Mixed-Signal VLSI Design Course Code: EE719 Department: Electrical - PowerPoint PPT Presentation

Mixed-Signal VLSI Design Course Code: EE719 Department: Electrical Engineering Lecture 5: January 15, 2018 Instructor Name: M. Shojaei Baghini E-Mail ID: mshojaei@ee.iitb.ac.in 1

2 2 Module 7 Speed and Accuracy Considerations of Analog Switches Reference Section: Sampling Switches Chapter: Introduction to Switched-Capacitor Circuits Book: Design of Analog CMOS Integrated Circuits Behzad Razavi, 2017 IIT-Bombay Lecture 5 M. Shojaei Baghini

3 3 Quantitative example of charge injection and clock feedthrough is provided in the class notes, which is not included in these slides. IIT-Bombay Lecture 5 M. Shojaei Baghini

4 4 Speed Requirement Speed specification must be accompanied by the • accuracy specification. We use this point in the class to derive maximum • value of 𝜐 as a function of target resolution for the design of the switch. IIT-Bombay Lecture 5 M. Shojaei Baghini

5 5 Figure of Merit (Speed-Accuracy Trade-off) 𝜐 × 𝛦 V (due to charge injection): Figure of merit for • speed-accuracy trade off of the sampling switch = 𝜈 $ % For scaled technologies with velocity saturation effect • 𝛦 V × C H / I switch ≈ v sat $ Scaling helps, of course V TH and mobility may dictate a length more than L min ! IIT-Bombay Lecture 5 M. Shojaei Baghini

6 6 Summary of Charge Injection Effect • Derived relation in the class ∆𝑊 = 𝛽 𝑋𝑀𝐷 -. 𝑊 // − 𝑊 12 − 𝑊 34 𝐷 4 • Error 𝛦 V: Gain and offset error • V TH includes body effect. • Charge injection cancellation using dummy switch? • Will dummy switch avoid clock feedthrough? IIT-Bombay Lecture 5 M. Shojaei Baghini

7 7 Other Conditions in the Arrangement of Dummy Switches C P of the order of C h IIT-Bombay Lecture 5 M. Shojaei Baghini

8 8 Practical Shortcomings of Complementary Switches • Enhancement of the input voltage range and speed improvement • Distortion if 𝐷𝑚𝑙 and Clk are not synchronized • One possible solution IIT-Bombay Lecture 5 M. Shojaei Baghini

9 9 Charge Injection Cancellation in Simple Complementary Switches How does complementary switch behave with respect to the charge injection cancellation? (input-dependent behavior) IIT-Bombay Lecture 5 M. Shojaei Baghini

10 10 Differential Sampling Differential sampling reduces (ideally nullifies) the offset • error. Gain error due to differential signal remains. • Question: Should we really be concerned about gain • error? IIT-Bombay Lecture 5 M. Shojaei Baghini

11 11 End of Lecture 5 IIT-Bombay Lecture 5 M. Shojaei Baghini