LMH3401 Datasheet, PDF (25/48 Pages) Texas Instruments – LMH3401 7-GHz, Ultra-Wideband, Fixed-Gain, Fully-Differential Amplifier

www.ti.com
LMH3401
SBOS695A – AUGUST 2014 – REVISED DECEMBER 2014
Feature Description (continued)
9.3.3 Differential to Differential Signals
The LMH3401 can also be used to amplify differential input signals to differential output signals. A basic block
diagram of the circuit is shown in Figure 56. The differential input impedance set by the on-chip resistors is lower
than optimal for most applications (25 Ω). In order to match a load such as 100 Ω, external resistors are required,
as shown in Figure 57.
Differential
Input
V _{IN -}
V _IN+
CM
12.5 :
12.5 :
LMH3401
200 :
200 :
:
:
Differential
Output
V _OUT+
V _OUT-
PD
Figure 56. Differential Input To Differential Output Amplifier
37.5 :
VIN-
100: Differential
Input
VIN+
37.5 :
CM
12.5 :
12.5 :
200 :
200 :
:
:
Differential
Output
V _OUT+
V _OUT-
LMH3401
Gain =20*log(200/50) =
12dB
PD
Figure 57. Differential Input Configured for a 100-Ω Source
9.3.4 Output Common-Mode Voltage
The CM input controls the output common-mode voltage. CM has no internal biasing network and must be driven
by an external source or resistor divider network to the positive power supply. The CM input impedance is very
high and bias current is not critical. Also, the CM input has no internal reference and must be driven from an
external source. Using a bypass capacitor is also necessary. A capacitor value of 0.01 µF is recommended. For
best harmonic distortion, maintain the CM input within ±1 V of the mid-supply voltage using a 5-V supply and
within ±0.5 V when using a 3.3-V supply. The CM input voltage can be operated outside this range if lower
output swing is used or distortion degradation is allowed. For more information, see Figure 18 and Figure 19.
Copyright © 2014, Texas Instruments Incorporated
Product Folder Links: LMH3401
Submit Documentation Feedback
25