Datasheet

V
IN
V
CM
R
L
275:
50:
V
CLAMP
a
+
-
275:
255:
255:
50:
26.7:
59:
R
S
= 50:
LMH6553
www.ti.com SNOSB07H –SEPTEMBER 2008–REVISED MARCH 2013
To match the input impedance of the circuit in Figure 56 to a specified source resistance, R
S
, requires that R
T
||
R
IN
= R
S
. The equations governing R
IN
and A
V
for single-to-differential operation are also provided in Figure 56.
These equations, along with the source matching condition, must be solved iteratively to achieve the desired gain
with the proper input termination. Component values for several common gain configurations in a 50Ω
environment are given in Table 1.
Table 1. Gain Component Values for 50Ω System
WSON Package
Gain R
F
R
G
R
T
R
M
0 dB 275Ω 255Ω 59Ω 26.7Ω
6 dB 275Ω 127Ω 68.1Ω 28.7Ω
12 dB 275Ω 54.9Ω 107Ω 34Ω
Table 2. Gain Component Values for 50Ω System
SO PowerPAD Package
Gain R
F
R
G
R
T
R
M
0 dB 325Ω 316Ω 56.2Ω 26.7Ω
6 dB 325Ω 150Ω 64.9Ω 28Ω
12 dB 325Ω 68.1Ω 88.7Ω 31.6Ω
Figure 57. Single Ended Input S-Parameter Test Circuit (50Ω System)
The circuit shown in Figure 57 was used to measure S-parameters for a single-to-differential configuration.
Figure 45 and Figure 46 in Typical Performance Characteristics are taken using the recommended component
values for 0 dB gain.
SINGLE SUPPLY OPERATION
Single supply operation is possible on supplies from 5V to 10V; however, as discussed earlier, AC input coupling
is recommended for low supplies due to input common mode limitations. An example of an AC coupled, single
supply, single-to-differential circuit is shown in Figure 58. Note that when AC coupling, both inputs need to be AC
coupled irrespective of single-to-differential or differential-to-differential configuration. For higher supply voltages,
DC coupling of the inputs may be possible provided that the output common mode DC level is set high enough
so that the amplifier's inputs and outputs are within their specified operating ranges.
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