ADG752
–6–
FREQUENCY – MHz
100
ATTENUATION – dB
101
–8
–4
–2
0
–6
T
A
= +258C
Figure 7. On Response vs. Frequency
GENERAL DESCRIPTION
The ADG752 is an SPDT switch constructed using switches in
a T configuration to obtain high “OFF” isolation while main-
taining good frequency response in the “ON” condition.
Figure 8 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 more 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.
Figure 8. 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.
V
DD
IN
ADG752
D
S1
S2
75V
V
OUT
75V
CH1
CH2
A
=
2
250V
250V
75V
75V
Figure 9. Multiplexing Between Two Video Signals
