MAX2620E Ver la hoja de datos (PDF) - Maxim Integrated
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MAX2620E Datasheet PDF : 11 Pages
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10MHz to 1050MHz Integrated
RF Oscillator with Buffered Outputs
Rn, the negative real impedance, is set by C3 and C4
VCC
VCC
and is approximately:
0.01µF
[Equation 2]
10Ω
0.01µF
10µH
27pF
( ) ( ) Rn =
gm
2πf
1
C3 + C03
2πf
1
C4 + C04
where gm = 18mS.
30pF
120pF
120pF
1
VCC1
2
TANK
0.01µF
8
OUT
OUT
VCC
7
VCC2
3
MAX2620
6
FDBK
GND
0.01µF
4
SHDN
5
OUT
0.01µF
OUT
SHDN
51Ω
0.01µF
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
Calculate: Rp = Q × 2π × f × L1
Using Equation 1, solve for varactor capacitance (CD1).
CD1 is the capacitance of the varactor when the volt-
age applied to the varactor is approximately at half-
supply (the center of the varactor’s capacitance range).
Assume the following values:
CSTRAY = 2.7pF, C17 = 1.5pF, C6 = 1.5pF, C5 = 1.5pF,
C03 = 2.4pF, C04 = 2.4pF, C3 = 2.7pF, and C4 = 1pF
VCC
X = STATEK AT-3004 10MHz
FUNDAMENTAL MODE CRYSTAL SURFACE MOUNT
CLOAD = 20pF
Figure 4. 10MHz Crystal Oscillator
Sample Calculation
According to the electrical model shown in Figure 5, the
resonance frequency can be calculated as:
[Equation 1]
The value of CSTRAY is based on approximate perfor-
mance of the MAX2620 EV kit. Values of C3 and C4 are
chosen to minimize Rn (Equation 2) while not loading
the resonant circuit with excessive capacitance. C03
and C04 are parasitic capacitors.
The varactor’s capacitance range should allow for the
desired tuning range. Across the tuning frequency
range, ensure that Rs < 1/2 Rn.
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
fO =
1
2π
L1 CSTRAY +
C17 x CD1
C17 + CD1
+ C6
+
C5
C5
x
+
Cn
Cn
where Cn =
(C3 + C03 )(C4 + C04 )
C3 + C03 + C4 + C04
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