iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC34/36
temperature oscillator frequency should be reduced
accordingly. See Electrical Characteristics in the iC-
TW8 data sheet for the actual value of the oscilla-
tor’s temperature coefficient.
The simplest LUT is a null table, where all values
are zero. This is equivalent to bypassing the LUT
and applies no correction to the sensor signal, but
serves as a starting point for understanding LUT
operation.
Using the LUT
1 Input Cycle
The iC-TW8 contains a 64-byte sensor distortion
look-up table (LUT) that can be used to apply an
arbitrary correction function to the calculated sensor
position (angle). To use the LUT, the correction
values must first be calculated and loaded into the
table using the design tool, the GUI software, or
commands sent via the serial ports. Then the LUT
must be enabled by setting ADPT_CFG.lut = 1 in
the CFG block in internal memory. When the LUT
is enabled, the maximum SPI port clock frequency
is reduced to fcore/4.If ADPT_CFG.lut = 0, the
LUT is bypassed and no correction is applied.
SIN
COS
360°
Sensor
Input
Angle
0°
14-bit Sensor
Position (Angle)
127
LUT
0
Values
SIN
1
ATAN
LUT
14-bit Corrected
Sensor Position
(Angle)
COS
–127
360°
0
LUT
Output
Angle
ADPT_CFG.lut
Figure 37: Sensor Distortion LUT
0°
The LUT divides the sensor Sin/Cos input cycle into
64 segments of 5.625° each and the table values de-
fine a 64-point piecewise linear correction curve.
Correction values for sensor angles within a LUT
table segment are linearly interpolated between the
two table values on either end of the segment. In
operation, the calculated correction value is added to
the sensor angle.
Figure 38: Null LUT
A constant LUT is one in which all the values are
the same. This adds a constant phase shift to the
sensor angle, shifting the 0° position left for positive
LUT values and right for negative values.
LUT table values have a range of ±127. The actual
correction applied to the 14-bit sensor angle is 4
times the table value, giving the LUT a correction
range of
4127
16384
360 11.16
The resolution of the LUT values is
4
360 0.088 5.3 arc minutes
16384
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