Electronic digital logic circuitry – Threshold – With field-effect transistor
Reexamination Certificate
2001-08-23
2002-11-26
Chang, Daniel D. (Department: 2819)
Electronic digital logic circuitry
Threshold
With field-effect transistor
C326S035000, C326S083000
Reexamination Certificate
active
06486700
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to logic circuits and in particular to an improved Muller C-element.
BACKGROUND OF THE INVENTION
Muller C-elements are common in asynchronous systems. See, for example, Sutherland, “Micropipelines,”
Communications of the ACM,
June 1989, which describes some operations and uses of Muller-C elements. A Muller C-element is often included in completion detectors for asynchronous systems and in asynchronous pipelines. In many circuits and systems, the overall speed of the circuit or system is dependent on the speed of the Muller C-elements that are part of the circuit or system. Because such circuits and systems are often designed for high-speed control systems, improving the speed of the Muller C-elements will often greatly improve the utility of the circuit or system. High speed control systems make possible high performance processors, communication buffers and so forth. For example, some asynchronous control systems might operate with as few as four gate delays per data element, whereas today's high performance synchronous systems typically operate no faster than ten or twelve gate delays per data element, to leave time for data processing steps.
In the simplest form of a Muller C-element, its output signals an event when an event is received at all of its inputs. In a specific Muller C-element, for example, events might be represented as transitions from a logical LO to a logical HI. Logical LO and HI might refer to a lower voltage and a higher voltage, respectively, but might instead be vice versa.
The speed of a Muller C-elements is limited by the number of gates that a transition must pass through, so that is a consideration in designing a Muller C-element. Another consideration is whether the element will draw large currents (“crossover currents”) between the rails, as that makes the circuit inefficient and crossover currents introduce delay. It is therefore desirable to have a Muller C-element with faster responses to events and that waste less energy.
U.S. Pat. No. 5,638,009 issued to Sutherland et al. (hereinafter “the Sutherland patent”) shows the use of three-wire encoding referred to as “screw logic”, but in some applications other than three-wire encoding is preferred. U.S. Pat. No. 6,281,707 (U.S. application Ser. No. 09/401,747, filed Sep. 23, 1999 and entitled “Two-stage Muller C-Element”) describes a two-input Muller C-element.
SUMMARY OF THE INVENTION
This invention provides an improved Muller C-element. In one aspect of the invention, a Muller C-element is a “one-hot” Muller C-element that uses 1-2 fork where the one-stage branch of the fork is associated with the transition that carries event information. In a specific embodiment, the branch that carries event information uses N-type transistors to effect the transition.
In another aspect of the invention, control circuits comprising strings of one-hot Muller C-elements are used to provide asynchronous control.
REFERENCES:
patent: 5737614 (1998-04-01), Durham et al.
Lu, “Improved design of CMOS multiple-input Muller-C-elements”, Sep. 1993, Electronics Letters, vol. 29, No. 19, pp. 1680-1682.*
Santos et al.,“A CMOS Delay Locked Loop and Sub-Nanosecond Time-to-Digital Converter Chip”, Jun. 1996, IEEE Transactions on Nuclear Science, vol. 43, No. 3, pp. 1717-1719.
Fairbanks Scott M.
Molnar Charles E.
Molnar Donna A.
Albert Philip H.
Chang Daniel D.
Molnar Donna A.
Sun Microsystems Inc.
Townsend and Townsend and Crew
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