Opamp
1. CHARACTERISTICS AND PARAMETERS OF
OPERATIONAL AMPLIFIERS
The characteristics of an ideal operational amplifier are described first, and the characteristics and performance limitations of a practical operational amplifier are described next. There is a section on classification of operational amplifiers and some notes on how to select an operational amplifier for an application.
1.1 IDEAL OPERATIONAL AMPLIFIER
1.1.1 Properties of An Ideal Operational Amplifier
The characteristics or the properties of an ideal operational amplifier are:
i. Infinite Open Loop Gain, ii. Infinite Input Impedance, iii. Zero Output Impedance, iv. Infinite Bandwidth,
v. Zero Output Offset, and vi. Zero Noise Contribution.
The opamp, an abbreviation for the operational amplifier, is the most important linear IC. The circuit symbol of an opamp shown in Fig. 1.1. The three terminals are: the non-inverting input terminal, the inverting input terminal and the output terminal. The details of power supply are not shown in a circuit symbol.
1.1.2 Infinite Open Loop Gain
From Fig.1.1, it is found that vo = - Ao × vi, where `Ao' is known as the open-loop gain of the opamp. Let vo be -10 Volts, and Ao be 105. Then vi is 100 :V. Here
2
the input voltage is very small compared to the output voltage. If Ao is very large, vi is negligibly small for a finite vo. For the ideal opamp, Ao is taken to be infinite in value. That means, for an ideal opamp vi = 0 for a finite vo. Typical values of Ao range from 20,000 in low-grade consumer audio-range opamps to more than 2,000,000 in premium grade opamps ( typically 200,000 to 300,000).
The first property of an ideal opamp: Open Loop Gain Ao = infinity.
1.1.3 Infinite Input Impedance and Zero Output Impedance
An ideal opamp has an infinite input impedance and zero output impedance. The sketch in Fig. 1.2 is used to illustrate these properties. From Fig. 1.2, it can be seen that iin is zero if Rin is equal to infinity.
The
OPERATIONAL AMPLIFIERS
The characteristics of an ideal operational amplifier are described first, and the characteristics and performance limitations of a practical operational amplifier are described next. There is a section on classification of operational amplifiers and some notes on how to select an operational amplifier for an application.
1.1 IDEAL OPERATIONAL AMPLIFIER
1.1.1 Properties of An Ideal Operational Amplifier
The characteristics or the properties of an ideal operational amplifier are:
i. Infinite Open Loop Gain, ii. Infinite Input Impedance, iii. Zero Output Impedance, iv. Infinite Bandwidth,
v. Zero Output Offset, and vi. Zero Noise Contribution.
The opamp, an abbreviation for the operational amplifier, is the most important linear IC. The circuit symbol of an opamp shown in Fig. 1.1. The three terminals are: the non-inverting input terminal, the inverting input terminal and the output terminal. The details of power supply are not shown in a circuit symbol.
1.1.2 Infinite Open Loop Gain
From Fig.1.1, it is found that vo = - Ao × vi, where `Ao' is known as the open-loop gain of the opamp. Let vo be -10 Volts, and Ao be 105. Then vi is 100 :V. Here
2
the input voltage is very small compared to the output voltage. If Ao is very large, vi is negligibly small for a finite vo. For the ideal opamp, Ao is taken to be infinite in value. That means, for an ideal opamp vi = 0 for a finite vo. Typical values of Ao range from 20,000 in low-grade consumer audio-range opamps to more than 2,000,000 in premium grade opamps ( typically 200,000 to 300,000).
The first property of an ideal opamp: Open Loop Gain Ao = infinity.
1.1.3 Infinite Input Impedance and Zero Output Impedance
An ideal opamp has an infinite input impedance and zero output impedance. The sketch in Fig. 1.2 is used to illustrate these properties. From Fig. 1.2, it can be seen that iin is zero if Rin is equal to infinity.
The