REV. 0

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-

µF surface mount

capacitor to ground mounted as close as possible to the device

itself.