High Performance Automotive Sonar Intrusion – Data Sheet

AS8413

March 2001

Page 9 of 15

Fig. 4 - Recommended pre-amplifier

As a general rule, the best approach is to measure the voltage at the “valley”, that normally oc-

curs at the end of the echo waveform. If it is above 1.8 V, then the system could benefit from

some extra gain.

Sensitivity Programming

The AS8413 allows the sensitivity to intrusions and movements to be programmed at produc-

tion, so the manufacturer can adapt the detector to different requirements.

There are two possible ways of programming the sensitivity:

• Digital programming by the pins SENS1 and SENS0: controls the criteria used by the dis-

criminator to validate intrusions or movements. Four sensitivities are available, as shown at

Table 1.

Table 1. Digital programmable sensitivities

SENS1

SENS0

Sensitivity

1

1

High

1

0

Mid-high

0

1

Mid-low

0

0

Low

• Capacitor at the pin VCAP: controls the analog processing of the echo signal at the envelope

detector. With smaller capacitors, the digitized echo signal will have a higher resolution and,

as a result, a higher sensitivity will be obtained.

The best combination of digital programming and VCAP capacitor is usually determined by

experiment. A generally good choice is to use sensitivity mid-high with a 270-pF capacitor at

VCAP.