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 ac‑
curate 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 equiva‑
lent to the capacitance of the diode by itself. The equiva‑
lent diagonal and adjacent capaci‑tances can then be cal‑
culated by the formulas given below.
In a quad, the diagonal capacitance is the capacitance be‑
tween points A and B as shown in the gure below. The
diagonal capacitance is calculated using the following
formula
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 effectively model the packaged HSMS-281x 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 Model Diode Chip
ESD WARNING:
Handling Precautions Should Be Taken To Avoid Static Discharge.
SPICE Parameters
Parameter Units HSMS-281x
B
V
V 25
C
J0
pF 1.1
E
G
eV 0.69
I
BV
A E‑5
I
S
A 4.8E‑9
N 1.08
R
S
Ω 10
P
B
V 0.65
P
T
2
M 0.5
C
1
x C
2
C
3
x C
4
C
DIAGONAL
= _______ + _______
C
1
+ C
2
C
3
+ C
4
1
C
ADJACENT
= C
1
+ ____________
1 1 1
–– + –– + ––
C
2
C
3
C
4
R
j
=
8.33 X 10
-5
nT
I
b
+ I
s
C
1
x C
2
C
3
x C
4
C
DIAGONAL
= _______ + _______
C
1
+ C
2
C
3
+ C
4
1
C
ADJACENT
= C
1
+ ____________
1 1 1
–– + –– + ––
C
2
C
3
C
4
R
j
=
8.33 X 10
-5
nT
I
b
+ I
s
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
This information does not apply to cross‑over quad di‑
odes.
