ATF-521P8 Datasheet, PDF (18/23 Pages) List of Unclassifed Manufacturers – High Linearity Enhancement Mode Pseudomorphic HEMT in 2x2 mm2 LPCC Package

Input
Match
50 Ohm
2PL
Output
Match
50 Ohm
S11* = 0.89∠ -169 Γ_L = 0.53∠ -176
Figure 13. ATF-521P8 Matching.
As described previously the input impedance must
be matched to S11* in order to guarantee return loss
greater than 10 dB. A high pass network is chosen for
this match. The output is matched to Γ_L with another
high pass network. The next step is to choose the
proper DC biasing conditions. From the data sheet,
ATF-521P8 produces 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_R = 10 mA
V_dd = 5 V
V_ds = 4.5V
V_g = 0.62V
V_be1 = 0.65 V
Using equations 4, 5, 6, and 7, the biasing resistor values
are calculated in column 2 of table 1, and the actual
values used are listed in column 3.
Table 1. Resistors for Active Bias.
Resistor
Calculated
Actual
R1
50Ω
49.9Ω
R2
385Ω
383Ω
R3
2.38Ω
2.37Ω
R4
62Ω
61.9Ω
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
between the two bypass capacitors.
Performance of ATF-521P8 at 2140 MHz
ATF-521P8 delivers excellent performance in the
WCDMA 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.
I_R
R2=383Ω
Vg
R4=61.9Ω
C4=1µF
R1=49.9Ω
Q1
Vbe1+
+5V
C5=1µF
Vds
Q2
R3=2.37Ω
IC2
C6=.1µF
C3=4.7pF ^R5=10Ω
R6=1.2Ω
C7=150pF
L2=12nH
L3=39nH
RF_in
C1=1.2pF
L1=1.0nH _{2 2PL 7}
C8=1.5pF
RF_out
C2=1.5nH
ATF-521P8
L4=3.9nH
Figure 14. 2140 MHz Schematic.
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