Local logic substitution algorithm for post-layout re-synthesis

Centralized controllers commonly used in high-level synthesis often cause long wires and high load capacitance and that is why critical paths typically occur on paths from controllers to data registers. However, conventional high level synthesis has focused on the delay of datapaths making it difficult to solve the timing closure problem during physical synthesis. This paper presents a hardware architecture with a distributed controller, which makes the timing closure problem much easier. It also presents a novel high-level synthesis flow for synthesizing such hardware through datapath partitioning and controller optimization. According to our experimental results, the proposed approach reduces the controller and interconnect delay by 20.3-27.4% and the entire critical path delay by 6.6~10.3% with 0.2~13.3% area overhead. Even without area overhead, it reduces the critical path delay by 5.8~10%.

3-D technology promises higher integration density and lower interconnection complexity and delay. At present, however, not much work on circuit applications has been done due to lack of insight into 3-D circuit architecture and performance. One of the purposes of realizing 3-D integration is to reduce the Interconnect complexity and delay of 2-D, which is widely avowed as the barrier to the continued performance gains in the future technology generations. Therefore, in this paper, we present a stochastic 3-D interconnect model, study the impact of 3-D integration on circuit performance and power consumption. We show that 3-D structures effectively reduce the number of long delay nets, significantly reduce the number of repeaters, and dramatically improve the circuit performance. With 3-D integration, a circuit can be clocked at frequencies much higher (double, even triple) than with 2-D. However, we also show that the impacts of vertical wires on chip area and interconnect delay can be limiting factors on the vertical integration of device layers; and that 3-D integration offers limited relief of power consumption.

The interconnect temperature of very large scale integration (VLSI) circuits keeps rising due to self-heating and substrate temperature, which can increase the delay and power dissipation of interconnect wires. The thermal vias are regarded as a promising method to improve the temperature performance of VLSI circuits. In this paper, the extra thermal vias were used to decrease the delay and power dissipation of interconnect wires of VLSI circuits. Two analytical models were presented for interconnect temperature, delay and power dissipation with adding extra dummy thermal vias. The influence of the number of thermal vias on the delay and power dissipation of interconnect wires was analyzed and the optimal via separation distance was investigated. The experimental results show that the adding extra dummy thermal vias can reduce the interconnect average temperature, maximum temperature, delay and power dissipation. Moreover, this method is also suitable for clock signal wires with a large root mean square current.

Conventional voltage scaling systems require a delay margin to maintain a certain level of robustness across all possible device and wire process variations and temperature fluctuations. This margin is required to cover for a possible change in the critical path due to such variations. Moreover, a slower interconnect delay scaling with voltage compared to logic delay can cause the critical path to change from one operating voltage to another. With technology scaling, both process variation and interconnect delay are growing and demanding more margin to guarantee an error-free operation. Such margin is translated into a voltage overhead and a corresponding energy inefficiency. In this paper, a critical path emulator architecture is shown to track the changing critical path at different process splits by probing the actual transistor and wire conditions. Furthermore, voltage scaling characteristics of the actual critical path is closely tracked by programming logic and interconnect delay lines to achieve the same delay combination as the actual critical path. Compared to conventional open-loop and closed-loop systems, the proposed system is up to 39% and 24% more energy efficient, respectively. A 0.18-mum technology test chip is designed to verify the functionality of the proposed system showing critical path tracking of a 16times16 bit multiplier

A new field programmable gate array (FPGA) design algorithm, Maple-opt, is proposed for technology mapping, placement, and global routing subject to a given upper bound of critical signal path delay. The basic procedure of Maple-opt is viewed as top-down hierarchical bipartition of a layout region. In each bipartitioning step, technology mapping onto logic blocks of FPGAs, their placement, and global routing are determined simultaneously, which leads to a more congestion-balanced layout for routing. In addition, Maple-opt is capable of estimating a lower bound of the delay for a constrained path and of extracting critical paths based on the difference between the lower bounds and given constraint values in each bipartitioning step. Two delay-reduction procedures for the critical paths are applied; routing delay reduction and logic-block delay reduction. The routing delay reduction is done by assigning each constrained path to a single subregion when bipartitioning a region. The logic-block delay reduction is done by mapping each constrained path onto a smaller number of logic blocks. Experimental results for benchmark circuits demonstrate that Maple-opt reduces the maximum number of tracks per channel by a maximum of 38% compared with existing algorithms while satisfying almost all the path delay constraints.

Through silicon via (TSV) based 3D integrated circuits have inspired a novel design paradigm which explores the vertical dimension, in order to alleviate the performance and power limitations associated with long interconnects in 2D circuits. TSVs enable vertical interconnects across stacked and thinned dies in 3D-IC designs, resulting in reduced wirelength, footprint, faster speed, improved bandwidth, and lesser routing congestion. However, the usage of TSVs itself gives rise to many critical design challenges towards the minimization of chip delay and power consumption. Therefore, realization of the benefits of 3D ICs necessitates an early and realistic prediction of circuit performance during the early layout design stage. The goal of this thesis is to meet the design challenges of 3D ICs by providing new capabilities to the existing floorplanning framework [87]. The additional capabilities included in the existing floorplanning tool is the co-placement of TSV islands with circuit blocks and performing non-deterministic assignment of signals to TSVs. We also replace the wirelength and number of TSVs in the floorplanning cost function with the total delay in the nets. The delay-aware cost function accounts for RC delay impact of TSVs on the delay of individual signal connection, and obviates the efforts required to balance the weight contributions of wirelength and TSVs in the wirelength-aware floorplanning. Our floorplanning tool results in 5% shorter wirelength and 21% lesser TSVs compared to recent approaches. The delay in the cost function improves total delay in the interconnects by 10% - 12% compared to wirelength-aware cost function. The influence of large coupling capacitance between TSVs on the delay, power and coupling noise in 3D interconnects also offers serious challenges to the performance of 3D-IC. Due to the degree of design complexity introduced by TSVs in 3D ICs, the importance of early stage evaluation and optimization of delay, power and signal integrity of 3D circuits cannot be ignored. The unique contribution of this work is to develop methods for accurate analysis of timing, power and coupling noise across multiple stacked device layers during the floorplanning stage. Incorporating the impact of TSV and the stacking of multiple device layers within floorplanning framework will help to achieve 3D layouts with superior performance. Therefore, we proposed an efficient TSV coupling noise model to evaluate the coupling noise in the 3D interconnects during floorplanning. The total coupling noise in 3D interconnects is included in the cost function to optimize positions of TSVs and

3-D technology promises higher integration density and lower interconnection complexity and delay. At present, however, not much work on circuit applications has been done due to lack of insight into 3-D circuit architecture and performance. In this paper, we investigate the interconnect distributions of 3-D circuits. We divide the 3-D interconnects into horizontal wires and vertical wires and derive their wire-length distributions, respectively. Based on the stochastic wire-length distributions, we calculate 3-D circuit interconnect delay distribution. We show that 3-D structures effectively reduce the number of long delay nets, significantly reduce the number of repeaters needed, and dramatically improve the performance. With 3-D structures, a circuit can work at a much higher clock rate (double, even triple) than with 2-D. However, we also show that the impacts of vertical wires on chip area and interconnect delay may limit the number of device layers that we can integrate.

The crosstalk noise induced on a net depends on its wire size, its driver size and the sizes of the aggressor gates driving its coupled nets. The problem of crosstalk noise optimization at post-route level is difficult due to the cyclic dependency on aggressor and victim driver sizes, resulting in a conflicting situation. Game theory provides a natural framework for handling conflicting objectives and allows simultaneous optimization of multiple parameters. The formulation of a convex objective function is a requirement in order to obtain better optimization in a game theoretic framework. This property is exploited to solve the cyclic dependency of crosstalk noise on its gate and wire sizes, while modeling the problem of simultaneous optimization of interconnect delay and crosstalk noise. A game is modeled with the crosstalk noise and interconnect delay of the chosen net as the players, the possible gate and wire sizes as the strategy set and the analytical expressions for crosstalk noise and interconnect delay as their respective expected payoffs. The time and space complexity of the proposed integrated sizing algorithm is linear in terms of the number of gates and wires in the design. Experimental results on several medium and large open core designs indicate average improvements of 27.52% and 34.03% for interconnect delay and crosstalk noise respectively, achieved by game theoretic gate sizing based on noise criticality over and above the optimization from the Cadence place and route tools without any area overhead or the need for rerouting

In the physical chip design under the ultra-deep submicron (UDSM) process, interconnect delay, internal resistance drop (IR drop), and signal integrity (SI) has become the key factors affecting timing convergence and design cycle. This paper introduces a reconfigurable array processor architecture chip to solve the above problems. It discusses the requirements of the chip, the logic synthesis, and the physical design under the SMIC 55nm process in detail. First, four different timing optimization methods are employed to optimize the critical path that affects the timing, thus accelerating the execution time of the subsequent placement and routing. Secondly, the edge placement method based on data flow is adopted to reduce the interconnect length and delay of interconnection. Finally, the power network synthesis, placement, clock tree synthesis, and routing are completed. The results demonstrate that the working frequency can reach 320MHz. Meanwhile, the resource consumption is 80506 logic gates, and the chip area is 12mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Interconnection delay of VLSI has been a major bottleneck in the design of high-speed digital systems. The authors present a rigorous analysis of the signal propagation delay in VLSI circuits. They show that wire inductance is an important factor in determining the delay when the delay is in the subnanosecond range and that this delay cannot be well estimated by the conventional modeling of the interconnection by RC circuits. The effect of feature size scaling on circuit performance is also evaluated, and the inherent limitations on scaling due to interconnection delay is discussed. Finally, the relationship between the delay and the technology parameters, such as wire resistance, wire capacitance, wire inductance, wire width, wire length, and load capacitance is investigated to provide guidelines for the interconnection technology development. >

Multi-Threshold CMOS (MTCMOS) circuits combine high performance during active mode with low leakage during sleep, but have a fundamental difficulty when trying to keep the state during sleep mode. We propose several novel master-slave MTCMOS flip-flops which use an outer feedback connection in order to maintain state. These MTCMOS with Outer Feedback (MTOF) flip-flops are fast since they use only low threshold transistors on the forward (critical) path and minimum extra load. The area overhead is low since the outer feedback is simple and transistors not on the critical path can have high threshold and be reused for maintaining the state during sleep. A 100nm predictive technology with power supply ranging from 0.8V to 1.2V is used for verifying the circuits performance through simulation.

The implementation of 2D DWT is a challenge using CMOS technology for miniature device (65nm minimum). For applications like biomedical engineering the area and power consumption are to be reduced. The Limitation of Existing methods is addressed in this paper and an alternate method of implementing the algorithm is presented. In addition, problems lie on high critical path due to the presence of multipliers, Delay is high due to critical path and computation, Execution Speed is less due to multipliers in existing DWT architecture. On the other hand below 45nm the problems in CMOS devices on leakage current, limitations on threshold voltage, short channel effect, high field effects and dopant number fluctuations, and interconnect delays are faced. The work focuses on designing the 2D DWT architecture using FinFETs which has leakage power superiority and power minimization. The proposed VLSI architecture for lifting based 2D-Discrete wavelet transforms (DWTs) using FinFET in 32nm technology is efficient when compared to the existing convolution- based architecture. The Predict and update stage of lifting based DWT without multiplier is implemented using HSPICE. The critical delay due to multiplier usage is eliminated. The multiplier less design enhances the performance of the system.

There is an increasing need for configurable quasi-cyclic low-density parity-check (QC-LDPC) decoders that can support a family of structurally compatible codes instead of a single code. The key component in a configurable QC-LDPC decoder is a programmable circular-shift network that supports cyclic shifts of any size up to a predefined maximum submatrix size. This paper presents a QC-LDPC shift network (QSN), which has two key advantages over state-of-the-art solutions in recent literature. First, the QSN reduces the number of stages in the critical path, which improves the clock frequency and makes it scalable, particularly in a field-programmable gate array (FPGA)-based implementation where an interconnect delay is dominant. Second, the QSN's control logic is simple to generate and occupies a significantly smaller area. The QSNs for a variety of codes suitable for emerging applications are implemented, targeting both a 180-nm Taiwan Semiconductor Manufacturing Company Ltd. complimentary metal-oxide-semiconductor library and a Xilinx Virtex 4 FPGA. The proposed implementation is shown to be 2.1 times faster than the best known implementation in literature and requires almost eight times less control area. Furthermore, this paper presents analytical models of the critical-path and datapath complexity for arbitrary-sized submatrices and proves that the QSN indeed generates all the output combinations required for implementing reconfigurable QC-LDPC decoders.

Coupling Of Synthesis And Layout: Challenges And Solutions

In this work, the design of an energy-efficient FPGA interconnect architecture has been investigated. It concerns a dual-supply solution, where the logic blocks are powered by a nominal voltage supply and the interconnect part is powered by a reduced voltage supply. The behaviour of a fully-buffered, a fully pass-transistor based and a hybrid buffer and pass-transistor architecture has been investigated over a range of power supply voltages. It is found that there exists an optimal ratio between the number of pass-transistor and tri-state buffer switches depending on the load and power supply involved. By reducing the signal voltage swing on the interconnect, the need for a fully tri-state buffer-based interconnect is eliminated, thus saving valuable area and power.Through benchmark studies, it is confirmed that using an optimal composite of pass-transistor and tri-state buffer switches operating at a reduced power supply can meet the same speed as compared to the full-swing scenario at a much lower power consumption. An average reduction in power-delay of 4.4x for low-load critical paths and 2.7x for high-load critical paths is achieved using buffer receivers. Using levelshifter receivers, an average reduction in power-delay of 4.7x for low-load critical paths and 2.8x for high-load critical paths is obtained. It is also found that due to partially replacing tri-state buffers by pass-transistor switches and inspite of using levelshifters, we can save up to a factor of 4x in interconnect area as compared to fully-buffered architectures. The results have been validated over various benchmarks in a 0.13 m CMOS technology.