adl5561acpz-wp Analog Devices, Inc., adl5561acpz-wp Datasheet - Page 13

• Manufacturer Part Number: adl5561acpz-wp
• Description: 2.9 Ghz Ultralow Distortion Rf/if Differential Amplifier
• Manufacturer: Analog Devices, Inc.

CIRCUIT DESCRIPTION
BASIC STRUCTURE
The ADL5561 is a low noise, low power, fully differential ampli-
fier/ADC driver that uses a 3.3 V supply. It provides three gain
options (6 dB, 12 dB, and 15.5 dB) without the need for external
resistors and has wide bandwidths of 2.6 GHz for 6 dB, 2.3 GHz
for 12 dB, and 2.1 GHz for 15.5 dB. Input impedance is 400 Ω
differential for 6 dB, 200 Ω for 12 dB, and 133 Ω for 15.5 dB. It
has a differential output impedance of 10 Ω and an output
common-mode adjust voltage of 1.25 V to 1.85 V.
The ADL5561 is composed of a fully differential amplifier with
on-chip feedback and feed-forward resistors. The two feed-
forward resistors on each input set this pin-strappable amplifier
in three different gain configurations of 6 dB, 12 dB, and 15.5 dB.
1
1
/
/
2
2
AC
R
R
S
S
0.1µF
0.1µF
Figure 30. Basic Structure
VIP2
VIP1
VIN1
VIN2
100Ω
100Ω
200Ω
200Ω
400Ω
400Ω
5Ω
5Ω
R
L
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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 a 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. The low distortion and noise are realized
with a 3.3 V power supply at 40 mA.
The ADL5561 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 distortion performance. Due to the
internal connections between the inputs and outputs, the user
should keep the output common-mode voltage between 1.25 V
and 1.85 V for the best distortion.
For a dc-coupled input, the input common mode should be
between 1 V and 2.3 V for the best distortion. The device has been
characterized using 2 V p-p into 200 Ω. 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 ADL5561
provides an output common-mode voltage set by VCOM,
which allows driving an ADC directly without external
components, such as a transformer or ac-coupling capacitors,
provided the VCOM of the amplifier is within the VCOM of the
ADC. For dc-coupled requirements, the input VCM must be set
by the VCOM pin in all three gain settings.
ADL5561