The Ideal Operational Amplifier

In order to introduce operational amplifier circuitry, we will use an ideal model of the operational amplifier to simplify the mathematics involved in deriving gain expressions, etc., for the circuits presented. With this understanding as a basis, it will be convenient to describe the properties of the real devices themselves in later sections, and finally to investigate circuits utilizing practical operational amplifiers.

To begin the presentation of operational amplifier circuitry, then, it is necessary first of all to define the properties of a mythical “perfect” operational amplifier. The model of an ideal operational amplifier

Defining the Ideal Operational Amplifier-       

1.    Gain: The primary function of an amplifier is to amplify, so the more gain the better. It can always be reduced with external circuitry, so we assume gain to be infinite.

2.  Input Impedance: Input impedance is assumed to be infinite. This is so the driving source won’t be affected by power being drawn by the ideal operational amplifier.

3.   Output Impedance: The output impedance of the ideal operational amplifier is assumed to be zero. It then can supply as much current as necessary to the load being driven.

4.  Response Time: The output must occur at the same time as the inverting input so the response time is assumed to be zero. Phase shift will be 180.  Frequency response will be flat and bandwidth infinite because AC will be simply a rapidly varying DC level to the ideal amplifier.

5. Offset: The amplifier output will be zero when a zero signal appears between the inverting and non-inverting inputs.