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ADL5565

Data Sheet

Rev. G | Page 16 of 26

CIRCUIT DESCRIPTION

BASIC STRUCTURE

The ADL5565 is a low noise, fully differential amplifier/ADC

driver that can operate from 2.8 V to 5.2 V. It provides three

gain options, 6 dB, 12 dB, and 15.5 dB, without the need for

external resistors and has wide bandwidths of greater than

6 GHz for all gains. Differential input impedance is 200 Ω for

6 dB, 100 Ω for 12 dB, and 67 Ω for 15.5 dB. It has a differential

output impedance of 10 Ω.

1/2 RS

100

Ω

200

Ω

0.1µF

200

Ω

100

Ω

VIP2

VIP1

VIN1

VIN2

Ω

Figure 30. Basic Structure

The ADL5565 is composed of a fully differential amplifier with

on-chip feedback and feed forward resistors. The two feedforward

resistors on each input set this pin-strappable amplifier in three

different gain configurations of 6 dB, 12 dB, and 15.5 dB, and by

using two external resistors, any gain from 0 dB to 15.5 dB can be

realized. The amplifier is designed to provide high differential

open-loop gain and an output common-mode circuit that enables

the user to change the common-mode voltage from the VCOM

pin. The amplifier is designed to provide superior low distortion at

frequencies up to and beyond 300 MHz with low noise and low

power consumption from a 3.3 V power supply at 70 mA.

The ADL5565 is very flexible in terms of I/O coupling. It can be

ac-coupled or dc-coupled at the inputs and/or the outputs within

the specified input and output common-mode levels. The input

of the device can be configured as single-ended or differential

with similar third-order distortion performance. Due to the

internal connections between the inputs and outputs, an output

common-mode voltage between 1.4 V and 1.8 V at 3.3 V and

1.4 V to 3 V at 5 V must be maintained for the best distortion.

For a dc-coupled input, the input common mode should be

between 1.2 V and 2 V at the 3.3 V supply, and 1.2 V to 3.8 V at

the 5 V supply. The device has been characterized using 2 V p-p

into a 200 Ω ac-coupled output. If the inputs are ac-coupled, the

input and output common-mode voltages are set by VCC/2 when

no external circuitry is used. The ADL5565 provides an output

common-mode voltage set by VCOM, which allows driving an

ADC directly without external components. Although distortion is

similar over the specified frequency range at both 3.3 V and 5 V,

lower distortion results on the 5 V supply for signal swings larger

than 2 V p-p.

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