ADG701BRMZ-REEL71 View Datasheet(PDF) - Analog Devices

Part Name

Description

MFG CO.

ADG701BRMZ-REEL71

CMOS Low Voltage 2 Ω SPST Switches

Analog Devices 

ADG701L/ADG702L

APPLICATIONS INFORMATION

The ADG701L/ADG702L belong to the Analog Devices new

family of CMOS switches. This series of general-purpose switches

have improved switching times, lower on resistance, higher

bandwidth, low power consumption, and low leakage currents.

SUPPLY VOLTAGES

Functionality of the ADG701L/ADG702L extends from 1.8 V to

5.5 V single supply, making the parts ideal for battery-powered

instruments where power, efficiency, and performance are

important design parameters.

It is important to note that the supply voltage affects the input

signal range, the on resistance, and the switching times of the

part. The effects of the power supplies can be clearly seen in the

Typical Performance Characteristics and the Specifications

sections.

For VDD = 1.8 V operation, RON is typically 40 Ω over the

temperature range.

BANDWIDTH

Figure 19 illustrates the parasitic components that affect the ac

performance of CMOS switches (a box surrounds the switch).

Additional external capacitances further degrade some perform-

ance. These capacitances affect feedthrough, crosstalk, and

system bandwidth.

CDS

S

D

VOUT

VIN

RON

CD

CLOAD

RLOAD

Figure 19. Switch Represented by Equivalent Parasitic Components

The transfer function that describes the equivalent diagram of

the switch (see Figure 19) is of the form A(s), as shown in the

following equation:

A(s)

=

RT

⎡

⎢

⎣

s(RON CDS ) + 1

s(RONCT RT ) + 1

⎤

⎥

⎦

where CT = CLOAD + CD + CDS.

The signal transfer characteristic is dependent on the switch

channel capacitance, CDS. This capacitance creates a frequency

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 CDS and the load capacitance. The

frequency pole corresponding to these capacitances appears in

the denominator of A(s).

The dominant effect of the output capacitance, CD, causes the

pole breakpoint frequency to occur first. In order to maximize

bandwidth, a switch must have a low input and output capaci-

tance and low on resistance. The on response versus frequency

for the ADG701L/ADG702L is shown in Figure 11.

OFF ISOLATION

Off isolation is a measure of the input signal coupled through

an off switch to the switch output. The capacitance, CDS, couples

the input signal to the output load when the switch is off (see

Figure 20).

CDS

S

D

VOUT

VIN

CD

CLOAD

RLOAD

Figure 20. Off Isolation Is Affected by External Load Resistance and

Capacitance

The larger the value of CDS, the larger the values of feedthrough

produced. Figure 10 illustrates the drop in off isolation as a

function of frequency. From dc to roughly 1 MHz, the switch

shows better than −75 dB isolation. Up to frequencies of

10 MHz, the off isolation remains better than −55 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 CDS possible. The values

of load resistance and capacitance also affect off isolation, as

they contribute to the coefficients of the poles and zeros in the

transfer function of the switch when open.

A(s)

=

RT

⎡

⎢

⎣

s(RLOADCDS ) + 1

s(RLOAD )(CT ) + 1

⎤

⎥

⎦

Rev. 0 | Page 10 of 12

Share Link: