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ADL5569

Data Sheet

Rev. C | Page 14 of 23

THEORY OF OPERATION

The ADL5569 is a high gain, fully differential, dual amplifier

and ADC driver that operates on a single power supply

voltage (VS) of 5 V. Internal resistors preset the gain to 20 dB,

and external resistors can be added to reduce this gain. The

−3 dB bandwidth is 6.5 GHz, and the device has a differential

input impedance of 100 Ω. The ADL5569 has a differential

output impedance of 14 Ω and an operating output common-

mode voltage range of 2.0 V to 3.0 V with a 5 V supply.

The ADL5569 is composed of a pair of fully differential amplifiers

with on-chip feedback and feedforward resistors. The gain is

fixed at 20 dB but can be reduced by adding two resistors in

series with the two inputs. The amplifier provides a high differ-

ential, open-loop gain and has an output common-mode circuit

that enables the user to change the output common-mode voltage

by applying a voltage to the VCOM or VCOM2 pin.

Each amplifier provides superior low distortion for frequencies

near dc to beyond 2000 MHz, with low noise and low power

consumption. This amplifier achieves an IMD3 of −82 dBc at

100 MHz, and −80 dBc IMD3 at 500 MHz for 2 V p-p operation.

In addition, the ADL5569 can deliver 5 V p-p operation under

heavy loads. The internal gain is set at 20 dB, and the device has

a noise figure of 9.3 dB at 2 GHz. When comparing noise figure

and distortion performance, this amplifier delivers the best in

category spurious-free dynamic range (SFDR).

The ADL5569 features flexible input and output coupling.

The device can be ac-coupled or dc-coupled. For dc coupling,

the output common-mode voltage can be adjusted (using the

VCOM and VCOM2 pins) from 2.5 V to 0.5 V for VS at 3.3 V

and ground at −2.0 V.

The distortion performance as a function of output common-

mode voltage is shown in Figure 21. Note that the VCOM and

VCOM2 pins set the common-mode voltage at the outputs of

the amplifier, the VOP, VOP2, VON, and VON2 pins, when

configured for ac-coupled applications.

For ac-coupled applications with series capacitors at the inputs,

as shown in Figure 38, the input common-mode level is set to

the same as the voltage at VCOM or VCOM2.

Due to the wide input common-mode voltage range, this device

can easily be dc-coupled to many types of mixers, demodulators,

and amplifiers. If the outputs are ac-coupled, no external VCOM

or VCOM2 voltage adjustment is required because the amplifier

output common-mode level is set to VS/2.

ADL5569

0.1µF

50Ω

500Ω

–

0.1µF

Figure 38. Basic Structure

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