iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC8/36
Digital Hysteresis
Z Signal Path
Digital hysteresis may be added to the interpolated
sensor input angle to reduce AB output dithering
(instability) at standstill at the expense of position
error on direction reversal. A hysteresis range of 0 –
22.5° of an input cycle in 0.044° steps is available.
The actual hysteresis, hyst[°], is determined by the
MAIN_HYST register in the CFG block in internal
memory.
The Z signal path is similar to the front end of the
AB signal path except that a 1-bit ADC (compara-
tor) is used.
zgain = 8
zth
Comparator
Delay Match
ZERO+
ZERO–
To
Output
Generator
Delay
Figure 7: Z Signal Path
Interpolation Factor
The 16-bit sensor input angle value is scaled to the
resolution required by the desired interpolation fac-
tor. A range of 4 – 65,536 AB output edges per sen-
sor Sin/Cos input cycle in steps of 1 edge is availa-
ble. This is equivalent to a interpolation range of
x1.00 – x16,384.00 AB output cycles per input cy-
cle in steps of 0.25 AB output cycle. The actual in-
terpolation factor, inter, is determined by the
MAIN_INTER register in the CFG block in internal
memory.
A fixed analog gain of 8 is applied to the differential
ZERO sensor input. A threshold offset is then added
to the amplified ZERO signal to set the switching
threshold of the comparator. The actual analog
threshold level, zth, is determined by MAIN_Z in
the CFG block in internal memory and has a range
of ±300mV in 20mV steps. The effective ZERO
input threshold therefore has a range of ±37.5mV in
2.5mV steps.
To ensure that the digital ZERO signal stays in syn-
chronization with the digital sensor angle at all sen-
sor speeds, a delay matching the inherent latency of
the AB signal path is introduced into the Z signal
path. The delayed and conditioned digital ZERO
signal is then sent to the output generator where the
Z output is generated and can be synchronized to the
AB outputs.
Output Generator
The output generator generates quadrature AB out-
puts or a pulse-width modulated (PWM) bit stream
output depending on the output mode. The output
mode is determined by MAIN_OUT.mode in the
CFG block in internal memory. The output genera-
tor also uses the conditioned ZERO signal from the
Z signal path to generate a Z output that can be syn-
chronized to the AB outputs.
Auto Calibration and Auto Adaption
The iC-TW8 provides sophisticated automatic cali-
bration and adaption features to allow optimal pa-
rameter values for the AB signal path to be set and
maintained during operation. Auto calibration is
used to determine initial parameter values when the
iC-TW8 is first commissioned. The CALIB input
(pin 5) or commands over one of the serial interfac-
es may be used to initiate auto calibration.
The output generator contains an optional divider
that can be used in AB output mode to produce frac-
tional interpolation factors. This is useful in situa-
tions where the desired output resolution is not an
integer multiple of the input resolution.
Auto adaption is used to maintain (adapt) optimal
parameter values for the AB signal path during op-
eration. Auto adaption can adjust analog gain, ana-
log offset correction, digital offset correction, digital
gain match, and digital phase correction to ensure
maximum interpolator accuracy under all operating
conditions. Auto adaption is controlled by variables
in the ADPT_CORR and ADPT_DETAIL registers
in the CFG block of internal memory.
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