Datasheet

Application Note No. 058
Predicting Distortion in PIN-Diode Switches
Application Note 5 Rev. 2.1, 2006-10-20
Figure 3 Intercept point
From a given intercept point (IP
3
) and input power the inter-modulation distortion products can be easily
determined (1). A PIN-diode is expected to exhibit the same distortion effects when the input level changes.
However, as illustrated in Figure 3, above a certain power level the distortion in PIN-diode switches rises much
more rapidly than predicted.
In the following we will relate the intermodulation distortion to physical parameters of the PIN-diode and show the
limits of the basic
IP
3
concept.
1.2 Third-Order Distortion in Forward-Biased PIN-Diodes
Origin of Distortion
If the PIN-diode is forward biased, as for example it is the case in the “on”-state of an antenna switch (Figure 6),
electrons and holes are injected into the instrinsic region. Under this condition the steady state forward resistance
of the instrinsic region is given by
Figure 4 Formula (3)
Where W denotes the width of the intrinsic zone, τ the carrier lifetime and µ
n
and µ
p
appropriate mobilities.
AN058_OutputPower_InputPower.vs
d
0 10203040
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
P
max
output power [dBm]
input power [dBm]
P
0
P
IM3
intercept point IP3
Theoretical power dependence of fundamental (P
0
) and third-order inter modulation product
(P
IM3
). Actually, above a certain input power P
max
, inter-modulation of a PIN-diode shows a
significant increase (dashed) and therefore cannot be calculated from the intercept point IP
3
.
AN058_formula_3.vsd
(3)
I
W
fr
pn
f
)(
)0(
2
τµµ +
==