ELECTRIC CIRCUITS ECSE-2010 Spring 2003 Class 9

ASSIGNMENTS DUE Today (Monday): Tuesday/Wednesday: Thursday: Homework #3 Due Activity 9-1, Op-Amp ILM (In Class) Tuesday/Wednesday: Will do Experiment #4 in Class (EP-4) Activity 10-2 (There is no 10-1) Thursday: Experiment #2 Report is Due Will do Computer Project #1 in Class (CP-1) Will spend second hour reviewing for Exam I Exam I Monday, 2/10, 7-9, DCC 308

THEVENIN EQUIVALENT CIRCUIT Define v, i using Active Convention

ACTIVITY 8-1

ACTIVITY 8-1

REVIEW Real Voltage Sources: Model with Ideal Voltage Source, Vs, in Series with Resistor, Rs Vs = Open Circuit Voltage Rs = Source Resistance Vs in Series with Rs can be viewed as the Model for a Real Voltage Source or as the Thevenin Equivalent Circuit for any Source Network

REAL SOURCES

REVIEW Power Transfer: For PMAX to RL: Model Any Source or Source Network with Vs in Series with Rs Model Any Load Network with Req Rs is Usually Fixed Want to Get Maximum Power to Load, RL For PMAX to RL: Choose Req = Rs Best you can do

MAXIMUM POWER TRANSFER

END OF MATERIAL FOR EXAM I

VOLTAGE AMPLIFIER

AMPLIFIER CIRCUIT MODEL

AMPLIFIERS An Amplifier is a Circuit that Multiplies a Voltage or Current by some Constant: Vout = A x Vin A is called the “Gain” of the Amplifier Circuit Model for Voltage Amplifier: Rin is called the Input Resistance Could be Req of a complicated circuit Rout is called the Output Resistance Amplification Modeled with VCVS; A Vin Gain = Vout / Vin = A

AMPLIFIER CIRCUIT

AMPLIFIERS Use Voltage Divider Rule at Input: vin = [Rin / (Rin + Rs)] vs Use Voltage Divider Rule at Output: vout = [Req / (Req + Rout)] A vin Overall Voltage Gain for Complete Circuit is vout / vs: Gain = [Req / (Req + Rout)] A [Rin / (Rin + Rs)] Choose Rout << Req; Rin >> Rs ; Design Challenge Gain = vout / vs ~ A

AMPLIFIER CIRCUIT

OPERATIONAL AMPLIFIERS Special Type of Amplifier: Rin ~ 10 M; (Very Large) Rout ~ 100 ohms; (Very Small) Gain = A ~ 105; (Very Large) Building Blocks for Electronic Circuits Will Use Special Symbol for Op Amp: Triangle: 2 Inputs, vp, vn; 1 Output, vout vout = A (vp - vn); Difference Amplifier See Circuit Model for Real Op Amp Requires DC Sources; +VDC, -VDC vout Can Never Be Greater than VDC

OPERATIONAL AMPLIFIERS

REAL OP AMP MODEL

Fig. 10.1 The 741 op-amp circuit. Q11, Q12, and R5 generate a reference bias current, IREF, Q10, Q9, and Q8 bias the input stage, which is composed of Q1 to Q7. The second gain stage is composed f Q16 and Q17 with Q13 acting as active load. The class AB output stage is formed by Q14 and Q20 with biasing devices Q18 and Q19 and an input buffer Q23. Transistors Q15, Q21, Q24, and Q22 serve to protect the amplifier against output short circuit and are normally off.

IDEAL OP AMP Ideal Op Amp is Op Amp with: Rin ~ Infinite Rout ~ 0 A ~ Infinite Ideal Op Amp is a Good Circuit Model for Almost All Real Op Amps: We will assume all Real Op Amps can be modeled by Ideal Op Amps Will see in Computer Project 1 that the difference between a circuit with a Real Op Amp and an Ideal Op Amp is very small

IDEAL OP AMP

IDEAL OP AMP For Ideal Op Amp: Ideal Op Amp => Comparator Circuit: ip = in = 0; Ideal Op Amp Draws NO Current! This is because Rin is Infinite BUT! vout Can Never Be Greater than VDC Ideal Op Amp => Comparator Circuit: If vp > vn => vout = +VDC If vp < vn => vout = -VDC

OP AMP CIRCUITS To Make Op Amp Circuits Useful We Must Add Negative Feedback: Circuit connection between vout and vn This will always keep vp = vn Output, vout, will be Finite Negative Feedback Creates “Virtual Short” at Input: ip = in = 0; Always vp - vn = vin = 0 With Negative Feedback

IDEAL OP AMP WITH NEGATIVE FEEDBACK

REAL OP AMP WITH NEGATIVE FEEDBACK

ISOLATION AMPLIFIER

ISOLATION AMPLIFIER Connect vout to vn: Connect vin to vp: => Negative Feedback => Virtual Short between + and – terminals vp = vn; ip = in = 0 Connect vin to vp: vout = vn = vp = vin; vout = vin No Voltage Gain, BUT No Current is Drawn from Source! “Isolates” Load from Source; A very common application of an Op Amp

OP AMP CIRCUITS Assume Op Amp is Ideal Use Virtual Short to find vout / vin Virtual Short: ip = in = 0, vp = vn Will Look at Effects of Real Op Amps Later Computer Project 1 on Thursday Will Use Circuit Model for Real Op Amp Finite Rin, Non-Zero Rout, Finite A Compare Performance of Circuit with that obtained by assuming an Ideal Op Amp

NON-INVERTING VOLTAGE AMPLIFIER

NON-INVERTING VOLTAGE AMPLIFIER Use Resistors R1 and RF to Create Negative Feedback: Ckt Path Between vout and vn => Negative Feedback Creates Virtual Short ip = in = 0

NON-INVERTING VOLTAGE AMPLIFIER Connect vin to vp : vn = vp = vin ; Virtual Short i1 = vin / R1; Ohm’s Law iF = i1; KCL vout = vin + iF RF = vin (1 + RF/R1) Non-Inverting Voltage Amplifier Output Voltage is Same Sign as Input Voltage Gain > 1

INVERTING VOLTAGE AMPLIFIER

INVERTING VOLTAGE AMPLIFIER Use Resistor RF to Create Negative Feedback: Note Change in Terminals Ckt Path Between vout and vn Creates Virtual Short ip = in = 0

INVERTING VOLTAGE AMPLIFIER Connect vin to vn Through R1 and Connect vp to Ground: vp = 0 = vn i1 = (vin - vn) / R1 = vin / R1; iF = i1 vout = 0 - iF RF = - (vin / R1) RF = - vin (RF / R1) Output is Opposite Sign from Input Inverting Voltage Amplifier Gain > or < 1

SUMMING AMPLIFIER

ACTIVITY 9-1

ACTIVITY 9-1 Look for Known Amplifiers Op Amp 1 is a Non-Inverting Voltage Amplifier vx = (1 + 38 / 2) vin = 20 vin vp for Op Amp 2 is vx: vn2 = vx i = (vin - vx) / 3k = - 19 vin / 3k = iF2 vout = vx - iF2 60k vout = 20 vin - (-19 vin / 3k) 60k = 400 vin Gain = vout / vin = 400

ACTIVITY 9-1

OP AMP CAD MODULE

OP AMP CAD MODULE

OP AMP CAD MODULE

OP AMP CAD MODULE

TRANSISTOR BIAS POINT

TRANSISTOR BIAS POINT

EXPERIMENT #4

EXPERIMENT 4

OP AMP PACKAGE

741 LAYOUT

EXPERIMENT #4