Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
1999-05-06
2001-07-17
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S544000, C326S056000, C326S082000
Reexamination Certificate
active
06262605
ABSTRACT:
BACKGROUND
1. Field of the Present Invention
The present invention generally relates to the field of power management in an electronic system and more particularly to the circuit and method for controlling line drivers in a system with multiple power modes.
2. History of Related Art
Electronic systems including computer systems are frequently designed with a multiple power supply scheme to permit multiple power mode operation. Multiple power modes enable the system to assume one of two or more power states depending upon various factors. In one example familiar to many users of computer systems, portions of the computer system including disk drives, display screens, and possibly an attached printer will be effectively turned off if the devices has not detected any recent activity. Low power modes beneficially reduce power consumption and preserve or extend the useful life of system components by decreasing the amount of thermal stress to which the components are subjected. Semiconductor components, for example, are susceptible to failure or breakdown from sustained thermal stress. Moreover, there is a direct relationship between the power consumed by a semiconductor device and the temperature of the device. For these reasons, it is highly desirable to design the system that consumes the lowest possible power consumption in its low power mode. Unfortunately, it is not uncommon to have a low power mode portion of a system connected to another portion of the system that is not operating in low power mode. This arrangement can lead to undesirable results in the form of increased low power mode current and possibly even damaged components when an output driver or line driver of the preceding stage remains powered while power is terminated to the driven stage. Accordingly, it would be highly desirable to implement an elegant yet practical solution to managing line drivers in a power managed system.
SUMMARY OF THE INVENTION
Broadly speaking, the invention contemplates a driver circuit for use in a power managed system. The system includes first, second, and possibly more power supplies. The driver circuit includes a first line driver with an output connected to a first receiver circuit and a second line driver with an output connected to a second receiver circuit. A first output enable control circuit is connected to an output enable of the first line driver. In the preferred embodiment, the first output enable assumes a high impedance state when the first power supply is off and the second output enable is independent of the first power supply. The first power supply provides an input to first output enable control circuit such that the state of first line driver output enable is a function of the first power supply. In one embodiment, the first receiver circuit is powered by the first power supply and the second receiver circuit is powered by the second power supply. In one embodiment, the first power supply is the Vcc power supply of the system and the second power supply is the Vccsb (Vcc standby) power supply of the system. In one implementation, the driver circuit is comprised of a gate array. In this embodiment, the gate array may further include an output enable register. Each bit of the output enable register corresponds to a respective line driver of the driver circuit and the state the output enable of the respective line driver is a function of the corresponding output enable register bit. In one arrangement, for example, the output enable register bit determines whether the output enable of the corresponding line driver is a function of the Vcc power supply (i.e., whether turning off the Vcc power supply tri-states the line driver output stage).
The invention further contemplates a computer system that includes the driver circuit described above. The computer system would include first and second power supplies, a CPU connected to a host bus, a one or more bus bridges coupled between the host bus and a peripheral bus, such as an ISA bus. In one arrangement, the driver circuit is coupled to and accessible from the peripheral bus. The computer system may further include a service processor powered the Vccsb power supply of the system. The service processor is preferably coupled to the driver circuit via a service processor bus such as a Motorola 68000 type bus. The driver circuit may be implemented as a field programmable gate array accessible to both the CPUs and the service processor. The gate array may include an output enable register that controls which of the line drives should be tri-stated when the system enters standby mode. In this embodiment, the service processor may configure the line drivers when the system is booted.
The invention further contemplates a control method for use in a power managed system. Initially, the voltage of a Vcc power supply of the system is detected. In response, an output enable of a first line driver is controlled by a first output enable control circuit whose output depends upon or is a function of the voltage of the Vcc power supply. The output of the first line driver is preferably connected to a first receiver circuit that is powered by the Vcc power supply. In addition, an output enable of a second line driver is controlled by a second output enable control circuit whose output is independent of the Vcc power supply voltage. In the preferred embodiment, detecting the voltage of the Vcc power supply is accomplished by routing the Vcc power supply to the input of a first output enable control circuit. Controlling the first output enable preferably comprises forcing the first line driver output stage to a high impedance condition when the first power supply is off. In the preferred embodiment, the first receiver circuit is powered by the Vcc power supply and the second receiver circuit is powered by a Vccsb power supply.
REFERENCES:
patent: 4963766 (1990-10-01), Lundberg
patent: 5021683 (1991-06-01), Schemmel
patent: 5650672 (1997-07-01), Curd
patent: 5777496 (1998-07-01), Herman
patent: 5778235 (1998-07-01), Robetson
patent: 5825215 (1998-10-01), Sugio et al.
patent: 5929654 (1999-06-01), Park et al.
patent: 6070211 (2000-05-01), Neal et al.
patent: 6073198 (2000-06-01), Meyer et al.
patent: 6144251 (2000-11-01), Ogawa
Cunningham Terry D.
International Business Machines - Corporation
Lally Joseph P.
Leeuwen Leslie A. Van
Nguyen Long
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