Electrical computers and digital processing systems: support – Computer power control – Having power source monitoring
Reexamination Certificate
1998-09-21
2001-07-03
Lefkowitz, Sumati (Department: 2181)
Electrical computers and digital processing systems: support
Computer power control
Having power source monitoring
C713S300000
Reexamination Certificate
active
06256744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to personal computers, and more particularly to an apparatus and method of internally isolating personal computer components powered by an auxiliary power supply from components powered only by a main power supply.
2. Description of the Related Art
Recently, in certain personal computers an auxiliary power supply has been used to keep part of the system functional when a main computer power supply is down. The components in such a part of the system receiving power from the auxiliary power supply are used to “wake up” the machine at the appropriate time.
When the main power turns off, an auxiliary powered component with an output connected to an input of a component powered only by the main power supply should be prevented from driving a signal on that signal line to the “high” state. The auxiliary powered component must be prevented from driving a signal to the high state, because applying a voltage to the input of the component without power may supply enough voltage/current to cause the component to start operating randomly. Random operation is not desirable as randomly active signals can potentially disturb internal circuitry of the auxiliary powered components.
Further, inputs to auxiliary powered components connected to a component powered by the main power supply would float in voltage level in certain cases. This would occur, for example when the main power turns off if the inputs to the auxiliary powered components were not properly terminated. Many personal computer components are complementary metal oxide semiconductor (CMOS) integrated circuits. Leaving unused inputs of a CMOS component floating causes problems. A CMOS component with an input left floating may enter the active mode of operation with only minimal leakage current, due to the component's high input impedance. Normally, leakage currents are such that a CMOS component with an input floating will enter the active mode. Also, the unpowered input signal line can act like an antenna and begin to absorb signal energy present in the machine. After doing so, it can supply a valid logic voltage to the auxiliary powered component. This can disturb circuits not expecting such levels on that signal line. In addition, switching of the internal CMOS circuitry is inefficient as it needlessly consumes power.
One solution to this problem has been to couple an external pull-down resistor between ground and the signal line being isolated, or an external pull-up resistor between a positive rail of an active power supply and the signal line being isolated.
However, this approach had several undesirable features. The pull-up or pull-down resistors were separate or discrete circuit elements. If a large number of signal lines needed isolation, large amounts of board space could be consumed by the added resistor elements. Further, the additional resistors increased the computer system cost in terms of both the cost of the added resistors and the burden to the system of extra components.
SUMMARY OF THE PRESENT INVENTION
The present invention provides a technique for selectively isolating a signal line in a computer system using multiple power supplies. When a main power supply is inactive, an auxiliary power supply provides power to a component powered by the auxiliary power supply. Isolation circuitry according to the present invention implements gating circuitry and buffer circuitry, that is controlled by various enable signals, to isolate the signal line. The signal line is isolated by coupling the signal line to an appropriate power rail through a resistance provided by the buffer circuitry. In an embodiment of the present invention, the isolation circuitry is implemented on a monolithic integrated circuit with the component powered by the auxiliary power supply.
In one embodiment, the isolation circuitry selectively isolates an input signal line of the component powered by the auxiliary power supply from an output signal line of a component powered by the main power supply. In another embodiment, the isolation circuitry selectively isolates an output signal line of the component powered by the auxiliary power supply from an input signal line of the component powered by the main power supply. In either of the previous embodiments, the isolation circuitry is electrically coupled between the signal line and internal logic of the component powered by the auxiliary power supply. Alternatively, when the isolation circuitry is integrated within the component powered by the auxiliary power supply, the isolation circuitry is electrically coupled between a bonding pad and the internal logic of the component.
A technique of isolation that does not require external resistors is highly desirable, since added external resistors result in additional cost and can potentially deplete considerable amounts of printed circuit board space that could be used for other circuitry. When there are multiple components that require isolation, the reduction in the number of external isolation resistors and the availability of the printed circuit board area previously used by the external isolation resistors can result in significant benefits.
REFERENCES:
patent: 4435764 (1984-03-01), El-Gohary
patent: 4754160 (1988-06-01), Ely
patent: 4763013 (1988-08-01), Gvoth, Jr. et al.
patent: 4908790 (1990-03-01), Little et al.
patent: 4964011 (1990-10-01), Sternglass
patent: 5391940 (1995-02-01), Linn
patent: 5534791 (1996-07-01), Mattos et al.
patent: 5644251 (1997-07-01), Colwell et al.
patent: 5670890 (1997-09-01), Colwell et al.
patent: 5701072 (1997-12-01), Jeon et al.
patent: 5793226 (1998-08-01), Park et al.
patent: 5917250 (1999-06-01), Kakalec et al.
patent: 5977656 (1999-11-01), John
Simonich Christopher E.
Tran Robin T.
Akin Gump Strauss Hauer & Feld & LLP
Compaq Computer Corporation
Lefkowitz Sumati
LandOfFree
Personal computer component signal line isolation for an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Personal computer component signal line isolation for an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Personal computer component signal line isolation for an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2555810