Circuit Note

CN-0147

Circuits from the Lab™ tested circuit designs address

common design challenges and are engineered for

quick and easy system integration. For more information

and/or support, visit www.analog.com/CN0147.

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

Rev. C

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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.

2700pF

1200pF

39nF

680

Ω

360

Ω

ADF4350

AGND

1nF

1nF

4.7k

Ω

LE

DATA

CLK

MUXOUT

10

28

16

29

1

2

3

22

8

31

9

11

18

21

27

LOCK

DETECT

51

Ω

14

15

19

23

24

25

30

LD

17

20

7

26

6

32

5

SW

10pF

0.1µF 10pF

0.1µF 10pF

0.1µF

4

13

12

3.9nH

3.9nH

1nF

1nF

NC = NO CONNECT

ADP150

1

2

3

5

4

1µF

1µF

VOUT

NC

VIN

GND

EN

OFF

ON

NC = NO CONNECT

ADP150

1

2

3

5

4

1µF

1µF

VOUT

NC

VIN

GND

EN

OFF

ON

Figure 1. ADP150 Regulators Connected to ADF4350 (Simplified Schematic: All Connections and Decoupling Not Shown)