Radio Frequency Integrated Circuit Design - Webs

28 Radio Frequency Integrated Circuit Design
Figure 2.12 Plot of input output power of fundamental and IM3 versus input power.
IM3 = 3
4 k 3v 3 i
(2.51)
Note that for small vi , the fundamental rises linearly (20 dB/decade) and
that the IM3 terms rise as the cube of the input (60 dB/decade). A theoretical
voltage at which these two tones will be equal can be defined:
This can be solved for v IP3:
3
4 k 3v 3 IP3
= 1 (2.52)
k 1v IP3
v IP3 = 2 √ k 1
3k 3
(2.53)
Note that (2.53) gives the input voltage at the third-order intercept point.
The input power at this point is called the input third-order intercept point
(IIP3). If IP3 is specified at the output, it is called the output third-order intercept
point (OIP3).