MAX2620
10MHz to 1050MHz Integrated
RF Oscillator with Buffered Outputs
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resonators or high-Q inductors. Also, keep C5 and C17
(see the Typical Operating Circuit) as small a value as
possible while still maintaining desired frequency and
tuning range to maximize loaded Q.
There are many good references on the topic of oscilla-
tor design. An excellent reference is “The Oscillator
as a Reflection Amplifier, an Intuitive Approach to
Oscillator Design,” by John W. Boyles, Microwave
Journal, June 1986, pp. 83–98.
Output Matching Configuration
Both of the MAX2620’s outputs (OUT and OUT) are
open collectors. They need to be pulled up to the sup-
ply by external components. An easy approach to this
pull-up is a resistor. A 50Ω resistor value would inher-
ently match the output to a 50Ω system. The Typical
Operating Circuit shows OUT configured this way.
Alternatively, a choke pullup (Figure 1), yields greater
output power (approximately -8dBm at 900MHz).
When maximum power is required, use an inductor as
the supply pull-up, and match the inductor’s output
impedance to the desired system impedance. Table 1
in the Typical Operating Characteristics shows recom-
mended load impedance presented to OUT and OUT
for maximum power transfer. Using this data and stan-
dard matching-network synthesis techniques, a match-
ing network can be constructed that will optimize power
output into most load impedances. The value of the
inductor used for pullup should be used in the synthe-
sis of the matching network.
