EE 551 Linear Integrated Circuits Daid W. Graham West Virginia Uniersity Lane Department of Computer Science and Electrical Engineering Daid W. Graham, 2009-2013 1
What You Are Expected To Know Basic circuit analysis KVL, KCL, oltage diiders, etc. Basic familiarity with transistors Basic signal processing Laplace transforms Frequency response Use of MATLAB Basic pn junction deice physics 2
How To Do Well in EE 551 Come to Class Pay attention Take good notes If I talk about it in class, then it is probably important Do whateer you hae to do to stay awake Do the homework problems Do them again Do them yet again (These problems are typical of analog IC problems) Hide the solutions when you do them Write out eery step Do not assume that if you can follow the solutions you will be able to do the problems at test time Start early on the projects Do the indiidual parts as they are coered in class Do not wait until the last minute If you do not understand, then ask questions In class In office hours 3
Analyze and Design V in- V in V out 4
What Design eally Looks Like 5
Why Analog? Can be much less power than digital Can perform many computations faster and more efficiently than digital Must be used to interface with outside world ~20% of IC market since 1970 6
Why This Class Is Important To You If you re a 20- to 30-year-old analog engineer, you re sitting pretty right now. It s a buyer s market for you. - Freescale Semiconductor From IEEE Spectrum, Aug. 2008 7
Why This Class Is Important To You Een if you hae no plans of going into analog IC design, you will hae a hard time not using analog ICs in your work. Understanding the guts of analog IC design will enable you to better ealuate their performance and choose the right parts. 8
The Future of Analog Analog chips enable computers to interact with the physical world to see, listen, touch...the next ten years will see a shift in emphasis to analog technologies... In the coming years, look for analog not digital chips to attract the new talent and inestment... - ed Herring Magazine, February 2003 9
Why Analog for Linear Systems? Outside World Sensor / Transducer Interface (Analog) µprocessor (Digital) Interface (Analog) Outside World Amplifiers, Filters, Data Conerters The real world is analog, so if we need to interface with it, then we must hae analog circuitry. 10
Why Integrated Circuits? Cheaper (and easier to mass produce) Smaller educes power Keeps eerything contained educes noise educes coupling from the enironment Need a large number of transistors to perform real-world computations/tasks Allows a high density of circuit elements (therefore, VLSI reduces costs) 11
Difference Between Discrete and IC Design Deice Size and Values esistors Inductors Parasitics Matching Power Analog ICs elatiely Small ex. Capacitors 10fF-100pF Mostly bad Very expensie (large real estate) Only feasible for ery high frequencies Extremely expensie Very big concern Seriously alter system performance Difficult to deal with Major concern Stuck with whateer was fabricated ex. 50% mismatch is not uncommon Efficient (Small currents pa-ma) Discrete Analog Large ex. Capacitors 100pF-100µF Easy to Use Cheap Use when needed Exist, but rarely affect performance (Large size of deices and currents) Concern Can more easily match/replace Use more power (Large currents >ma) 12
Process Considerations What processes are A specific technology for producing integrated circuits Typically specified by their Type (bipolar, CMOS, or BiCMOS) Minimum deice size (length) for CMOS (e.g. 0.5µm, 0.35µm) Various other parameters (e.g. maximum/supply oltage, intended disposition digital or mixed-signal, etc.) Fabricated by a trusted foundry (e.g. AMS, TSMC, etc.) Eerything is geared towards a digital process Processes not designed with analog in mind Easiest (best method / most flexible) to design with standard process rules Typically not able to construct many analog circuits in a brand new process 13
Moore s Law and Its Affect on CMOS Processes Moore s Law (1965) The number of transistors on an integrated circuit doubles eery (approximately) 18-24 months Processes s. time Introduction of a new process approximately eery two years This shrinks the transistors, so more can fit in a gien space Minimum transistor length decreases oer time Most digital circuits are purely [minimum-sized] transistors Greatly speeds up processing speeds Greatly reduces power consumption Intended to reduce cost, as well (but new processes can be quite expensie) 14
Effect of Changing Processes What changing processes mean (for design) Supply oltages drop (big difference) e.g. 0.5µm V dd = 3.3V; 0.18µm V dd = 1.8V New techniques for reduced operating range Deice sizes Transistor sizes decrease with eery process Capacitors may not Short channel effects Traditional MOSFET models are a poor fit to small deices Varying design rules from process to process (submicron processes) Must relearn design rules for each process Specific rules to make sure nothing breaks 15
Process Type Bipolar s. CMOS Pros for Bipolar Work well for analog High gain High speed Pros for CMOS Cheap, cheap, cheap! Scales nicely with Moore s Law Mixed-signal ICs (SOC) 16
System-On-A-Chip (SOC) The real reason why CMOS dominates analog ICs Systems on a chip Complete Integrated Circuit Analog Digital Easier, cheaper, and better to do a complete design on a single chip. eal designs include both analog and digital portions Digital Portion Scales nicely with Moore s Law Straightforward design procedures Uses mostly small transistors (can really pack them in) and ery few capacitors Analog Portion Scaling mostly comes through ingenuity No straightforward/automated design procedures Uses often relatiely large transistors and capacitors Consumes a large amount of the chip real estate and design time 17
To Summarize Good Things about Analog IC Design Inexpensie Compact Power Efficient Not So Good Things about Analog IC Design (not necessarily bad) Limited to transistors and capacitors (and sometimes resistors if a ery good reason) Parasitics and deice mismatch are big concerns You are stuck with what you built/fabricated (no swapping parts out) 18
Important Considerations We will limit our discussion to CMOS technologies Only MOSFETs Limited use of BJTs Therefore, we will discuss only silicon processes 19
Linear Integrated Circuits Outside World Sensor / Transducer Interface (Analog) µprocessor (Digital) Interface (Analog) Outside World Amplifiers, Filters, Data Conerters Circuits and systems are linear only oer a specific range We will constantly talk about Large-signal operation Nonlinear equations DC operating point, bias conditions Small-signal analysis Linear equations Amplification region Eery circuit must be analyzed with both the large- and small-signal analyses 20
Large-Signal s. Small-Signal Typical Amplifier Transfer Function V out Gain = Slope V in Linear, high-gain region (amplifier) Nonlinear portions Must first do a large-signal analysis to get the amplifier into range Bias in the amplification region DC operating point (DC oltages and currents) from the large-signal operation Once in the amplification region, assume a small-signal input Eerything will stay within the linear region / linear range Linear, time-inariant (LTI) analysis applies 21
Large-Signal s. Small-Signal Typical Amplifier Transfer Function V out DC Operating Point V in Large signal (Biases / DC conditions) Moes amplifier into range Amplifier is now ready to perform amplification Small signal (AC inputs / outputs) Small sinusoidal inputs makes bigger sinusoidal outputs 22
Creating Linear Blocks What are the characteristics of the ideal blocks we need in order to make linear circuits and systems? 23
Input / Output elationships Deice Z in Z out eason Independent Voltage Source Independent Current Source - 0Ω - Ω 0V output no oltage drop; no resistance 0V output replace with a short circuit 0A output no current flows; infinite resistance 0A output replace with an open circuit Voltmeter Ω - Ammeter 0Ω - Minimizes loading effects No resistance in parallel Minimizes loading effects No resistance in series Voltage-Controlled Voltage Source (VCVS) Voltage-Controlled Current Source (VCCS) Current-Controlled Voltage Source (CCVS) Current-Controlled Current Source (CCCS) Ω Ω 0Ω 0Ω 0Ω Ω 0Ω Ω 24
Input / Output Impedances Lessons learned Inputs Voltage sensing Want high input impedance Current sensing Want low input impedance Outputs Voltage output Want low output impedance Current output Want high output impedance 25
Input Impedances Inputs Voltage sensing Desire high input impedance Current sensing Desire low input impedance Voltage Sensing Current Sensing Norton Equialent Theenin Equialent I N N V sense sense V Th - Th I sense sense V = I sense N N sense I = V / sense Th ( ) Th sense V sense I N N as sense I sense V Th / as 0 Th sense Norton and Theenin equialents represent the circuit we are sensing 26
Output Impedances Outputs Voltage outputs Desire low output impedance Current outputs Desire high output impedance Voltage Output Current Output Theenin Equialent Norton Equialent V Th V out Th - in I N N I out in V V out out = V V Th Th in as in Th Th 0 I I out out = I I N N N as N in N Norton and Theenin equialents represent the circuit supplying oltage/current. in represents the input impedance of the subsequent stage. 27
Ideal Operational Amplifier V V- i=0 i=0 Vout Ideal Opamp Model Zero input current Infinite input impedance Zero output impedance Vout = A(V - V - ) Gain is infinite If negatie feedback, V = V - V in V out Example Voltage Buffer Infinite input impedance No loading on preious circuit Zero output impedance No loading on following circuit Closed-loop gain = 1 Looks like a VCVS Completely buffers a oltage Passes V from one circuit to another with no loading effects 28
Two-Port Models Most important parameter in an amplifier is gain Must determine how loading affects gain Two-port models simplifies this process 1 - i 1 i 1 Two-Port Equialent i 2 i 2 2 - One parameter at each port is independent The other port is dependent on both the first port and the two-port network Admittance Parameter Equations Voltage is independent i1 = y111 y122 Current is dependent (Typical of most oltage-mode circuits) i2 = y211 y222 29
Two-Port Model Admittance Parameters i 1 i 2 i 1 i 2 1 - Two-Port Equialent 2-1 y 12 y 12 2 y 21 1 y 22 2 i 1 i 2 - - y 11 = i 1 1 2 = 0 Input admittance Output short circuited y y 12 21 = = i 1 i 2 2 1 = 0 1 2 = 0 eerse transconductance Input short circuited Forward transconductance Output short circuited i i 1 2 = = y y 11 21 1 1 y y 12 22 2 2 y 22 = i 2 2 = 0 1 Output admittance Input short circuited 30
Unilateral Two-Port Model Typically, there is no feedback y 12 = 0 y 21 is referred to as transconductance (G m ) Conert admittances into impedances Z in = input impedance Z out = output impedance Unilateral Two-Port Model (Norton Output) Unilateral Two-Port Model (Theenin Output) i 1 i 2 i 1 Z out i 2 1 Z in G m 1 Z out 2 1 Z in - a 1 2 - - - - a = 2 1 i Gain 2 =0 = G m Z out 31
Connecting a Two-Port Network to a Circuit Theenin Source Two-Port Model Theenin Load s i 1 i 2 in - 1 in G m 1 out 2 out L - - - a = = = out in in in in = in in 1 in s in out s 1 ( G ( )) m Gm 1 out 1 L out L Assuming s and L are fixed a as in a as out Therefore, need high output impedance for high gain a = G out (But want low output impedance for opamps to reduce loading) m Z 32
Typical Opamp Design V in Differential Gain Stage High-Gain Stage Output Stage V out V in- High Z out Low Z out Dries large current Only needed for resistie loads If not included, called an operational transconductance amplifier (OTA) 33
Complete Opamp Design Compensation V in V in- Differential Gain Stage High-Gain Stage V out Output Stage V out ' Bias Circuitry One size does not fit all. 34
The Approach for the Semester Gain appreciation of deices from physics Build models of basic deices Create small circuits Use small circuits to build large circuits Focus on opamp design and supporting circuitry 35