mlx90333 Melexis Company, mlx90333 Datasheet - Page 11

• Manufacturer Part Number: mlx90333
• Description: Triaxis? 3d-joystick Position Sensor
• Manufacturer: Melexis Company

The conditioned analog signals are converted through an ADC (configurable − 14 or 15 bits) and provided
to a DSP block for further processing. The DSP stage is based on a 16 bit RISC micro-controller whose
primary function is the extraction of the two (2) angular information from the three (3) raw signals (after so-
called front-end compensation steps) through the following operations:
where k
vs. V
normalization of the raw signals prior to performing the “ATAN” function.
In a joystick based on a “ball & socket” joint as shown on Figure 3 (right), the magnet (axial
magnetization) moves on a hemisphere centered at the pivot point. The flux density is described through
slightly more complex equations but the MLX90333 offers an alternate algorithm to extract both angular
informations:
where k
The DSP functionality is governed by the micro-code (firmware − F/W) of the micro-controller which is
stored into the ROM (mask programmable). In addition to the ″ATAN″ function, the F/W controls the whole
analog chain, the output transfer characteristic, the output protocol, the programming/calibration and also
the self-diagnostic modes.
In the MLX90333, the ″ATAN″ function is computed via a look-up table (i.e. it is not obtained through a
CoRDiC algorithm).
Due to the fact that the ″ATAN″ operation is performed on the ratios ″V
information are intrinsically self-compensated vs. flux density variations (due to airgap change, thermal or
ageing effects) affecting the magnetic signal. This feature allows therefore an improved thermal accuracy
vs. joystick based on conventional linear Hall sensors.
Once the angular information is computed (over 360 degrees), it is further conditioned (mapped) vs. the
target transfer characteristic and it is provided at the output(s) as:
3901090333
Rev. 001
•
•
•
X
& V
Z
Z
an analog output level through a 12 bit DAC followed by a buffer
a digital PWM signal with 12 bit depth (programmable frequency 100 Hz … 1 kHz)
a digital Serial Protocol (SP − 14 bits computed angular information available)
and k
is a programmable parameter. First of all, k
Y
. On the other hand, k
t
are programmable parameters.
α
β
Z
=
=
allows also a targeted reduction of the linearity error through a
ATAN
ATAN
α
β
=
=
⎛
⎜
⎜
⎝
⎛
⎜
⎜
⎝
ATAN
ATAN
Page 11 of 43
Tria⊗is™ 3D-Joystick Position Sensor
(
(
k
k
Z
Z
Z
V
V
⎛
⎜ ⎜
⎝
⎛
⎜ ⎜
⎝
is used to compensate the smaller amplitude of V
Z
Z
k
k
)
)
V
V
V
V
2
Z
2
Z
V
V
X
Y
X
Y
+
+
Z
Z
(
(
⎞
⎟ ⎟
⎠
⎞
⎟ ⎟
⎠
k
k
t
t
V
V
Y
X
)
)
2
2
⎞
⎟
⎟
⎠
⎞
⎟
⎟
⎠
Z
/V
X
″ and ″V
MLX90333
Z
/V
Y
″, the angular
Data Sheet
Jan 08
Z