Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2000-08-09
2001-10-16
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C326S014000
Reexamination Certificate
active
06304112
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an integrated circuit comprising a first supply voltage bondpad; a second supply voltage bondpad; a combined input/output bondpad; an output driving stage for supplying a digital output signal comprising a first transistor and a second transistor, the first transistor having a first main terminal coupled to the second supply voltage bondpad, a second main terminal, and a control terminal, the second transistor having a first main terminal coupled to the second main terminal of the first transistor, a second main terminal coupled to the combined input/output bondpad, and a control terminal; a further output driving stage coupled between the combined input/output bondpad and the first supply voltage bondpad; and a pre-drive circuit for receiving a digital input signal and for supplying a first voltage to the control terminal of the first transistor, a second voltage to the control terminal of the second transistor, and a third voltage to a control terminal of the further output driving stage.
Such an integrated circuit is known from the general state of the art as shown in FIG.
1
.
A problem of the known integrated circuit is that it has not a reliable fail-safe mode.
In a fail-safe mode of an integrated circuit, the power supply of said integrated circuit may be switched off while there is a relatively high voltage applied between the combined input/output bondpad and the first supply voltage bondpad. This situation can occur in systems where multiple integrated circuits are connected to a bus, or where multiple integrated circuits communicate with each. For these reasons it can occur that an integrated circuit is powered up and starts to try to communicate with other integrated circuits before one or more of the other integrated circuits are powered up. Thus it can occur that the voltage at the second supply voltage bondpad is for instance 0 Volt, as is indicated in
FIG. 1B
, instead of for example 5 Volt, as is indicated in
FIG. 1A
, while the voltage at the combined input/output bondpad is (for instance) 5 Volt, and the voltages at the control terminals of the first and the second transistors are respectively (for instance) 5 Volt and 2.5 Volt. Then in the situation of
FIG. 1B
the voltage at the common node formed by the drain of the first transistor and the source of the second transistor, is about 5 Volt (compared to V
SS
). Thus both the voltage between the control terminal and the first main terminal of the first transistor and the voltage between the first main terminal and the second main terminal of the first transistor are 5 Volt. In a lot of modern IC-processes, especially in MOS-processes, these voltages would be too high and would seriously decrease the lifetime of the first transistor.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an integrated circuit which does not have the problem of the known integrated circuit.
To this end, according to the invention, the integrated circuit of the type defined in the opening paragraph is characterized in that the integrated circuit further comprises a control circuit having a first input coupled to the second supply voltage bondpad, a second input coupled to the combined input/output bondpad, and an output for supplying a binary selection signal which is dependent on the voltage difference between the input and the output of the control circuit; and switching means for the coupling of either the first voltage to the control terminal of the first transistor and the coupling of the second voltage to the control terminal of the second transistor, or the coupling of the first voltage to the control terminal of the second transistor and the coupling of the second voltage to the control terminal of the first transistor, under command of the binary selection signal.
REFERENCES:
patent: 4884165 (1989-11-01), Kong et al.
patent: 5959472 (1999-09-01), Nagamatsu et al.
patent: 5969926 (1999-10-01), Whitaker
Annema Anne Johan
Geelen Godefridus Johannes Gertrudis Maria
Biren Steven R.
Nu Ton My-Trang
U.S. Philips Corporation
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