LMH6552 Datasheet, PDF (19/38 Pages) Texas Instruments – 1.5-GHz Fully Differential Amplifier

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Typical Applications (continued)
LMH6552
SNOSAX9I – APRIL 2007 – REVISED JANUARY 2015
357:
R_S = 50:
a ^VS
58:
357:
+
V_CM
R_S = 50:
357:
58:
-
ENABLE
50:
R_L
50:
357:
Figure 40. Differential S-Parameter Test Circuit
Gain
0 dB
6 dB
12 dB
Table 1. Gain Component Values for 50Ω System WSON Package
R_F
275Ω
275Ω
275Ω
R_G
255Ω
127Ω
54.9Ω
R_T
59Ω
68.1Ω
107Ω
R_M
26.7Ω
28.7Ω
34Ω
357:
50:
R_S = 50:
348:
a ^VS
56.2:
+
V_CM
R_L
-
348:
26.4:
ENABLE
50:
357:
Figure 41. Single Ended Input S-Parameter Test Circuit (50Ω System)
The circuit shown in Figure 41 was used to measure S-parameters for a single-to-differential configuration.
Figure 34 and Figure 35 in Typical Performance Characteristics are taken using the recommended component
values for 0 dB gain.
9.2.1.2.3 Driving Capacitive Loads
As noted previously, capacitive loads should be isolated from the amplifier output with small valued resistors.
This is particularly the case when the load has a resistive component that is 500 Ω or higher. A typical ADC has
capacitive components of around 10 pF and the resistive component could be 1000 Ω or higher. If driving a
transmission line, such as 50Ω coaxial or 100Ω twisted pair, using matching resistors will be sufficient to isolate
any subsequent capacitance.
9.2.1.2.3.1 Balanced Cable Driver
With up to 15 V_PP differential output voltage swing and 80 mA of linear drive current the LMH6552 makes an
excellent cable driver as shown in Figure 42. The LMH6552 is also suitable for driving differential cables from a
single ended source.
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