NBB-301 RFMD [RF Micro Devices], NBB-301 Datasheet - Page 3

• Manufacturer Part Number: NBB-301
• Description: Bias Scheme for NBB-Series Amplifiers
• Manufacturer: RFMD [RF Micro Devices]

In the case of the NBB-300 with a bias resistor of 120
1.64dB.
In order to prevent loading of the output of the amplifier, a reactance of five to 10 times the characteristic impedance is
desired. At upper microwave frequencies where lumped element chokes are not available, a microstrip bypass circuit is
desirable. Such as choke circuit would consist of a 90° high-impedance line with a short-circuit radial stub. If the toler-
ances are an issue with the short-circuit stub, a short circuit may be provided from a suitable capacitor instead. In such
instances the self-resonance frequency of the capacitor must be considered.
Bias Resistor Selection
The output voltage of the amplifier (V
ation of device voltage versus current is supplied on each data sheet. From this data, a coefficient may be calculated for
the change in V
increases with increasing current. A large bias resistor is desirable because it reduces the variation in bias current,
reducing the change in important amplifier parameters such as P1dB and IP3. Selecting a large bias resistor, R
requires selecting a higher voltage supply (V
(see Figure 3) provides a steady current and minimizes variations in amplifier parameters as well.
Table 1. Summary of the coefficient of the change in device voltage (V
Device voltage (V
device voltage versus temperature is calculated and provided in the table. The device voltage can be expressed as a
function both current and temperature as follows.
Table 2. Summary of the dependence of the amplifier output voltage (V
NBB-300
NBB-301
NBB-400
NBB-401
NBB-410
NBB-500
NBB-300
NBB-301
NBB-400
NBB-401
NBB-410
NBB-500
Number
NBB Amplifier Model Number
Model
The data is calculated from the plot provided with each datasheet. The positive coefficient indicates
that the device voltage increases with increasing current.)
The coefficient of the change in device voltage (V
tabular data. The negative coefficient indicates that the device voltage decreases with increasing current.
P
V
REDUCTION
D
I
CC
D
T
versus current (see Figure 4). Notice that all coefficients are positive, indicating that the device voltage
Current (mA)
D
) decreases with increasing temperature as shown in Figure 5. An average rate of change of the
Amplifier
=
V
=
50
50
65
35
O
20 LOG
+


----------- -
I
V
CC
D
Copyright 1997-2002 RF Micro Devices, Inc.


Device Voltage (V


D
---------------------------------- -
) varies as a function of both the bias current (I
-45°C
I
2R
4.03
4.09
4.19
4.12
CC
2R
Typical Device Voltage Variation with Current,
BIAS
+
BIAS


CC
--------- -
+
V
) to maintain the desired bias current (I
T
50
D




+25°C
D
T T
3.86
3.90
4.00
3.94
) versus Temperature
D
(V
–
) versus ambient temperature is calculated from the
V
CC
D
O
/ I
=10V), the reduction in power delivered to a 50
CC
+4
+4
+7
+3
(in V/A)
+85°C
3.70
3.74
3.88
3.78
D
D
) versus amplifier current (I
) versus temperature.
Temp. Coef.
CC
(mV/°C)
) and the temperature. The vari-
CC
-2.75
-2.80
-2.85
-2.70
). The current steering circuit
AN0014
CC
).
load is
15-25
Eq. 4
Eq. 5
BIAS
,
15