High Performance Automotive Sonar Intrusion – Data Sheet

AS8412

March 2001

Page 8 of 14

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

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

some extra gain.

A pre-amplifier that satisfies the bias requirements is shown at the Fig. 4. Its gain is around

8 dB.

Fig. 4 - Recommended pre-amplifier

Sensitivity Programming

The AS8412 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 enve-

lope 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 and 270-pF capacitor at

VCAP.