iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC21/36
Z Configuration
Auto Adaption Configuration
In the Z Configuration tab, enter Yes or No as to
whether an index sensor is connected to the ZERO+
and ZERO– inputs. If an index sensor is not used,
the ZERO inputs of the iC-TW8 should be connect-
ed to AVDD and AVSS as explained on page 13
and the remaining entries on this sheet can be ig-
nored. Not using an index sensor allows higher
speeds with high interpolation factors.
In the Auto Adaption Configuration tab, select
which parameters are automatically adjusted
(adapted) during operation to maintain low interpo-
lation error and jitter. Analog gain, analog offset,
digital offset, digital gain match, and phase may be
individually selected although there are certain de-
pendencies that cause the design tool to override the
entered selections. In this case, a red warning is dis-
played by the design tool.
If an index sensor is used, enter the desired width of
the Z output pulse in AB edges. The actual Z output
pulse width is confirmed; it is always equal to the
desired width unless the post-AB divider is used
(see page 32) or a fractional desired width is en-
tered. The design tool shows the equivalent Z output
pulse width in AB output cycles, mechanical de-
grees of rotation (°m), arc-minutes of rotation, pre-
divider edges, and sensor input cycle degrees for
reference.
It is recommended to disable analog gain and offset
adaption and enable only digital offset, gain match,
and phase adaption during operation. In this case,
analog gain and offset remain at their calibrated set-
tings during operation. This prevents changes in an-
alog gain and offset (which can be quite large) from
causing disturbances in the interpolated output dur-
ing operation. Analog gain and offset adaption may
be enabled if large changes in sensor signal ampli-
tude or offset are expected during operation.
Next, enter the desired polarity for the Z output as
either active high or active low. If the post-AB di-
vider is not used and the actual interpolation factor,
inter, is an integer, the states of the A and B outputs
at the beginning of the Z output (zpos) can be en-
tered to specify the desired synchronization of the
A, B, and Z outputs.
If digital offset adaption is enabled, enter the desired
digital offset tolerance and the design tool confirms
the closest actual tolerance that can be achieved.
Digital offset tolerance is the amount of un-
corrected offset that the iC-TW8 tolerates before
auto adaption corrects it. Small tolerance values
must be used for highest accuracy, but also cause
offset corrections to occur more frequently during
operation and thus may lead to increased output jit-
ter. Digital offsets of less than the entered tolerance
are not corrected. In general, set the digital offset
tolerance to the smallest value that prevents dither-
ing of the digital offset correction value during nor-
mal operation.
Set both the Z position (zpos) and desired ZERO
threshold to 0 initially. Proper values for these pa-
rameters are determined when the Z signal path is
calibrated (see page 26).
Finally, configure the iC-TW8’s internal 32-bit po-
sition counter to be reset to 0 by the Z output, the
ZERO input, or not at all. If “On zpos” is selected,
the counter is reset at zpos whenever the ZERO in-
put is active. If “On ZERO” is selected, the counter
is reset—and stays reset—whenever the ZERO in-
put is active.
If digital gain match adaption is enabled, enter the
desired digital gain match tolerance and the design
tool confirms the closest actual tolerance that can be
achieved. Digital gain match tolerance is the amount
of un-corrected gain mismatch between the sensor
Sin and Cos channels that the iC-TW8 tolerates be-
fore auto adaption corrects it. Small tolerance values
must be used for highest accuracy, but also cause
gain corrections to occur more frequently during
operation and may lead to increased output jitter.
Digital gain mismatch of less than the entered toler-
ance is not corrected. In general, set the digital gain
match tolerance to the smallest value that prevents
dithering of the digital gain match correction value
during normal operation.
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