Comparative Analysis of Ultra-Low Voltage Flip-Flops for Energy Efficiency

Bo Fu and Paul Ampadu IEEE International Symposium on Circuits and Systems,pp.1173-1176, 27-30 May 2007

指導老師 : 魏凱城 老師 學 生 : 蕭荃泰 日 期 : 97 年 3 月 3 日

彰化師範大學積體電路設計研究所

Outline

Abstract Flip Flop Design Metrics Experimental Setup Simulation Results Conclusions

Abstract In this paper, the impact of voltage scaling on the

performance of flip-flops is analyzed.

Four representative flip-flops are compared at ultra-low voltages, for delay, energy and energy-delay-product (EDP).

Voltage scaling has become one of the most effective techniques to reduce system energy consumption.

Flip Flop Design Metrics PowerPC Master-slaver latch

0

1 0

1

0

01

1

Modified Clock CMOS (mC2MOS) Master-slave latch

0

0

0

1

1

1

0

1

0

0

0

0

1

1

1

1

Hybrid-latch Flip Flop (HLFF)

011

0

1

1

0

0

1

1

Sense-Amplifier-based Flip Flop (SAFF)

01

Q 不變

10

設 =1 0

11

10

0

1

1

0Q 改變

Timing parameters Definition of Tsetup

Experimental Setup

The simulation test bench.

Simulation Results Experiments were performed using the 90 nm

Predictive Technology Model (PTM) [11] at room temperature (27oC).

The flip-flops are optimized for minimum energy at a nominal supply voltage 1.2 V using the sizing schemes mentioned in [4].

a. Effects of Voltage Scaling on Timing Parameters

Supply voltages of various flip-flop designs failing tolatch the proper data

(a) Function failure voltages (b) Function failure in HLFF

Low-to-high Low-to-highHigh-to-low High-to-low(a) TC->Q (b) Tsetup

Timing parameters of the flip-flop as a function of the supply voltage.

(c) Worst case delay of TD->Q

Timing parameters of the flip-flop as a function of the supply voltage.

(a) Supply voltage 1.2 V (b) Supply voltage 0.3 V

High-to-low transition of HLFF with a varied TD->C time.

b. Effect of Voltage Scaling on Energy Consumption

The energy dissipation of selected flip-flop designs from 0.3 V to 1.2 V with a clock frequency of 50 MHz.

The result shows that PowerPC consumes the least energy compared to other flip-flops examined.

(a) Activity 1 (b) Activity 0.5

Energy dissipation as a function of the supply voltage fordifferent switching activities.

(c) Activity 0 (all 1) (d) Activity 0 (all 0)

Energy dissipation as a function of the supply voltage fordifferent switching activities.

c. Effect of Voltage Scaling on Energy-Delay Product

(a) Activity 1 (b) Activity 0 (all 1)

EDP as a function of supply voltage and switching activities.

EDP as a function of supply voltage and switching activities.

(c) Voltage 1.2 V (d) Voltage 0.3 V

Conclusions The performance of various flip-flops at ultra-low

voltages was analyzed in this paper.

The impact of supply voltage scaling on timing parameters of a flip-flop depends on the type of flip-flop and input transition.

For energy efficient operation at ultra-low voltages, HLFF achieves the smallest EDP when switching activity is high and a transistor based flip-flop achieves the smallest EDP at low switching activities.

THE END