Two-Stage Operational Amplifier Design by Using Direct and ...

1 Two-Stage Operational Amplifier Design by Using Direct andIndirect Feedback CompensationsJiayuan ZhangThesis submitted to the Faculty of theVirginia Polytechnic Institute and State Universityin partial fulfillment of the requirements for the degree ofMaster of ScienceinElectrical EngineeringYang Yi (Cindy), ChairLingjia LiuXiaoting JiaMay 11, 2021 Blacksburg, VirginiaKeywords: Op-Amp, CMOS, Miller Compensation, 2021, Jiayuan ZhangTwo-Stage Operational Amplifier Design by Using Direct and Indi-rect Feedback CompensationsJiayuan Zhang(ABSTRACT)This paper states the stability requirements of the Amplifier system, and then presents, andsummarizes, the classic two stage CMOS Op-Amp Design by employing several popular fre-quency compensation techniques including traditional Miller compensation, nulling resistor,voltage buffer, and current buffer. The advantages and disadvantages of all these compen-sation strategies are evaluated based on a standard performance which has a 70dB DC gain,a 60 phase margin, a 25 MHz gain bandwidth, and a slew rate of 20 V/us the designs and simulation results are based on a 180mm V standard TSMC CMOS technology.

2 Ultimately, the traditional Miller compensated Op-Amp (a single compensationcapacitor Amplifier ) cannot meet all the requirements but all other techniques could withalso a boost of performance in various Operational Amplifier Design by Using Direct and Indi-rect Feedback CompensationsJiayuan Zhang(GENERAL AUDIENCE ABSTRACT) Two-Stage CMOS Operational Amplifier has two input pins and one output pin. it is used toamplify the differential inputs signal and transfer it to the output side. Usually the inputsignals are too weak to be processed by the rest of the system units. So the Op-Amp canamplify the weak input signals which then can either be further modified for some specificapplications by the rest units of the system or be the final output of this entire role of the Op-Amp in analog and digital systems is as the role of transformers in thepower system. So the output signal is required to have fast and stable responses to theinputs.

3 This paper states some standard requirements of the Op-Amp in aspects of gain,stability, and operating frequency. Due to the classic Design of Two-Stage Op-Amp has poorperformance of stability and operating frequency, some compensation techniques are appliedas the feedback networks to improve its performance. These techniques include traditionalMiller compensation, nulling resistor, voltage buffer, and current buffer. The advantagesand disadvantages of all these compensation strategies are evaluated based on a 180mm standard TSMC CMOS my families for their support and would like to thank for giving me the opportunity to work two years under her MICS group. I would also like to thank and all the members in the MICS lab group forguidance, advice and support throughout my research. I would also like to thank and Jia for their willingness to serve as committee members of my would like to thank all the professors at Virginia Tech for their teaching and guidancethroughout my electrical engineering bachelor s and master s of FiguresviiiList of Tablesxi1 Introduction and Introduction.

4 Overview..22 Background and Conceptual Background of Amplifier System Stability.. Compensated Op-Amp Survey.. Miller Compensation Technique Principle.. Nulling Resistor Technique Principle.. Nulling Resistor Technique Background.. Nulling Resistor Technique Frequency Response.. Voltage Buffer Technique Principle.. Indirect Compensation Technique Principle.. Indirect Compensation Background.. Common Gate Stage ( current Buffer) Compensation..21vi3 Two Stage Operational Amplifier Designs and Simulation Design Specifications.. Cadence Design and Simulation Result of Traditional Miller Design Procedure.. Cadence Design Result.. Cadence Design and Simulation Result of Nulling Resistor Technique.. Design Procedure.. Cadence Design Result.. Cadence Design and Simulation Result of Voltage Buffer Technique.. Cadence Design and Simulation Result of Common Gate Compensation.

5 454 Conclusions495 Application and Future work50 Bibliography52viiList of Block diagram of a Miller compensated Operational Amplifier [8].. Block Diagram of a Single Loop Feedback System.. Phase Margin Demonstration [8].. Uncompensated Frequency Response of Two Stage Operational Amplifier [8] Two-Stage Op-Amp with Miller Compensation.. Small Signal Model of Miller Compensation Technique.. Pole Splitting Demonstration [2].. Compensated Frequency Response of Two Stage Operational Amplifier [2]. Compensated Two-Stage Op-Amp with Nulling Resistor.. Locations of Ploes and the Zero [22].. Transmission Gate [18].. Small Signal Model of Nulling Resistor Technique.. Frequency Response of the Miller Compensated Operational Amplifier withNulling Resistor [34].. Block Diagram of Voltage Buffer Implementation [2].. Compensated Two-Stage Op-Amp with Voltage Buffer [34].. Block Diagram of Indirect Compensation [8].

6 2 Stage Op-Amp with Common Gate Stage Compensation [34].. Small Signal Model of Common Gate Stage Compensation Op-Amp [34] [13][10].. 2 Stage Op-Amp with Common Gate Stage Compensation Design II [30] [15] Uncompensated Two Stage Operational Amplifier .. Design Schematic of Miller Compensation Amplifier .. Frequency Response of Miller Compensation Amplifier .. Output Response of a Step Function Input.. Test Bench of Miller Compensation Amplifier .. Design Schematic of Amplifier with Nulling Resistor.. Frequency Response of Amplifier with Nulling Resistor.. Output Response of a Step Function Input.. Test Bench of Miller Compensation Amplifier with Nulling Resistor.. Design Schematic of Amplifier with Voltage Buffer.. Frequency Response of Amplifier with Voltage Buffer.. Output Response of a Step Function Input.. Design Schematic of Amplifier with Common Gate Compensation.

7 Frequency Response of Amplifier with Common Gate Compensation.. Output Response of a Step Function Input.. MAC Operator [4].. Delay Calibration Module [3]..51xList of Survey of various op amps topologies.. Design Specifications of Two Stage Amplifier .. Transistor Sizing.. Results of Miller Compensation Amplifier .. Transistor Sizing.. Results of 2 Stage Amplifier with Nulling Resistor.. Transistor Sizing.. Results of 2 Stage Amplifier with Voltage Buffer.. Transistor Sizing.. Results of 2 Stage Amplifier with Voltage Buffer..47xiList of Abbreviations The angular frequencyCMOS:Complementary Metal-Oxide-SemiconductorCMRRC ommon mode rejection ratioLHP:Left Hand PlaneOp-Amp: Operational AmplifierPSRRP ower supply rejection ratioRHP:Right Hand PlaneLPH and RPH present where poles or zeros at when graphing complex number. is the angular frequency which unit is rad/sec.

8 1Hz = 2 1 Introduction and IntroductionOver the last few years, CMOS technology including CMOS Operational Amplifier (Op-Amp)has been developed rapidly. CMOS Op-Amp is one of the most fundamental, versatile andintegral circuit blocks of many analog and mixed-signal systems [28] [35] [23] [6]. They arewidely used in many applications such as comparators, differentiators, dc bias applicationsand so on [26] [19]. For most of the cases, a single stage Amplifier is not adequate due toits limited gain and output voltage range. So CMOS Operational Amplifier architecturesthat use two or more gain stages are developed and widely used [20]. However, more stagesintroduce more phase shifts that require frequency compensation networks to maintain thesystem stability. To increase the Amplifier stability, multiple compensation approaches havebeen developed by IC designers in the recent this paper, some of popular compensation methods will be summarized, evaluated andcompared in the Design of Two-Stage Op-Amp including Direct and indirect from the Miller Compensation, which is one the most popular approaches to stabilizethe Op-Amp, an undesired right-hand-plane (RPH) zero will come out in the open-loop gaindue to the Direct connection of the feedback compensation capacitor from the output toinput.

9 To resolve this RPH zero, there are several methods can be applied including: NullingResistor, Voltage Buffer, and current Buffer. Nulling Resistor is added in series with the12 CHAPTER 1. INTRODUCTION AND OVERVIEW compensation capacitor to move the zero from RPH to left-hand-plane (LPH), which is themost popular and straightforward method among all others [30]. Voltage Buffer and CurrentBuffer techniques are used to remove this RPH zero by blocking the feed-forward current flowin the compensation circuit. Moreover, all the Design processes will also be discussed furtherregarding the performance improvement of compensated Two-Stage Op-Amp. The Cadencedesigns and simulation results have been obtained by TSMC 180nm CMOS technology. Allthe compensation designs will also be discussed and compared based on a given standardOp-Amp OverviewChapter2presents the significance of stability of Op-Amp and then states all the compen-sation techniques in the order of traditional Miller Compensation, Nulling Resistor, VoltageBuffer, and current the Cadence Design procedures and demonstrates the simulation resultswhere evaluations, improvements, and comparisons among all techniques are a conclusion from all the works presented in the previous 2 Background and Conceptual Background of Amplifier System StabilityTwo or more stages amplifiers can be implemented to achieve high gain and high output swingregardless of the limitations of the power supply voltage or power consumption comparedto single stage amplifiers.

10 However, multiple stage amplifiers are generally complicated tocompensate. An uncompensated Two-Stage Operational Amplifier has a two-pole transferfunction, and both poles are located below the unity gain : Block diagram of a Miller compensated Operational Amplifier [8]Therefore, a compensation circuitry must be implemented to enlarge the phase margin so34 CHAPTER 2. BACKGROUND AND CONCEPTUAL PRINCIPLE does the stability, which will be talked further in this chapter. This compensation circuitrycan also be called as a compensator or a feedback network in Operational amplifiers shown in the , the Miller capacitor is used as a negative feedback network tocompensate the system, which feeds a current back from the output to the middle of the twostages A1 and : Block Diagram of a Single Loop Feedback SystemHowever, Operational amplifiers operating on a close-loop with a negative-feedback systemare susceptible to oscillation.