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15-26
AN0014
15
Copyright 1997-2002 RF Micro Devices, Inc.
Equation 5 may be substituted into Equation 1 and solved for ICC to get:
Eq. 6
Equation 6 may be differentiated with respect to temperature to get an expression which is useful to observe the effect of
the bias resistor (and supply voltage) selected by the user:
Eq. 7
For example, an NBB-400 biased from a 5V supply (VCC) using a 22Ω resistor (RCC) will exhibit the following current
change with respect to temperature,
Eq. 8
which translates into a variation of 14mA over the temperature range from -40°C to +85°C. By comparison, if a 12V sup-
ply rail is with a 162
Ω bias resistor, then a change in current with respect to temperature reduces to 0.016mA/°C. This
translates into a current variation of only 2.2mA over the same operating temperature range.
I
CC
V
CC
δV
D
δT
----------
TT
O
–
()
×
–
R
BIAS
δV
D
δI
CC
------------
+
------------------------------------------------------------
=
δI
CC
δT
------------
δV
D
δT
----------
–
R
BIAS
δV
D
δI
CC
------------
+
--------------------------------------
=
δI
CC
δT
------------
2.8
–
()
–
22
4
+
()
--------------------
0.108mA
°C
⁄
==
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