CPE-MIX 03 Operational Amplifier 2-1.pdf
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29 August 2023 MIXED SIGNALS AND SENSORS OPERATIONAL AMPLIFIERS Adonis S. Santos, ECE, MSECE 1. Introduction 2. Op-Amp Input Modes and Parameters 3. Negative Feedback 4. Op-Amps with Negative Feedback OUTLINE 5. Effects of...
29 August 2023 MIXED SIGNALS AND SENSORS OPERATIONAL AMPLIFIERS Adonis S. Santos, ECE, MSECE 1. Introduction 2. Op-Amp Input Modes and Parameters 3. Negative Feedback 4. Op-Amps with Negative Feedback OUTLINE 5. Effects of Negative Feedback on Op-Amp Impedances 6. Open-Loop Frequency and Phase Responses 7. Closed-Loop Frequency Response 1. Describe the basic operational amplifier and its characteristics 2. Discuss op-amp modes and several parameters 3. Explain negative feedback in op-amps 4. 5. Analyze op-amps with negative feedback Describe how negative feedback affects OBJECTIVES op-amp impedances 6. Analyze the open-loop frequency response of an op-amp 7. Analyze the closed-loop frequency response of an op-amp Process whereby a portion of the output voltage of an amplifier is returned to the input with a phase NEGATIVE angle that opposes the input FEEDBACK signal. NEGATIVE FEEDBACK Aol of op-amp is very high (100k) Extremely small input voltage WHY USE drives the op-amp into saturated NEGATIVE output state (even the offset voltage) FEEDBACK NEGATIVE FEEDBACK The closed-loop voltage gain (Acl) can be reduced and controlled so WHY USE that the op-amp can function as a NEGATIVE linear amplifier FEEDBACK NEGATIVE FEEDBACK CLOSED-LOOP GAIN (Acl) OP-AMPS Voltage gain of an op-amp with external feedback WITH An op-amp and an external NEGATIVE negative feedback circuit that FEEDBACK connects the output to the inverting input. OP-AMPS WITH NEGATIVE FEEDBACK "! 𝑉! = 𝑉 "! #"" $%& 𝑉! = β𝑉$%& NON-INVERTING AMPLIFIER 𝑉!"# = 𝑉$% − 𝑉& 𝐴!' 𝑉$%& 1 = 𝑉$%& = 𝑉'( − β𝑉$%& 𝐴$) 𝑉'( 1 𝐴$) + β 𝑉$%& 𝑉$%& 1 = 𝑉'( − β𝑉$%& = 𝐴$) 𝑉'( 1 + 𝐴$) β 𝐴$) 𝑉$%& + β𝑉$%& = 𝑉'( 𝑉$%& 𝐴$) 𝐴$) = 𝑉'( 1 + 𝛽𝐴$) OP-AMPS WITH 1 + β 𝑉$%& = 𝑉'( NEGATIVE FEEDBACK 𝐴$) (NON-IDEAL Aol) "! 𝑉! = 𝑉 "! #"" $%& 𝑉! = β𝑉$%& NON-INVERTING AMPLIFIER 𝑉#$% = 𝐴#( 𝑅& 𝑉&' 1 + 𝛽𝐴#( 𝛽= 𝑅& + 𝑅) 𝐼𝑓 𝛽𝐴#( >> 1 𝑅# 𝑉#$% 1 𝑅& + 𝑅) ≈ = 𝐴!" = 1 + 𝑉&' 𝛽 𝑅& 𝑅$ (IDEAL Aol) Acl is not at all dependent on the op-amps open- OP-AMPS WITH loop gain under the condition AolB>>1, where B NEGATIVE FEEDBACK is the feedback factor. 1. Determine the closed-loop voltage gain of the NON-INVERTING OP-AMP amplifier. Given: 𝑅! = 100𝑘Ω 𝑅' = 4.7𝑘Ω Example Req’d: 𝐴*) =? Sol’n: 𝑅! 𝐴*) = 1 + 𝑅' 𝑨𝒄𝒍 = 𝟐𝟐. 𝟐𝟖 100𝑘Ω 𝐴*) = 1 + 4.7𝑘Ω VOLTAGE- FOLLOWER 𝐴!" = 1 The straight feedback connection has a voltage gain of 1. Very high input impedance and its very low OP-AMPS WITH output impedance, ideal buffer amplifier NEGATIVE FEEDBACK 𝑖! = 𝑖"# 𝑖"# 0 𝑉$%& 𝐴 − INVERTING 𝐴 AMPLIFIER 𝑉$%&5 𝑅! 7𝑅 − 𝑉'( − − 𝐴 𝑉$%& ' (NON-IDEAL Aol) 𝑖'( = = 𝑅' 𝑉'( 𝑅 1 + !7𝑅 ' 𝑉$%&5 1+ 𝐴 𝑉'( + 𝐴 = 𝑅) -𝑅 ≪ 𝐴 𝑅' 𝐼𝑓 1+ & 𝑉$%& 𝑅# 𝑉$%& =− − 𝑖'( 𝑅! 𝐴!" = − (IDEAL Aol) 𝐴 𝑅$ OP-AMPS WITH The closed-loop gain is independent of the NEGATIVE FEEDBACK op-amp’s internal open-loop gain. The negative sign indicates inversion 1. Given the op-amp configuration, determine the INVERTING OP-AMP value of Rf required to produce a closed-loop voltage gain of -100. Given: 𝑅' = 2.2𝑘Ω Example 𝐴*) = −100 Req’d: 𝑅! =? 𝑅! Sol’n: 𝐴*) = − 𝑅' 𝑅! = 220𝑘𝛺 𝑅! = −𝐴*) 𝑅' 𝑅! = −(−100)2.2𝑘Ω Input Impedance IMPEDANCES OF THE NONINVERTING AMPLIFIER 𝑍%&(()) = 1 + 𝐴+) 𝛽 𝑍%& Zin(cl) > Zin EFFECTS OF NEGATIVE FEEDBACK ON OP-AMP IMPEDANCES Output Impedance IMPEDANCES OF THE NONINVERTING AMPLIFIER 𝑍+,- 𝑍+,- (()) = EFFECTS OF NEGATIVE 1 + 𝐴+) 𝛽 FEEDBACK ON OP-AMP IMPEDANCES Zout(cl)
