Radio Frequency Integrated Circuit Design - Webs

24 Radio Frequency Integrated Circuit Design
Figure 2.9 Distorted output waveforms: (a) input; (b) output, clipping; and (c) output, bias
wrong.
Symmetrical saturation as shown in Figure 2.8(b) can be modeled with
odd order terms; for example,
y = x − 1 3
x
10
(2.41)
looks like Figure 2.10. In another example, an exponential nonlinearity as shown
in Figure 2.8(a) has the form
x +
x 2
2!
+ x 3
3!
+ . . . (2.42)
which contains both even and odd power terms because it does not have
symmetry about the y-axis. Real circuits will have more complex power series
expansions.
One common way of characterizing the linearity of a circuit is called the
two-tone test. In this test, an input consisting of two sine waves is applied to
the circuit.
Figure 2.10 Example of output or input nonlinearity with first- and third-order terms.