3
Quad Capacitance
Capacitance of Schottky diode quads is measured using
an HP4271 LCR meter. This instrument eectively isolates
individual diode branches from the others, allowing
accurate capacitance measurement of each branch or
each diode. The conditions are: 20 mV R.M.S. voltage at 1
MHz. Avago denes this measurement as “CM”, and it is
equivalent to the capaci tance of the diode by itself. The
equivalent diagonal and adja cent capacitances can then
be calculated by the formulas given below.
In a quad, the diagonal capaci tance is the capacitance
between points A and B as shown in the gure below.
The diagonal capacitance is calculated using the follow-
ing formula
C
1
x C
2
C
3
x C
4
C
DIAGONAL
= _______ + _______
C
1
+ C
2
C
3
+ C
4
C
1
C
2
C
4
C
3
A
B
C
The equivalent adjacent capacitance is the capacitance
between points A and C in the gure below. This capaci-
tance is calculated using the following formula
1
C
ADJACENT
= C
1
+ ____________
1 1 1
–– + –– + ––
C
2
C
3
C
4
This information does not apply to cross-over quad
diodes.
SPICE Parameters
Parameter Units HSMS-280x
B
V
V75
C
J0
pF 1.6
E
G
eV 0.69
I
BV
A E-5
I
S
A 3.00E-08
N 1.08
R
S
Ω30
P
B
V 0.65
P
T
2
M 0.5
C
j
R
j
R
S
R
j
=
8.33 X 10
-5
nT
I
b
+ I
s
where
I
b
= externally applied bias current in amps
I
s
= saturation current (see table of SPICE parameters)
T
= temperature, K
n = ideality factor (see table of SPICE parameters)
Note:
To eectively model the packaged HSMS-280x product,
please refer to Application Note AN1124.
R
S
= series resistance (see Table of SPICE parameters)
C
j
= junction capacitance (see Table of SPICE parameters)
Linear Equivalent Circuit, Diode Chip
