Linear Integrated Circuits (UE22EC342AB3) Unit 1 - PES University

LINEAR INTEGRATED CIRCUITS (UE22EC342AB3) Elective 1 course 4 credit course Offered in EC and RR campus Content of Unit 4 added compared to last year syllabus Dr Shashidhar Tantry Electronics and Communication Engineering LINEAR...

LINEAR INTEGRATED CIRCUITS (UE22EC342AB3) Elective 1 course 4 credit course Offered in EC and RR campus Content of Unit 4 added compared to last year syllabus Dr Shashidhar Tantry Electronics and Communication Engineering LINEAR INTEGRATED CIRCUITS Dr Shashidhar Tantry Electronics and Communication Engineering Unit 1 Syllabus Unit 1: Development of the Ideal OpAmp Equations: Ideal Op Amp Assumptions, The Noninverting Op Amp, The Inverting Op Amp, The Adder, The Differential Amplifier, Complex Feedback Networks, Video Amplifiers, Low pass filter, High pass filter Single Supply Op Amp Design Techniques: Single Supply versus Dual Supply Simultaneous equations Textbook Textbook Op Amp for everyone Fifth edition Bruce Carter and Ron Mancini Analog Filter Design, Van Valkenburg, Oxford University Press Unit 1 Reference book Reference books Linear Integrated Design Handbook (Analog Devices) Operational amplifiers and linear ICs by James M Fiore 2016 Unit 1 Background of op amps Background Importance of op amp First analog computer Made of vacuum tubes Later transistor and IC came in Op amp types LM308 Works from 5Khz GBW to 5GHz GBW Power supply from 60V to 0.9V Op amp as block box It performs all analog tasks Op amps are designed specific to application Unit 1 Background of op amp Background Concept of op amp, a block that can do many things Op amps are always used in negative feedback configurations Unit 1 Ideal op amp Ideal op amp assumptions Ideal op amp assumes input offset is zero Ideal op amp assumes gain maximum at DC and minimum at high frequencies Input current is zero Op amp gain assumed to be infinity Voltage between input leads is zero Input impedance is infinite Output impedance is zero Unit 1 Ideal op amp Unit 1 Op amp model Unit 1 Op amp model Example on input impedance Rin = Ri Rm = Rs Unit 1 Op amp model Example on output impedance Ramp = Ro RL = RL Unit 1 Op amp model Example on Gain Case 1 Best case Case 2 Worst Case Ri = 2Kohm Ri = 500ohm Rs = 200ohm Rs = 200ohm Ro = 2ohm Ro = 10ohm RL = 8ohm RL = 8ohm Aoc = 500 Aoc = 200 Unit 1 Noninverting Op amp Input connected to non-inverting input No offset voltage Difference between two inputs should be zero Current in RF makes both inputs same When RG is very large, Vin = Vout Under this condition, it works as unity gain buffer or voltage follower circuit Unit 1 Noninverting Op amp Unit 1 Non Inverting Op amp What is input impedance and gain of the circuit shown in the figure?  Unit 1 Inverting Op amp noninverting input is grounded No offset voltage Difference between two inputs should be zero Current in RF equal current flow in RG Input impedance is set by RG Unit 1 Inverting Op amp What is input impedance and output voltage of the circuit shown in the figure? Unit 1 Inverting Op amp Unit 1 Adder (Summing Amplifier) Non-inverting input is grounded More than one input is connected to inverting input Circuit is also called summing amplifier Unit 1 Inverting Op amp Design a circuit whose output is Vout = -2(3V1+4V2+2V3) Unit 1 Differential Amplifier Amplifies difference between two signals applied at the input Superposition theorem is used to calculate output When R1 = R3 and R2 = R4 Unit 1 Differential amplifier Unit 1 Instrumentation amplifier Specialized op amp Offers very high input impedance Derived from differential amp Unit 1 Instrumentation amplifier Specialized op amp with higher precision Derived from differential amp Unit 1 Instrumentation amplifier Analysis From Difference amp relation, Voltage drop across R1 is given by, From Ideal op amp relation, Current IR2 is given by, Value of Va is given by,  Unit 1 Instrumentation amplifier Analysis After substitution, For gain matching R3 is set equal to R1. And after substitution After combining terms, Unit 1 Complex Feedback Network T Network in feedback path, need to provide low resistance path to ground Use Thevenin’s theorem Unit 1 Complex Feedback Network Use Thevenin’s theorem for feedback circuit calculations It reduces feedback resistance requirements Unit 1 Impedance matching amplifier (Video amplifier) Coaxial cables used to transmit high frequency signals To match characteristic impedance, input and output impedance should be set accordingly RIN = 50ohm RM is used to adjust output impedance Unit 1 Capacitors Capacitors have impedance = XC= 1/2πfC Break frequency occurs at f = 1/2πRC where gain is reduced to -3db At low frequency, RF dominates and at high frequency CF dominates Circuit is also called as integrator Unit 1 Capacitors Capacitors have impedance = XC= 1/2πfC Break frequency occurs at f = 1/2πRC where is gain is reduced to -3db At low frequency, RF dominates and at high frequency CF dominates Unit 1 Single supply op amp design techniques Importance Dual power supply always takes mid point reference as ground, This is not useful for batter operated devices Concept of virtual ground is built around signal swing from positive to negative taking virtual ground as mid point Create localised ground, so called DC operating point DC operating points are isolated using capacitors Unit 1 Single supply op amp design techniques 1 For AC signal, it acts as inverting amplifier For DC signal, it acts as non inverting amplifier with unity gain Positive input, negative input and output are at DC potential Note : DC operating point need not be always V/2 Unit 1 Single supply op amp design techniques 2 Voltage divider circuit can be used to generate mid point voltage value Resistor value to be larger to reduce power consumption Capacitor C3 used to supress noise Unit 1 Single supply op amp design techniques 3 Voltage reference circuit or IC can be used to produce reference voltage instead of resistor divider circuit Unit 1 Single supply op amp design techniques 4 Reference can be taken from other circuits like ADC reference C1 and C3 selected based on signal frequency R1 is used for isolation of op amp Unit 1 Issues with Non inverting stage in single supply mode For DC, Non inverting terminal is floating ! Unit 1 Issues with Non inverting stage in single supply mode We can define inverting input using R1 and R2 for DC For output voltage equal to V, DC is defined. However for output voltage equal to 0, DC is not defined ! Unit 1 Non inverting stage in single supply mode A capacitor C3 is added which does not allow DC to flow For DC, gain is unity and for AC gain is 1+RF/RG Unit 1 DC Coupled Single supply op amp design techniques Need to preserve DC level for applications like transducers If positive supply is 10V, output voltage range is from 0 to 10V Output should support both positive and negative inputs Any difference in DC levels of two inputs lead to offset Unit 1 DC Coupled Single supply op amp design techniques Input bias voltage is used instead of a reference Use same RG and RF for both terminals. This avoids variations in the voltage due to resistance value variations VREF can be considered as common mode voltage DC operating point is VREF/2 Unit 1 DC coupled Single supply op amp design analysis Reference is set by divider circuit AC Gain by resistors connected to inverting terminal Using relations from difference amplifier, Unit 1 DC Coupled Single supply op amp design analysis When VREF = VIN, When VREF = 0, When VREF = 0, and VIN is positive When VREF = 0, and VIN is negative Unit 1 DC coupled Single supply op amp design analysis AC Gain by resistors connected to non inverting terminal Using relations from difference amplifier, Unit 1 DC coupled Single supply op amp design analysis When VREF = VIN, When VREF = 0, When VREF = 0, and VIN is negative When VREF = 0, and VIN is positive Unit 1 DC coupled Single supply op amp design analysis When VREF = VCC, the supply voltage Transfer Curve Unit 2 DC coupled Single supply op amp design analysis AC Gain by resistors connected to non inverting terminal Using relations from difference amplifier, Unit 2 DC coupled Single supply op amp design analysis When VREF = VIN, When VREF = 0, When VREF = 0, and VIN is positive When VREF = 0, and VIN is negative Unit 1 DC coupled Single supply op amp design analysis When VREF = VCC, Transfer Curve Unit 1 Simultaneous equations Linear op amp transfer function is limited to equation of straight line y = +/-mx+/-b Four possible cases based on m and b Unit 1 Simultaneous equations An example Circuit Requirement A sensor output signal ranging from 0.1V to 0.2V must be interfaced with analog to digital converter that has an input range of 1V to 4V From requirement, Unit 1 Simultaneous equations An example After inserting data points, Solving for b, b = -2 Gain is 30 Solving for m, m = 30 Offset is -2 Final equation is, Unit 1 Simultaneous equations in form y = mx+b (case 1) Both input and reference connected to non inverting input Both m and b are positive Compare with  Unit 1 Case 1 example Circuit has following specifications VOUT = 1V at VIN = 0.01V VOUT = 4.5V at VIN = 1V  Unit 1 Case 1 example (continued) Circuit has following specifications VOUT = 1V at VIN = 0.01V VOUT = 4.5V at VIN = 1V Unit 1 Case 2 y = mx-b Input connected to non inverting input and reference connected to inverting Unit 1 Case 2 example Circuit has following specifications VOUT = 1.5V at VIN = 0.2V VOUT = 4.5V at VIN = 0.5V Simultaneous equations Unit 1 Case 2 example (continued) Circuit has following specifications VOUT = 1.5V at VIN = 0.2V VOUT = 4.5V at VIN = 0.5V Unit 1 Case 3 y = -mx+b Input connected to inverting input and reference connected to non inverting Unit 1 Case 3 example Circuit has following specifications VOUT = 1.0V at VIN = -0.1V VOUT = 6V at VIN = -1V VREF = 10V Simultaneous equations Unit 1 Case 3 example (continued) Circuit has following specifications VOUT = 1.0V at VIN = -0.1V VOUT = 6V at VIN = 1V VREF = 10V Unit 1 Case 4 y = -mx-b Input connected to inverting input and reference connected to inverting Unit 1 Case 4 example Circuit has following specifications VOUT = 1.0V at VIN = -0.1V VOUT = 5V at VIN = -0.3V VREF = 5V Simultaneous equations Unit 1 Case 4 example (continued) Circuit has following specifications VOUT = 1.0V at VIN = -0.1V VOUT = 6V at VIN = -0.3V VREF = 5V Unit 1 Reference Op Amp for Everyone : Bruce Carter and Ron Mancini Fifth Edition 2017 Operational amplifiers and linear ICs by James M Fiore 2016 THANK YOU Dr Shashidhar Tantry Electronics & Communication Engineering [email protected]