1. High-speed Current- based Comparators ECE 1352 Presentation By: Duy Nguyen

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

3. 3 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.

4. 4 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.

5. 5 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.

6. 6 Advanced current comparator

7. 7 Input stage

8. 8 Current amplifying stage

9. 9 Current to voltage

10. 10 Voltage follower

11. 11 SR flip flop

12. 12 Compensation

13. 13 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.

14. 14 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.