Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Utility Patent
1998-11-09
2001-01-02
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C326S081000, C326S083000, C326S077000, C327S436000
Utility Patent
active
06169432
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to voltage switches for providing reference voltages in a circuit using 2.5 volt process transistors. More particularly, the present invention relates to an output buffer using such voltage switches.
2. Description of the Related Art
With microprocessors manufactured using process technology enabling transistor size to be reduced well below submicron level, the maximum source to drain, gate to drain, and gate to source voltage which such transistors can tolerate is likewise reduced. For instance, with one process referred to here as a 2.5 volt circuit process, transistor gate oxide thickness is reduced so that the maximum gate to source, gate to drain, or drain to source voltage a microprocessor transistor can tolerate without failure is approximately 2.7 volts.
The reduced size of the transistors utilized in microprocessors enables an increase in operation speed as well as an increase in density of transistors which can be integrated onto a single chip. Because of the increase in speed and density of transistors, the process technology utilized in manufacturing microprocessors is also desirable for use in other circuits.
For example programmable logic devices (PLDs), such as field programmable gate arrays (FPGAs), are some times utilized to perform the function similar to a microprocessors. The desirable operation speed and transistor density for PLDs is similar to microprocessors, so it would be desirable to use the same processing technology to manufacture such PLDs. However, unlike microprocessors, PLDs are utilized as glue logic to connect to devices with an operation voltage range which transistors made using the 2.5 volt circuit process will not tolerate.
For instance, PLDs typically connect to CMOS logic devices which operate over a 0-5 volt range, as well as TTL devices which operate over a 0-3.3 volt range. Although a transistor made using the 2.5 volt circuit process can produce a TTL output high of 2.4 volts, it is desirable for such a device to produce a voltage significantly higher than the 2.4 volt legal output high to assure errors do not occur.
SUMMARY OF THE INVENTION
The present invention provides a high voltage switch for an output buffer made with 2.5 volt process transistors. The high voltage switch includes 2.5 volt process transistors configured to switch voltages significantly greater than 2.5 volts.
The high voltage switch of the present invention includes an input provided to the source of a first NMOS cascode transistor, and through an inverter to the source of a second NMOS cascode transistor. A cascode transistor is defined as being connected so that it is turned on and off by varying source voltage with gate voltage fixed, rather than varying gate voltage. The gates of the first and second cascodes are connected to Vcc, which in one embodiment is 2.5 volts. First and second PMOS cascode transistors connect the drains of the respective first and second NMOS cascode transistors to first and second PMOS transistors. The first and second PMOS transistors have sources connected to a high voltage potential, in one embodiment 4.5 volts. A third PMOS transistor has a gate tied to the drain of the second cascode and provides Vcc to the switch output. A fourth PMOS transistor has a gate tied to the second PMOS transistor gate and is connected to supply the high voltage potential to the switch output.
In operation, the high voltage switch functions to selectively transition its output between Vcc and the high voltage potential without applying greater than 2.7 volts from the gate to source, gate to drain, or source to drain of any of its transistors.
REFERENCES:
patent: 5406141 (1995-04-01), Yero et al.
patent: 5465054 (1995-11-01), Erhard
patent: 5723987 (1998-03-01), Ronen
patent: 5892371 (1999-04-01), Maley
patent: 5952865 (1999-09-01), Rigazio
patent: 6031394 (2000-02-01), Cranford, Jr. et al.
Fleisler, Dubb, Meyer & Lovejoy
Nguyen Long
Vantis Corporation
Wells Kenneth B.
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