ad15-138z-0reel Analog Devices, Inc., ad15-138z-0reel Datasheet - Page 8

• Manufacturer Part Number: ad15-138z-0reel
• Description: Cmos 1.8 V To 5.5 V, 2.5
  2 1 Mux/spdt Switch In Sot-23
• Manufacturer: Analog Devices, Inc.

ADG719
APPLICATIONS INFORMATION
The ADG719 belongs to Analog Devices’ new family of
CMOS switches. This series of general-purpose switches has
improved switching times, lower on resistance, higher band-
widths, low power consumption, and low leakage currents.
ADG719 Supply Voltages
Functionality of the ADG719 extends from 1.8 V to 5.5 V single
supply, which makes it ideal for battery-powered instruments
where power efficiency and performance are important design
parameters.
It is important to note that the supply voltage effects the input
signal range, the on resistance, and the switching times of the part.
By taking a look at the Typical Performance Characteristics and the
Specifications, the effects of the power supplies can be clearly seen.
For V
temperature range.
On Response vs. Frequency
Figure 1 illustrates the parasitic components that affect the ac perfor-
mance of CMOS switches (the switch is shown surrounded by a
box). Additional external capacitances will further degrade some
performance. These capacitances affect feedthrough, crosstalk,
and system bandwidth.
The transfer function that describes the equivalent diagram of
the switch (Figure 1) is of the form A(s) shown below:
where:
Figure 1. Switch Represented by Equivalent Parasitic
Components
C
R
T
T
DD
=
=
C
V
R
= 1.8 V operation, R
IN
LOAD
LOAD
S
+
(
R
A s
C
LOAD
( )
D
+
C
R
=
DS
ON
C
+
R
DS
T
R



ON
s R R
(
s R
(
)
ON
C
T
D
ON
is typically 40 Ω over the
ON
D
C
DS
C
T
C
)
LOAD
+
)
+
1
1



R
LOAD
V
OUT
–8–
The signal transfer characteristic is dependent on the switch
channel capacitance, C
zero in the numerator of the transfer function A(s). Because the
switch on resistance is small, this zero usually occurs at high
frequencies. The bandwidth is a function of the switch output
capacitance combined with C
frequency pole corresponding to these capacitances appears in
the denominator of A(s).
The dominant effect of the output capacitance, C
pole breakpoint frequency to occur first. Therefore, in order to
maximize bandwidth, a switch must have a low input and
output capacitance and low on resistance. The On Response
vs. Frequency plot for the ADG719 can be seen in TPC 9.
Off Isolation
Off isolation is a measure of the input signal coupled through an
off switch to the switch output. The capacitance, C
input signal to the output load when the switch is off, as shown
in Figure 2.
The larger the value of C
that will be produced. TPC 7 illustrates the drop in off isolation as
a function of frequency. From dc to roughly 200 kHz, the switch
shows better than –95 dB isolation. Up to frequencies of 10 MHz,
the off isolation remains better than –67 dB. As the frequency
increases, more and more of the input signal is coupled through to
the output. Off isolation can be maximized by choosing a switch
with the smallest C
capacitance also affect off isolation, since they contribute to the
coefficients of the poles and zeros in the transfer function of the
switch when open.
Figure 2. Off Isolation Is Affected by External Load
Resistance and Capacitance
V
IN
A s
( )
=
S



s R
DS
(
possible. The values of load resistance and
C
LOAD
DS
DS
. This capacitance creates a frequency
DS
, the larger the values of feedthrough
) (
s R
DS
C
(
LOAD
C
and the load capacitance. The
LOAD
D
D
+
C
C
DS
D
C
)
LOAD
+
C
DS
)
DS
R
LOAD
+
D
, couples the
 1
, causes the
V


OUT
REV. B