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Data Sheet

ADRF6521

Rev. 0 | Page 31 of 33

APPLICATIONS INFORMATION

BASIC CONNECTIONS

Figure 125 shows the basic connections for a typical ADRF6521

application.

SUPPLY DECOUPLING

Decouple each supply pin, VPOS and VNEG, to ground with at

least one low inductance, surface-mount ceramic capacitor of

0.1 µF placed as close as possible to the ADRF6521 device.

INPUT SIGNAL PATH

Each signal path has an input VGA, accessed through the INP1,

INM1, INP2, and INM2 pins, which sets a differential input

impedance of 100 Ω.

The inputs can be dc-coupled or ac-coupled, but ac coupling is

strongly recommended. There is no mechanism to change the

common-mode voltage. Therefore, if the user wants to use dc

coupling, the common-mode voltage of the previous stage must

match the ADRF6521 input common-mode voltage of (VPOS +

VNEG)/2 V.

OUTPUT SIGNAL PATH

The low impedance (20 Ω) output buffers are designed to drive

a 100 Ω impedance load. However, the buffers can drive larger

resistive loads. The output pins (OPP1, OPM1, OPP2, and OPM2)

sit at a nominal output common-mode voltage of (VPOS +

VNEG)/2 V. The outputs can be dc-coupled or ac-coupled.

However, dc coupling is required to take advantage of the output

dc offset voltage functionality. To change the output common-

mode voltage, the user must apply a dc voltage to the VOCM

pin different than (VPOS + VNEG)/2 V. Left open, VOCM

defaults to (VPOS + VNEG)/2 V. To change the output dc offset

voltage, the user must apply a voltage to the OFS1 and OFS2

pins different than 0.75 V. Left open, these pins are pulled to

ground via an on-chip 5 kΩ resistor, which creates an

approximately −670 mV dc output offset.

OPP1

OPM1

VOCM

0.1µF

100pF

VPOS

0.1µF

100pF

GAIN

0.1µF

100pF

0.1µF

100pF

VPOS

0.1µF

100pF

OFS2

0.1µF

100pF

VNEG

0.1µF

100pF

VNEG

0.1µF

100pF

OFS1

0.1µF

100pF

OPP2

OPM2

INM1

COMM

INP1

INP2

INPUT1 (+)

INPUT1 (–)

INPUT2 (+)

INPUT2 (–)

OUTPUT1 (+)

OUTPUT1 (–)

OUTPUT2 (+)

OUTPUT2 (–)

INM2

ADRF6521

PWD

Figure 125. Basic Connections

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