measure of the time it takes for the Thus, for a given current and
Linear Equivalent Circuit
charge stored in the I layer to
decay, when forward bias is
replaced with reverse bias, to some resistance than the bulk diode.
junction capacitance, the epi
diode will always have a lower
In order to predict the perfor-
mance of the HMPP-3890 as a
switch, it is necessary to construct
a model which can then be used in
one of the several linear analysis
programs presently on the market.
predetermined value. This lifetime
can be short (35 to 200 nsec. for
epitaxial diodes) or it can be
relatively long (400 to 3000 nsec.
for bulk diodes). Lifetime has a
strong influence over a number of
PIN diode parameters, among
which are distortion and basic
diode behavior.
The thin epi diode, with its
physically small I region, can
easily be saturated (taken to the
point of minimum resistance) with Such a model is given in Figure 11,
very little current compared to the where RS + Rj is given in Figure 1
much larger bulk diode. While an
epi diode is well saturated at
currents around 10 mA, the bulk
diode may require upwards of
100 mA or more. Moreover, epi
diodes can achieve reasonable
values of resistance at currents of
and Cj is provided in Figure 2.
Careful examination of Figure 11
will reveal the fact that the
package parasitics (inductance
and capacitance) are much lower
for the MiniPak than they are for
leaded plastic packages such as
the SOT-23, SOT-323 or others.
This will permit the HMPP-389x
family to be used at higher fre-
quencies than its conventional
leaded counterparts.
To study the effect of lifetime on
diode behavior, we first define a
cutoff frequency fC = 1/τ. For short 1 mA or less, making them ideal
lifetime diodes, this cutoff fre-
quency can be as high as 30 MHz
while for our longer lifetime
diodes fC 400 KHz. At frequen-
cies which are ten times fC (or
more), a PIN diode does indeed
act like a current controlled
variable resistor. At frequencies
for battery operated applications.
Having compared the two basic
types of PIN diode, we will now
focus on the HMPP-3890 epi
diode.
20 fF
3
4
Given a thin epitaxial I region, the
diode designer can trade off the
30 fF
30 fF
2
1.1 nH
1
which are one tenth (or less) of fC, device’s total resistance (RS + Rj)
a PIN diode acts like an ordinary
PN junction diode. Finally, at
and junction capacitance (Cj) by
varying the diameter of the
20 fF
Single diode package (HMPP-3890)
0.1fC ≤ f ≤ 10fC, the behavior of the contact and I region. The
20 fF
diode is very complex. Suffice it to HMPP-3890 was designed with the
0.05 nH
0.5 nH
0.5 nH
0.5 nH
0.05 nH
mention that in this frequency
range, the diode can exhibit very
strong capacitive or inductive
reactance—it will not behave at
930 MHz cellular and RFID, the
1.8 GHz PCS and 2.45 GHz RFID
markets in mind. Combining the
low resistance shown in Figure 10
3
2
4
1
12 fF
30 fF
30 fF
0.05 nH
0.5 nH
0.05 nH
all like a resistor. However, at zero with a typical total capacitance of
20 fF
bias or under heavy forward bias,
all PIN diodes demonstrate very
high or very low impedance
(respectively) no matter what
their lifetime is.
0.27 pF, it forms the basis for high
performance, low cost switching
networks.
Anti-parallel diode package (HMPP-3892)
20 fF
0.05 nH
0.5 nH
0.5 nH
0.5 nH
0.05 nH
3
2
4
1
1000
12 fF
30 fF
30 fF
0.05 nH
HSMP-3880 Bulk PIN Diode
0.5 nH
0.05 nH
Diode Resistance vs. Forward Bias
If we look at the typical curves for
resistance vs. forward current for
bulk and epi diodes (see Figure
10), we see that they are very
different. Of course, these curves
apply only at frequencies > 10 fC.
One can see that the curve of
100
10
20 fF
Parallel diode package (HMPP-3895)
Figure 11. Linear Equivalent Circuit of the
MiniPak PIN Diode.
HMPP-389x
Epi PIN Diode
1
resistance vs. bias current for the
bulk diode is much higher than
that for the epi (switching) diode.
0.01
0.1
1
10
100
BIAS CURRENT (mA)
Figure 10. Resistance vs, Forward Bias.
5