LMH6881 Datasheet, PDF (25/35 Pages) Texas Instruments – Small Signal Bandwidth: 2400 MHz

www.ti.com
8.2.1.3 Application Curves
LMH6881
SNOSC72F – JUNE 2012 – REVISED FEBRUARY 2015
50
45
40
35
30
Voltage Gain
25
26 dB
16 dB
6 dB
20
0 50 100 150 200 250 300 350 400
FREQUENCY (MHz)
Figure 48. OIP3 vs Frequency
30
25
20
15
10
5
0
6 8 10 12 14 16 18 20 22 24 26
VOLTAGE GAIN (dB)
Figure 49. Noise Figure vs Voltage Gain
8.2.2 LMH6881 Used as Twisted-Pair Cable Driver
V_CC
: 0.01 PF
:
100: LMH6881
49.9:
CAT5
Rx
100:
0.01 PF
49.9:
5
GAIN 0-3
SD
OCM
1.25V
Figure 50. LMH6881 Used as Twisted-Pair Cable Driver
8.2.2.1 Design Requirements
Table 9 shows a design example for LMH6881 used as cable driver for driving unshielded twisted-pair (UTP)
CAT-5 cables.
Table 9. Example Design Requirement for a Cable Driver
SPECIFICATION
Supply Voltage and Current
Input to Output Device Configuration
Input frequency range
Voltage Gain Range
Output voltage swing
Cable length to be driven
EXAMPLE DESIGN REQUIREMENT
4.75 V to 5.25 V, with a minimum 150-mA supply current
Single-ended input to differential output
0.1 to 100 MHz
26-dB to 6-dB gain range
4 Vppdiff into a 200-Ω load at the output
300 to 400 feet
8.2.2.2 Detailed Design Procedure
The LMH6881 device can be used as a cable driver to drive (UTP) CAT-5 cable by following these basic
procedures:
• Select an appropriate input buffer or drive circuitry to the LMH6881 that provides pre-equalization in the
frequency range of interest that needs to be driven down the CAT-5 cable. The cable usually presents
attenuation of the signal at the receive end which is proportional to the length of the cable and the frequency
being transmitted. In some cases, use of the pre-equalization buffer is not possible which mandates the use
of a post-equalizer at the receive end to gain up the received signal.
Copyright © 2012–2015, Texas Instruments Incorporated
Product Folder Links: LMH6881
Submit Documentation Feedback
25