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ADL5567

Data Sheet

Rev. A | Page 14 of 23

THEORY OF OPERATION

The ADL5567 is a high gain, fully differential dual amplifier/

ADC driver that operates on a single power supply voltage (VS) of

3.3 V or 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

4.3 GHz, and it has a differential input impedance of 100 Ω. It has

a differential output impedance of 10 Ω and an operating output

common-mode voltage range of 1.25 V to 3 V with 5 V supply.

The ADL5567 is composed of a pair of fully differential amplifiers

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

at 20 dB, but it can be reduced by adding two resistors in series with

the two inputs (see the Gain Adjustment and Interfacing section).

The amplifier provides a high differential 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 a

VCOMx pin.

Each amplifier provides superior low distortion for frequencies

near dc to beyond 500 MHz, with low noise and low power

consumption. The low distortion and noise are realized with a

3.3 V power supply at 140 mA. This amplifier achieves an IMD3

of −104 dBc at 200 MHz, and −90 dBc IMD3 at 500 MHz for

2 V p-p operation. In addition, the ADL5567 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 7.1 dB and a RTI voltage

NSD of 1.29 nV/√Hz at 200 MHz. When comparing noise

figure and distortion performance, this amplifier delivers the

best in category spurious-free dynamic range (SFDR).

The ADL5567 is very flexible in terms of input/output coupling.

It can be ac-coupled or dc-couplied. For dc coupling, the output

common-mode voltage can be adjusted (using the VCOMx pins)

from 1.25 V to 1.8 V for VS at 3.3 V, and up to 3 V with VS at 5 V.

The distortion performance as a function of common-mode

voltage is shown in Figure 22 and Figure 23. Note that the input

common-mode voltage follows the output common-mode

voltage when at the inputs are ac-coupled.

ADL5567

0.1µF

50Ω

500Ω

5Ω

–

5Ω

0.1µF

Figure 38. Basic Structure

For dc-coupled inputs, the input common-mode voltage must

stay between 1.2 V and 1.8 V for a 3.3 V supply and 1.3 V to 3.5 V

for a 5 V supply. Note again that for ac-coupled applications with

series capacitors at the inputs, as shown in Figure 38, the input

common-mode level is set to be the same as the voltage at VCOMx.

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

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

and amplifiers. Forcing a higher input common-mode level does

not affect the output common-mode level in dc-coupled opera-

tions. If the outputs are ac-coupled, no external VCOMx voltage

adjustment is required because the amplifier output common-

mode level is set to VS/2.

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