CSE 598 AEE 597 G Spring 2006 Basic
CSE 598 A/EE 597 G Spring 2006 Basic Amplifiers and Differential Amplifier Insoo Kim, Kyusun Choi Mixed Signal CHIP Design Lab. Department of Computer Science & Engineering The Penn State University
Don’t let the computer think for you In today’s analog design, simulation of circuits is essential because the behavior of short-channel MOSFETs cannot be predicted accurately by hand calculations. Nonetheless, if the designer avoids a simple and intuitive analysis of the circuits and hence skips the task of gaining insight, then he/she cannot interpret the simulation results intelligently. For this reason, we say, “Don’t let the computer think for you. ” - Behzad Razavi 10/30/2020 Insoo Kim
Contents n Fundamentals n Basic Amplifiers: Low Frequency Analysis n Basic Amplifiers: High Frequency Analysis n Differential Amplifier n Feedback 10/30/2020 Insoo Kim
Fundamentals q q Definitions DC Operating Point & Load line Large Signal Analysis vs. Small Signal Analysis MOSFET intrinsic Capacitances
Definitions mb 10/30/2020 Insoo Kim
DC Operating Point & Load Line 10/30/2020 Insoo Kim
Large Signal Analysis vs. Small Signal Analysis n Large Signal Analysis 10/30/2020 Insoo Kim
Large Signal Analysis vs. Small Signal Analysis n Small Signal Analysis How convenient !! 10/30/2020 Insoo Kim
MOSFET Intrinsic Capacitances 10/30/2020 Insoo Kim
(cont’d) MOSFET Intrinsic Capacitances 10/30/2020 Insoo Kim
Basic Amplifiers: Low Frequency Analysis q q Single Stage Amplifiers Multi Stage Amplifiers
Single Stage Amplifiers: CS, CD, and CG Stage 10/30/2020 Insoo Kim
Common Source Stage : Voltage Gain 10/30/2020 Insoo Kim
Common Drain Stage: Output Resistance 10/30/2020 Insoo Kim
Common Gate Stage : Input Resistance 10/30/2020 Insoo Kim
Summary 10/30/2020 Insoo Kim
Quiz n CD stage amplifier is suitable for output stage of OPAmp due to its low output impedance and large bandwidth. However, in CMOS analog IC, CS stage is more widely used for output stage OPAmp than CD stage. Why? 10/30/2020 Insoo Kim
Loads for basic amplifiers 10/30/2020 Insoo Kim
(cont’d) Loads for basic amplifiers n Diode Connected Load 10/30/2020 Insoo Kim
(cont’d) Loads for basic amplifiers n Source degeneration 10/30/2020 Insoo Kim
Cascode Stage n Small Signal Analysis n Rout 10/30/2020 Insoo Kim
Folded Cascode Stage 10/30/2020 Insoo Kim
(cont’d) Folded Cascode Stage n What are the advantages of folded cascode amplifier? n Disadvantages: Ø Ø Ø Limited Output swing Large Voltage Headroom Large Power Consumption 10/30/2020 Insoo Kim
Basic Amplifiers: High Frequency Analysis q q Frequency Analysis Dominant Pole Approach
Frequency Analysis 10/30/2020 Insoo Kim
(cont’d) Frequency Analysis n Bode Plot 10/30/2020 Insoo Kim
Dominant Pole Approach 10/30/2020 Insoo Kim
BW Estimation by Dominant Pole Approach 10/30/2020 Insoo Kim
Bandwidth Comparison 10/30/2020 Insoo Kim
Quiz n Design an amplifier which satisfy following features using basic single-stage amplifiers. Ø Ø High gain Large Bandwidth High input impedance Low output impedance 10/30/2020 Insoo Kim
Differential Amplifier q q Single Stage Amplifiers Multi Stage Amplifiers
Why differential Amplifier? n Single Ended Signal can be easily contaminated n A Differential Signal can be cleaned up n Power Supply noise can be reduced 10/30/2020 Insoo Kim
Differential Amplifier Analysis n Classic Diff Amp 10/30/2020 Insoo Kim
(cont’d) Differential Amplifier Analysis 10/30/2020 Insoo Kim
Diff Amp with Current Mirror Load Common Mode Input Voltage Range VSS+VTN 1+VDSAT 5+VDSAT 1 < VIC < VDD–|VDSAT 3|–|VTP 3|+| VTN 1| 1. What is CM Input Voltage? 2. How do we prove this equation? 10/30/2020 Insoo Kim
(Std. Library) Design Exercise n Design Flow Ø Determine Specifications - Ø Ø Determine minimum channel length Determine channel width - Ø Ø Power Consumption (ex. 1 m. W) Voltage Gain (ex. >30) Active Common Mode Input range (as large as possible) Others: slew rate, CMRR, PSRR, etc. Determine W 1, 2 from voltage gain spec. Determine W 5 & Bias Voltage from power consumption & CM min. Determine W 3, 4 from CM max. Determine Bias Level of current source tr. Check other specifications 10/30/2020 Insoo Kim
Feedback q q q Feedback & Stability Voltage Amplifier Model Common Mode Feedback
Feedback & Stability 10/30/2020 Insoo Kim
Voltage Amplifier Model n Models 10/30/2020 Insoo Kim
(cont’d) Voltage Amplifier Model n 1 st Order Model 10/30/2020 Insoo Kim
(cont’d) Voltage Amplifier Model n 2 nd Order Model 10/30/2020 Insoo Kim
(cont’d) Voltage Amplifier Model n Time Response of the 2 nd Order Model 10/30/2020 Insoo Kim
(cont’d) Voltage Amplifier Model 10/30/2020 Insoo Kim
Feedback Characteristics n n Gain desensitization Band width extension 10/30/2020 n Noise Reduction n Non-linearity Reduction (a) w/o feedback (b) w feedback Insoo Kim
Common Mode Feedback n Why is CMFB circuit needed? Ø Ø n Due to TR mismatch, TRs may not be in saturation region at operating point. DM Gain decreases and CM gain increases Since output CM level is sensitive to device properties and mismatches, it cannot be stabilized by means of differential feedback. General Topology of CMFB Circuit 10/30/2020 Insoo Kim
(cont’d) Common Mode Feedback n Examples of CMFB Folded cascode amplifier with CMFB 10/30/2020 Useful for low gain applications Insoo Kim
References n n n Joongho Choi, “CMOS analog IC Design, ” IDEC Lecture Note, Mar. 1999. B. Razavi, “Design of Analog CMOS Integrated Circuits, ” Mc. Graw-Hill, 2001. Hongjun Park, “CMOS Analog Integrated Circuits Design, ” Sigma Press, 1999. 10/30/2020 Insoo Kim
- Slides: 47