LMH6555EVAL National Semiconductor, LMH6555EVAL Datasheet - Page 14

• Manufacturer Part Number: LMH6555EVAL
• Manufacturer: National Semiconductor

Specifications of LMH6555EVAL

• Lead Free Status / Rohs Status: Not Compliant

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As can be seen in Figure 7, the source impedance of the input
side being driven has a bigger effect on gain than the undriven
source impedance. R
posite directions. Manipulating the value of R
control has another advantage over doing the same to R
and that is the signal input termination is not affected by it.
This is especially important in applications where the signal
is applied to the LMH6555 through a transmission line which
needs to be terminated in its characteristic impedance for
minimum reflection.
For reference, Figure 8 shows the effect of source impedance
misbalance on overall gain and output offset voltage with dif-
ferential input drive.
FIGURE 7. Gain & Output Offset Voltage vs. Source
Impedance Shift for Single Ended Input Drive
S1
and R
S2
affect the output offset in op-
S2
for offset
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S1
14
It is possible to manipulate output offset with little or no effect
on source resistance balance, gain, and, cable termination.
R
the input to achieve the required output shift. For a positive
shift, positive current would need to be injected into the V
terminal (Figure 9(a)) and for a negative shift, to the V
minal (Figure 9(b)). Figure 10 shows the effect of R
output with V
X
FIGURE 8. Gain & Output Offset Voltage vs. Source
, shown in Figure 9(a) and Figure 9(b), injects current into
FIGURE 9. Differential Output Shift Circuits
Impedance Shift for Differential Input Drive
X
= 3.3V or 5V, and R
(a)
(b)
S1
= R
S2
= 50Ω.
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20127752
X
20127732
IN
on the
−
ter-
IN
+