Radio Frequency Integrated Circuit Design - Webs

Voltage-Controlled Oscillators
Figure 8.36 Conceptual figure to show the effect of nonlinear mixing.
The magnitude of this noise can be estimated with the following analysis.
The analysis begins by considering a transistor being driven by a large sinusoidal
voltage, as shown in Figure 8.37, and a small noise source. It is assumed that
the transistor can be described by the following power series:
iC ≈ IC� 1 + v i
vT
1
+ 2� vi vT� 2
+ 1
6� vi vT� 3
...+ 1
n !� vi vT� n
�
= k o + k 1vi + k 2v 2 i + ...+ k n v n i (8.96)
Note that truncation after only a few terms is not possible due to the fact
that the oscillation tone is much greater than vT . Now let us assume that the
input is given by
293
vi = vo cos (�o t) + vn cos (�n t) (8.97)
Figure 8.37 A transistor driven by a large sinusoid in the presence of noise.