EL2140C/2141C
150 MHz Differential Twisted Pair Driver
Applications Information Ð Contd.
H3 The third harmonic should be the dominant
harmonic and is primarily affected by output
load current which, of course, is unavoidable.
However, this should encourage the user not to
waste current in the gain setting resistors, and to
use values that consume only a small proportion
of the load current, so long as peaking does not
occur. The more load current, the worse the dis-
tortion, but depending on the frequency, it may
be possible to reduce the amplifier gain so that
there is more internal gain left to cancel out any
distortion.
H5 The fifth harmonic should always be below
the third, and will not become significant until
heavy load currents are drawn. Generally, it
should respond to the same efforts applied to re-
ducing the third harmonic.
H6 The sixth harmonic should not be a problem
and is the result of poor power supply decou-
pling. While 100 nF chip capacitors may be suffi-
cient for some applications, it would be insuffi-
cient for driving full signal swings into a twisted
pair line at 100 kHz. Under these conditions, the
addition of 4.7 mF tantalum capacitors would
cure the problem.
Typical Applications Circuits
2140-15
Figure 1. Typical Twisted Pair Application
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ELANTEC [ ELANTEC SEMICONDUCTOR ]
