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.

2 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: 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.

4 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 ).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)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)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.

6 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. 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.

7 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 .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.

8 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 . +=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.

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 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 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). apply KCL at output node(output current is unknown).