EE40 Final Exam Review Prof Nathan Cheung 12 01 2009 Practice with past exams http hkn eecs berkeley edu exam list exam course EE 2040 EE40 Fall 2009 Slide 1 Prof Cheung Overview of Course Circuit components R C L sources I V characteristics energy storage dissipation Circuit analysis Laws Ohm s KVL KCL Equivalent circuits series parallel Thevenin Norton Superposition for linear circuits Nodal analysis Mesh analysis Phasor I and V First order transient excitation analysis Second Order RLC circuits Bode Plots EE40 Fall 2009 Slide 2 2 Prof Cheung Overview of Course Logic gates Combinatorial logic sum of products Karnaugh maps sequential logic etc Semiconductors Devices pn diodes many types FETs n channel p channel CMOS Useful Diode and FET circuits Amplifiers op amp negative feedback rectifiers wave shaping circuits EE40 Fall 2009 Slide 3 3 Prof Cheung Diode Circuit Analysis by Assumed Diode States 1 Specify Ideal Diode Model or Piecewise Linear Diode Model ID A ID A forward bias forward bias reverse bias VD V reverse bias VDon 2 Each diode can be ON or OFF 3 Circuit containing n diodes will have 2n states 4 The combination of states that works for ALL diodes consistent with KVL and KCL will be the solution EE40 Fall 2009 Slide 4 Prof Cheung Example Problem Perfect Rectifier Model Sketch Vout versus Vin Suggested problem What if there is a 0 6V drop when diodes are on EE40 Fall 2009 Slide 5 Prof Cheung Diode with Capacitor Circuit e g Level Shifter VIN C VC VIN VC t VOUT VIN min VOUT 1 3 VOUT t VC t VIN t Finds out what happens to VC when VIN changes 2 t 1 Diode open VC t 0 VOUT t VIN t 2 Diode short VC t VIN t VOUT t 0 3 Diode open VC t VIN min VOUT t VIN t VIN min EE40 Fall 2009 Slide 6 Prof Cheung Example Diode with RL Circuit Sketch i t Answer Note i t is continuous L R 0 05 msec EE40 Fall 2009 Slide 7 Prof Cheung Load Line Analysis We have a circuit containing a two terminal non linear element NLE and some linear components First replace the entire linear part of the circuit by its Thevenin equivalent Then define I and V at the NLE terminals typically associated signs D Nonlinear 9 A element 250K 1M 1V S EE40 Fall 2009 Slide 8 N L E D ID V DS 200K 2V S Prof Cheung Example of Load Line Analysis con t Given the graphical properties of two terminal non linear circuit i e the graph of a two terminal device And have this connected to a linear Th venin circuit D N L E Whose I V can also be graphed on the same axes load line N L E EE40 Fall 2009 V DS 200K 2V S Application of KCL KVL gives circuit solution ID A D ID S ID 10 The solution 200K 2V Slide 9 1 VDS V 2Prof Cheung Example Voltage controlled Attenuator VC and RC Determines rd at Q point of diode EE40 Fall 2009 Slide 10 Prof Cheung Example Voltage Controlled Attenuator The large capacitors and DC bias source are effective shorts for the ac signal in small signal circuits EE40 Fall 2009 Slide 11 Prof Cheung Three Terminal Parametric Graphs ID 3 Terminal Device G VGS ID A D 10 VGS 3 VGS 2 VGS 1 S Concept of 3 Terminal Parametric Graphs We set a voltage or current at one set of terminals here we will apply a fixed VGS IG 0 1 2 VDS V and conceptually draw a box around the device with only two terminals emerging so we can again plot the two terminal characteristic here ID versus VDS But we can do this for a variety of values of VGS with the result that we get a family of curves EE40 Fall 2009 Slide 12 12 Prof Cheung Graphical Solutions for 3 Terminal Devices ID G V S ID A D 200K 10 2V VGS 3 VGS 2 VGS 1 We can only find a solution for one input VGS at a time First select VGS e g 2V and draw ID vs VDS for the 3 Terminal device Now draw ID vs VDS for the 2V 200K Thevenin source ID A 1 10 The solution The only point on the I vs V plane which obeys KCL and KVL is ID 5 A at VDS 1V 1 EE40 Fall 2009 Slide 13 VDS V 2 2 13 VDS V Prof Cheung SOLVING MOSFET CIRCUITS STEPS 1 Guess the mode of operation for the transistor We will learn how to make educated guesses 2 Write the ID vs VDS equation for this guess mode of operation 3 Use KVL KCL etc to come up with an equation relating ID and VDS based on the surrounding linear circuit 4 Solve these equations for ID and VDS 5 Check to see if the values for ID and VDS are possible for the mode you guessed for the transistor If the values are possible for the mode guessed stop problem solved If the values are impossible go back to Step 1 EE40 Fall 2009 Slide 14 Prof Cheung CHECKING THE ANSWERS NMOS Saturation Cut off 0 Vto 1 VGS VT N in triode or saturation VGS VT N in cutoff Triode vGS vDS Vto PMOS Triode Saturation vDS Vto EE40 Fall 2009 Vto Cut off 0 vGS 2 VDS VGS VT N in triode VDS VGS VT N in saturation 1 VGS VT P in triode or saturation VGS VT P in cutoff 2 VDS VGS VT P in triode VDS VGS VT P in saturation Slide 15 Prof Cheung Example Problem MOSFET Circuit EE40 Fall 2009 Slide 16 Prof Cheung Example Problem MOSFET Circuit Find VGS such that VDS 2V Answer Guess Saturation Mode Check VDS 2V VGS VT 1 5 0 5 1V MOSFET indeed is in saturation mode EE40 Fall 2009 Slide 17 Prof Cheung Example Problem MOSFET Circuit Find small signal model parameters 10 5 Siemens EE40 Fall 2009 Slide 18 Prof Cheung How do you guess the right mode Often the key is the value of VGS We can often find VGS directly without solving the whole circuit ID ID VGS VT N probably saturation definitely cutoff VDS EE40 Fall 2009 VGS VT N VGS VT N Slide 19 VDS Prof Cheung How do you guess the right mode When VGS VTH N it s harder to guess the mode ID triode mode saturation mode VGS VTH N If ID is small probably triode mode EE40 Fall 2009 Slide 20 VDS Prof Cheung EXAMPLE 1 Since VGS VTH N not in cutoff mode Guess saturation mode 1 5 k 2 Write transistor ID vs VDS D G I D I Dsa t 250 10 6 3 V 1 V 3 Write ID vs VDS equation using KVL S VDS 1 5 k ID 4V 0 GIVEN VTH N 1 V K 250 A V2 0 V 1 EE40 Fall 2009 2 1mA VDS V 3V G S 4V ID Slide 21 Prof …
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