Page 54 - Op Amps Design, Applications, and Troubleshooting

Amplifier Fundamentals 37

There are no units for gain; it is simply a ratio of two numbers. It is also convenient
to express a gain ratio in its equivalent decibel (dB) form. The conversion equa-
tions are listed below:

The voltage gain of 2.5 on the amplifier discussed in the prior example could be
expressed in decibels by applying Equation (2.2):

Thus, we see that an amplifier with a voltage gain of 2.5 also has a voltage
gain of 7.96 dB. It should be noted that, technically, the equations cited previously
for calculating voltage and current gains in their decibel form require that the
input and output impedances be equal. In practice, this is rarely the case. Despite
this known error, it is common in the industry to calculate and express the gains as
described.
You should also be reminded that fractional gains (i.e., losses) are expressed
as negative decibel values.

2.1.2 Frequency Response

The frequency response of an amplifier describes how its amplification varies
with changes in frequency. We often communicate the frequency response of an
amplifier in graphical form. Figure 2.1 shows a typical frequency response curve.
The vertical axis indicates the amplifier's voltage gain expressed in decibels.
The horizontal axis shows the input frequency range.