Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2001-03-09
2003-06-17
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S112000, C327S391000, C327S434000
Reexamination Certificate
active
06580306
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates, in general, to the field of integrated circuit (“IC”) devices. More particularly, the present invention relates to a switching circuit utilizing a high voltage transistor protection technique for integrated circuit devices having dual voltage supplies.
In certain integrated circuit devices (e.g. some memory ICs) a high voltage supply level (“VCCP”) may be required for proper device operation. Should this voltage be equal to or less than twice the supply voltage (“VCC”, i.e. VCCP≦2*VCC ), then a switching circuit comprising a relatively thick gate oxide P-channel transistor in series with a pair of series connected N-channel transistors may be coupled between VCCP and a reference voltage level (VSS or circuit ground) with the gate of the P-channel device coupled to a switched source of VCCP, the gate of the intermediate N-channel device coupled to VCC and the gate of the remaining N-channel device coupled to a switched source of VCC.
However, in those applications wherein the high voltage supply level is more than twice the device supply voltage (i.e. VCCP>2*VCC) and relatively thick gate oxide thickness transistors are used, the associated thin gate oxide transistors must still be protected from possible high gate oxide voltage stress.
SUMMARY OF THE INVENTION
The switching circuit incorporating a high voltage transistor protection technique of the present invention extends the maximum pumped voltage (“VCCP”) for reliable MOS transistor operation to VCCP=VTN+(2*VCC). This is effectuated by adding an additional relatively thick gate oxide transistor in series with the thin gate oxide MOS N-channel transistors in a conventional high voltage switching circuit to increase the reliable maximum voltage for the high voltage power supply.
Particularly disclosed herein is an integrated circuit device including a switching circuit comprising first and second series coupled MOS transistors having a gate oxide of a first thickness, each of the first and second MOS transistors having a gate terminal thereof. Third and fourth MOS series coupled transistors are also provided having a gate oxide of a second thickness lesser than the first thickness, each of the third and fourth MOS transistors having a gate terminal thereof. The first, second, third and fourth MOS transistors are coupled in series between a high voltage source and a reference voltage source with an output node defined intermediate the first and second MOS transistors. A first signal input is coupled to the gate terminal of the first transistor for receiving a first input signal capable of transitioning between a level of the high voltage source and a level of the reference voltage source with the gate terminal of the second transistor being coupled to the high voltage source. A supply voltage source having a voltage level lesser than that of the high voltage source is coupled to the gate terminal of the third transistor. A second signal input is coupled to the gate terminal of the fourth transistor for receiving a second input signal capable of transitioning between a level of the supply voltage source and a level of the reference voltage source.
REFERENCES:
patent: 3623023 (1971-11-01), Oleksiak
patent: 4069430 (1978-01-01), Masuda
patent: 5389842 (1995-02-01), Hardee
patent: 5748025 (1998-05-01), Ng et al.
patent: 6266291 (2001-07-01), Sher et al.
patent: 6320414 (2001-11-01), Annema et al.
Hogan & Hartson LLP
Kubida William J.
Tran Toan
United Memories Inc.
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