TQ9222 データシートの表示（PDF） - TriQuint Semiconductor
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TQ9222 Datasheet PDF : 16 Pages
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TQ9222
Data Sheet
Calculation of Nominal L Value
The node between the LO buffer amplifier and the mixer FET is
brought out to Pin 7 (L_tune) and connected to a shunt inductor
to AC ground. This inductor is selected to resonate with internal
capacitance at the L0 frequency in order to suppress out-of-
band gain and improve noise performance.
The internal capacitance of the LO amplifier output plus the
stray capacitance on the board surrounding Pin 7 is
approximately 1.8 pF. The inductor is selected to resonate with
the total capacitance at the LO frequency using the following
equation:
L=
1
C(2Π f )2
, where ⋅C
=
1.5 pF
but must be confirmed with measurements on a board
approximating the final layout.
Measuring the LO Frequency Response
The frequency response of the LO driver amplifier can be
measured using a semi-rigid probe (see Fig. 6) and a network
analyzer.
Connect port 1 to the LO input (Pin 8) of the TQ9222 with the
source power set to deliver -7 dBm. Connect the coaxial probe
to Port 2 and place the probe tip approximately 0.1 inch away
from either Pin 7 or the inductor.
Network
Analyzer
Port 1 Port 2
Probe
7
8
TQ9222
-30
-32
-34
-36
-38
-40
-42
700 800 900 1000 1100 1200
Frequency (MHz)
Fig 6. LO Buffer Amplifier Tuning
If the calculated shunt inductor (L2) is not a standard value, the
AC ground, implemented with C3, can be slide along the
transmission line to adjust for the right inductance (see Fig 7).
Once this is completed, the peak of the response should be
centered at the center of the LO frequency band.
Ground
7
Placement of inductor
will adjust between
standard values
Fig 7. Adjusting AC Ground
Mixer IF Port
The Mixer IF output is an "open-drain" configuration, allowing for
flexibility in efficient matching to various filter types and at
various IF frequencies.
For evaluation of the LNA and mixer, it is usually necessary to
impedance match the IF port to the 50Ω test systems. When
verifying or adjusting the matching circuit on the prototype circuit
board, the LO drive should be injected at pin 8 for the Low Band
and pin 5 for the High Band at the nominal power level of -7
dBm, since the LO level does have an impact on the IF port
impedance.
There are several networks that can be used to properly match
the IF port to the SAW or crystal IF filter. The mixer supply
voltage is applied through the IF port, so the matching circuit
topology must contain either an RF choke or shunt inductor. An
extra DC blocking capacitor is not necessary if the output will be
attached directly to a SAW or crystal bandpass filters.
Figure 8 shows the IF matching network for the low band. A
shunt L, series C, shunt C, is the simplest and requires the
fewest components. The only difference with the high band is
the series capacitor value of 10pF as opposed to 8.2pF. DC
current can be easily injected through the shunt inductor and the
series C provides a DC block, if needed. The shunt C, is used
to reduce the LO leakage.
10
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