CN-0245 [ADI]

Wideband LO PLL Synthesizer with Simple Interface to Quadrature Demodulators; 宽带LO PLL合成器，简单的界面，正交解调器


型号：	CN-0245
厂家：	ADI
描述：	Wideband LO PLL Synthesizer with Simple Interface to Quadrature Demodulators 宽带LO PLL合成器，简单的界面，正交解调器
文件：	总5页 (文件大小：429K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

Circuit Note

CN-0245

Devices Connected/Referenced

Wideband Synthesizer with

Integrated VCO

Circuits from the Lab™ reference circuits are engineered and

tested for quick and easy system integration to help solve today’s

analog, mixed-signal, and RF design challenges. For more

information and/or support, visit www.analog.com/CN0245.

ADF4350

ADL5387 50 MHz to 2 GHz Quadrature Demodulator

400 MHz to 6 GHz Quadrature

Demodulator

ADL5380

Wideband LO PLL Synthesizer with Simple Interface to Quadrature Demodulators

The ADF4350 offers RF differential outputs and, likewise, the

ADL5380/ADL5387 accept differential inputs. This interface

offers both ease of use and performance advantages. The

EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Boards

ADL5387 Evaluation Board (ADL5387-EVALZ)

differential signal configuration provides common-mode noise

reduction and even order cancellation of the LO harmonics,

which maintains the quadrature accuracy of the I/Q

demodulators. Additionally, the output power level of the

ADF4350 matches the input power requirements of the

quadrature demodulators very well. As a result, an LO buffer is

not necessary.

ADL5380 Evaluation Board (ADL5380-30A-EVALZ)

CN0134 Evaluation Platform (CFTL-CN0134-EVALZ)

Design and Integration Files

Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTION AND BENEFITS

The circuit, shown in Figure 1, highlights the ease of interfacing

the ADF4350 wideband synthesizer with integrated VCO with

the ADL5380 and ADL5387 wideband I/Q demodulators. In

this circuit, the ADF4350 provides the high frequency, low

phase noise local oscillator (LO) signal to the wideband I/Q

demodulator.

The ADF4350 outputs cover a wide frequency range from

137.5 MHz to 4400 MHz. The ADL5387 frequency range spans

from 50 MHz to 2 GHz, and the ADL5380 covers the higher

frequency range from 400 MHz to 6 GHz. Between the

ADL5380 and ADL5387 the RF input range can span from

50 MHz to 6 GHz. Therefore, the two chip circuit configuration

as shown in Figure 1 offers coverage of a wide frequency range

from 50 MHz to 4400 GHz.

This circuit configuration offers quite a few benefits that make

it an attractive solution in applications requiring quadrature

mixing down to baseband or to an intermediate frequency.

3.3V

RF+ RF–

BIAS

Q+

LOIP

LOIN

Q–

A+

A–

OUT

0°

ADF4350

BIAS

90°

LPF

OUT

I+

I–

WIDEBAND

SYNTHESIZER

ADL5380/ADL5387

QUADRATURE DEMODULATOR

Figure 1. Simple Interface Between the ADF4350 PLL Synthesizer and the ADL5380 or ADL5387 Quadrature Demodulator

(Simplified Schematic: All Connections and Decoupling Not Shown)

Rev. 0

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www.analog.com

CN-0245

Circuit Note

LO_I (0°)

CIRCUIT DESCRIPTION

The ADF4350 is a wideband fractional-N and integer-N phase-

locked loop frequency synthesizer covering the frequency range

of 137.5 MHz to 4400 MHz. The ADF4350 has an integrated

voltage controlled oscillator (VCO) with a fundamental

frequency range of 2200 MHz to 4400 MHz. The ADF4350

offers high quality synthesizer performance. However,

depending on the demodulator architecture, LO filtering may

be required to minimize the effects of harmonics from the PLL

on the quadrature accuracy of the I/Q demodulator.

LO_IN

LO_Q (90°)

Figure 3. Simplified First Order Polyphase Filter

Figure 3 shows a simplified first order polyphase circuit, as

implemented in the ADL5380. The polyphase circuit consists of

complementary RC subcircuits that create a low-pass transfer

function from input to one output, and a high-pass transfer

function to the other output. If the R and C values of the two

polyphased paths are matched, then both paths have the same

corner frequency and, more importantly, the phase of one

output tracks the other with a 90° phase shift.

Analog Devices offers quadrature demodulators that cover a

wide frequency range. The ADL5387 frequency range spans

from 50 MHz to 2 GHz, and the ADL5380 covers the higher

frequency range from 400 MHz to 6 GHz. The ADL5387 and

ADL5380 utilize two different architectures to generate the 90°

phase shift between the I and Q paths. The ADL5387 utilizes a

2 × LO architecture where the local oscillator is at twice the RF

frequency, while the ADL5380 uses a polyphase filter-based

phase splitter. The polyphase architecture has a narrower

fractional bandwidth (i.e., operates across less octaves) and is

more sensitive to PLL harmonics compared to a 2 × LO-based

phase splitter. As a result, the ADL5380 requires harmonic

filtering of the LO to maintain the quadrature accuracy of

the I/Q demodulator, while filtering is only required for the

2 × LO-based ADL5387 at the top end of its frequency range.

Interfacing the ADF4350 PLL with the ADL5387 I/Q

Demodulator

The ADL5387 and ADL5380 I/Q demodulators utilize different

architectures to achieve the ultimate goal of generating precise

quadrature signals. When interfacing with an LO synthesizer

like the ADF4350, it is important to consider how the

architectures respond to the LO signal and its harmonics.

This will determine the requirement for LO filtering. Figure 4

shows the basic interface between the ADF4350 and ADL5387.

Depending on the frequency of operation, an LO harmonic

filter may or may not be required between the ADF4350

and ADL5387.

LO_I (0°)

3.3V

LO_IN

BIAS

A+

A–

OUT

LOIP

LOIN

ADF4350

ADL5387

BIAS

LO_Q (90°)

OUT

WIDEBAND

SYNTHESIZER

QUADRATURE

DEMODULATOR

Figure 2. Simplified 2 × LO-Based Phase Splitter

Figure 4. ADF4350 PLL Interface to the 2 × LO-Based Phase Splitter of the

ADL5387 Demodulator

In a 2 × LO-based phase splitter, the quadrature accuracy is

dependent on the duty cycle accuracy of the incoming LO.

Figure 2 shows a simplified 2 × LO phase splitter as

implemented in the ADL5387. The 90° phase split of the LO

path is achieved via digital circuitry that uses D-type flip-flops

and an inverter. This architecture requires an external LO

operating at twice the frequency of the desired LO.

The matching of the internal divider flip-flops also affects

quadrature accuracy but to a much lesser extent. So a 50% duty

cycle of the externally applied LO is critical for minimizing

quadrature errors. Additionally, any imbalance in the rise and

fall times causes even order harmonics to appear. When

driving the demodulator LO inputs differentially, even order

cancellation of the harmonics is achieved and results in

improved overall quadrature generation.

Rev. 0 | Page 2 of 5

Circuit Note

CN-0245

With a target image suppression of −40 dBc, Figure 5 shows the

performance of the ADL5387 with the ADF4350 providing the

differential LO source with and without filtering. The blue

signal trace representing the “Signal Generator” is the ideal case

where the LO is generated using a Rhode & Schwarz signal

generator with a sinusoidal output and much lower harmonic

levels compared to the ADF4350. This is the ideal case and the

target comparison point. From Figure 5, it can be seen that

filtering is not required at frequencies below 1 GHz. However,

above 1 GHz small errors due to harmonics of the LO become a

larger percentage of the input period. In this case, filtering

should be used to further attenuate the even order harmonics of

the LO and so that the I/Q demodulator’s specified quadrature

accuracy can be achieved.

Interfacing the ADF4350 PLL with the ADL5380

Quadrature Demodulator

Unlike the ADL5387, the polyphase architecture of the

ADL5380's phase splitter requires filtering of the ADF4350

outputs, as shown in Figure 6. Filtering is required to attenuate

the odd order harmonics of the LO to minimize errors in the

quadrature generation block of the ADL5380. From

measurement and simulation as explained in CN-0134, the odd

order harmonics contribute more than even order harmonics to

quadrature errors. Figure 7 shows the measurement results

when the ADF4350 outputs are filtered before they are applied

to the differential LO inputs of the ADL5380. After filtering, the

resulting image rejection is comparable to what is achievable

from a low harmonic signal generator.

–10

–20

–25

–30

–35

–40

–45

–50

–55

–60

–65

–70

ADF4350, NO FILTER

SIGNAL GENERATOR

ADF4350 + FILTER

ADF4350, NO FILTER

–30

–40

SIGNAL GENERATOR

–50

ADF4350 + FILTER

–60

–70

850

1350

1850

2350

RF FREQUENCY (MHz)

425

525

625

725

825

925

1025

1125

1225

RF FREQUENCY (MHz)

Figure 7. ADFL5380 Image Rejection vs. Frequency.

Figure 5. ADL5387 Image Rejection vs. RF Frequency

Filtering Requirements

In summary, LO filtering the ADF4350 outputs to suppress the

harmonics of the fundamental helps to maintain the phase

accuracy of the quadrature signals of the demodulator. In the

case of the ADL5380, which uses a polyphase architecture,

filtering is a requirement. The ADL5387 architecture consists of

digital circuitry which is more immune to the harmonics of the

LO signal. Therefore filtering may not be required, depending

on the frequency of operation.

3.3V

BIAS

A+

A–

OUT

LOIP

LOIN

ADF4350

ADL5380

BIAS

LPF

OUT

In the case where filtering is necessary, Figure 8, shows an

example LO output filter schematic, and Table 1, summarizes

the filter component values. This circuit is flexible and provides

four different filter options to cover four different bands The

filters were designed for a 100 Ω differential input and 50 Ω

differential output to match the LO input requirements of the

demodulator. A Chebyshev response was used for optimal filter

roll-off at the expense of increased pass-band ripple. Please

refer to CN-0134 for a more detailed discussion on the filtering

of the ADF4350 outputs.

WIDEBAND

SYNTHESIZER

QUADRATURE

DEMODULATOR

Figure 6. ADF4350 Interface to the Polyphase Filter Architecture of the

ADL5380 Demodulator

Rev. 0 | Page 3 of 5

CN-0245

Circuit Note

Table 1. ADF4350 RF Output Filter Component Value (DNI = Do Not Insert)

Frequency Range

(MHz)

(nH)

C1a

(pF)

C1c

(pF)

C2a

(pF)

C2c

(pF)

C3a

(pF)

C3c

(pF)

Z_BIAS

a. 500–1300

b. 850–2450

c. 1250–2800

d. 2800–4400

27 nH|| 50 Ω

3.9

2.7

0 Ω

3.9

2.7

3.6

0 Ω

DNI

3.3

4.7

DNI

4.7

5.6

DNI

3.3

19 nH || (100 Ω in position C1c)

100 Ω

DNI

50 Ω

DNI

2.2

1.5

3.9 nH

DNI

3.3V

Table 2. Evaluation Board Information

120pF

0.1µF

Evaluation Board

ADL5387

ADL5387-EVALZ

C1a

C2a

C3a

1nF

ADL5380

BIAS

Low Band (400 MHz to 3 GHz)

Mid Band (3 GHz to 4 GHz)

CN-0134

ADL5380-30A-EVALZ

ADL5380-29A-EVALZ

CFTL-0134-EVALZ

LOIP

LOIN

A+

A–

OUT

C1c

C2c

C3c

1nF

BIAS

Equipment Needed

C1a

C2a

C3a

ADF4350

ADL5380

•

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

(32-bit) PC with USB port

Figure 8. ADF4350 RF Output Filter Schematic

•

Evaluation boards as listed in Table 2

RF source (Rohde & Schwarz SMT06 or equivalent)

COMMON VARIATIONS

Spectrum analyzer (Rohde & Schwarz FSEA30 or

equivalent)

The interface discussed above is applicable to any PLL with

differential LO outputs and to any 1 × LO or 2 × LO-based I/Q

demodulator. The ADL5382 is a 1 × LO-based I/Q demodulator

that operates from 700 MHz to 2700 MHz and provides slightly

higher IP3 than the ADL5380. TheAD8347 (1 × LO) and

AD8348 (2 × LO) are lower power I/Q demodulators that

integrate front-end variable gain amplifiers and fixed-gain

baseband amplifiers.

•

Power supplies:

•

ADL5387-EVALZ: +5 V

ADL5380-30A-EVALZ: +5 V

CFTL-0134-EVALZ: +5.5 V

Test

The CN-0134 evaluation platform allows easy evaluation and

has an integrated crystal oscillator on board. A PC with the

ADF4350 software is required to program the synthesizer to the

desired LO frequency. The ADL5387/ADL5380 quadrature

demodulator will downconvert the RF frequency to baseband.

The differential I and Q baseband outputs are applied to the

FSEA spectrum analyzer in the FFT mode, and image rejection

is measured.

CIRCUIT EVALUATION AND TEST

The circuits shown in Figure 4 and Figure 6 were implemented

using the CN-0134 evaluation board (CFTL-0134EVALZ) and

the ADL5387 or ADL5380 evaluation boards. The CN-0134

evaluation platform includes the ADF4350, pads for an LO

filter, and differential LO outputs to SMA connectors.

The ADF4350 must be programmed, and the software is

contained on the CD that accompanies the evaluation board.

Additional documentation can be found in the following design

support packages for CN-0245, CN-0134, and CN-0144:

Table 2 provides the ordering guide for the various evaluation

boards.

CN-0245 Design Support Package:

The CN-0134 evaluation board is configured by default to an

850 MHz to 2450 MHz filter design as specified in Table 1. To

implement an alternative filter, the appropriate components

must be swapped out.

www.analog.com/CN0245-DesignSupport

CN-0134 Design Support Package:

www.analog.com/CN0134-DesignSupport

CN-0144 Deign Support Package:

www.analog.com/CN0144-DesignSupport

Rev. 0 | Page 4 of 5

Circuit Note

CN-0245

ROHDE & SCHWARZ

SMT06 SIGNAL GENERATOR

I+

I–

LO+

LO–

USB

CN-0134

EVALUATION PLATFORM

(CFTL-0134-EVALZ)

Q+

Q–

ADL5380 OR ADL5387

EVALUATION BOARD

PC CONTROLLER

+5.5V

+5.0V

ROHDE & SCHWARZ

FSEA30 SPECTRUM ANALYZER

AGILENT

E3631 POWER SUPPLY

Figure 9. Functional Block Diagram of Test Setup

LEARN MORE

Data Sheets and Evaluation Boards

Nash, Eamon, AN-1039 Application Note. Correcting

Imperfections in IQ Modulators to Improve RF Signal

Fidelity. Analog Devices.

ADL5387 Data Sheet and Evaluation Board

ADL5380 Data Sheet and Evaluation Board

ADF4350 Data Sheet and Evaluation Board

CN-0245 Design Support Package:

www.analog.com/CN0245-DesignSupport

REVISION HISTORY

CN-0134 Design Support Package:

www.analog.com/CN0134-DesignSupport

12/11—Revision 0: Initial Version

CN-0144 Design Support Package:

www.analog.com/CN0144-DesignSupport

ADIsimRF Design Tool

ADIsimPLL Design Tool

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CN10224-0-12/11(0)

Rev. 0 | Page 5 of 5

CN-0245 [ADI]

相关型号：

CN-0248

CN-0255

CN-0259

CN-0267

CN-0268

CN-0274

CN-0279

CN-0283

CN-0285

CN-0294

CN-0300

CN-0311