LMH6555EVAL National Semiconductor, LMH6555EVAL Datasheet - Page 12

• Manufacturer Part Number: LMH6555EVAL
• Manufacturer: National Semiconductor

Specifications of LMH6555EVAL

• Lead Free Status / Rohs Status: Not Compliant

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SINGLE-ENDED INPUT
The following is the procedure for determining the device op-
erating conditions for single ended input applications. This
example will use the schematic shown in Figure 3.
1. Determine the driven input’s (V
2. Calculate V
3. Determine the peak-to-peak differential current
4. Determine the swing across the input terminals
knowing that each input common mode impedance to
ground (R
For Figure 3
For Figure 3
(I
impedance (R
calculated in step 2:
For Figure 3
(V
in step 3 above.
V
V
V
A
where R
R
V
IN_DIFF
I
I
IN_DIFF
IN_DIFF
IN_DIFF
IN
IN
OUT
V_DIFF
S
OUT
+ (or V
+ = 0.3 V
= 50Ω
FIGURE 3. Single-Ended Input Drive
= (V
= (0.3 V
) through the device’s differential input
) which would give rise to the I
= V
= 724.5 mV
= 2 · R
F
IN
IN
= 430Ω & R
OUT
→
) is 50Ω:
IN
OUT
/2) · A
−) = V
PP
A
IN_DIFF
PP
V_DIFF
knowing the Insertion Gain (A
/ R
F
· 50/(50+50) = 0.15 V
/ (2R
/2) · 4.83 V/V= 724.5 mV
F
V_DIFF
IN
) which would result in the V
PP
· R
S
= 4.83 V/V
/ 430Ω = 1.685 mA
IN_DIFF
+ R
IN
/(R
IN_DIFF
IN
= 78Ω
IN
+ R
+ or V
)
S
)
PP
IN_DIFF
IN
−) swing
PP
PP
calculated
V_DIFF
OUT
20127710
):
12
The values determined with the procedure outlined here are
shown in Figure 4.
5. Calculate the undriven input’s swing, based on V
6. Determine the DC average of the two inputs (V
FIGURE 4. Input Voltage for Figure 3 Schematic
For Figure 3
determined in step 4 and V
For Figure 3
using the following expression:
For Figure 3
V
V
V
V
V
where R
to the LMH6555)
R
V
IN_DIFF
IN_DIFF
IN
IN
I_CM
S
I_CM
− = V
− = 150 mV
= 50Ω
= 12.6 mA · R
= 15.75/ (50+64) = 138.2 mV
= I
= 1.685 mA
E
IN
+ - V
= 25Ω & R
→
IN_DIFF
V
I_CM
PP
IN_DIFF
· R
- 131.4 mV
= 15.75 / (R
PP
E
IN_DIFF
G
· R
= 39Ω (both internal
· 78Ω = 131.4 mV
S
IN
/ (R
+ calculated in step 1:
PP
S
S
= 18.6 mV
+ R
+ 64)
G
+ R
PP
E
20127764
PP
)
I_CM
IN_DIFF
) by