LH4266 Datasheet, PDF (5/8 Pages) National Semiconductor (TI) – SPDT RF Switch

Leakage Current Equivalent Test Circuit
Same test for Input 2
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Test Circuit for Isolation Input to Output
for ease of use Thus for high frequency applications bypass
capacitors are not required however at low frequencies (10
MHz or less) a 4 7 mF bypass capacitor for each supply is
recommended
Due to the unique design of the LH4266 it can easily be
used as a multiplexer or demultiplexer In fact several units
can be connected to give a 1 to 4 multiplexer or a 4 to 1
demultiplexer by simply adding the required units as shown
in Figures 2 to 5
The action of the switches can be seen in the following truth
table
LH4266 Truth Table
Control
Low e 0
High e 1
Pin 24
Input 2
On
Off
Pin 13
Input 1
Off
On
Double Sided Board Bottom Side
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Applications Information LH4266
The LH4266 uses hybrid technology to give increased cir-
cuit performance In order to maintain its excellent cross
talk and feedthru specifications proper RF grounding and
shielding should be incorporated in the printed circuit board
layout For example the input traces should not run next to
output traces and grounds should be provided by a ground
plane under the device (see Figure 1a b for suggested PC
board layout)
The device contains two internal termination resistors and
switches If termination of the non-selected input is desired
connect the termination pin to the adjacement input pin and
the deselected input will be terminated with approximately
50X
Note that the internal termination resistors are internally
connected to the device’s ground pin Thus if the internal
termination resistors are used then the input ground planes
should remain isolated from the output ground plane (as in
Figure 1 ) so as not to form a ground loop When using exter-
nal termination resistors at the input the resistors should be
connected to their respective ground planes and pin 16
should be tied to input1’s ground plane while pin 21 is tied
to input2’s ground plane Since pins 16 and 21 are internally
connected to the device ground pin the input and output
ground planes should remain isolated LH4266’s power sup-
plies are internally bypassed with high frequency capacitors
5
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FIGURE 1a LH4266 Recommended
Printed Circuit Board Layout
Double Sided Board Top Side
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FIGURE 1b LH4266 Recommended
Printed Circuit Board Layout