CN-0147 [ADI]

Powering a Fractional-N Voltage Controlled Oscillator with Low Noise LDO Regulators for Reduced Phase Noise; 供电的小数N分频压控振荡器，低噪声LDO稳压器的精简相位噪声


型号：	CN-0147
厂家：	ADI
描述：	Powering a Fractional-N Voltage Controlled Oscillator with Low Noise LDO Regulators for Reduced Phase Noise 供电的小数N分频压控振荡器，低噪声LDO稳压器的精简相位噪声振荡器压控振荡器稳压器
文件：	总4页 (文件大小：258K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

Circuit Note

CN-0147

Devices Connected/Referenced

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.

ADF4350

ADP150

Fractional-N PLL IC with Integrated VCO

Low Noise 3.3 V LDO

Powering a Fractional-N Voltage Controlled Oscillator (VCO) with Low Noise

LDO Regulators for Reduced Phase Noise

Wideband voltage controlled oscillators (VCOs) may have

increased sensitivity to power supply noise, hence, ultralow

noise regulators are recommended for best performance.

EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Boards

ADF4350 Evaluation Board (EVAL-ADF4350-EB1Z)

Design and Integration Files

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.

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.

LOCK

DETECT

V_VCO

V_DD

V_VCO

MUXOUT LD

PDB_RF

SDV_DD

DV_DDAV_DDCE

V_P

= 5.5V

= 3.3V

OUT

1nF 1nF

VIN

VOUT

FREF_IN

REF_IN

RF_OUTB+

51Ω

ADP150

GND

1µF

V_VCO

3.9nH

RF_OUTB–

CLK

DATA

3.9nH

1nF

OFF

RF_OUTA+

RF_OUTA–

ADF4350

NC = NO CONNECT

22 R_SET

4.7kΩ

= 5.5V

= 3.3V

OUT

VIN

VOUT

V_TUNE20

OUT

ADP150

GND

680Ω

1µF

CP_OUT

39nF

2700pF

1200pF

V_REF

OFF

360Ω

CP_GNDSD_GND

A_GNDVCOD_GND

AGND

TEMP VCOM

19 23

NC = NO CONNECT

11 18 21

10pF

0.1µF 10pF

10pF

0.1µF

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

Rev. C

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CN-0147

Circuit Note

Table 1. ADF4350 VCO Pushing

VCO Frequency (MHz) V_TUNE(V)

VCO Pushing (MHz/V)

2200

3300

4400

2.5

0.73

1.79

5.99

POWER SUPPLY

SPECTRUM ANALYZER

[R&S FSUP 26]

5.5V

RF OUT

EVAL-ADF4350EB1Z

REV B BOARD

USB

CABLE

Figure 2. EVAL-ADF4350EB1Z Rev. B Evaluation Board

Featuring ADP150 Low Noise Regulators

Figure 3. ADF4350 Measurement Setup

The lower integrated rms noise of the ADP150 LDO of only

9 µV rms (10 Hz to 100 kHz) helps to minimize VCO phase

noise and reduce the impact of VCO pushing (the VCO

equivalent of power supply rejection).

Experiments showed pushing to be at its maximum at

4.4 GHz VCO output frequency, so the comparison of

VCO performance with different regulators was made at this

frequency. Rev. A evaluation boards of the ADF4350 used the

ADP3334 LDO regulator. The integrated rms noise of this

regulator is 27 µV (integrated from 10 Hz to 100 kHz). This

compares to 9 µV for the ADP150, which is used on the

EVAL-ADF4350EB1Z, Rev B. In order to measure the impact

of the power supply noise, a narrow PLL loop bandwidth (10

kHz) was used to facilitate greater examination of VCO phase

noise. A diagram of this setup is shown in Figure 3. A more

detailed examination of the output noise density with frequency

is available from the data sheets of both the ADP3334 and

ADP150.

Figure 2 shows a photo of the evaluation board, which uses the

ADP150 LDOs to power the ADF4350. The ADP150 represents

the industry’s lowest noise LDO in the smallest package at the

lowest cost. It is available in a 4-ball, 0.8 mm × 0.8 mm, 0.4 mm

pitch WLCSP or a convenient 5-lead TSOT package. Adding the

ADP150’s to the design, therefore, has minimal impact on

system cost and board area while providing a significant

improvement in phase noise.

CIRCUIT DESCRIPTION

The ADF4350 is a wideband PLL and VCO consisting of

three separate multiband VCOs. Each VCO covers a range of

approximately 700 MHz (with some overlap between VCOs).

Lower frequencies are generated by output dividers.

Figure 4 shows that the noise spectral density of the ADP3334

regulator is 150 nV/√Hz at 100 kHz offset. The same plot for

the ADP150 (Figure 5) shows 25 nV/√Hz.

VCO pushing is measured by applying a steady dc tuning voltage

to the ADF4350 V_TUNEpin, varying the power supply voltage,

and measuring the frequency change. The pushing figure (P)

equals the frequency delta divided by the voltage delta, as shown

in Table 1.

The formula for calculating the degradation in phase noise due

to the power supply noise is as follows:













P × Sfm

2 × fm

L_(LDO)= 20log

In a PLL system, higher VCO pushing means that power supply

noise will degrade the VCO phase noise. If VCO pushing is low,

then power supply noise will not significantly degrade phase

noise. However, for high VCO pushing, noisy power supplies

will have a measurable impact on phase noise performance.

Where L_(LDO)is the noise contribution from the regulator to the

VCO phase noise (in dBc/Hz), at an offset fm; P is the VCO

pushing figure in Hz/V; Sfm is the noise spectral density at a

given frequency offset in V/√Hz; and fm is the frequency offset

at which the noise spectral density is measured in Hz.

Rev. C | Page 2 of 4

Circuit Note

CN-0147

100

Table 2. Calculation and Measurement of VCO Noise

ADP3334 ADP150

= 2.2V

OUT

= 1mA

Noise contribution from regulator

(nV/√Hz)

Noise contribution from regulator

(dBc/Hz)

Total calculated noise at VCO output

(dBc/Hz)

Measured VCO noise at 100 kHz offset

(dBc/Hz)

= 10µF

= 0

150

= 10µF

= 1µF

= 10nF

= 0

−104

−103

−102.6

−119.5

−109.5

−108.5

0.1

= 1µF

= 10nF

0.01

0.001

100

10k

100k

FREQUENCY (Hz)

Figure 4. ADP3334 Output Noise Spectrum

0.501

0.451

0.401

0.351

0.301

0.251

0.201

0.151

0.101

0.051

0.001

= 1.8V

OUT

= 2.8V

= 3.3V

Figure 6. ADF4350 Phase Noise at 4.4 GHz with ADP3334 Regulators

100

10k

100k

FREQUENCY (Hz)

Figure 5. ADP150 output noise spectrum

The noise contribution from the supply is then rss summed

with the noise contribution of the VCO (itself measured with a

very low noise supply) to give the total noise at the VCO output

with a given regulator.

These noise performances are rss summed together to give the

expected VCO phase noise:

L_(TOTAL)

L_(VCO)²+ L_(LDO)

Or expressed in dB

L_(TOTAL)= 10log

[

(

10^{LVCO / 20}

)

(

10^{LLDO / 20}

)

]

In this example, a 100 kHz noise spectral density offset is

Figure 7. ADF4350 Phase Noise at 4.4 GHz with ADP150 Regulators

chosen, a 6 MHz/V pushing figure is used, and −110 dBc/Hz is

taken as the VCO noise with an ideal supply.

The integrated phase noise improves from 1.95° to 1.4° rms

also. The measured results correlate very closely with the

calculations and clearly show the benefit of using the ADP150

with the ADF4350.

Using a dedicated signal source analyzer (like Rohde & Schwarz

FSUP), the VCO phase noise is compared. At 100 kHz offset the

ADP3334 delivers −102.6 dBc/Hz (Figure 6), and in the same

configuration the ADP150 measures −108.5 dBc/Hz (Figure 7).

A complete design support package for this circuit note can be

found at http://www.analog.com/CN0147-DesignSupport.

Rev. C | Page 3 of 4

CN-0147

Circuit Note

COMMON VARIATIONS

LEARN MORE

Additional regulators can be added for greater isolation

between power supplies, if desired. Also, one ADP150

regulator can be used to power the entire ADF4350 part.

However, care needs to be taken in this case to ensure the

maximum rated current of the single ADP150 regulator is not

exceeded. This is possible if the lowest output power setting

on the ADF4350 is selected.

CN0147 Design Support Package:

http://www.analog.com/CN0147-DesignSupport

ADIsimPLL Design Tool

ADIsimPower Design Tool

Basso, C., C. Fourtet, and P. Kadanka. “Get the Best from Your

Low-Dropout Regulator.” EDN, 18 Feb. 1999.

Data Sheets and Evaluation Boards

ADF4350 Data Sheet

CIRCUIT EVALUATION AND TEST

This circuit note, CN-0147, uses the EVAL-ADF4350EB1Z

board for evaluation of the described circuit, allowing for quick

setup and evaluation. The EVAL-ADF4350EB1Z board uses the

standard ADF4350 programming software, contained on the

CD that accompanies the evaluation board.

ADF4350 Evaluation Board

ADP150 Data Sheet

ADP3334 Data Sheet

Equipment Needed

REVISION HISTORY

Windows® XP, Windows, Vista (32-bit), or Windows 7 (32-bit)

PC with USB Port, the EVAL-ADF4350EB1Z, the ADF4350

programming software, 5.5 V power supply, and a spectrum

analyzer such as a Rhode and Schwartz FSUP26. See this circuit

note CN-0147 and UG-109 user guide for evaluation board

EVAL-ADF4350EB1Z and the ADF4350 data sheet.

6/11—Rev. B to Rev. C

Changes to Circuit Description.......................................................2

11/10—Rev. A to Rev. B

Added Evaluation and Design Support Section............................1

Added Circuit Evaluation and Test Section...................................4

Getting Started

7/10—Rev. 0 to Rev. A

This circuit note, CN-0147, contains a description of the circuit,

the schematic, and a block diagram of the test setup. The ser

guide, UG-109, details the installation and use of the EVAL-

ADF4350 evaluation software. UG-109 also contains board

setup instructions and the board schematic, layout, and bill of

materials.

Changes to Figure 1...........................................................................1

Changes to Figure 3...........................................................................2

4/10—Revision 0: Initial Version

Functional Block Diagram

This circuit note, CN-0147, contains the function block

diagram of the described test setup in Figure 3.

Setup and Test

After setting up the equipment, standard RF test methods

should be used to measure the spectral purity of the output

signal.

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registered trademarks are the property of their respective owners.

CN08876-0-6/11(C)

Rev. C | Page 4 of 4

CN-0147 [ADI]

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