iC-MN 25-BIT NONIUS ENCODER
WITH 3-CH. SAMPLING 13-BIT Sin/D INTERPOLATION
Rev D1, Page 24/59
Gain Adjustment
Offset Calibration
The gain is set in three stages. The gain range When calibrating the offset the offset reference source
is first determined for sine and cosine using register must first be selected using REFVOS (1:0). This set-
GR_x (2:0). Register GFC_x (4:0) can then be used ting is valid for all three tracks. If VDC is selected
to finely adjust the gain of the cosine track. In the as the offset reference SVDCx is the reference for the
final stage of the process the amplitude of the sine sine track and CVDCx for the cosine. The VDC refer-
track is adapted to suit the cosine track using regis- ence enables the offset calibration to be automatically
ter GFS_x (10:0). With differential input signals the tracked dependent on the DC level of the input signal.
overall sine gain of one track is thus calculated as If ACO is chosen as the offset reference the voltage at
1
GAINS_x = GR_x * GFS_x; the total cosine gain is then pin ACOx, divided into /20, acts as a reference. This
GAINC_x = GR_x * GFC_x.
enables the offset to be calibrated dependent on the
supply voltage of the sensor.
GR_M
Addr. 0x00; bit 2:0
GR_S
Addr. 0x10; bit 2:0
Addr. 0x20; bit 2:0
GR_N
Code
Coarse gain
0
1
2
3
4
5
6
7
6.0
12.4
16.2
20.2
26.0
31.6
39.5
48.0
Table 16: Gain range sine/cosine
GFC_M
GFC_S
GFC_N
Code k
0x00
Addr. 0x00; bit 7:3
Addr. 0x10; bit 7:3
Addr. 0x20; bit 7:3
k
31
Fine gain GFC = 6.25
1
0x01
1.07
1.13
...
0x02
...
Figure 9: Principle offset calibration circuit with se-
lectable reference sources.
0x1F
6.25
Table 17: Gain factor cosine
REFVOS
Addr. 0x0A; bit 5:4
Type of source
Code
GFS_M
GFS_S
GFS_N
Addr. 0x02; bit 2:0
Addr. 0x01; bit 7:0
Addr. 0x12; bit 2:0
Addr. 0x11; bit 7:0
Addr. 0x22; bit 2:0
0
1
2
3
Feedback of pin ACO
Reference V05
REFVOS = V(ACOx)/20
REFVOS = 0.5 V
Reference V025
REFVOS = 0.25 V
Tracked source VDC
REFVOS = SVDCx,
CVDCx
Addr. 0x21; bit 7:0
k
Table 19: Offset reference source
1984
Code k
0x000
0x001
0x002
...
Fine gain GFS = 6.25
1
1.0009
1.0018
...
Source VDC is to be used as reference for current
inputs. The average potentials of sine (SVDCx) and
cosine (CVDCx) are determined by:
0x7FF
6.6245
Table 18: Gain factor sine
SVDCx = (1 − ks) · V(PSi) + ks · V(NSi)
ICHAUS [ IC-HAUS GMBH ]
