ADG719

Rev. D | Page 12 of 16

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 bandwidths, 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.

temperature range.

ON RESPONSE VS. FREQUENCY

Figure 22 illustrates the parasitic components that affect the ac

performance 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.

S

D

Figure 22. Switch Represented by Equivalent Parasitic Components

The transfer function that describes the equivalent diagram of

the switch (Figure 22) is of the form A(s) shown below:

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

+

+

=

1

)

(

1

)

(

)

(

T

ON

T

DS

ON

T

C

R

R

s

C

R

s

R

s

A

where:

The signal transfer characteristic is dependent on the switch

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

frequency pole corresponding to these capacitances appears in

the denominator of A(s).

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 Figure 12.

OFF ISOLATION

Off isolation is a measure of the input signal coupled through

the input signal to the output load when the switch is off, as

shown in Figure 23.

S

D

Figure 23. Off Isolation Is Affected by External Load Resistance and

Capacitance

that will be produced. Figure 10 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

and 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.

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

+

+

+

=

1

)

(

)

(

)

(

)

(

DS

D

LOAD

LOAD

DS

LOAD

C

C

C

R

s

C

R

s

s

A