Radio Frequency Integrated Circuit Design - Webs

LNA Design
In the special case where there is no emitter degeneration, the above
expression can be simplified to
v IP3 = 2√ 2vT
Example 6.11 Linearity Calculations in Common-Emitter Amplifier
175
(6.86)
For a common-emitter amplifier with no degeneration, if the input is assumed
to be composed of two sine waves of amplitude A 1 and A 2, compute the relevant
frequency components to graph the fundamental and third-order products and
predict what the IIP3 point will be. Assume that ICA = 1mAandv T =
25 mV.
Solution
The first step is to calculate the coefficients k 1, k 2, and k 3 for the power series
expansion from (6.83) as
k 3 =� 1
2I 2
1 1
k 1 = = = 0.04
R E + re 0 + 25
k 2 = 1 re 1
2IC� R E + re��RE + re� 2
= 1
2IC
= 0.8
re 3 =
(R E + re )
re
R E + r C� e� 2
=� 3� re
R E + re� 2
re
− 2�
=�
25 3�0 + 25� 2
1
2 � 1m
25
(0 + 25) 3
− 1
3I 2
re 1
R E + r C� e���R E + re� 3
R E + re��� 1
1 1
= [3 − 2]�6 � 1m 2��0 + 25� 3
= 10.667
resulting in an expression for current as follows:
6I 2
C�� 1
R E + re� 3
− 2� 25 1 1
0 + 25���6 � 1m 2��0 + 25� 3