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MAX2620E_D

10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs

Maxim Integrated 

10MHz to 1050MHz Integrated

RF Oscillator with Buffered Outputs

Keeping the resonant tank circuit’s real component less

than one-half the magnitude of the negative real com-

ponent ensures that oscillations will start. After start-up,

the oscillator’s negative resistance decreases, primarily

due to gain compression, and reaches equilibrium with

the real component (the circuit losses) in the resonant

tank circuit. Making the resonant tank circuit reactance

tunable (e.g., through use of a varactor diode) allows

for tuneability of the oscillation frequency, as long as

the oscillator exhibits negative resistance over the

desired tuning range. See Figures 3 and 4.

The negative resistance of the MAX2620 TANK pin can

be optimized at the desired oscillator frequency by

proper selection of feedback capacitors C3 and C4.

For example, the one-port characteristics of the device

are given as a plot of 1/S11 in the Typical Operating

Characteristics. 1/S11 is used because it maps inside

the unit circle Smith chart when the device exhibits

negative resistance (reflection gain).

VTUNE

1kΩ

C17

33pF

D1

VCC

10Ω

1000pF

VCC

1000pF

10µH

27pF

C5

150pF

C6

L1

33pH 2.2µH

C3

270pF

C4

270pF

1

VCC1

8

OUT

MAX2620

2

7

TANK

VCC2

3

FDBK

6

GND

4

SHDN

5

OUT

SHDN

0.01µF

VCC

1000pF

0.01µF

51Ω

1000pF

OUT TO

MIXER

OUT TO

SYNTHESIZER

D1 = SMV1200-155 DUAL VARACTOR

VCC

Figure 3. 10MHz VCO LC Resonator

8 _______________________________________________________________________________________

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