Horowitz, ieee abstroctthis paper describes the design of a custom inte grated circuit for. Recursive approach to the design of a parallel selftimed. Redundant logic insertion and latency reduction in selftimed. Abstract a logic style known as phased logicpl is applied to arithmetic circuits. The amount of charge and voltage change, required on bit lines for resolving a bit of data stored in a memory cell during the pulse width of the self timed. Selftimed blocks can be easily integrated in new designs. Poole, 1994 6 in this work presented some of the key principles behind selftimed operation.
Contemporary design styles including a survey of logic families, robust dynamic circuits, asynchronous logic, selftimed pipelines, and fast arithmetic units latches, clocks and clock distribution, phaselocked and delaylocked loops register file, cache memory, and embedded dram design highspeed signaling techniques and io design. A forward singlerail selfresetting reset circuit is utilized to reset a logic circuit to a selected state subsequent to each iteration of a logical operation on inputted data into the logic circuit. Advanced digital integrated circuits lecture 24 asynchronous and selftimed logic uc berkeley ee241 b. Multi bit adders are often constructed from single bit adders using combinational and sequential circuits for asynchronous or synchronous design. Pdf an optimal approach to implementing selftimed logic. The output data out is sent to reset circuit 20, which operates to reset each of logic circuits 1n.
Having no highprecision oscillator, a selftimed circuit s execution speed is heavily dependent on temperature and supply voltage. Singlerail selftimed logic circuits in synchronous designs. As a result, prototype selftimed circuits can be developed. Vittoz swiss federal institute of technology epfl microelectronic systems laboratory lsm lausanne, ch1015, switzerland email. This short paper is intended to explain why the subject of selftimed logic is relevant to a conference on vlsi. Brian petrasko committee member committee member dr. It is based on a recursive formulation for performing multibit binary addition. The general block diagram of the parallel self timed adder pasta is presented in fig. A hierarchical approach to selftimed circuit verification ut cs. General block diagram of parallel self timed adder. Then, the performance of the circuits are compared by measuring the average.
Request pdf singlerail self timed logic circuits in synchronous designs this paper presents a self timed scheme for dynamic singlerail logic integrated in a single phase clock design. In this dissertation, three 8bit differential logic circuits are designed using self timed technique. Redundant logic can be incorporated to generate efficient selftimed realizations of iterative logic specifications. Selftimed logic and the design of selftimed adders a thesis submitted to the university of manchester for the degree of doctor of philosophy in the faculty of engineering and physical sciences 2010 by balasubramanian padmanabhan school of computer science. Phased logic is a dualrail ledr logic style that allows automatic translation from a clocked netlist to a selftimed. The self timed circuits employ dual rail data encoding to implement ternary logic of 0, 1, andundefined states.
The control and sequencing of these logic blocks is done with synchronizing circuits using muller cgates meng9l. Early evaluationtechniques have been applied to asynchronous circuits in the past in order to achieve throughput increases. Design of completion detection circuits for selftimed systems operating in subthreshold regime omer can akgun, yusuf leblebici, eric a. Singlerail selftimed logic circuits in synchronous. Selftimed design, function block, indication, ripple carry adder, cmos, standard cells. The reset circuit receives at least one of the data inputs and its complement signal so that the reset signal produced by the reset circuit is activated regardless of the voltage level of the. In addition to realizing the requisite functionality, the selftimed logic block has to be. Self timed circuits allow the minimisation of the interface between the reader and writer processes and the acms. The only constraint that must be respected is the handshake protocol. In digital electronics, an asynchronous circuit, or selftimed circuit, is a sequential digital logic circuit which is not governed by a clock circuit or global clock signal. In this letter we present a timing and control strategy that can be used to realize synchronous systems with the. The proposed concept is universal in the sense that it can be extended to a variety of selftimed design methods. Hal, fujitsu, amd all used variants of a williams selftimed divider.
A hierarchical approach to selftimed circuit verification. We present a novel application of a thermally sensitive circuit to automatically regulate the performance and power consumption of asynchronous circuits, with minimal implementation overhead. Logic depth and power consumption in selftimed circuits. While asynchronous logic has many potential advantages compared to traditional synchronous designs, one of the major drawbacks is its. Selfchecking circuits detect at least some of their own faults.
We describe selftimed circuits, including combinational logic and sequential machines, which either halt or generate illegal output if they include any single stuckat faults. Ncl circuits exploit null as its control element to achieve self timed behavior, where the circuit remains in standby mode means that the output propagates null and is ready to propagate a new data wavefront. Self timed refers to logic circuits that depend on andor engineer timing assumptions for the correct operation. Request pdf singlerail selftimed logic circuits in synchronous designs this paper presents a selftimed scheme for dynamic singlerail logic integrated in a single phase clock design. Asynchronous sequential machine design and analysis provides a lucid, indepth treatment of asynchronous state machine design and analysis presented in two parts. Phased logic has been proposed as a technique for realizing self timed circuitry that is delayinsensitive and requires no globalclock signals. The proposed concept is universal in the sense that it can be extended to a variety of self timed design methods. While asynchronous logic has many potential advantages compared to traditional synchronous designs, one of the major drawbacks is its unpredictability with respect to temporal behavior. In this dissertation, three 8bit differential logic circuits are designed using selftimed technique. This short paper is intended to explain why the subject of self timed logic is relevant to a conference on vlsi. This type of circuit is contrasted with synchronous circuits, in which changes to the signal. Implementation of selftimed circuits onto fpgas using. Introduction leakage power has gone from a negligible fraction of total power to about 33% for some current circuits. In this voltage range extremely high voltagedependent delay uncertainties arise which make the use of synchronous circuits rather inefficient or their reliability doubtful.
Self timed adders have the potential to run faster averaged for dynamic data, as early completion sensing can avoid the need for the worst case bundled delay mechanism of synchronous circuits. Phased logic is a dualrail ledr logic style that allows automatic translation from a clocked netlist to a selftimed implementation. Arithmetic logic circuits using selftimed bit level dataflow. We describe self timed circuits, including combinational logic and sequential machines, which either halt or generate illegal output if they include any single stuckat faults. Self checking circuits detect at least some of their own faults. As a result, prototype self timed circuits can be developed. These are two common methods of determining when the data is valid in a data driven system. The peak performance of a sequential circuitkystem, e. Bit level dataflow, early evaluation and automatic filtering of transient computations. Ncl circuit to accomplish this criterion, ncl system should consist.
Oct 10, 2007 a study on self timed asynchronous subthreshold logic abstract. Selftimed refers to logic circuits that depend on andor engineer timing assumptions for the correct operation. Global versus local weakindication selftimed function. Padmanabhan, self timed logic and the design of self timed adders, phd thesis, school of computer science, the university of manchester 2010. Self timed logic block a self timed logic block is also referred to as a function block and represents the robust asynchronous equivalent of a traditional synchronous combinational logic circuit. Phased logic is a dualrail ledr logic style that allows automatic translation from a clocked netlist to a self timed. Throughput optimizations for null convention self timed digital circuits of scott christopher smith, defended april 2, 2001. Introduction the relation between logic depth and power consumption is well known cha92, lem94. This type of circuit is contrasted with synchronous circuits.
Timing circuits 31, 32, 33 and 34 operate to properly time the resetting of the logic circuits 1n so that the reset occurs at the proper time, e. On digitrecurrence division algorithms for selftimed circuits 5 redundant number system. Throughput optimizations for null convention selftimed digital circuits of scott christopher smith, defended april 2, 2001. What if the data path has delay due to gates or logic. Domino logic, selftimed circuits, asynchronous circuits 1. We have chosen the linkjoint model as the basis for our acl2 formalization of selftimed circuits and systems. Nikolic reading chapter 9, selftimed pipelines, by t. Selftimed circuits allow the minimisation of the interface between the reader and writer processes and the acms. Ncl circuits exploit null as its control element to achieve selftimed behavior, where the circuit remains in standby mode means that the output propagates null and is ready to propagate a new data wavefront. Small fluctuations of these parameters already result in noticeable changes of. Us5550490a singlerail selfresetting logic circuitry.
Asynchronous communication mechanisms using selftimed. Redundantlogicinsertionandlatencyreductionin selftimedadders. A novel concept of logic redundancy insertion is presented that facilitates significant latency reduction in selftimed adder circuits. Selftimed and asynchronous design techniques are currently proposed as a vehicle for pushing digital integrated circuits to higher levels of density and performance. Introduction if functional data path blocks are to be used in an asynchronous or self timed system they should also use handshaking techniques to communicate with the other circuit blocks in the system. Phased logic is a dualrail ledr logic style that allows automatic translation from a clocked netlist to a self timed implementation. It can be explained by considering that the average dynamic power consumption of a cmos circuit is. Abstract a logic style known as phased logic pl is applied to arithmetic circuits. A study on selftimed asynchronous subthreshold logic. A study on selftimed asynchronous subthreshold logic abstract. An optimal approach to implementing selftimed logic circuits from signal transition graphs article pdf available january 1993 with 57 reads how we measure reads. We have chosen the linkjoint model as the basis for our acl2 formalization of self timed circuits and systems. In phase 1, when the upstream stage has a new output and gotx is deasserted, it asserts its hereisx signal and then waits to see the downstream stages reply on.
Initial analysis shows that these vlsi solutions are more robust with regard to steering logic metastability, and can potentially run faster than solutions under fundamental mode assumptions. A general method for computing early evaluation functions is presented for. A mechanism that controls logical ordering of circuit switching events and insures that circuit physical timing constraints are met is required for proper operation of. This work will show a similar result in the specic case of digitrecurrence division algorithms. The designs we are studying consist of a set of self timed combinational logic blocks made up of dcvsl circuits. Selftimed adders have the potential to run faster averaged for dynamic data, as early completion sensing can avoid the need for the worst case bundled delay mechanism of synchronous circuits. Behavior of self timed null convention logic circuits with. Recursive approach to the design of a parallel selftimed adder abstract. Padmanabhan, selftimed logic and the design of selftimed adders, phd thesis, school of computer science, the university of manchester 2010. This problem will probably only get worse as technology scales to smaller and smaller dimensions making. This paper investigates self timed asynchronous design techniques for subthreshold digital circuits. The designs we are studying consist of a set of selftimed combinational logic blocks made up of dcvsl circuits. Arithmetic logic circuits using selftimed bit level.
On digitrecurrence division algorithms for selftimed. In this letter we present a timing and control strategy that can be used to realize synchronous systems with the performance of asynchronous circuits or systems. A self timed logic circuit is used to generate a self timed memory clock to access data in a memory. Self timed logic and the design of selftimed adders a thesis submitted to the university of manchester for the degree of doctor of philosophy in the faculty of engineering and physical sciences 2010 by balasubramanian padmanabhan school of computer science. Contemporary design styles including a survey of logic families, robust dynamic circuits, asynchronous logic, self timed pipelines, and fast arithmetic units latches, clocks and clock distribution, phaselocked and delaylocked loops register file, cache memory, and embedded dram design highspeed signaling techniques and io design. Design of completion detection circuits for selftimed. In addition to realizing the requisite functionality, the self timed logic block has to be. The next key design concept in a self timed system is the signaling between elements commonly called. Its possible, although considerably more difficult, to build a clockfree asynchronous selftimed system that uses a similar handshake protocol. In automata theory, an asynchronous circuit, or selftimed circuit, is a sequential digital logic circuit which is not governed by a clock circuit or global clock signal. There are a variety of control protocols used in asynchronous or self timed. Timed logic circuits are sometimes called combinational or asynchronous logic, a b and or a b c a b xor and or a b a b a b c. Asynchronous communication mechanisms using selftimed circuits.
An approach for selftimed synchronous cmos circuit design. The arguments for and against the adoption of these techniques are presented with illustrations from practical development projects. An asynchronous circuit, or self timed circuit, is a sequential digital logic circuit which is not governed by a clock circuit or global clock signal. There are a variety of control protocols used in asynchronous or selftimed. This paper investigates selftimed asynchronous design techniques for subthreshold digital circuits.
A logic style known as phased logic pl is applied to arithmetic circuits. Selftimed logic block a selftimed logic block is also referred to as a function block and represents the robust asynchronous equivalent of a traditional synchronous combinational logic circuit. Selftimed circuits relieve the designer of problems like clock distribution, but introduce new constraints in the form of isochronic forks and equipotential regions. The self timed asynchronous circuits are effective in the view point of both speed performance and energy dissipation in the future technologies. This paper shows how the combination of oor and geometryplanning tools can be used to address these new problems. Self timed logic and the design of self timed adders a thesis submitted to the university of manchester for the degree of doctor of philosophy in the faculty of engineering and physical sciences 2010 by balasubramanian padmanabhan school of computer science. Redundant logic insertion and latency reduction in self. The selftimed circuits employ dual rail data encoding to implement ternary logic of 0, 1, andundefined states. Part i on the background fundamentals related to asynchronous sequential logic circuits generally, and part ii on selftimed systems, highperformance asynchronous programmable sequencers, and arbiters. Self timed and asynchronous design techniques are currently proposed as a vehicle for pushing digital integrated circuits to higher levels of density and performance. Introduction if functional data path blocks are to be used in an asynchronous or selftimed system they should also use handshaking techniques to communicate with the other circuit blocks in the system. The origins of various aspects of the paradigm, including the null or spacer logic state from which ncl derives its name, can be traced back to mullers work on speedindependent circuits in the 1950s and 1960s 5.
Poole, 1994 6 in this work presented some of the key principles behind self timed operation. Self timed circuits relieve the designer of problems like clock distribution, but introduce new constraints in the form of isochronic forks and equipotential regions. This brief presents a parallel singlerail selftimed adder. Self timed, self tuned state machines using low power pass. Instead it often uses signals that indicate completion of instructions and operations, specified by simple data transfer protocols. Feedback techniques for dualrail selftimed circuits. Redundant logic can be incorporated to generate efficient self timed realizations of iterative logic specifications. Lecture 12 asynchronous circuits stanford university.
891 1414 564 1517 1097 1056 258 241 191 1324 1374 947 361 631 1083 780 740 1481 449 1070 1396 1190 1086 134 4 965 692 22 571 36 582 1106 642 533