AN0014 Ver la hoja de datos (PDF) - RF Micro Devices
Número de pieza
componentes Descripción
Lista de partido
AN0014 Datasheet PDF : 4 Pages
| |||
AN0014
PREDUCTION = 20 × LOG(---2---R---2-B--R-I--A-B---S-I--A+---S--5---0----)
Eq. 4
In the case of the NBB-300 with a bias resistor of 120Ω (VCC=10V), the reduction in power delivered to a 50Ω load is
1.64 dB.
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 (VD) varies as a function of both the bias current (ICC) and the temperature. The vari-
ation of device voltage versus current is supplied on each data sheet. From this data, a coefficient may be calculated for
the change in VD versus current (see Figure 4). Notice that all coefficients are positive, indicating that the device voltage
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, RBIAS,
requires selecting a higher voltage supply (VCC) to maintain the desired bias current (ICC). The current steering circuit
(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 (VD) versus amplifier current (ICC).
The data is calculated from the plot provided with each datasheet. The positive coefficient indicates
that the device voltage increases with increasing current.)
NBB Amplifier Model Number
Typical Device Voltage Variation with Current,
δVD/δICC (in V/A)
NBB-300
+4
NBB-301
NBB-400
+4
NBB-401
NBB-410
+7
NBB-500
+3
Device voltage (VD) decreases with increasing temperature as shown in Figure 5. An average rate of change of the
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.
VD ( I C C,
T)
=
VO
+
δ-δ---I-V-C---D-C-
×
ICC
+
δ--δ--V--T--D-
×
(T
–
TO)
Eq. 5
15
Table 2. Summary of the dependence of the amplifier output voltage (VD) versus temperature.
The coefficient of the change in device voltage (VD) versus ambient temperature is calculated from the
tabular data. The negative coefficient indicates that the device voltage decreases with increasing current.
Model
Number
Amplifier
Current (mA)
Device Voltage (VD) versus Temperature
-45°C
+25°C
+85°C
Temp. Coef.
(mV/°C)
NBB-300
NBB-301
50
4.03
3.86
3.70
-2.75
NBB-400
NBB-401
50
4.09
3.90
3.74
-2.80
NBB-410
65
4.19
4.00
3.88
-2.85
NBB-500
35
4.12
3.94
3.78
-2.70
Copyright 1997-2002 RF Micro Devices, Inc.
15-25
Share Link: 