IC-TW8_13 Datasheet, PDF (56/63 Pages) IC-Haus GmbH – 16-BIT SIN/COS INTERPOLATOR WITH AUTO-CALIBRATION

iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
preliminary
Jan 9, 2013 Page SC29/36
grammer’s Reference). This forces the internal Z
gating signal onto OUTA (pin 18), as shown follow-
ing, where it can be observed using an oscilloscope.
ZERO+
ZERO–
Internal Z pulse,
zth
once per input cycle
Delay
OUTZ
OUTA
Figure 28: Observing the Z Gating Signal
Set the Z comparator switching threshold, zth, by
adjusting the value of MAIN_Z.th to produce a sin-
gle pulse at the Z gating signal output (OUTA) as
shown.
Analog
Index Sensor
Signal
zth
Z Gating
Signal
Figure 29: Setting the Z Comparator Threshold
Variable MAIN_Z.th can be accessed using the GUI
or by writing to the MAIN_Z register in the CFG
block in internal memory via the serial ports (see
Programmer’s Reference).
To calibrate zpos, it is necessary to observe both the
Z output and the internal Z gating signal simultane-
ously. Calibrate zpos by incrementing MAIN_ZPOS
(the zpos location within an input cycle) until the Z
output is centered within the Z gating signal, as
shown in Figure 27. MAIN_ZPOS can be accessed
using the GUI or by writing to the MAIN_ZPOS
register in the CFG block in internal memory via the
serial ports (see Programmer’s Reference). Finally,
disable Index Gating Test Mode in the Test Mode
pane of the Settings tab in the GUI or reset the Ena-
ble Z Test Mode bit (ztest) in the RB_TEST1 regis-
ter and then store the updated MAIN_ZPOS register
value to EEPROM using a Write All command via
one of the serial ports or the Write EEPROM button
in the GUI.
In general, the synchronization the of analog index
sensor signal to the Sin and Cos input signals is
fixed. It is determined by the physical alignment of
the incremental and Z tracks on the encoder disc or
wheel and the physical alignment of the incremental
and index sensors to each other. Since these physi-
cal alignments cannot typically be easily adjusted, it
is important that they be carefully controlled from
unit to unit to allow interchangeability of encoder
wheels and sensors in series production.
To guarantee one and only one Z output pulse per
revolution, the width of Z gating signal as set by zth
must be at least as wide as the desired width of the Z
output pulse and no longer than two input cycles
minus the width of the Z output pulse under all op-
erating conditions. Specifically,
zwidth[]  indexwidth[]  720  zwidth[]
Analog sensors often have side lobes on their output
signals as shown in Figure 29. It is important that
these side lobes not cross the comparator threshold
under any operating condition otherwise multiple Z
outputs may result.
where indexwidth[°] is the width of the Z gating
signal in input cycle degrees.
The Z comparator switching threshold, zth, has a
range of ±300mV in ±20mV steps (see Figure 28).
However, since the ZERO input amplifier has a
fixed gain of 8, the actual switching threshold range
referenced to the ZERO input signal level is
±37.5mV in steps of 2.5mV.
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