iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC7/36
The following P mode filter instances1 and approx-
imate filter bandwidths (–3dB) are available.
The following PI mode filter instances and approx-
imate filter bandwidths (–3dB) are recommended
(instances not shown may cause unstable filter re-
sponse).
P Mode Filter Instances
Instance
Noise and Jitter Bandwidth [kHz]
(Minimum lag)
2.5 fcore[MHz]
112
Recommended PI Mode Filter Instances
Instance
Noise and Jitter Bandwidth [kHz]
2.5 3 fcore[MHz]
2.5 7 fcore[MHz]
2.5 15 fcore[MHz]
2.5 31 fcore[MHz]
2.5 63 fcore[MHz]
2.5 127 fcore[MHz]
114
116
118
120
122
124
2.5 7 fcore[MHz]
2.5 15 fcore[MHz]
2.5 31 fcore[MHz]
2.5 63 fcore[MHz]
(Minimum overshoot)
52
70
88
(Max. overshoot)
106
(Maximum lag)
In general, use the maximum filter bandwidth (in-
stance 52); this gives the fastest response and mini-
mum position and speed overshoot. Another in-
stance may be used if additional noise and jitter fil-
tering is required.
In general, use the maximum filter bandwidth (in-
stance 112); this gives the fastest response and min-
imum filter lag. Another instance may be used if
additional noise and jitter filtering is required.
Lag Recovery Mode adds delay to the feedback path
of the PI mode filter, reducing latency-induced posi-
tion lag at constant sensor input velocity at the ex-
pense of under-damped filter response. In lag recov-
ery mode, the signal path filter configuration is as
shown in Figure 4 on page 6.
PI Mode adds igain to the P mode filter, eliminating
filter lag at constant sensor input velocity at the ex-
pense of critically damped filter response. In PI
mode, the signal path filter configuration is
pgain
igain
In lag recovery mode, position lag at constant sensor
input velocity due to interpolator latency is reduced,
but filter response is under-damped and position and
speed overshoot are inversely proportional to filter
bandwidth. The following lag recovery mode filter
instances and approximate filter bandwidths (–3dB)
are recommended (instances not shown may cause
unstable filter response).
1
s
1
s
-
Figure 6: PI Mode Filter Configuration
In PI mode, filter lag at constant sensor input veloci-
ty is eliminated, but position and speed overshoot
are inversely proportional to filter bandwidth.
Recommended Lag Recovery Mode Filter Instances
Instance
Noise and Jitter Bandwidth [kHz]
2.5 15 fcore[MHz]
2.5 31 fcore[MHz]
2.5 63 fcore[MHz]
(Min. overshoot)
71
89
(Max. overshoot)
107
In general, use the maximum filter bandwidth (in-
stance 71); this gives the fastest response and mini-
mum position and speed overshoot. Another in-
stance may be used if additional noise and jitter fil-
tering is required.
1 The filter instance is the MAIN_FLTR register value
necessary to realize the given filter.
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