CN-0205 Datasheet, PDF (1/9 Pages) Analog Devices – Interfacing the ADL5375 I/Q Modulator to the AD9122 Dual Channel, 1.2 GSPS High Speed DAC

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CN-0205
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Devices Connected/Referenced
AD9122
Dual Channel, 1.2 GSPS, 16-Bit, TxDAC®
Digital-to Analog Converter
ADL5375
Broadband Quadrature Modulator
Interfacing the ADL5375 I/Q Modulator to the
AD9122 Dual Channel, 1.2 GSPS High Speed DAC
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
AD9122/ADL5375 Evaluation Board (AD9122-M5375-EBZ)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
CIRCUIT FUNCTION AND BENEFITS
This circuit provides a simple and flexible interface between
the AD9122 dual high speed TxDAC digital-to-analog
converter and the ADL5375-05 broadband I/Q modulator.
Because the DAC outputs and ADL5375-05 I/Q modulator
inputs share a common bias level of 0.5 V, there is no need
for any active or passive level shifting circuitry. The dc coupled
interface facilitates I/Q modulator local oscillator (LO) leakage
compensation by the DAC.
The 1.2 GSPS AD9122 DAC sampling rate and the wide
bandwidth of the ADL5375-05 modulator I and Q inputs
ensure that both zero-IF (ZIF) or complex-IF (CIF)
architectures can be supported. In addition to filtering Nyquist
images, the baseband filter provides excellent rejection of both
differential-mode and common-mode DAC spurs.
CIRCUIT DESCRIPTION
The circuit and board shown in Figure 1 and Figure2 utilize the
AD9122 TxDAC and the ADL5375-05 wideband transmit
modulator. Signal biasing and scaling in the interface circuit is
controlled by the four ground-referenced resistors (RBIP, RBIN,
RBQP, RBQN) and the two shunt resistors (RSLI,RSLQ),
respectively.
AD9122
IOUT1P
IOUT1N
67
RBIP
50Ω
RBIN
66 ^50Ω
IOUT2N
IOUT2P
59
RBQN
50Ω
RBQP
58 ^50Ω
LOW-PASS
FILTER
ADL5375-05
21
IBBP
RSLI
100Ω
22
IBBN
9
QBBN
LOW-PASS _RSLQ
FILTER
100Ω
10
QBBP
Figure 1. Interface Between the AD9122 and ADL5375-05 with 50 Ω Resistors to Ground to Establish the
500 mV DC Bias for the ADL5375-05 Baseband Inputs (Simplified Schematic)
Rev. 0
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