REV.
ADG751
–8–
GENERAL DESCRIPTION
The ADG751 is an SPST switch constructed using switches in a
T configuration to obtain high “OFF” isolation while maintain-
ing good frequency response in the “ON” condition.
Figure 12 shows the T-switch configuration. While the switch is
in the OFF state, the shunt switch is closed and the two series
switches are open. The closed shunt switch provides a signal
path to ground for any of the unwanted signals that find their
way through the off capacitances of the series’ MOS devices.
This results in improved isolation between the input and output
than with an ordinary series switch. When the switch is in the
ON condition, the shunt switch is open and the signal path is
through the two series switches which are now closed.
D
IN
S
SERIES
SHUNT
Figure 12. Basic T-Switch Configuration
LAYOUT CONSIDERATIONS
Where accurate high frequency operation is important, careful
consideration should be given to the printed circuit board layout
and to grounding. Wire wrap boards, prototype boards and
sockets are not recommended because of their high parasitic
inductance and capacitance. The part should be soldered di-
rectly to a printed circuit board. A ground plane should cover all
unused areas of the component side of the board to provide a
low impedance path to ground. Removing the ground planes
from the area around the part reduces stray capacitance.
Good decoupling is important in achieving optimum perfor-
mance. V
DD
should be decoupled with a 0.1 µF surface mount
capacitor to ground mounted as close as possible to the device
itself.
