LMH3401 Datasheet, PDF (21/48 Pages) Texas Instruments – LMH3401 7-GHz, Ultra-Wideband, Fixed-Gain, Fully-Differential Amplifier

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9 Detailed Description
LMH3401
SBOS695A – AUGUST 2014 – REVISED DECEMBER 2014
9.1 Overview
The LMH3401 is a very high-performance, differential amplifier optimized for radio frequency (RF) and
intermediate frequency (IF) or high-speed, time-domain applications with signal bandwidths up to 2 GHz. The
device is ideal for dc- or ac-coupled applications that may require a single-ended to differential conversion when
driving an analog-to-digital converter (ADC). The necessary feedback (R_F) and gain set (R_G) resistors are
fabricated on the device silicon and provide 16 dB of gain when configured for single-ended inputs driven from a
50-Ω source. When used in a fully-differential configuration, 12 dB is obtained when matching the input to a
100-Ω differential. The on-chip resistors simplify PCB implementation and ensure the highest performance over
the useable bandwidth of 2 GHz.
A common-mode reference input pin is provided to align the amplifier output common-mode with the ADC input
requirements. Power supplies between 3.3 V and 5.0 V can be selected and dual-supply operation is supported
when required by the application. A power-down feature is also available for power savings.
In addition to the on-chip feedback resistors, the LMH3401 offers two on-chip termination resistors, one for each
output with values of 10 Ω each. For most load conditions the 10-Ω resistors are only a partial termination,
consequently external termination resistors are required in most applications. Some common load values and the
matching resistors; see Table 1.
9.2 Functional Block Diagram
200
R_G
IN-
12.5
CM
R_G
IN+
12.5
R_F
LMH3401
R_F
200
PD
10
OUT+
OUT-
10
9.3 Feature Description
The LMH3401 includes the following features:
• Fully-differential amplifier
• Fixed gain with on-chip resistors
• Output common-mode control
• Single- or split-supply operation
• Small-signal bandwidth of 7 GHz
• Linear bandwidth of 2 GHz
• Power down
9.3.1 Fully-Differential Amplifier
The LMH3401 is a voltage feedback (VFA)-based fully-differential amplifier (FDA) offering a 7-GHz signal
bandwidth with on-chip gain set and feedback resistors. The core differential amplifier is a slightly
decompensated voltage feedback design with a high slew rate, and best-in-class linearity up to 2 GHz. The on-
chip feedback network provides a gain of 16 dB when used as a single-ended amplifier or 12 dB when used as a
differential amplifier and matched to a 100-Ω source with external, series 37.5-Ω resistors.
Copyright © 2014, Texas Instruments Incorporated
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