Datasheet
LMH6570
R
OUT
45:
C
L
10 pF
R
L
1 k:
V
OUT
R
2
D
1
C
1
R
1
TO SD
LMH6570
www.ti.com
SNCS104C –APRIL 2005–REVISED MAY 2013
Figure 30. Delay Circuit Implementation
If it is important in the end application to make sure that no two inputs are presented to the output at the same
time, an optional delay block can be added, to drive the SHUTDOWN pin of each device, as shown. Figure 30
shows one possible approach to this delay circuit. The delay circuit shown will delay SHUTDOWN's H to L
transitions (R
1
and C
1
decay) but won’t delay its L to H transition. R
2
should be kept small compared to R
1
in
order to not reduce the SHUTDOWN voltage and to produce little or no delay to SHUTDOWN.
Other Applications
The LMH6570 could support a dual antenna receiver with two physically separate antennas. Monitoring the
signal strength of the active antenna and switching to the other antenna when a fade is detected is a simple way
to achieve spacial diversity. This method gives about a 3dB boost in average signal strength and is the least
expensive method for combining signals.
DRIVING CAPACITIVE LOADS
Capacitive output loading applications will benefit from the use of a series output resistor R
OUT
. Figure 31 shows
the use of a series output resistor, R
OUT
, to stabilize the amplifier output under capacitive loading. Capacitive
loads of 5 to 120 pF are the most critical, causing ringing, frequency response peaking and possible oscillation.
Figure 32 gives a recommended value for selecting a series output resistor for mitigating capacitive loads. The
values suggested in the charts are selected for 0.5 dB or less of peaking in the frequency response. This gives a
good compromise between settling time and bandwidth. For applications where maximum frequency response is
needed and some peaking is tolerable, the value of R
OUT
can be reduced slightly from the recommended values.
Figure 31. Decoupling Capacitive Loads
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