CN-0245 Datasheet, PDF (1/5 Pages) Analog Devices – Wideband LO PLL Synthesizer with Simple Interface to Quadrature Demodulators

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Circuit Note
CN-0245
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
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.
3.3V
RF_OUTA+
ADF4350
RF_OUTA–
WIDEBAND
SYNTHESIZER
Z_BIAS
Z_BIAS
LPF
RF+ RF–
LOIP
LOIN
Q+
Q–
0°
90°
I+
I–
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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