Circuit Note

CN-0245

Circuits from the Lab™ reference circuits are engineered and

testedfor quickandeasysystemintegrationtohelpsolvetoday’s

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

informationand/orsupport, visitwww.analog.com/CN0245.

Devices Connected/Referenced

ADF4350

Wideband Synthesizer with

Integrated VCO

ADL5387

50 MHz to 2 GHz Quadrature Demodulator

ADL5380

400 MHz to 6 GHz Quadrature

Demodulator

Wideband LO PLL Synthesizer with Simple Interface to Quadrature Demodulators

Rev.

0

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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.

0°

90°

LOIP

LOIN

ADF4350

ADL5380/ADL5387

QUADRATURE DEMODULATOR

WIDEBAND

SYNTHESIZER

LPF

3.3V

RF+ RF–

Q+

Q–

I+

I–

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

(Simplified Schematic: All Connections and Decoupling Not Shown)