Positive Feedback Source-coupled Logic Research Articles

On improving the performance of dynamic positive-feedback source-coupled logic (D-PFSCL) through inclusion of transmission gates

Dynamic positive feedback source-coupled logic (D-PFSCL) gates are used as a low power alternative in mixed signal applications over static positive feedback source coupled logic (PFSCL) gates. In this paper, transmission gates (TG) are included in the dynamic positive-feedback source coupled logic (D-PFSCL) architecture. The proposed scheme allows implementation of logic functions which in existing schemes is restricted to NOR/OR only or three input AND/OR only realization forms. The significant reduction in the number of stages, dynamic current sources and self-timed buffer with proposed scheme leads to efficient D-PFSCL design in comparison to the existing ones. Simulations using PTM 65 nm technology node at frequency of 1 GHz are performed. A maximum improvement of 40.8%, 73% and 97% in delay, dynamic power consumption and EDP respectively is been observed for D-PFSCL exclusive-OR(XOR2) gate implemented using proposed scheme with respect to existing D-PFSCL schemes. Further, a study on the trade-off between power dissipation and frequency of operation is included for the completeness.

Impact of multi threshold transistor in positive feedback source coupled logic (PFSCL) fundamental cell

Impact of multi threshold transistor in positive feedback source coupled logic (PFSCL) fundamental cell

A new realization scheme for dynamic PFSCL style

In this paper, a new scheme of logic function realization in dynamic positive feedback source-coupled logic (D-PFSCL) style is proposed. The existing scheme implements only NOR/OR based realization of a logic function. Thus, a complex function in D-PFSCL has high gate count which degrades the overall circuit performance measured in terms of power and delay. This paper therefore aims to resolve the issue by proposing a scheme which modifies the structure of a D-PFSCL gate. The modified gate exhibits AND/OR functionality and is used to realize various functions. Simulations have been carried out by implementing various functions and comparing their performance with the existing schemes at 1 GHz. The results of performance comparison with existing schemes indicates significant reuduction in gate count resulting in overall performance improvement.

New Sleep-Based PFSCL Tri-State Inverter/Buffer Topologies

This paper describes new sleep-based positive feedback source-coupled logic (PFSCL) tri-state inverter/buffer topologies. The tri-state behavior is obtained by disconnecting the circuit from both power supply and ground. This is achieved by placing additional transistors, driving the load transistor to cut off or disabling the current source. The combination of the three methods results in six new topologies. The functionality and performance of the proposed topologies is studied through SPICE simulations. A comparison with available sleep-based PFSCL tri-state buffer circuit shows a maximum reduction of 11% and 60% in the propagation delay and output enable time, respectively. The usefulness of the proposed topologies is illustrated through bus and D latch implementation.

Dynamic positive feedback source-coupled logic (D-PFSCL)

ABSTRACTThis paper presents dynamic positive feedback source-coupled logic (D-PFSCL) style which is derived from positive feedback source-coupled logic (PFSCL). The proposed logic style uses dynamic current source in contrast to constant current source of PFSCL to attain lower power consumption. Two techniques for D-PFSCL style-based multistage applications are suggested. Several D-PFSCL gates are simulated and compared with the respective PFSCL counterparts through SPICE simulations by using Taiwan semiconductor manufacturing company 0.18 µm CMOS technology parameters. A maximum power reduction of 84% is achieved for D-PFSCL gates. The effect of process variation on the power consumption of the D-PFSCL gates shows a maximum variation factor of 1.5 between the best and the worst cases.

Bus Implementation Using New Low Power PFSCL Tristate Buffers

This paper proposes new positive feedback source coupled logic (PFSCL) tristate buffers suited to bus applications. The proposed buffers use switch to attain high impedance state and modify the load or the current source section. An interesting consequence of this is overall reduction in the power consumption. The proposed tristate buffers consume half the power compared to the available switch based counterpart. The issues with available PFSCL tristate buffers based bus implementation are identified and benefits of employing the proposed tristate buffer topologies are put forward. SPICE simulation results using TSMC 180 nm CMOS technology parameters are included to support the theoretical formulations. The performance of proposed tristate buffer topologies is examined on the basis of propagation delay, output enable time, and power consumption. It is found that one of the proposed tristate buffer topology outperforms the others in terms of all the performance parameters. An examination of behavior of available and the proposed PFSCL tristate buffer topologies under parameter variations and mismatch shows a maximum variation of 14%.

An efficient triple-tail cell based PFSCL D latch

In this paper, an efficient positive feedback source-coupled logic (PFSCL) D latch topology is proposed. It uses triple-tail cell concept which results in lesser number of stages as well as gate count in comparison to the traditional PFSCL D latch. The operation of the proposed D latch is described and is supported with mathematical formulations. The functionality is verified through SPICE simulations using TSMC 0.18µm CMOS technology parameters. It is found that the proposed D latch topology significantly reduces the power consumption and delay in comparison to the traditional PFSCL D latch. The impact of process variation on the proposed and traditional PFSCL D latch at different design corners shows similar variations.

New Low-Power Tristate Circuits in Positive Feedback Source-Coupled Logic

Two new design techniques to implement tristate circuits in positive feedback source-coupled logic (PFSCL) have been proposed. The first one is a switch-based technique while the second is based on the concept of sleep transistor. Different tristate circuits based on both techniques have been developed and simulated using 0.18 μm CMOS technology parameters. A performance comparison indicates that the tristate PFSCL circuits based on sleep transistor technique are more power efficient and achieve the lowest power delay product in comparison to CMOS-based and the switch-based PFSCL circuits.

Power–Delay–Area–Noise Margin Tradeoffs in Positive-Feedback MOS Current-Mode Logic

In this paper, positive feedback source-coupled logic (PFSCL) gates are analyzed from a design point of view. The design space is explored through analytical relationships which relate the gate delay, power consumption and noise margin, which are modeled through a simplified circuit analysis. To be more specific, a simple and accurate model of the noise margin is used to derive a systematic design strategy to size the transistors' aspect ratios ensuring an assigned noise margin for a given bias current. From the knowledge of the transistor sizes, the gate delay is then expressed as a function of the bias current and the supply voltage, both of which define the static power consumption of PFSCL gates, as well as of the logic swing, which determines the noise margin. Therefore, this delay model simply relates the speed performance, the power consumption and the noise margin of PFSCL gates, and accounts for the dependence on the fan-in and fan-out. Extensive SPICE simulations with a 0.18-m CMOS process confirm the adequate accuracy of the analytical models and the validity of the approximations introduced to simplify the analysis, and a practical design example of an equality comparator is also presented. In order to derive clear guidelines to manage the delay-power-noise margin tradeoff, PFSCL gates are analyzed in typical design cases (i.e., design for high speed, low power and power efficiency). For the sake of completeness, the effect of each design parameter on the silicon area occupied by a PFSCL gate is also qualitatively analyzed. The resulting criteria are thus useful to design PFSCL gates without resorting to time-consuming design iterations with a trial and error approach based on simulations.

Exploiting Hysteresys in MCML Circuits

In this brief, hysteresis is introduced to improve the noise margin of positive-feedback source-coupled logic (PFSCL) gates, that are a modification of MOS current-mode logic recently proposed by the same authors. To better understand the effect of hysteresis on the performance and the design of these circuits, a simple analytical model of the noise margin is developed. Extensive simulations on a 0.18-mum CMOS process confirm the adequate accuracy of the model. The noise margin improvement due to the hysteresis is then exploited to reduce the logic swing, which can be beneficial in terms of the speed performance or the power consumption. Practical cases where hysteresis is advantageous are identified, and a comparison with PFSCL gates without hysteresis is carried out. Simulations confirm that, in some well-defined cases, hysteresis can significantly reduce the gate delay under a power constraint, or achieve a power saving under a speed constraint. As a fundamental result, hysteresis turns out to be an interesting design option to improve the power efficiency of PFSCL gates

Modeling and Evaluation of Positive-Feedback Source-Coupled Logic

Positive feedback source-coupled logic (PFSCL) is proposed as an alternative logic style to traditional SCL logic, which is often used in high-resolution mixed-signal integrated circuits. Positive feedback allows for significantly reducing the NMOS transistors' aspect ratio compared to traditional single-ended SCL gates for equal values of design constraints. The resulting reduction in NMOS parasitic capacitances permits a significant speed up, which can be traded off to achieve a power saving for a given speed constraint, as well as a silicon area reduction. PFSCL gates are analytically modeled in terms of their static parameters and delay, which are expressed as a function of bias current, transistors' aspect ratios and process parameters. Spectre simulations by using a 0.35-/spl mu/m CMOS process confirm that the proposed models are sufficiently accurate in practical cases. PFSCL gates are also compared with traditional SCL circuits by resorting to two different metrics: the gate delay in a Ring Oscillator and that of an inverter with a fan-out of 4. The comparison confirms that PFSCL logic is faster than SCL logic in most cases, and design conditions leading to a speed advantage are identified. As a result, PFSCL gates are an interesting alternative to traditional SCL circuits in mixed-signal applications requiring a high speed or a good balance with power dissipation.