Electronic digital logic circuitry – Clocking or synchronizing of logic stages or gates – Field-effect transistor
Reexamination Certificate
2003-03-14
2004-11-02
Le, Don (Department: 2819)
Electronic digital logic circuitry
Clocking or synchronizing of logic stages or gates
Field-effect transistor
C326S093000, C326S112000
Reexamination Certificate
active
06812745
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to reduced power operation of digital circuitry and more specifically to a method and apparatus for operating logic circuitry with alternating power phases.
2. Description of the Related Art
Advances in VLSI fabrication in recent years have greatly increased the levels of integration in digital integrated circuitry with the advent of submicron geometries. However, there has also been an increase in the speed and functionality in such circuitry. One example is the Pentium III microprocessor, which has several million transistors in a 1 cm
2
area. While these trends are good from the standpoint of delivering increased capabilities to the electronics consumer there has developed a major problem, which is the power consumption of these devices. The Pentium III processor, while having exceptional performance, also has exceptional power dissipation—in the range of about 27 watts for an 866 MHz Pentium III. Adding to the problem, many portable computer systems, such as laptops, personal organizers and cellular telephones, demand the use of the highest performance integrated circuitry but do not have the battery power to run such circuitry for extended periods of time. Battery systems simply have not kept pace with the demands of the technology. To make matters worse, many portable or mobile systems have physical size constraints that preclude the use of extensive cooling devices to remove the power from the integrated circuitry.
Most of the digital integrated circuitry used for today's high performance and high power devices is CMOS circuitry. Power consumption for CMOS circuitry is the sum of static power dissipation and dynamic power dissipation. The former P
S
is the result of leakage current while the latter P
D
is the sum of transient power consumption P
T
and capacitive-load power consumption P
L
.
Transient power consumption P
T
, in turn, results from current that travels between the supply and ground (known as through current) when the CMOS device switches and current required to charge internal switching nodes within the device (known as switching current), the charging and discharging of internal nodes being the predominant cause. Capacitive-load power consumption P
L
is caused by charging and discharging an external load capacitance.
FIG. 1
shows a typical CMOS inverter circuit
10
which includes a p-channel MOS transistor
12
and an n-channel MOS transistor
14
, the gates
16
,
18
of the transistors
12
,
14
being connected together and to the inverter input
20
, the drains
22
,
24
of the transistors being connected together and to the inverter output
26
. The source
30
of the p-channel transistor
12
is connected to the voltage supply Vdd and the source
28
of the n-channel transistor
14
is connected to ground (Vss). The output of the inverter
26
is connected to other CMOS circuitry whose loading characteristics are capacitive in nature. This external capacitive loading is modeled by a capacitor
32
connected to the inverter output
26
. When the input
20
to the logic circuit
10
is driven low, p-channel transistor
12
turns on, causing the capacitive load
32
with value C
L
to be charged from the supply Vdd through the p-channel transistor
12
and registering a logic ONE at the output
26
. Similarly, when the input
20
is driven high, the p-channel transistor
12
turns off and the n-channel transistor
14
turns on, allowing charge stored in the capacitive load
32
to be transferred through the n-channel transistor
14
to ground, thus registering a logic ZERO at the output
26
. Each cycle of the input signal results in a transfer of charge to and from the capacitive load, which is equivalent to an energy transfer of (½×C
L
×&Dgr;V
c
2
) to charge and (½C
L
&Dgr;V
d
2
) to discharge the capacitive load, where C
L
is the value of the capacitive load, &Dgr;V
c
is the change in voltage across the capacitive load when charging the load and &Dgr;V
d
is change in voltage across the capacitive load when discharging the load. This energy ½×C
L
×(&Dgr;V
c
2
+&Dgr;V
d
2
is dissipated as heat. Ultimately, the dynamic energy, on the order of 10
−12
Joules (assuming C
L
to be about 1 pf, which includes load and wiring capacitance, and &Dgr;V to be about a volt), used to operate the circuit of
FIG. 1
over a single cycle is lost.
Furthermore, if the cycle of charging and discharging occurs at a frequency f, then the power consumed by the circuit of
FIG. 1
is approximately f×C×(&Dgr;V)
2
where equal voltage changes are assumed for charging and discharging. Currently, the frequency of operation of CMOS circuits is as high as 10
9
Hz. This means that even though the energy consumed over one cycle by a simple CMOS gate is very low, the power consumed when a gate is operated continuously at very high frequencies can be appreciable (on the order of 10
31 3
Watts). When there are millions of such gates on a semiconductor die the problem is again multiplied resulting in many tens of Watts being consumed and a large fraction of that power being dissipated as heat.
A common approach to alleviate this problem has been to reduce the supply voltage because the savings in power consumption is proportional to the square of the voltage reduction. However, reduction of the power supply voltage causes other problems which include increasing the susceptibility of the circuit to noise and increased transistor leakage current because the threshold voltage of the MOS transistors must be reduced to permit the devices to operate on the lower supply voltage.
Therefore, there is a need for high-speed, high-functionality integrated circuit devices that have very low power consumption without depending on low supply voltages to achieve the reduction in power consumption.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed towards such a need. A system in accordance with the present invention includes logic circuitry having a node for storing energy and a return node, where the logic circuitry operative, using the stored energy, to determine a logic output based on at least one logic input to the logic circuitry during a first phase, and energy storage circuitry connected to the logic circuitry return node and configured to store energy on the node in the logic circuitry, to capture a portion of the stored energy during the operation of the logic circuitry and, to transfer a portion of the captured energy back to the node in the logic circuitry during a second phase, where the energy storage circuitry oscillates with a determinable period, a portion of which determines the first phase and a remaining portion of which determines the second phase.
A method in accordance with the present invention includes storing energy on a node in the logic circuitry, operating the logic circuitry using the stored energy to determine a logic output based on at least one logic input to the logic circuitry during a first phase, capturing by energy storage circuitry connected to the logic circuitry a portion of the stored energy during the operation of the logic circuitry, transferring a portion of the captured energy back to the node in the logic circuitry during a second phase, where the energy storage circuitry resonates at a determinable period, a portion of which determines the first phase and a remaining portion of which determines the second phase.
An advantage of the present invention is that higher performance and greater functionality is available for portable devices.
Another advantage is that the need for special cooling equipment is avoided or reduced and yet another advantage is that the battery life of portable equipment is longer.
Yet another advantage is that the packaging for the logic circuitry has fewer power supply and ground pins because the operating power for the logic circuitry is substantially reduced. This results in a simpler and less costly package.
REFERENCES:
patent: 5559
Guo Weiwei
Wu Jianbin
Yao Yuan
Dechert LLP
Diepenbrock III Anthony B.
Le Don
Piconetics, Inc.
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