Datasheet CN-0245 Datasheet (ANALOG DEVICES)

Circuit Note

CN-0245

Wideband Synthesizer with
Integrated VCO

400 MHz to 6 GHz Quadrature
Demodulator

0

its from Analog Devices have been designed and built by Analog Devices

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whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page)

Fax: [phone] ©2011 Analog Devices, Inc. All rights reserved.

0°

90°

LOIP

LOIN

ADF4350

ADL5380/ADL5387

QUADRATURE DEMODULATOR

WIDEBAND

SYNTHESIZER

RF

OUT

A+

RF

OUT

A–

LPF

3.3V

RF+ RF–

Q+

Q–

I+

I–

Z

BIAS

Z

BIAS

10224-001

Devices Connected/Referenced

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.

Wideband LO PLL Synthesizer with Simple Interface to Quadrature Demodulators

ADF4350

ADL5387 50 MHz to 2 GHz Quadrature Demodulator

ADL5380

EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Boards

ADL5387 Evaluation Board (ADL5387-EVALZ)
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.

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.

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
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.

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.

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

Rev.

Circuits from the Lab™ circu

each circuit, and their function and performance have been tested and verified in a lab environment at

be liable f

(Simplified Schematic: All Connections and Decoupling Not Shown)

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]

www.analog.com

CN-0245 Circuit Note

D Q

Q

LO_IN

CK

D Q

QCK

LO_I (0°)

LO_Q (90°)

10224-002

LO_I (0°)

LO_Q (90°)

LO_IN

10224-003

ADF4350

WIDEBAND

SYNTHESIZER

RF

OUT

A+

RF

OUT

A–

3.3V

Z

BIAS

Z

BIAS

12

13

ADL5387

QUADRATURE

DEMODULATOR

LOIP

LOIN

3

4

10224-004

CIRCUIT DESCRIPTION

The ADF4350 is a wideband fractional-N and integer-N phase­locked 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.

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.

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.

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.

Figure 2. Simplified 2 × LO-Based Phase Splitter

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.

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.

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

–20

–70

425 1225

10224-005

IMAGE REJECTION (dBc)

RF FREQUENCY (MHz)

–25

–30

–35

–40

–45

–50

–55

–60

–65

525 625 725 825 925 1025 1125

ADF4350, NO FILTER

SIGNAL GENERATOR

ADF4350 + FIL TER

ADF4350

WIDEBAND

SYNTHESIZER

RF

OUT

A+

RF

OUT

A–

LPF

3.3V

Z

BIAS

Z

BIAS

12

13

ADL5380

QUADRATURE

DEMODULATOR

LOIP

LOIN

3

4

10224-006

–10

–70

850

10224-007

–20

–30

–40

–50

–60

1350 1850

2350

IMAGE REJECTION (dBc)

RF FREQUENCY (MHz)

ADF4350, NO FILTER

SIGNAL GENERATOR

ADF4350 + FIL TER

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.

Figure 5. ADL5387 Image Rejection vs. RF Frequency

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

ADL5380 Demodulator

Figure 7. ADFL5380 Image Rejection vs. 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.

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.

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) Z

BIAS

a. 500–1300 27 nH|| 50 Ω 3.9 3.9 DNI 4.7 DNI 5.6 DNI 3.3
b. 850–2450 19 nH || (100 Ω in position C1c) 2.7 2.7 3.3 100 Ω 4.7 DNI 3.3 DNI
c. 1250–2800 50 Ω 0 Ω 3.6 DNI DNI 2.2 DNI 1.5 DNI
d. 2800–4400 3.9 nH 0 Ω 0 Ω DNI DNI DNI DNI DNI DNI

3.3V

120pF 120pF

RF

RF

12

A+

OUT

A–

13

OUT

Figure 8. ADF4350 RF Output Filter Schematic

0.1µF

C1a C2a C3a

Z

BIAS

Z

BIAS

L1 L2

C1c C2c C3c

L1 L2

C1a C2a C3a

1nF

1nF

3

4

COMMON VARIATIONS

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.

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.

Table 2 provides the ordering guide for the various evaluation
boards.

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.

LOIP

LOIN

ADL5380ADF4350

L1
(nH)

L2
(nH)

C1a
(pF)

C1c
(pF)

C2a
(pF)

C2c
(pF)

C3a
(pF)

C3c
(pF)

Table 2. Evaluation Board Information

Evaluation Board

ADL5387 ADL5387-EVALZ
ADL5380

Low Band (400 MHz to 3 GHz)
Mid Band (3 GHz to 4 GHz)

ADL5380-30A-EVALZ
ADL5380-29A-EVALZ

CN-0134 CFTL-0134-EVALZ

Equipment Needed

10224-008

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

(32-bit) PC with USB port

• Evaluation boards as listed in Table 2

• RF source (Rohde & Schwarz SMT06 or equivalent)

• Spectrum analyzer (Rohde & Schwarz FSEA30 or

equivalent)

• Power supplies:

• ADL5387-EVA L Z: +5 V

• ADL5380-30A-EVA LZ : +5 V

• CFTL-0134-EVA LZ : +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.

Additional documentation can be found in the following design
support packages for CN-0245, CN-0134, and CN-0144:

CN-0245 Design Support Package:

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 SIG NAL GENERATOR

USB

PC CONTROLLER

CN-0134

EVALUATION PLATFORM

(CFTL-0134-EVALZ)

E3631 POWER SUPPLY

Figure 9. F

LEARN MORE

Nash, Eamon, AN-1039 Application Note. Correcting

Imperfections in IQ Modulators to Improve RF Signal
Fidelity. Analog Devices.

CN-0245 Design Support Package:

www.analog.com/CN0245-DesignSupport

CN-0134 Design Support Package:

www.analog.com/CN0134-DesignSupport

CN-0144 Design Support Package:

www.analog.com/CN0144-DesignSupport

ADIsimRF Design Tool

ADIsimPLL Design Tool

LO+

ADL5380 OR ADL5387

LO–

AGILENT

EVALUATION BOARD

+5.0V+5.5V

unctional Block Diagram of Test Setup

Data Sheets and Evaluation Boards

ADL5387 Data Sheet and Evaluation Board

ADL5380 Data Sheet and Evaluation Board

ADF4350 Data Sheet and Evaluation Board

REVISION HISTORY

12/11—Revision 0: Initial Version

RF

I+

I–

Q+

Q–

ROHDE & SCHWARZ

FSEA30 SPECT RUM ANALYZER

10224-009

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011 A
registered trademarks are the property of their respective owners.
CN

10224-0-12/11(0)

erwise under any patents or other intellectual property by

Rev. 0 | Page 5 of 5