Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2003-04-08
2004-02-03
Sherry, Michael (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C363S065000, C323S282000
Reexamination Certificate
active
06686727
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to the area of powering low voltage, high current electronics. In particular, the invention may be applicable in the field of computing, and much of the following description is presented in that context. It should be understood, however, that the invention is in no way limited to the field of computing, and may be applicable to a wide variety of circumstances wherein a variety of power absorbing loads may abruptly change their power absorbing characteristics (that is to say, their impedance may undergo a rapid change). The invention may also be applicable if such loads are separated physically such that the voltage which may be dropped across the dynamic impedance of the power carrying conductors is a significant fraction of the voltage delivered to such loads. It may also be increasingly applicable to applications wherein design tradeoffs are forcing a steady decrease in operating voltages. Such situations may arise in telecommunications, radar systems, vehicle power systems and the like, as well as in computing systems.
The architecture of computing systems has undergone tremendous changes in the recent past, due principally to the advance of microcomputers from the original four-bit chips running at hundreds of kilohertz to the most modern 32 and 64 bit microprocessors running at hundreds of megahertz. As the chip designers push to higher and higher speeds, problems may arise which relate to thermal issues. That is, as the speed of a circuit is increased, the internal logic switches each may discharge its surrounding capacitance that much faster. Since the energy stored in that capacitance may be considered fixed (at a given voltage), as the speed is increased, that energy, which may be dissipated in the switches, may be dumped into the switch that many more times per second. Since energy per second may be defined as power, the power lost in the switches therefore increases directly with frequency.
On the other hand, the energy stored in a capacitance may increase as the square of the voltage, so a capacitor charged to two volts may store only 44% of the energy that may be stored in that same capacitor charged to three volts. For this reason, a microcomputer designed to operate at two volts will, when run at the same speed, dissipate much less power than the same microprocessor operating at three volts. There may be a tendency, therefore, to lower the operating voltage of microprocessors.
Other considerations may cause the microprocessor to exhibit a lower maximum speed if operated at a lower voltage as compared to a higher operating voltage. That is, if a circuit is operating at full speed, and the voltage on that circuit is simply reduced, the circuit may not operate properly, and the speed of the circuit (the “clock speed”) may have to be reduced. To maintain full speed capability and still operate at lower voltage, the circuit may have to be redesigned to a smaller physical size. For the past few years, these steps may have been considered the general course of microprocessor design. Microprocessor designers, seeking the maximum speed for their products, may expend considerable effort evaluating any number of considerations, including:
higher speed chips and potential chip value;
higher speed chips and potential heat dissipation;
potential limitations to the removal of heat;
lower voltages and the potential reduction of heat generated at a given speed; and
smaller devices and potential speed at a given voltage.
There may be many more important trade-off considerations for the designers in evaluating microprocessor design.
The evaluation of microprocessor considerations may have lead to the production of designs that operate at lower and lower voltages. Early designs may have operated at higher voltages, such as five volts, which have been subsequently reduced to current designs operating at lower voltages, such as 2.0 volts. Further reductions may occur, and future designs might be operated at 1.8, 1.5, 1.3, 1.0, and even below one volt, perhaps as low as 0.4 volts.
Meanwhile, advances in heat removal may permit processors to run at higher and higher heat dissipation levels. Early chips may have dissipated perhaps a watt; current designs may operate at the 50 watt level, and heat removal designs in the near future may be able to dissipate as much as 150 watts of power generated by the processor. Since the power dissipated may be considered proportional to the square of the operating voltage, even as the ability to remove heat is improved, lower operating voltages may still be desirable.
All of this might be viewed in the context of higher speed chips having a higher monetary value. Therefore, designers may be driven to increase the speed, potentially driving the size of the chips smaller, the voltages lower, and the power up. As may be generally known, as the voltage drops the current increases for a given power, power being defined as voltage times current. If at the same time improvements in heat removal permit higher powers, the current may increase still further. This may mean that the current rises very rapidly. Early chips may have drawn small fractions of an ampere of supply current to operate, whereas current designs may use up to 50 amperes, and future designs may use as much as 150 amperes or more.
As the speed of the processors increase, the dynamics of their power supply requirements may also increase. A processor may be drawing very little current because it is idling, and then an event may occur (such as the arrival of a piece of key data from a memory element or a signal from an outside event) which may cause the processor to suddenly start rapid computation. This may produce an abrupt change in the current drawn by the processor, which may potentially have serious electrical consequences.
As may be generally known, inductance is the measure of energy storage in magnetic fields. Current-carrying conductors have associated with the current a magnetic field, which represents energy storage. As it may be generally known, the energy stored in a magnetic field is half the volume integral of the square of the magnetic field. Since the field may be considered linearly related to the current in the conductor, it may be shown that the energy stored by a current-carrying conductor is proportional to half the square of the current, and the constant of proportionality may be called the “inductance” of the conductor. The energy stored in the system may be supplied by the source of electrical current, and for a given power source there may be a limit to the rate at which energy can be supplied, which means that the stored energy must be built up over time. Therefore, the presence of an energy storage mechanism may slow down a circuit, as the energy may be produced and metered into the magnetic field at some rate before the current can build up.
The available voltage, the inductance, and the rate of change of current in a conductor may be related by the following equation, well known to those skilled in the art:
V=L*∂I/∂t,
where
L
is the inductance of the conductor, and ∂
I/∂t
is the rate of change of current in the conductor.
This equation may be read to provide that the voltage required to produce a given current in a load on a power system increases as the time scale is reduced, and also increases as the inductance of any connection to that load is increased. In a corresponding fashion, as the speed of microprocessors may be increased, the time scale may be reduced, and as the voltage may be reduced, the equation may be read to require the inductance to be dropped proportionally.
Often, in powering semiconductor devices, a designer may not need to consider the inductance of the connections to the device, but with modem high speed circuits these considerations may force the attention to be brought to lowering the inductance of the connections. Microprocessors may currently operate at about two volts, and may tolerate a voltage transient on their supply lines of about 7%
Gurov Gennady G.
Ledenev Anatoli V.
Porter Robert M.
Advanced Energy Industries Inc.
Laxton Gary L.
Santangelo Law Offices P.C.
Sherry Michael
LandOfFree
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