EECS 105 Spring 2004 Lecture 24 Lecture 24 Single stage amplifiers Prof J S Smith Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Context In today s lecture we will discuss general amplifier topology and how to use transistors to make single stage amplifiers of various kinds Department of EECS University of California Berkeley 1 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Reading For about a a week after spring break we continuing in chapter 8 in the text single stage amplifiers There is no homework assignment over spring break Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Lecture Outline z z Review Small Signal Analysis Two Port Circuits z Department of EECS Voltage Amplifiers Current Amplifiers Transconductance Amps Transresistance Amps Example MOS Amp Again University of California Berkeley 2 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Small Signal Analysis z Step 1 Find DC operating point Calculate estimate the DC voltages and currents ignore small signals sources z Substitute the small signal model of the MOSFET BJT Diode and the small signal models of the other circuit elements z Solve for desired parameters gain input impedance Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Amplifier Terminology z z z z z Sources Signal its source resistance and bias voltage or current Load Use resistor in Chap 8 but could be a general impedance Port A pair of terminals across which a voltage and an associated current are defined Source Load one port Amplifier two port Department of EECS University of California Berkeley 3 EECS 105 Spring 2004 Lecture 24 Prof J S Smith One Port Models EECS 40 z A terminal pair across which a voltage and associated current are defined iab vab Circuit Block iab vab iab Rthev vthev vab Rthev ithev Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Small Signal Two Port Models iin z z vin vout We assume that input port is linear and most of the time that the amplifier is unilateral z iout Output depends on input but input is independent of output Output port depends linearly on the current and voltage at the input and output ports Unilateral assumption is good as long as overlap capacitance is small MOS Department of EECS University of California Berkeley 4 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Math 54 Perspective Can write linear system of equations for either iout or vout in terms of two of iin vin iout or vout possibilities are iout 1vin 2 vout iout 3iin 4 vout vout 5vin 6iout vout 7iin 8iout What is physical meaning of 1 of 6 Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith EE Perspective z Four amplifier types determined by the output signal and the input signal both of which we select usually obvious z Voltage Amp V V Current Amp I I Transconductance Amp V I Transresistance Amp I V We need methods to find the 6 parameters for the four models and equivalent circuits for unilateral two ports Department of EECS University of California Berkeley 5 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Two Port Small Signal Amplifiers Rout Rs vin vs Rin Av vin RL Voltage Amplifier iin is Rs Rin Ai iin Rout RL Current Amplifier Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Two Port Small Signal Amplifiers Rs vin vs Rin Gm vin RL Rout Transconductance Amplifier Rout iin is Rs Rin Rmiin RL Transresistance Amplifier Department of EECS University of California Berkeley 6 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Measuring the small signal parameters The meaning of the small signal parameters can be made more clear by setting up measurements of them z For a single port model we just need to set the voltage and measure the currents or set the curent and measure the voltage and we will get a linear relationship or I V R V RI But for a two port model we need to decide what to hold constant what to vary and what to measure z Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Input Resistance Rin Looks like a Thevenin resistance measurement but note that the output port has the load resistance attached for a unilateral device The output resistance has no effect Rin vt it RS removed RL attached OR Department of EECS University of California Berkeley 7 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Output Resistance Rout Looks like a Thevenin resistance measurement but note that the input port has the source resistance attached for a unilateral device the input resistance won t have an effect Rout vt it RL removed RS attached OR Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Finding the Voltage Gain Av Key idea the output port is open circuited and the source resistance is shorted Department of EECS University of California Berkeley 8 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Measuring Av By setting Rs 0 vin vs By setting RL vout Av vs Rout Rs vin vs Rin Av vin RL Voltage Amplifier Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Finding the Current Gain Ai Key idea the output port is shorted and the source resistance is removed Department of EECS University of California Berkeley 9 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Finding the Transresistance Rm Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Finding the Transconductance Gm Department of EECS University of California Berkeley 10 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Common Source Amplifier again How to isolate DC level Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith DC Bias 5V Neglect all AC signals 2 5 V Choose IBIAS W L Department of EECS University of California Berkeley 11 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Load Line Analysis to find Q I RD VDD Vout RD Q ID slope 5V 10k ID 1 10k 0V 10k Department of EECS University of California Berkeley EECS 105 Spring 2004 Lecture 24 Prof J S Smith Small Signal Analysis Rin Department of EECS University of California Berkeley 12 EECS 105 Spring 2004 Lecture 24 Prof J S Smith Two Port Parameters Find Rin Rout Gm Generic Transconductance Amp Rs vs vin Rin Gm vin RL Rout
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