6: Operational Amplifiers

1 6: Operational Amplifiers6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 1 / 12 Operational Amplifier6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 2 / 12An op amp ( Operational amplifier) is acircuit with two inputs and one (V+ V ) Operational Amplifier6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 2 / 12An op amp ( Operational amplifier) is acircuit with two inputs and one (V+ V )The gain,A, is usually very large: 105at low Amplifier6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 2 / 12An op amp ( Operational amplifier) is acircuit with two inputs and one (V+ V )The gain,A, is usually very large.

2 105at low input currents are very small: Amplifier6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 2 / 12An op amp ( Operational amplifier) is acircuit with two inputs and one (V+ V )The gain,A, is usually very large: 105at low input currents are very small: it is a complicated circuit withabout 40 components, but we can forgetabout that and treat it asan almostperfect dependent voltage Amplifier6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 2 / 12An op amp ( Operational amplifier) is acircuit with two inputs and one (V+ V )The gain,A, is usually very large: 105at low input currents are very small: it is a complicated circuit withabout 40 components, but we can forgetabout that and treat it asan almostperfect dependent voltage circuit pins arenumbered anti-clockwise fromblob or notch (when lookingfrom above).

3 Negative Feedback6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 3 / 12In a central heating system, if the temperature falls too lowthe thermostatturns on the heating, when it rises the thermostat turns it off Feedback6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 3 / 12In a central heating system, if the temperature falls too lowthe thermostatturns on the heating, when it rises the thermostat turns it off feedbackis when the occurence of an event causes something tohappen that counteracts the original Feedback6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 3 / 12In a central heating system, if the temperature falls too lowthe thermostatturns on the heating, when it rises the thermostat turns it off feedbackis when the occurence of an event causes something tohappen that counteracts the original op-amp outputYfallsthenV will fall bythe same amount so(V+ V )willincrease.

4 This causesYtorisesinceY=A(V+ V ).Negative Feedback6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 3 / 12In a central heating system, if the temperature falls too lowthe thermostatturns on the heating, when it rises the thermostat turns it off feedbackis when the occurence of an event causes something tohappen that counteracts the original op-amp outputYfallsthenV will fall bythe same amount so(V+ V )willincrease. This causesYtorisesinceY=A(V+ V ).Y=A(X Y)Negative Feedback6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 3 / 12In a central heating system, if the temperature falls too lowthe thermostatturns on the heating, when it rises the thermostat turns it off feedbackis when the occurence of an event causes something tohappen that counteracts the original op-amp outputYfallsthenV will fall bythe same amount so(V+ V )willincrease.

5 This causesYtorisesinceY=A(V+ V ).Y=A(X Y)Y(1 +A) =AXNegative Feedback6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 3 / 12In a central heating system, if the temperature falls too lowthe thermostatturns on the heating, when it rises the thermostat turns it off feedbackis when the occurence of an event causes something tohappen that counteracts the original op-amp outputYfallsthenV will fall bythe same amount so(V+ V )willincrease. This causesYtorisesinceY=A(V+ V ).Y=A(X Y)Y(1 +A) =AX Y=11+1/AX Xfor largeANegative Feedback6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 3 / 12In a central heating system, if the temperature falls too lowthe thermostatturns on the heating, when it rises the thermostat turns it off feedbackis when the occurence of an event causes something tohappen that counteracts the original op-amp outputYfallsthenV will fall bythe same amount so(V+ V )willincrease.

6 This causesYtorisesinceY=A(V+ V ).Y=A(X Y)Y(1 +A) =AX Y=11+1/AX Xfor largeAIfY=A(V+ V )thenV+ V =YAwhich, sinceA 105, isnormallyvery Feedback6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 3 / 12In a central heating system, if the temperature falls too lowthe thermostatturns on the heating, when it rises the thermostat turns it off feedbackis when the occurence of an event causes something tohappen that counteracts the original op-amp outputYfallsthenV will fall bythe same amount so(V+ V )willincrease. This causesYtorisesinceY=A(V+ V ).Y=A(X Y)Y(1 +A) =AX Y=11+1/AX Xfor largeAIfY=A(V+ V )thenV+ V =YAwhich, sinceA 105, isnormallyvery Rule:Negative feedback adjusts the output to makeV+ V.

7 Analysing op-amp circuits6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 4 / 12 Nodal analysis is simplified by making some op-amp circuits6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 4 / 12 Nodal analysis is simplified by making some for negative feedback:to ensure that an increase inYmakes(V+ V )decrease,Ymust be connected (usually via othercomponents) toV .Analysing op-amp circuits6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 4 / 12 Nodal analysis is simplified by making some for negative feedback:to ensure that an increase inYmakes(V+ V )decrease,Ymust be connected (usually via othercomponents) toV.

8 +=V :Since(V+ V ) =YA, this is the same asassuming thatA= .Requires negative op-amp circuits6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 4 / 12 Nodal analysis is simplified by making some for negative feedback:to ensure that an increase inYmakes(V+ V )decrease,Ymust be connected (usually via othercomponents) toV . +=V :Since(V+ V ) =YA, this is the same asassuming thatA= .Requires negative zero input current:in most circuits, the current at the op-ampinput terminals is much smaller than the other currents in the circuit , sowe assume it is op-amp circuits6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 4 / 12 Nodal analysis is simplified by making some for negative feedback:to ensure that an increase inYmakes(V+ V )decrease,Ymust be connected (usually via othercomponents) toV.

9 +=V :Since(V+ V ) =YA, this is the same asassuming thatA= .Requires negative zero input current:in most circuits, the current at the op-ampinput terminals is much smaller than the other currents in the circuit , sowe assume it is KCL at each op-amp input node separately(input currents = 0).Analysing op-amp circuits6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 4 / 12 Nodal analysis is simplified by making some for negative feedback:to ensure that an increase inYmakes(V+ V )decrease,Ymust be connected (usually via othercomponents) toV . +=V :Since(V+ V ) =YA, this is the same asassuming thatA= .Requires negative zero input current:in most circuits, the current at the op-ampinput terminals is much smaller than the other currents in the circuit , sowe assume it is KCL at each op-amp input node separately(input currents = 0).

10 Apply KCL at output node(output current is unknown).Analysing op-amp circuits6: Operational Amplifiers Operational Amplifier Negative Feedback Analysing op-amp circuits Non-inverting amplifier Voltage Follower Inverting Amplifier Inverting SummingAmplifier Differential Amplifier Schmitt Trigger Choosing Resistor Values Analysis of Circuits (2017-10110) Operational Amplifiers: 6 4 / 12 Nodal analysis is simplified by making some :The op-amp needs two power supplyconnections; usually+15 Vand 15 are almost always omitted from thecircuit currents only sum tozero (KCL) if all five connections for negative feedback:to ensure that an increase inYmakes(V+ V )decrease,Ymust be connected (usually via othercomponents) toV . +=V :Since(V+ V ) =YA, this is the same asassuming thatA= .Requires negative zero input current:in most circuits, the current at the op-ampinput terminals is much smaller than the other currents in the circuit , sowe assume it is KCL at each op-amp input node separately(input currents = 0).