-01), Kemp
patent: 5440254 (1995-08-01), Sundby
patent: 6222399 (2001-04-01), Imbornone et al.
Broach Michael Eugene
Frank Richard
Teo Siew Siong
National Semiconductor Corporation
Nelms David
Nguyen Thinh
Wagner , Murabito & Hao LLP
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