ATF-521P8 Avago Technologies, ATF-521P8 Datasheet - Page 18

• Manufacturer Part Number: ATF-521P8
• Description: Atf-521p8 Gaas Field Effect
• Manufacturer: Avago Technologies

18
Figure 13. ATF-521P8 Matching.
As described previously the input impedance must be
matched to S11* in order to guarantee return loss great‑
er than 10 dB. A high pass network is chosen for this
match. The output is matched to Γ
pass network. The next step is to choose the proper DC
biasing conditions. From the data sheet, ATF‑521P8 pro‑
duces good linearity at a drain current of 200mA and
a drain to source voltage of 4.5V. Thus to construct the
active bias circuit described, the following parameters
are given:
Ids = 200 mA
I
V
V
V
V
Using equations 4, 5, 6, and 7, the biasing resistor values
are calculated in column 2 of table 1, and the actual val‑
ues used are listed in column 3.
RF
Figure 14. 2140 MHz Schematic.
R
dd
ds
g
be1
= 10 mA
in
= 0.62V
50 Ohm
= 4.5V
= 5 V
= 0.65 V
Match
Input
S11* = 0.89∠ -169
C1=1.2pF
C2=1.5nH
C3=4.7pF
C4=1µF
R4=61.9Ω
R2=383Ω
2PL
L2=12nH
R5=10Ω
L1=1.0nH
Γ
L
I
V
R
= 0.53∠ -176
g
Output
Match
I
50 Ohm
Q1
Q2
C2
ATF-521P8
2
R6=1.2Ω
2PL
V
V
be1
ds
L
R1=49.9Ω
R3=2.37Ω
+
7
with another high
C7=150pF
C6=.1µF
L3=39nH
C8=1.5pF
C5=1µF
+5V
L4=3.9nH
RF
Resistor
R1
R2
R3
R4
Table 1. Resistors for Active Bias.
The entire circuit schematic for a 2.14 GHz Tx driver
amplifier is shown below in Figure 14. Capacitors C4,
C5, and C6 are added as a low frequency bypass. These
terminate second order harmonics and help improve
linearity. Resistors R5 and R6 also help terminate low
frequencies, and can prevent resonant frequencies be‑
tween the two bypass capacitors.
Performance of ATF-521P8 at 2140 MHz
ATF‑521P8 delivers excellent performance in the WCD‑
MA frequency band. With a drain‑to‑source voltage of
4.5V and a drain current of 200 mA, this device has 16.5
dB of gain and 1.55 dB of noise figure as show in Figure
15.
ou t
Calculated
50Ω
385Ω
2.38Ω
62Ω
Actual
49.9Ω
383Ω
2.37Ω
61.9Ω