Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits
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Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Electronics Operational Amplifier Basics Terry Sturtevant Wilfrid Laurier University September 3, 2014 Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Ideal Operational Amplifiers Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Ideal Operational Amplifiers Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Ideal Operational Amplifiers inverting input Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Ideal Operational Amplifiers non-inverting input inverting input Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Ideal Operational Amplifiers non-inverting input output inverting input Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Ideal Operational Amplifiers non-inverting input output inverting input Output is proportional to the difference between the non-inverting and inverting inputs Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Ideal Operational Amplifiers non-inverting input output inverting input Output is proportional to the difference between the non-inverting and inverting inputs Active device; requires power to work, even though power connections often not shown Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Showing power connections non-inverting input output inverting input Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Showing power connections V supply + non-inverting input output inverting input Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Showing power connections V supply + non-inverting input output inverting input V supply − Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Showing power connections V supply + non-inverting input output inverting input V supply − Supplies are usually not shown, but must be used. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules V supply + is the positive supply. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules V supply + is the positive supply. V supply − is the negative supply. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules V supply + is the positive supply. V supply − is the negative supply. In a single supply op amp, the negative supply can be ground. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules V supply + is the positive supply. V supply − is the negative supply. In a single supply op amp, the negative supply can be ground. The output of an op amp can’t go outside the supply voltages. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules V supply + is the positive supply. V supply − is the negative supply. In a single supply op amp, the negative supply can be ground. The output of an op amp can’t go outside the supply voltages. In fact, you usually can’t get closer than a volt or two from the supplies. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules V supply + is the positive supply. V supply − is the negative supply. In a single supply op amp, the negative supply can be ground. The output of an op amp can’t go outside the supply voltages. In fact, you usually can’t get closer than a volt or two from the supplies. These voltage limits are also called rails. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules V supply + is the positive supply. V supply − is the negative supply. In a single supply op amp, the negative supply can be ground. The output of an op amp can’t go outside the supply voltages. In fact, you usually can’t get closer than a volt or two from the supplies. These voltage limits are also called rails. → Single supply op amps are an exception; you usually can usually get within a few millivolts of the negative supply. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier supply voltage rules V supply + is the positive supply. V supply − is the negative supply. In a single supply op amp, the negative supply can be ground. The output of an op amp can’t go outside the supply voltages. In fact, you usually can’t get closer than a volt or two from the supplies. These voltage limits are also called rails. → Single supply op amps are an exception; you usually can usually get within a few millivolts of the negative supply. When an op amp hits one of the rails, its output can be called saturated, or we can say the op amp is in saturation. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Equivalent circuit Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Equivalent circuit Vin * Vout R @ Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier equivalent circuit Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier equivalent circuit Rin ≈ ∞ Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier equivalent circuit Rin ≈ ∞ → Rin ≈ MΩ for real op amps Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier equivalent circuit Rin ≈ ∞ → Rin ≈ MΩ for real op amps Rout ≈ 0 Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier equivalent circuit Rin ≈ ∞ → Rin ≈ MΩ for real op amps Rout ≈ 0 → Rout ≈ 100Ω for real op amps Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier equivalent circuit Rin ≈ ∞ → Rin ≈ MΩ for real op amps Rout ≈ 0 → Rout ≈ 100Ω for real op amps Av ≈ ∞ Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier equivalent circuit Rin ≈ ∞ → Rin ≈ MΩ for real op amps Rout ≈ 0 → Rout ≈ 100Ω for real op amps Av ≈ ∞ → Av ≈ 104 → 105 for real op amps Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Operational amplifier equivalent circuit Rin ≈ ∞ → Rin ≈ MΩ for real op amps Rout ≈ 0 → Rout ≈ 100Ω for real op amps Av ≈ ∞ → Av ≈ 104 → 105 for real op amps Vout = Av (V+ − V− ) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback Vout Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β Vout Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β Vout Vin Op amps are rarely used in the open-loop configuration. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β Vout Vin Op amps are rarely used in the open-loop configuration. → They usually use negative feedback. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β is called the feedback factor, and β ∈ (0, 1) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β is called the feedback factor, and β ∈ (0, 1) → It is the proportion of the output fed back into the input Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β is called the feedback factor, and β ∈ (0, 1) → It is the proportion of the output fed back into the input → If it goes into the inverting input, it is negative feedback Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β is called the feedback factor, and β ∈ (0, 1) → It is the proportion of the output fed back into the input → If it goes into the inverting input, it is negative feedback → If it goes into the non-inverting input, it is positive feedback Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β is called the feedback factor, and β ∈ (0, 1) → It is the proportion of the output fed back into the input → If it goes into the inverting input, it is negative feedback → If it goes into the non-inverting input, it is positive feedback Rin ≈ Rin (1 + βA) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β is called the feedback factor, and β ∈ (0, 1) → It is the proportion of the output fed back into the input → If it goes into the inverting input, it is negative feedback → If it goes into the non-inverting input, it is positive feedback Rin ≈ Rin (1 + βA) Rout ≈ Rout (1+βA) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Negative feedback β is called the feedback factor, and β ∈ (0, 1) → It is the proportion of the output fed back into the input → If it goes into the inverting input, it is negative feedback → If it goes into the non-inverting input, it is positive feedback Rin ≈ Rin (1 + βA) Rout ≈ Rout (1+βA) 1 β ; i.e. gain = the output depends only on the feedback, not on the op amp characteristics Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback You will virtually never use positive feedback! Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback You will virtually never use positive feedback! Note that all of the circuits that follow use negative feedback; Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback You will virtually never use positive feedback! Note that all of the circuits that follow use negative feedback; (i.e. feedback goes into the inverting input. ) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Terminology Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Terminology Without feedback is called open loop configuration. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Terminology Without feedback is called open loop configuration. With feedback is called closed loop configuration. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Terminology Without feedback is called open loop configuration. With feedback is called closed loop configuration. The gain without feedback is called open loop gain. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Basic Schematic Symbol Showing power connections Operational amplifier supply voltage rules Equivalent circuit Negative feedback Terminology Without feedback is called open loop configuration. With feedback is called closed loop configuration. The gain without feedback is called open loop gain. The gain with feedback is called closed loop gain. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Analyzing Op Amp Circuits; ideal assumptions with closed loop circuits Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Analyzing Op Amp Circuits; ideal assumptions with closed loop circuits No current goes into op amp inputs Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Analyzing Op Amp Circuits; ideal assumptions with closed loop circuits No current goes into op amp inputs Inputs are virtually equal ; i.e. inputs are at the same voltage Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Analyzing Op Amp Circuits; ideal assumptions with closed loop circuits No current goes into op amp inputs Inputs are virtually equal ; i.e. inputs are at the same voltage Frequency of input signal doesn’t matter Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Analyzing Op Amp Circuits; ideal assumptions with closed loop circuits No current goes into op amp inputs Inputs are virtually equal ; i.e. inputs are at the same voltage Frequency of input signal doesn’t matter These assumptions only hold if the output is not saturated! Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Analyzing Op Amp Circuits; ideal assumptions with closed loop circuits No current goes into op amp inputs Inputs are virtually equal ; i.e. inputs are at the same voltage Frequency of input signal doesn’t matter These assumptions only hold if the output is not saturated! → i.e. if the output is not at either of the rails Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Analyzing Op Amp Circuits; ideal assumptions with closed loop circuits No current goes into op amp inputs Inputs are virtually equal ; i.e. inputs are at the same voltage Frequency of input signal doesn’t matter These assumptions only hold if the output is not saturated! → i.e. if the output is not at either of the rails Instead of thinking of the device as an amplifier, you can think the purpose of the device is to keep the inputs equal Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit Buffer (or voltage follower) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit Buffer (or voltage follower) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit Buffer (or voltage follower) Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit Buffer (or voltage follower) Vout Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit Buffer (or voltage follower) Vout Vin V− = Vout and V+ = Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit Buffer (or voltage follower) Vout Vin V− = Vout and V+ = Vin V− ≈ V+ (virtual equality) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit Buffer (or voltage follower) Vout Vin V− = Vout and V+ = Vin V− ≈ V+ (virtual equality) ∴ Vout ≈ Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit 6V 4V 6V 4V Here’s a simulation. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit 12V -12V 12V -12V With a large amplitude signal, you can see the rails. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit 12V 11.1V This is a closer look at the positive rail. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit -12V -11.1V This is a closer look at the negative rail. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit Inverting amplifier - If Ri Vin Rf - Ii Vout Many op amp circuits are based on this. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit V+ = 0 (ground) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit V+ = 0 (ground) If Rf = Vout − V− Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit V+ = 0 (ground) If Rf = Vout − V− Ii Ri = V− − Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit V+ = 0 (ground) If Rf = Vout − V− Ii Ri = V− − Vin V− ≈ V+ (virtual equality) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit V+ = 0 (ground) If Rf = Vout − V− Ii Ri = V− − Vin V− ≈ V+ (virtual equality) If = Ii (no current into inputs) Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit V+ = 0 (ground) If Rf = Vout − V− Ii Ri = V− − Vin V− ≈ V+ (virtual equality) If = Ii (no current into inputs) ∴ Vout −0 Rf = 0−Vin Ri Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Buffer circuit Inverting amplifier circuit V+ = 0 (ground) If Rf = Vout − V− Ii Ri = V− − Vin V− ≈ V+ (virtual equality) If = Ii (no current into inputs) ∴ Vout −0 Rf ∴ Vout = 0−Vin Ri Rf − Ri Vin = Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Op amp circuit input resistance Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Op amp circuit input resistance Even though the input resistance of an op amp is very large, the input resistance of an op amp circuit may not be. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Op amp circuit input resistance Even though the input resistance of an op amp is very large, the input resistance of an op amp circuit may not be. Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Op amp circuit input resistance Even though the input resistance of an op amp is very large, the input resistance of an op amp circuit may not be. I≈0 Vin Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance Op amp circuit input resistance Even though the input resistance of an op amp is very large, the input resistance of an op amp circuit may not be. I≈0 Vin For the buffer circuit, since the signal goes directly into an op amp input, then the input resistance is very large. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance For a circuit like the inverting amplifier, the input signal doesn’t go directly into the op amp input. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance For a circuit like the inverting amplifier, the input signal doesn’t go directly into the op amp input. - If Ri Vin Rf - Ii Terry Sturtevant Vout Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance For a circuit like the inverting amplifier, the input signal doesn’t go directly into the op amp input. - Vin Rf If Ri - Ii K A A Vout A I A @ @ V+ ≈ V− = 0 Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance For a circuit like the inverting amplifier, the input signal doesn’t go directly into the op amp input. Ri Vin Ii ? It looks more like this. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance For a circuit like the inverting amplifier, the input signal doesn’t go directly into the op amp input. Ri Vin Ii ? Ii = Vin Ri It looks more like this. Terry Sturtevant Electronics Operational Amplifier Basics Ideal Operational Amplifiers Analyzing Op Amp Circuits Common Operational Amplifier Circuits Op amp circuit input resistance For a circuit like the inverting amplifier, the input signal doesn’t go directly into the op amp input. Ri Vin Ii ? Ii = Vin Ri It looks more like this. The effective input resistance is Ri . Terry Sturtevant Electronics Operational Amplifier Basics
