Understanding Operational Amplifier Specifications


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Introduction

The term operational amplifier, abbreviated op amp, was coined in
the 1940s to refer to a special kind of amplifier that, by proper
selection of external components, can be configured to perform a
variety of mathematical operations. Early op amps were made
from vacuum tubes consuming lots of space and energy. Later op
amps were made smaller by implementing them with discrete
transistors. Today, op amps are monolithic integrated circuits,
highly efficient and cost effective.


Ideal Op Amp Model

The Thevenin amplifier model shown in Figure 1 is redrawn in
Figure 2 showing standard op amp notation. An op amp is a
differential to single-ended amplifier. It amplifies the voltage
difference, Vd = Vp - Vn, on the input port and produces a voltage,
VO, on the output port that is referenced to ground.


Non-Inverting Amplifier

An ideal op amp by itself is not a very useful device since any
finite input signal would result in infinite output. By connecting
external components around the ideal op amp, we can construct
useful amplifier circuits. Figure 4 shows a basic op amp circuit, the
non-inverting amplifier. The triangular gain block symbol is used to
represent an ideal op amp. The input terminal marked with a +
(Vp) is called the non-inverting input; – (Vn) marks the inverting
input.


Inverting Amplifier

another useful basic op amp circuit, the inverting
amplifier. The triangular gain block symbol is again used to
represent an ideal op amp. The input terminal, + (Vp), is called the
non-inverting input, whereas – (Vn) marks the inverting input. It is
similar to the non-inverting circuit shown in Figure 4 except that
now the signal is applied to the inverting terminal via R1 and the
non-inverting terminal is grounded.