Building Blocks Of An Electronic Compass; Figure 3 Functional Block Diagram Of An Electronic Compass - Philips KMZ51 Application Note

Philips Semiconductors
Electronic Compass Design using
KMZ51 and KMZ52
3.

BUILDING BLOCKS OF AN ELECTRONIC COMPASS

Figure 3 shows a functional block diagram of an electronic compass. This is a minimum set-up, i.e. these
elements are principally required for any electronic compass. The functional blocks – except the field sensor –
can be realized either as hardware or as software. In the following, the functions of each block are summarized.
A detailed description of each block together with examples for realization are given in the following sections.
2-dimensional
field sensor
KMZ52
compensation
Iflip, Icomp
coil
S·Hex
flip
coil
Hex-Sensor
compensation
coil
Iflip, Icomp
flip
S·Hey
coil
Hey-Sensor
BLOCKDIA.AI
Figure 3
•
Magnetic field sensors
As already pointed out, the task of a compass is to measure the azimuth α, i.e. the angle between north and
heading direction, as defined by equation (1). Therefore, the strengths of two horizontal earth field components
have to be measured: one in heading direction (Hex) and one sidewards (Hey). This requires two magnetic field
sensors, both aligned parallel to the earth´s surface, but rotated by 90 degrees with respect to each other.
Philips´ magnetoresistive sensor technology is an optimum choice for measuring weak magnetic fields like the
earth´s field. The KMZ52 is a sensor device, which is perfectly matched to this application, as it comprises two
extremely sensitive field sensors in the required configuration in one SO16 package. Furthermore, the KMZ52
comprises for each of its sensors a set/reset coil needed for offset elimination and a coil for the compensation of
sensitivity temperature drift. Thus, the KMZ52 makes any external coils obsolete, which are required when using
other sensor products. Section 4 describes Philips´ magnetoresistive sensor technology and introduces those
products, which are dedicated to compass applications.
•
Signal conditioning unit (SCU)
The purpose of this block is to deliver output voltages proportional to the field strengths Hex and Hey
respectively. Therefore, the signals delivered by the magnetic field sensors have to be amplified. Also offsets
have to be eliminated. Beyond that, the amplification of one SCU channel should be trimable in order to allow
Signal Conditioning Unit
(SCU)
x-channel
- Amplification
- Offset elimination
(- Temperature
compensation of
sensitivity)
y-channel
- Amplification
- Offset elimination
(- Temperature
compensation of
sensitivity)
Functional block diagram of an electronic compass
Vx
Direction Determination
Unit (DDU)
azimuth derivation
Vy
10
Application Note
AN00022
Display
Interface to
other system,
e.g. navigation