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Op amplifier

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An operational amplifier (op-amp) is an electronic device that amplifies the difference between two input voltages. It has very high gain, very high input impedance, and very low output impedance. Op-amps can perform mathematical operations like addition, subtraction, integration, and differentiation. Key characteristics of an ideal op-amp include infinite input impedance, zero output impedance, infinite voltage gain, and zero offset voltage. Practical op-amps have finite characteristics. Op-amps can be configured as inverting or non-inverting amplifiers to produce output signals that are inverted or non-inverted versions of the input. Common op-amp applications include adders, subtractors, and active filters.

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Operational Amplifier 1. An amplifier is an electronic device for increasing the amplitude of electrical signals. 2. An amplifier with high gain and high input impedance (usually with external feedback), used especially in circuits for performing mathematical operations on an input voltage. 3. Gain is the ratio of output voltage to input voltage. 4. Op-amps can be used to perform various mathematical operations like addition, subtraction, differentiation and integration etc. 5. Basic diagram of an op-amp is shown in below figure:
Terminal Characteristics of an Op-amp Op-amps is also called as IC741. The pin diagram of an op-amp is shown in below figure: Pin 1 and Pin 5 are called as offset null, because they removes the offset voltage and balances the input voltage. Pin 2 is the inverting signal input and Pin 3 is the non-inverting signal input. Pin 4 is the ground or negative voltage supply input and Pin 7 is the positive voltage supply input.
Ideal characteristics of an op-amp: Pin 6 is the output terminal. Pin 8 is not connected, this terminal is only used when two op-amps are required to connected in series. The open loop voltage gain (AOL) without any feedback for an ideal op-amp is infinite. The input impedance (RIN)of an ideal op-amp is infinite, so there is no current flowing in the input circuit. The output impedance (ROUT)of an ideal op-amp is zero. An ideal op-amp has an infinite bandwidth, so it can amplify any signal from DC to the highest AC frequency without any losses. The offset voltage of an ideal op-amp is zero, which means that the output voltage will be zero if the difference between the inverting and non-inverting terminal is zero.
Op-amp as an Differential amplifier: AOL = Open-loop voltage gain The basic formula for output voltage of an op-amp VOUT = AOL (V+ -V-) From above equation , it is clearly seen that the output voltage amplifying the difference between two input signals, so an op-amp is also called the differential amplifier.
Practical Characteristics of an Op-amp: The open loop voltage gain (AOL) without any feedback for an op-amp is 105 . The input impedance (RIN) of an op-amp is 2M, so there is a small offset current flowing in the input circuit in the range of 20nA. The output impedance (ROUT) of an op-amp is 75. An op-amp has an bandwidth 1MHz. The offset voltage of an op-amp is 2mV. Virtual Ground concept in op-amp: In op-amps the term virtual ground means that the voltage at that particular node is almost equal to ground voltage (0V). This concept is very useful in analysis of op-amp circuits and it will make a lot of calculations very simple. We already know that the voltage gain of an ideal op-amp is infinite.
Gain = Vo/Vin As gain is infinite, Vin = 0 Vin = V2 V1 In the above circuit V1 is connected to ground, so V1 = 0. Thus V2 also will be at ground potential. V2 = 0 All the derivation of op-amps are based on this concept only.
Op-amp as an inverting amplifier: The operational amplifier as an inverting operational amplifier or an inverting op- amp when the op-amp circuit produces the output which is out of phase with respect to its input by 180o. This means that if the input pulse is positive, then the output pulse will be negative and vice versa. Applying KCL at node V2,
V2 Vin R1 + V2 Vout Rf = 0 ( ) But from figure V1=0, so from virtual ground concept V2=0. Hence putting the value of V2 in equation (i), we get 0Vin R1 + 0Vout Rf = 0 Vin R1 Vout Rf = 0 Vin R1 = Vout Rf Vin x Rf R1 = Vout Rf R1 Vin = Vout
Av= Vout Vin = Rf R1 So from above equation, it is seen that the closed loop voltage gain Av in an inverting op-amp is the ratio of its feedback resistance to the input resistance and negative sign (-) shows that the output voltage is 180尊 out of phase with respect to input. Op-amp as an non-inverting amplifier: The operational amplifier as an non-inverting operational amplifier or an non- inverting op-amp when the op-amp circuit produces the output which is in phase with its input. This means that if the input pulse is positive, then the output pulse will be positive and vice versa.
Applying KCL at node V2 V2 0 R1 + V2 Vout Rf = 0 But from figure V1= Vin, so from virtual ground concept V2= Vin. Hence putting the value of V2 in equation (i), we get Vin R1 + Vin Vout Rf = 0 Vin R1 + Vin Rf Vout Rf = 0 Vin( 1 R1 + 1 Rf ) = Vout Rf Vin( Rf R1 + Rf Rf ) = Vout
Vin( Rf R1 + 1) = Vout Av= Vout Vin = ( Rf R1 + 1) From above equation it is clear that the output voltage will be in phase with respect to input voltage, so it follows the same waveform as the input voltage, hence in non- inverting configuration the op-amp is called voltage follower circuit. Applications of an op-amp: (i) As an adder circuit: It is possible to apply more than one input signal to an inverting amplifier. This circuit will add all these input signals and produce their addition to output terminals. Such a circuit called as an Adder Circuit. The diagram for an adder circuit is shown in below figure:
Op amplifier

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Op amplifier

  • 1. Operational Amplifier 1. An amplifier is an electronic device for increasing the amplitude of electrical signals. 2. An amplifier with high gain and high input impedance (usually with external feedback), used especially in circuits for performing mathematical operations on an input voltage. 3. Gain is the ratio of output voltage to input voltage. 4. Op-amps can be used to perform various mathematical operations like addition, subtraction, differentiation and integration etc. 5. Basic diagram of an op-amp is shown in below figure:
  • 2. Terminal Characteristics of an Op-amp Op-amps is also called as IC741. The pin diagram of an op-amp is shown in below figure: Pin 1 and Pin 5 are called as offset null, because they removes the offset voltage and balances the input voltage. Pin 2 is the inverting signal input and Pin 3 is the non-inverting signal input. Pin 4 is the ground or negative voltage supply input and Pin 7 is the positive voltage supply input.
  • 3. Ideal characteristics of an op-amp: Pin 6 is the output terminal. Pin 8 is not connected, this terminal is only used when two op-amps are required to connected in series. The open loop voltage gain (AOL) without any feedback for an ideal op-amp is infinite. The input impedance (RIN)of an ideal op-amp is infinite, so there is no current flowing in the input circuit. The output impedance (ROUT)of an ideal op-amp is zero. An ideal op-amp has an infinite bandwidth, so it can amplify any signal from DC to the highest AC frequency without any losses. The offset voltage of an ideal op-amp is zero, which means that the output voltage will be zero if the difference between the inverting and non-inverting terminal is zero.
  • 4. Op-amp as an Differential amplifier: AOL = Open-loop voltage gain The basic formula for output voltage of an op-amp VOUT = AOL (V+ -V-) From above equation , it is clearly seen that the output voltage amplifying the difference between two input signals, so an op-amp is also called the differential amplifier.
  • 5. Practical Characteristics of an Op-amp: The open loop voltage gain (AOL) without any feedback for an op-amp is 105 . The input impedance (RIN) of an op-amp is 2M, so there is a small offset current flowing in the input circuit in the range of 20nA. The output impedance (ROUT) of an op-amp is 75. An op-amp has an bandwidth 1MHz. The offset voltage of an op-amp is 2mV. Virtual Ground concept in op-amp: In op-amps the term virtual ground means that the voltage at that particular node is almost equal to ground voltage (0V). This concept is very useful in analysis of op-amp circuits and it will make a lot of calculations very simple. We already know that the voltage gain of an ideal op-amp is infinite.
  • 6. Gain = Vo/Vin As gain is infinite, Vin = 0 Vin = V2 V1 In the above circuit V1 is connected to ground, so V1 = 0. Thus V2 also will be at ground potential. V2 = 0 All the derivation of op-amps are based on this concept only.
  • 7. Op-amp as an inverting amplifier: The operational amplifier as an inverting operational amplifier or an inverting op- amp when the op-amp circuit produces the output which is out of phase with respect to its input by 180o. This means that if the input pulse is positive, then the output pulse will be negative and vice versa. Applying KCL at node V2,
  • 8. V2 Vin R1 + V2 Vout Rf = 0 ( ) But from figure V1=0, so from virtual ground concept V2=0. Hence putting the value of V2 in equation (i), we get 0Vin R1 + 0Vout Rf = 0 Vin R1 Vout Rf = 0 Vin R1 = Vout Rf Vin x Rf R1 = Vout Rf R1 Vin = Vout
  • 9. Av= Vout Vin = Rf R1 So from above equation, it is seen that the closed loop voltage gain Av in an inverting op-amp is the ratio of its feedback resistance to the input resistance and negative sign (-) shows that the output voltage is 180尊 out of phase with respect to input. Op-amp as an non-inverting amplifier: The operational amplifier as an non-inverting operational amplifier or an non- inverting op-amp when the op-amp circuit produces the output which is in phase with its input. This means that if the input pulse is positive, then the output pulse will be positive and vice versa.
  • 10. Applying KCL at node V2 V2 0 R1 + V2 Vout Rf = 0 But from figure V1= Vin, so from virtual ground concept V2= Vin. Hence putting the value of V2 in equation (i), we get Vin R1 + Vin Vout Rf = 0 Vin R1 + Vin Rf Vout Rf = 0 Vin( 1 R1 + 1 Rf ) = Vout Rf Vin( Rf R1 + Rf Rf ) = Vout
  • 11. Vin( Rf R1 + 1) = Vout Av= Vout Vin = ( Rf R1 + 1) From above equation it is clear that the output voltage will be in phase with respect to input voltage, so it follows the same waveform as the input voltage, hence in non- inverting configuration the op-amp is called voltage follower circuit. Applications of an op-amp: (i) As an adder circuit: It is possible to apply more than one input signal to an inverting amplifier. This circuit will add all these input signals and produce their addition to output terminals. Such a circuit called as an Adder Circuit. The diagram for an adder circuit is shown in below figure: