8

FN6097.3

November 17, 2004

resistance degrade at lower supply voltages. Refer to the

electrical specification tables and Typical Performance

curves for details.

V+ and GND power the internal logic (thus setting the digital

switching point) and level shifters. The level shifters convert

the logic levels to switched V+ and V- signals to drive the

analog switch gate terminals.

Logic-Level Thresholds

This device is 1.8V CMOS compatible (0.5V and 1.4V) over

a supply range of 2.0V to 3.6V (see Figure 13). At 3.6V the

guaranteed high output minimum level of 1.4V, but noise

margin is reduced.

The digital input stages draw supply current whenever the

digital input voltage is not at one of the supply rails. Driving

the digital input signals from GND to V+ with a fast transition

time minimizes power dissipation.

High-Frequency Performance

In 50

Ω systems, signal response is reasonably flat even past

10MHz with a -3dB bandwidth of 70MHz (see Figure 17).

The frequency response is very consistent over a wide V+

range, and for varying analog signal levels.

An OFF switch acts like a capacitor and passes higher

frequencies with less attenuation, resulting in signal feed

through from a switch’s input to its output. Off Isolation is the

resistance to this feed through, while Crosstalk indicates the

amount of feed through from one switch to another.

Figure 18 details the high Off Isolation and Crosstalk

rejection provided by this family. At 100kHz, Off Isolation is

about 65dB in 50

Ω systems, decreasing approximately 20dB

per decade as frequency increases. Higher load

impedances decrease Off Isolation and Crosstalk rejection

due to the voltage divider action of the switch OFF

impedance and the load impedance.

Leakage Considerations

Reverse ESD protection diodes are internally connected

between each analog-signal pin and both V+ and GND.

One of these diodes conducts if any analog signal exceeds

V+ or GND.

Virtually all the analog leakage current comes from the ESD

diodes to V+ or GND. Although the ESD diodes on a given

signal pin are identical and therefore fairly well balanced,

they are reverse biased differently. Each is biased by either

V+ or GND and the analog signal. This means their leakages

will vary as the signal varies. The difference in the two diode

leakages to the V+ and GND pins constitutes the analog-

signal-path leakage current. All analog leakage current flows

between each pin and one of the supply terminals, not to the

other switch terminal. This is why both sides of a given

switch can show leakage currents of the same or opposite

polarity. There is no connection between the analog signal

paths and V+ or GND.

FIGURE 9. ON RESISTANCE vs SUPPLY VOLTAGE vs

SWITCH VOLTAGE

FIGURE 10. ON RESISTANCE vs SWITCH VOLTAGE

0

1

234

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.75

V+ = 3V

V+ = 1.8V

V+ = 3.6V

V+ = 1.65V

V+ = 2.7V

00.511.522.5

3

V+ = 3V

0.35

0.4

0.45

0.5

0.55

0.6

0.65

25

°C

85

°C

-40

°C

ISL84782