Yajun Ran

On designing via-configurable cell blocks for regular fabrics

In this paper we describe the design process of a via-configurable block for regular fabrics. The block consists of via-configurable functional cells, via-decomposable flip-flops, and via-configured sizable repeaters. The fabric has fixed layers up to M2. An M1-M2 via mask is used to define the blocks functionality. The upper-level metals are customized. Compared to other structures based on LUTs or PLAs, and fixed flip-flops, our block has much smaller area, higher performance and lower power consumption.

Via-Configurable Routing Architectures and Fast Design Mappability Estimation for Regular Fabrics

In this paper, we describe a new via-configurable routing architecture which shows much better throughput and performance than the previous structures. We demonstrate how to construct a single-via-mask fabric to reduce further the mask cost, and we analyze the penalties which it incurs. To solve the routability problem commonly existing in fabric-based designs, an efficient white-space allocation scheme is suggested, which provides a fast design convergence and early prediction of the circuit mappability to a given fabric.

An integrated design flow for a via-configurable gate array

In This work we present a complete physical design flow for a via-configurable gate array (VCGA). The VCGA is an array of prefabricated logic blocks and fixed metal masks. The block consists of via-configurable functional cells and a via-decomposable flip-flop. An M1-M2 via mask is used to define the blocks functionality. Interconnects are customized using via masks. We developed a physical design flow for VCGA, which integrates a set of effective techniques. Here, we highlight the packing, cell-binding, and detailed-routing problems. We use our design flow to compare the VCGA-based and standard-cell/FPGA-based designs. Experimental results show the efficiency of our flow.

The magic of a via-configurable regular fabric

In this paper, we provide a comprehensive study of the mappability of a via-configurable gate array (VCGA). Although, the base cell of the VCGA is simple, by customizing only via masks it can implement various combinational logic functions, sequential elements, and SRAM cells. Our VCGA can be efficiently configured into SRAM arrays, adders and multipliers. The strong configurability of our VCGA allows us to minimize the number of fixed parts in a general-purpose VCGA fabric, which greatly improves area utilization.

Designing via-configurable logic blocks for regular fabric

In this paper, we describe the design process of a via-configurable logic block for regular fabric. The block consists of a via-configurable functional cell and two via-configurable inverter arrays. A via-configurable functional cell can efficiently implement most commonly used CMOS static cells, and a via-configurable inverter array is efficient in implementing inverters, repeaters, and some pass-transistor logic. The cells have prefabricated transistors, contacts, and M1 wires. The M2 mask is fixed. All of the functions can be realized by customizing only an M1-M2 via mask. We construct a general-purpose fabric based on the via-configurable block and show its great flexibility in implementing a variety of functions. Compared to other fabrics based on look-up tables or programmable logic arrays, our fabric has much higher performance, smaller area, and lower power consumption.

Designing a via-configurable regular fabric

In this paper we present an architecture of a via-configurable regular fabric. The basic logic block is composed of via-configurable functional cells placed in a circular fashion along with a via-decomposable flip-flop. Segmented, prefabricated wires provide the intra-block and inter-block connections. All the interconnects can be customized using a set of programmable via masks. This architecture can achieve performance similar to that of standard-cell-based designs in a comparable area, but with greatly reduced mask cost.

General skew constrained clock network sizing based on sequential linear programming

We investigate the problem of clock network sizing subject to general skew constraints. A novel approach based on sequential linear programming is presented. The original nonlinear programming problem is transformed into a sequence of linear programs by taking the first-order Taylors expansion of clock path delay with respect to buffer and/or wire widths. For each linear program, the sensitivities of clock path delay, with respect to buffer and/or wire widths, are efficiently updated by applying time-domain analysis to the clock network in a divide-and-conquer fashion. Our technique can take into account power supply and process variations. We demonstrate experimentally that the proposed technique is not only capable of optimizing effectively the skew and area of clock network, but also of providing more accurate delay and skew results compared to the traditional approaches.

Temporofunctional crosstalk noise analysis

Noise affects circuit operation by increasing gate delays and causing latches to capture incorrect values. This paper proposes a method of characterizing correlation of signal transitions in multiple nets by considering both timing and functionality of the signals, and uses it in an analysis procedure to eliminate noise faults that cannot actually happen when such correlations are considered. It uses four-variable Boolean logic to characterize signal transitions in a time interval, and formulates Boolean satisfiability between aggressors and a victim under the min-max delay model for gates. The technique has been successfully applied to commercial ASIC designs and has eliminated up to 35% of delay noise faults reported by a state-of-the-art noise analysis tool.Noise affects circuit operation by increasing gate delays and causing latches to capture incorrect values. This paper proposes a method of characterizing correlation of signal transitions in multiple nets by considering both timing and functionality of the signals, and uses it in an analysis procedure to eliminate noise faults that cannot actually happen when such correlations are considered. It uses four-variable Boolean logic to characterize signal transitions in a time interval, and formulates Boolean satisfiability between aggressors and a victim under the min-max delay model for gates. The technique has been successfully applied to commercial ASIC designs and has eliminated up to 35% of delay noise faults reported by a state-of-the-art noise analysis tool.

Via-configurable routing architectures and fast design mappability estimation for regular fabrics

In this paper, we describe a new via-configurable routing architecture which shows a much better throughput and performance than the previous structures. We demonstrate how to construct a single-via-mask fabric to reduce the mask cost further, and we analyze the penalties which it incurs. To solve the routability problem commonly existing in fabric-based designs, an efficient white-space allocation and an incremental cell movement scheme are suggested, which help to provide a fast design convergence and early prediction of circuits mappability to a given fabric

Crosstalk noise in FPGAs

In recent years, due to rapid advances in VLSI manufacturing technology capable of packing more and more devices and wires on a chip, crosstalk has emerged as a serious problem affecting circuit reliability. Even though FPGAs are more immune to crosstalk noise than their ASIC counterparts manufactured in the same technological process, we have reached the point where FPGAs have become affected by crosstalk as well. Because FPGAs have regular interconnect structures, crosstalk noise can be more easily controlled. In this paper, we investigate the crosstalk noise in FPGAs and propose new strategies to reduce its impact on delay. Our methods can reduce crosstalk noise by statistically significant amounts with no penalty in performance, power, or area.