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Operational Amplifier (OpAmp)

Operational Amplifier (OpAmp)



For Engineering Students

For Engineering Students



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    Operational Amplifier (OpAmp) Operational Amplifier (OpAmp) Presentation Transcript

    • Opamp
    • The 741 Op-Amp Circuit • Schematic diagram of OP-AMP consists: • The input stage • The intermediate stage • The output stage • The biasing circuits
    • Schematic diagram of lm741
    • • 24 transistors, few resistors and only one capacitor • Two power supplies • Short-circuit protection General Description
    • • The input stage consists of transistors Q1 through Q7. • Q1-Q4 is the differential version of CC and CB configuration. • High input resistance. • Current source (Q5-Q7) is the active load of input stage. It not only provides a high- resistance load but also converts the signal from differential to single-ended form with no loss in gain or common-mode rejection. The Input Stage
    • • The intermediate stage is composed of Q16, Q17 and Q13B. • Common-collector configuration for Q16 gives this stage a high input resistance as well as reduces the load effect on the input stage. • Common-emitter configuration for Q17 provides high voltage gain because of the active load Q13B. The Intermediate Stage
    • • The output stage is the efficient circuit called class AB output stage. • Voltage source composed of Q18 and Q19 supplies the DC voltage for Q14 and Q20 in order to reduce the cross-over distortion. • Q23 is the CC configuration to reduce the load effect on intermediate stage. The Output Stage
    • (a) The emitter follower is a class A output stage. (b) (b) Class B output stage. The Output Stage
    • Wave of a class B output stage fed with an input sinusoid. Positive and negative cycles are unable to connect perfectly due to the turn-on voltage of the transistors. This wave form has the nonlinear distortion called crossover distortion. To reduce the crossover distortion can be implemented by supplying the constant DC voltage at the base terminals. The Output Stage
    • QN and QP provides the voltage drop which equals to the turn-on voltages of QN and QP. This circuit is call Class AB output stage. The Output Stage
    • • Short-circuit protection circuitry Forward protection is implemented by R6 and Q15. Reverse protection is implemented by R7, Q21, current source(Q24, Q22) and intermediate stage. Short-circuit protection
    • • Reference current is generated by Q12, Q11 and R5. • Wilder current provides biasing current in the order of μA. • Q13B provides biasing current for intermediate stage, Q13A for output stage. • Q5, Q6 and Q7 is composed of the current source to be an active load for input stage. The Biasing Circuits
    • Ideal Opamp
    • Equivalent Circuit of the Ideal Op Amp
    • Characteristics of the Ideal Op Amplifier The ideal OPAMP has the following characteristic : Differential Input resistance Ri= ∞ Output resistance Ro = 0 Differential voltage gain Av=- ∞ Bandwidth = ∞ Offset voltage and current is zero. a) No difference voltage between inverting and noninvertying terminals. b) No input currents. A Vo = (A V -A V ) = A (V - V ) + + - - OP AMP is a direct coupled high gain amplifier to which feedback is added to control its overall response characteristic
    • Operational Amplifier (OP AMP) Basic and most common circuit building device. Ideally, 1. No current can enter terminals V+ or V-. Called infinite input impedance. 2. Vout=A(V+ - V-) with A ∞→ 3. In a circuit V+ is forced equal to V-. This is the virtual ground property 4. An opamp needs two voltages to power it Vcc and -Vee. These are called the rails. A Vo = (A V -A V ) = A (V - V ) + + - -
    • OPAMP: COMPARATOR Vout=A(Vin – Vref) If Vin>Vref, Vout = +∞ but practically hits +ve power supply = Vcc If Vin<Vref, Vout = -∞ but practically hits –ve power supply = -Vee Compare the voltage of one input with the voltage with other input Two types: inverting comparator when the reference voltage apply to the inverting terminal non inverting comparator when the reference voltage apply to the non inverting terminal A (gain) very high
    • 24 (a) The unity-gain buffer or follower amplifier. (b) Its equivalent circuit model. V+ = VIN. By virtual ground, V- = V+ Thus Vout = V- = V+ = VIN !!!! OPAMP: VOLTAGE FOLLOWER
    • SJTU Zhou Lingling 25 The inverting closed-loop configuration. Virtual ground. OPAMP: The Inverting Configuration
    • 26 OPAMP: The Inverting Configuration
    • SJTU Zhou Lingling 27 OPAMP: The Inverting Configuration
    • OPAMP: INVERTING AMPLIFIER 1. V- = V+ 2. As V+ = 0, V- = 0 3. As no current can enter V- and from Kirchoff’s Ist law, I1=I2. 4. I1 = (VIN - V-)/R1 = VIN/R1 5. I2 = (V- - VOUT)/R2 = -VOUT/R2 => VOUT = -I2R2 6. From 3 and 5, VOUT = -I2R2 = -I1R2 = -VINR2/R1 7. Therefore VOUT = (-R2/R1)VIN 8. Gain = V / V = - R / R
    • SJTU Zhou Lingling 29 The noninverting configuration. Series-shunt negative feedback. OPAMP: The Non Inverting Configuration
    • 30 OPAMP: The Non Inverting Configuration
    • OPAMP: NON – INVERTING AMPLIFIER 1. V- = V+ 2. As V+ = VIN, V- = VIN 3. As no current can enter V- and from Kirchoff’s Ist law, I1=I2. 4. I1 = VIN/R1 5. I2 = (VOUT - VIN)/R2 => VOUT = VIN + I2R2 6. VOUT = I1R1 + I2R2 = (R1+R2)I1 = (R1+R2)VIN/R1 7. Therefore VOUT = (1 + R2/R1)VIN
    • SUMMING AMPLIFIER VOUT = -Rf (V1/R1 + V2/R2 + … + Vn/Rn) If Recall inverting amplifier and If = I1 + I2 + … + In Summing amplifier is a good example of analog circuits serving as analog computing amplifiers (analog computers)! Note: analog circuits can add, subtract, multiply/divide (using logarithmic components, differentiate and integrate – in real time and continuously.
    • 34 )()())(())(( 4 4 3 3 2 2 1 1 R R v R R v R R R R v R R R R vv cc b ca b ca o −−+= SUMMING AMPLIFIER
    • Difference AMPLIFIER •This type is of the same characteristic of the inverting and non inverting OPAMP. •Vo is the differences between the two inputs • Rin in both inputs must be equal, and equal to Rf Vo = Rf (V1 –V2)/ Rin Rf Rin Rin V2 V1 Rf Vo
    • 37 Linear amplifier. Theorem of linear Superposition. Difference AMPLIFIER
    • 38 Application of superposition Inverting configuration 1 1 2 1 Io v R R v −= Difference AMPLIFIER
    • 39 Application of superposition. Non inverting configuration. 2 34 4 1 2 2 )(1( Io v RR R R R v ) + += Difference AMPLIFIER
    • 40 The inverting configuration with general impedances in the feedback and the feed-in paths. Integrators AMPLIFIER
    • SJTU Zhou Lingling 41 The Miller or inverting integrator. The Inverting Integrators AMPLIFIER