Preliminary
3-39
RF3322
Rev A2 010518
3
Set signal generator to:
•45MHz,
•
-13.0dBm output power,
•
0dB offset.
Connect 50MHz coaxial filter to output, then to output
cable.
Zero and calibrate the power meter. Connect signal
generator to power meter and set offset on signal gen-
erator until power meter reads -13.0dBm. Make sure
power meter reads the same (±0.2 dBm) with modula-
tion enabled and disabled to verify power meter is
measuring average power rather than peak power.
Check positioning of the jumpers on the board. Refer
to the PCBA section of this application note to verify
proper positions. Connect the output of the signal gen-
erator to J2: RFIN of the PCB. Connect J7: RFOUT to
the power meter. Connect one end of the serial cable
into the computer and the other end into P1 of the
PCB. Connect +5.0VDC into VCC and ground into GND.
Turn on the DC power and turn on RF and modulation
from the signal generator. Set the GCW to 58 and
make sure TX Enable is checked. Measure and record
channel power at RFOUT using the power meter
(accounting for 75/50 conversion losses). Connect
RFOUT to spectrum analyzer and adjust offset of the
spectrum analyzer until the channel power displayed
by the spectrum analyzer is equal to the channel power
recorded in the previous step (Channel bandwidth=
200kHz). Now use the spectrum analyzer to measure
relative ACP (this way the uncertainties in the spec-
trum analyzer power measurement are immaterial).
The ACP is measured in 200kHz channel bandwidths
at a 220kHz offset (i.e., from 20kHz to 220kHz outside
the channel). As you increase the input power, you will
notice a degradation of the ACP upper and lower
bands. Datasheet performance is measured at an
input level of 34dBmV.
Transmit Turn-On and Turn-Off Transients
UseanArbitrary Waveform Generator settoa3V
square wave, 5% duty cycle, 120 Hz as the input to the
transmit enable. Set a signal generator to 10MHz,
-13.0dbm output power, 0dB offset. Connect output of
the signal generator to J2, RFIN of the PCB. Remove
the TXEN jumper and connect the arbitrary wave gen-
erator square wave output to the center pin of the
TXEN 3-pin header. Connect the output of the evalua-
tion board to the oscilloscope (channel 1). Connect the
TXEN signal from the arbitrary wave generator to
channel 2 of the oscilloscope and trigger off of the ris-
ingedge. As the TXENlineissent, theoscilloscope
will trigger and capture the pulsed RFOUT signal. This
will be displayed on the oscilloscope. Measure the
amount of time between 90% of the TXEN turn-on to
where the output signal reaches 90% of full turn-on.
This is defined as the transmit turn-on time.
To measure the transient pulse, replace the signal gen-
erator input with a 50
Ω terminator and repeat the steps
above. Measure the size of the transient. This can be
affected by the CRAMP capacitor (C7), and the output
balun and capacitor values around the balun. Larger
values of CRAMP will decrease the transient voltage
and increase the TX enable time.
PCB Layout Considerations
The RF3322 Evaluation board can be used as a guide
for the layout in your application. Care should be taken
in laying out the RF3322 in other applications. The
RF3322 will have similar results if the following guide-
lines are taken into consideration:
•
Make sure underside of package is soldered to a
good ground on the PCB.
•
Move C2, C9, C10, and C11 as close to T1 as pos-
sible.
•
Keep input and output traces as short as possible.
•
Ensure a good ground plane by using multiple vias
to the ground plane.
•
Use a low noise power supply along with decou-
pling capacitors.
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