10MHz to 1050MHz Integrated

RF Oscillator with Buffered Outputs

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9

Example Calculation

According to the electrical model shown in Figure 5, the

resonance

frequency

can

be

calculated

as:

[Equation 1]

and is approximately:

[Equation 2]

Using the circuit model of Figure 5, the following exam-

ple describes the design of an oscillator centered at

900MHz.

Choose: L1 = 5nH ±10%

Q = 140

π x f x L1

age applied to the varactor is approximately at half-

supply (the center of the varactor’s capacitance range).

Assume the following values:

C3 = 2.7pF, and C4 = 1pF.

mance of the MAX2620 EV kit. Values of C3 and C4 are

the resonant circuit with excessive capacitance.

The varactor’s capacitance range should allow for the

desired tuning range. Across the tuning frequency

The MAX2620’s oscillator is optimized for low-phase-

noise operation. Achieving lowest phase-noise charac-

teristics requires the use of high-Q (quality factor)

components such as ceramic transmission-line type

resonators or high-Q inductors. Also, keep C5 and C17

R

g

fC

fC

n

m

=

















1

2

3

1

2

4

π

π

VCC1

TANK

FDBK

SHDN

8

7

6

5

OUT

VCC2

GND

OUT

1

2

3

4

10

Ω

51

Ω

0.01

µF

10

µH

0.01

µF

OUT

30pF

120pF

120pF

0.01

µF

0.01

µF

0.01

µF

27pF

0.01

µF

SHDN

OUT

MAX2620

X = STATEK AT-3004 10MHz

FUNDAMENTAL MODE CRYSTAL SURFACE MOUNT

Figure 4. 10MHz Crystal Oscillator

f

1

2

L1 C

+

C

x C

C

+ C

C

C

C

C

C

C

C

C

C

O

STRAY

17

D1

17

D1

6

3

03

4

04

3

03

4

04

=

+

+

+

(

(

)

+

+

+

















π