Highspeed Currentbased Comparators ECE 1352 Presentation By Duy

High-speed Currentbased Comparators ECE 1352 Presentation By: Duy Nguyen

Overview Introduction to comparators n Current comparators n Advanced current comparators n Conclusions n 2

Introduction n 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. 3

Why current-based comparators? Low VDD => low power consumption and compatible with digital circuits. n Minimum size transistors => small area. n High speed. n Many signal sources from sensors are current-based. n 4

Simple current comparator n n n High output impedance to amplify small current difference. Low operating freq due to high output impedance. No compensation for charge-injection and offset voltage. 5

Advanced current comparator 6

Input stage 7

Current amplifying stage 8

Current to voltage 9

Voltage follower 10

SR flip flop 11

Compensation 12

Conclusions n Current comparators have many advantages over voltage ones: ¨ Small area. ¨ Low power. ¨ Potential high speed. n Future trends: ¨ Lower power consumption for portable wireless applications. ¨ Higher accuracy and speed. 13

References n n n n [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. 14