iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC25/36
Auto Calibration
Once the iC-TW8 has been configured, the signal
path must be calibrated to determine proper values
for gain, offset correction, gain match, and phase
correction. This is most easily done using the Auto
Calibration feature of the iC-TW8 to automatically
determine optimum values for these parameters. Al-
ternatively, initial parameter values may be written
to the parameter registers using the serial interface
and allowed to adapt. The adapted parameter values
must then be written to the EEPROM for use after
subsequent startups.
Auto calibration is initiated by pulling CALIB (pin
5) to DVSS. A pushbutton switch connected be-
tween CALIB and circuit ground (as shown in Fig-
ure 8 on page 10) is an easy way to achieve this in
series production. With CALIB held low, provide
sensor input of a few hundred Sin/Cos cycles and
the iC-TW8 “tunes” the analog gain, analog offset
correction, digital offset correction, digital gain
match, and digital phase correction parameters to
provide lowest error and jitter in the interpolated AB
outputs.
The sensor input used for auto-calibration does not
need to be at a constant frequency nor must it be
unidirectional. A rotary encoder can be calibrated by
moving the disc or wheel back and forth by a few
revolutions; a linear encoder by moving the sensor
back and forth on the scale by a few centimeters.
After providing sufficient input signals, release the
CALIB input (it is pulled high by an internal pull-up
resistor) and the iC-TW8 immediately stores all cal-
ibration parameters in the external EEPROM. These
auto-calibrated values are then used for subsequent
startups (see page 15).
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