ATS665LSG

TRUE ZERO-SPEED GEAR TOOTH SENSOR

SENSOR OPERATION: AUTOMATIC GAIN CONTROL (AGC)

The patented self-calibrating circuitry is unique. After each power up, the device measures the peak-to-peak magnetic

signal. The gain of the sensor is then adjusted which keeps the internal signal amplitude constant over the air gap range of

the device. This feature provides operational characteristics independent of air gap.

DIFFERENTIAL MAGNETIC SIGNAL

WITH INCREASING AIR GAP

-1000

-800

-600

-400

-200

0

200

400

600

800

1000

0123 456789 10 11 12 13 14 15

TARGET POSITION [DEGREES]

0.25 mm

0.50 mm

1.00 mm

1.50 mm

2.00 mm

Magnetic Signal with no Amplification

DIFFERENTIAL ELECTRICAL SIGNAL

WITH INCREASING AIR GAP

-1000

-800

-600

-400

-200

0

200

400

600

800

1000

0 123 4 56789 10 11 12 13 14 15

TARGET POSITION [DEGREES]

0.25 mm

0.50 mm

1.00 mm

1.50 mm

2.00 mm

Electrical Signal after AGC

SENSOR OPERATION: OFFSET ADJUST

In addition to normalizing performance over air gap, the gain control circuitry also reduces the effect of chip, magnet, and

installation offsets. This is accomplished using two D/A converters that capture the peak and valley of the signal and use it

as a reference for the switching comparator. If induced offsets bias the absolute signal up or down, AGC and the dynamic

DAC behavior work to normalize and reduce the impact of the offset on sensor performance.

Final Version, Rev 1.0; DSD; 01Aug03

Page 8

Worcester, Massachusetts 01615-0036 (508) 853-5000

Copyright © 1993, 1995 Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036