MAX2 6 2 0 Eva lu a t io n Kit
•
HP8561E spectrum analyzer, or equivalent high-
sensitivity spectrum analyzer with approximately
3GHz fre q ue nc y ra ng e . Conta c t the ins trume nt
manufacturer for information regarding phase-noise
measurement capabilities.
6) Se t a nothe r ma rke r to me a s ure the d iffe re nc e
between this peak and the signal level at 25kHz off-
set from the peak. (Phase noise can be observed at
frequencies other than 25kHz offset.)
7) Under the Marker function, select marker noise and
turn it on. This automatically scales the spectrum
analyzer’s output to take into account the resolution
BW filter’s non-ideal characteristics. If your spectrum
analyzer does not offer this feature, contact the man-
ufacturer for proper scaling for noise measurements.
•
Digital multimeter (DMM) to monitor DC supply and
VCONT, if desired
•
•
Male SMA 50Ω terminator
Network analyzer such as HP8753D (required only
if additional device characterization for oscillator
tank design at other frequencies is desired)
8) Verify that the resolution bandwidth is 1kHz.
9) Verify that the video bandwidth is 1kHz.
____________Co n n e c t io n s a n d S e t u p
1) Verify that the shunt on jumper SHDN is installed
10) Read the measurement directly from the screen.
Phase noise will be about -110dBc/Hz. In some envi-
ronments that have ambient pulse noise, this mea-
surement may be difficult to achieve without addi-
tional shielding or the use of a shielded enclosure.
b e twe e n p ins 1 a nd 2 (SHDN = V ). Pla c ing
CC
the shunt between pins 2 and 3 (SHDN = GND)
puts the MAX2620 into low-current shutdown mode.
2) Connect the spectrum analyzer to either OUT or
OUT. Connect a 50Ω terminator to the output (OUT
or OUT) not connected to the spectrum analyzer.
_____________________________Ou t p u t s
Evluates:MAX620
The MAX2620 EV kit is assembled with OUT matched
to 50Ω (at approximately 900MHz) using L3 and C13.
OUT is resistively pulled up to the supply with a 51Ω
resistor, R5. R5 provides a simple broadband 50Ω out-
put match but offers less output power than OUT. The
EV kit provides additional component pads at R4, C14,
L4, and C11 to accommodate any output match config-
uration for OUT and OUT. Refer to the Output Matching
Configuration section in the MAX2620 data sheet for
more information.
3) Connect a +2.7V to +5.25V supply across V
to
CC
GND. V should be the most positive terminal.
CC
4) Connect the tuning voltage supply to either VCONT
or JU1. This supply should be positive when refer-
enced to ground.
____________________________An a lys is
1) Using the spectrum analyzer, observe the voltage-
controlled oscillator’s output. With 1.5V applied to
VCONT, the fundamental output frequency will be
ne a r 900MHz. The outp ut p owe r le ve l will b e
approximately -2dBm at OUT, or -12.5dBm at OUT.
Varying the voltage applied to VCONT between 0V
___________Re s o n a t o r a n d Va ra c t o r
The resonator tank circuit is critical in determining VCO
performance. It typically contains a varactor (voltage-
variable capacitance) for voltage-tuning the center fre-
quency. For best performance, use high-Q components
and choose values carefully.
and V
changes the fundamental oscillation fre-
CC
quency. (Increasing the voltage applied to VCONT
increases the frequency, and vice versa.) The typi-
cal tuning range is a 30MHz band centered near
900MHz with VCONT between 0.5V and 3V. To
avoid damaging the varactor, do not apply voltages
greater than 15V to VCONT. (The varactor on the
EV kit board has a 15V breakdown specification.)
The external resonant circuit on the MAX2620 EV kit
has been designed to operate near 900MHz. To syn-
the s ize the c omp one nt va lue s for othe r fre q ue nc y
ranges, use the following procedure.
On the EV kit, C3 and C4 are feedback capacitors that
set the oscillator’s negative resistance and impedance.
Their values have been chosen to provide adequate
performance over a 650MHz to 1050MHz frequency
range. To optimize the values of these components for
a specific application, refer to the Feedback Capacitors
section in the MAX2620 data sheet.
2) Allow the oscillator to operate for about 5 minutes
to thermally stabilize the frequency. Since the fre-
quency is not phase-locked to a reference, this
minimizes frequency drift and measurement error.
3) Center the fundamental on the spectrum analyzer
and set the frequency span to 100kHz.
Measure the MAX2620 TANK pin’s input impedance
with feedback capacitors C3 and C4 but without the
resonant circuit. This measurement takes into account
parasitic circuit elements that are specific to board lay-
4) Set the spectrum analyzer for single sweep. This
minimizes errors due to oscillator frequency drift.
5) Set the marker on the waveform’s peak.
2
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