Test Circuitry; Magic Asic - Nokia NPL-4 Series Manual

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Test Circuitry

Based on constant current generator, which drives internal coil on magnetometer chip.
Circuit is controlled via general IO –pin on MagIC/RegCtrl. On current is 2.0mA, off cur-
rent is 0.00mA.
RegCtrl
with zero
Offset strap current will produce 320 to 420digit offset to raw x and y values.

MagIC ASIC

The electronic compass will have two magnetometer channels and it uses anisotropic
magnetoresistive (AMR) magnetometer component (containing both X- and Y-axes).
Each measurement axis is configured as a 4-element Wheatstone bridge converting the
magnetic field into a differential output voltage. This sensor element is capable of sens-
ing fields in milligauss range. In order to achieve the measurement resolution, the sensor
must be frequently reset by a current pulse that is driven through the set/reset coil of the
sensor element. The ASIC will interface the phone engine through either the CBUS or I2C
interface. The calculation of the compass heading and the calibration of the magnetom-
eter are carried out in the phone engine. The ASIC has a third magnetometer channel,
but it is not used in this project.
Copyright © 2005 Nokia Corporation. All rights reserved.
Issue 2 05/05
Figure 18: Test Circuitry
Vana_Ext
Constant
current
driver
Figure 19: Offset strap coil current effect
y
System Module and User Interface
sensor
with set
x
NPL-4/5/
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