High-speed Current-based Comparators

ECE 1352 Presentation

By: Duy Nguyen

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Overview

Introduction to comparators Current comparators Advanced current comparators Conclusions

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Introduction

Comparators are widely used in many analog circuits (A/D converters, sensor circuits…)

Voltage comparators can be implemented using an op amp.

Limitation: speed, offset voltage, power.

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Why current-based comparators?

Low VDD => low power consumption and compatible with digital circuits.

Minimum size transistors => small area. High speed. Many signal sources from sensors are

current-based.

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Simple current comparator

High output impedance to amplify small current difference.

Low operating freq due to high output impedance.

No compensation for charge-injection and offset voltage.

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Advanced current comparator

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Input stage

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Current amplifying stage

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Current to voltage

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Voltage follower

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SR flip flop

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Compensation

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Conclusions Current comparators have many

advantages over voltage ones:Small area.Low power.Potential high speed.

Future trends: Lower power consumption for portable

wireless applications.Higher accuracy and speed.

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References [1] H. Traff – “Novel Approach To High Speed CMOS Current Comparators” – Electronics

Letters, Vol. 28 No. 3, January 1992. [2] G. Palmisano, G. Palumbo – “High performance CMOS current Comparator Design” –

IEEE Trans. Circuits Sytem II, vol.43, pp. 785-790, December 1996. [3] R. Rio-Fernandez, G. Linan-Cembrano, R. Dominguez, A. Rodriguez-Vazquez, “A

Mismatch-Insensitive High-Accuracy High-Speed continuous -time Current Comparator in Low-Voltage CMOS” – Proc. Analog and Mixed IC Design, 1997.

[4] L. Chen, B. Shi, C. Lu – “A High Speed/Power Ratio continuous-time CMOS current Comparator” – Conf. Electronics, Circuits and Systems, 2000.

[5] L. Luh, J. Choma, J. Draper – “A high-speed High-resolution CMOS Current Comparator” – Proc. ICECS, Vol. 1999.

[6] David A. Johns, Ken Martin – “Analog integrated circuit design” – John Wiley & Sons, 1997

[7] M. Bracey, W. Redman-White, J. Richardson, J. Hughes – “A full Nyquist 15 MS/s 8-b Differential Switched-Current A/D converter” – IEEE JSSC, Vol. 31 No. 7, 1996.

[8] A. Worapishet, J. Hughes, C. Toumazou – “Speed and Accuracy Enhancement Techniques for high performance Switched-Current Comparators” – IEEE JSSC, Vol. 36 No. 4, 2001.