Static information storage and retrieval – Addressing – Particular decoder or driver circuit
Reexamination Certificate
1999-06-21
2001-08-28
Nelms, David (Department: 2818)
Static information storage and retrieval
Addressing
Particular decoder or driver circuit
Reexamination Certificate
active
06282146
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a voltage level shifter, and more particularly to a dual supply voltage input/out buffer capable of interfacing between two circuitry having different voltage swings.
Integrated circuits are becoming more dense as the dimensions of semiconductor devices decrease. The decreased dimensions also provide for faster devices that require less power to operate. In particular, semiconductor devices, such as transistors, operate on less voltage than the previous generation designs. At the beginning, 5 V power supply was commonly used. In the past few years, 3.3 V power supply has been replacing 5 V power supply as the dominant design. Recently, a move to 1.8 V power supply has been popularized among low power and high speed circuit designers.
One benefit of having lower operating voltage, and consequently lower power consumption, is that demands on the power supply is decreased. This is especially important where the portability of an electronic device incorporating these semiconductor devices is desired. Thus, applications may arise where both low and high voltage integrated circuits are connected together. An integrated circuit operating on a lower voltage must then provide an output at the higher voltage. Simply utilizing the high voltage in the low voltage integrated circuit is not practical. The structural integrity of the thin film oxide will suffer if exposed to voltage potentials in excess of the maximum rated supply, typically about 10% above the normal rated voltage. For example, a 3.7 V drop from the gate to the drain, source, or substrate will tend to break down the thin oxide manufactured by a 3.3 V process. A long term reliability issue will result, with the oxide breakdown eventually causing catastrophic damage to the transistor.
A specific concern of the above problems exist for 3.3 V drivers for 1.8 V process. Although various circuit design methods have been employed to allow 1.8 V devices to be built in 1.8 V processes that are tolerant of an incoming 3.3 V signal, true 3.3 V output drivers in a 1.8 process are sometimes required.
SUMMARY OF THE INVENTION
It is therefore the object of this invention to provide a voltage shifter that is capable of interfacing between two circuitry running within different voltage ranges.
It is another object of this invention to construct a voltage shifter using low voltage process capable of handling high voltage signals.
The present invention discloses a voltage shifter comprises of an input buffer for converting an external input signal switching within a high voltage range to an internal input signal switching within a low voltage range, an output driver for converting an internal output signal switching with the low voltage range to an external output signal switching within the high voltage range; and a reference voltage generator for generating a reference voltage to the input buffer and the output driver.
The voltage shifter according to the present invention is designed such that each of the transistors within is protected against voltage breakdown so that the voltage shifter can be built by transistors using the low voltage process.
Additional objects, features and advantages of various aspects of the present invention will become apparent from the following description of its preferred embodiments, which description should be taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5455526 (1995-10-01), Runas
patent: 5598122 (1997-01-01), McClure
patent: 5684415 (1997-11-01), McManus
patent: 5698993 (1997-12-01), Chow
patent: 5821800 (1998-10-01), Le et al.
Guo Frank Tzen-Wen
Hung Tzu-Chien
Lam Yat Fai
Rajivan Sathyanandan
Nelms David
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rise Technology Inc.
Tran M.
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