CN-0147 Datasheet, PDF (1/4 Pages) Analog Devices – Powering a Fractional-N Voltage Controlled Oscillator with Low Noise LDO Regulators for Reduced Phase Noise

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Circuit Note
CN-0147
Devices Connected/Referenced
ADF4350 Fractional-N PLL IC with Integrated VCO
ADP150
Low Noise 3.3 V LDO
Powering a Fractional-N Voltage Controlled Oscillator (VCO) with Low Noise
LDO Regulators for Reduced Phase Noise
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
ADF4350 Evaluation Board (EVAL-ADF4350-EB1Z)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
CIRCUIT FUNCTION AND BENEFITS
This circuit uses low noise, low dropout (LDO) linear regulators
to supply power to a wideband integrated PLL and VCO.
Wideband voltage controlled oscillators (VCOs) may have
increased sensitivity to power supply noise, hence, ultralow
noise regulators are recommended for best performance.
The circuit shown in Figure 1 utilizes the ADF4350, a fully
integrated fractional-N PLL and VCO that can generate
frequencies from 137.5 MHz to 4400 MHz. The ADF4350 is
powered from the ultralow noise 3.3 V ADP150 regulator for
optimal LO phase noise performance.
V_IN = 5.5V
C_IN
1µF
ON
OFF
1 VIN VOUT 5
ADP150
2 GND
V_OUT = 3.3V
C_OUT
1µF
3 EN
NC 4
NC = NO CONNECT
V_IN = 5.5V
C_IN
1µF
ON
OFF
1 VIN VOUT 5
ADP150
2 GND
V_OUT = 3.3V
C_OUT
1µF
3 EN
NC 4
NC = NO CONNECT
V_VCO
V_DD
LOCK
DETECT
FREF_IN
16 17 28 10 4 26 6 32
30 25
V_VCO DV_DD AV_DD CE PDB_RF V_P SDV_DD MUXOUT LD
1nF 1nF
29 REFIN
51Ω
1 _CLK
RF_OUTB+ 14
RF_OUTB– 15 ^VVCO
2 DATA
3 LE
3.9nH 3.9nH
1nF
ADF4350
RF_OUTA+ 12
4.7kΩ
22 R_SET
RF_OUTA– 13
1nF
V_TUNE 20
CP_OUT 7
SW 5
CP_GND SD_{GND AGND} A_GNDVCO D_{GND TEMP VCOM VREF}
8
31 9 11 18 21 27 19 23 24
680Ω
2700pF
39nF
360Ω
1200pF
10pF
0.1µF 10pF
0.1µF 10pF
0.1µF
Figure 1. ADP150 Regulators Connected to ADF4350 (Simplified Schematic: All Connections and Decoupling Not Shown)
Rev. C
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