EB212 Datasheet, PDF (2/8 Pages) Motorola, Inc – Using Data Sheet Impedances for RF LDMOS Devices

EB212
Freescale Semiconductor, Inc.
SINGLE–ENDED DEVICES
The data sheet impedance format for single- ended devices
is illustrated in Figure 3. The impedance data is taken by
tuning the fixture for optimum* performance and then
measuring the impedance at the device reference plane.
Figure 4 shows the format for in- band frequency - depend -
ent impedances that should be presented to the device for
optimal performance. This measured data can be turned into
an S1P file as shown in Figure 5.
Note: The imaginary portion of the measured impedance
data has been conjugated from the data shown in Figure 4.
The impedances are to be conjugated from the data sheet
to account for rotation of reference frames. This means that
when data is first acquired, the measured data represents
impedances as seen by looking into the input side RF launch
point. However, the data needs to be presented as looking into
the part for S_1,1 optimization. This is the reason for the
redirection of the arrows as well as the conjugation of the
measured impedance data.
* An optimum tuned fixture will be tuned for overall peak performance considering all major parameters:
input return loss (IRL), efficiency, P_1dB, linearity, maximum output power (P_out) and bandwidth.
Input
Matching
Network
Device
Under Test
Output
Matching
Network
Z _source
Z _load
Z_source = Test circuit impedance as measured from
gate to ground.
Z_load = Test circuit impedance as measured
from drain to ground.
Figure 3. Data Sheet Impedance Format for
Single–Ended Devices
f
MHz
1930
1960
1990
Z_source
Ω
1.43 - j5.01
1.51 - j4.88
1.56 - j4.93
Z_load
Ω
0.75 - j0.93
0.71 - j0.89
0.68 - j1.02
Z_source = Test circuit impedance as measured from
gate to ground.
Z_load = Test circuit impedance as measured
from drain to ground.
Input
Matching
Network
Device
Under Test
Output
Matching
Network
Z _source
Z _load
Figure 4. Optimal Impedances for an MRF19125
Test Fixture
! S11 (input) file
! Circuit
: MRF19125
! Author
: John Q. Designer
! Date
: 01/01/2003
! File
: mrf19125_zin.s1p
!
! File Format:
#
MHz Z
RE
IM
!
!
1930
1.43 5.01
1960
1.51 4.88
1990
1.56 4.93
!
! End of File
Figure 5. S1P File of Impedances to Be Used
at Input Block
2
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