IC-MG_14 Datasheet, PDF (14/22 Pages) IC-Haus GmbH – 8-Bit Sin/Cos INTERPOLATION IC WITH RS422 DRIVER

iC-MG
8-Bit Sin/Cos INTERPOLATION IC WITH RS422 DRIVER
Rev D1, Page 14/22
S/C Offset Calibration
To calibrate the offset the reference source must first
be selected using VOSSC. Two fixed voltages and two
dependent sources are available for this purpose. The
fixed voltage sources should be selected for external
sensors which already provide stable, self-regulating
signals.
For the operation of photosensors in optical encoders,
iC-MG tracks changes in offset voltages via the signal-
dependent source VDC when used in conjunction with
the controlled power supply output supplying the en-
coder LED (pin PWR). The VDC potential automati-
cally tracks higher DC photocurrents. To this end inter-
mediate potentials VDCS and VDCC must be adjusted
to a minimal AC ripple using the selectable k factor (this
calibration must be repeated when the gain setting is
altered).
The feedback of pin voltage V(PWR) fulfills the same
task as source VDC when MR bridge sensors are sup-
plied by the controlled power supply output. In this in-
stance the VDC sources do not need adjusting.
VOSSC
Code
0x0
0x1, 0x2
0x3
Adr 0x0E, bit 5:4
Type of source
Feedback of PWR pin voltage: V(PWR)/20
for supply-dependent differential voltage signals
for Wheatstone sensor bridges
to measure VDDS
Fixed reference of 500 mV, 250 mV
for single-ended current or voltage signals
for single-ended or differential stabilized signals
(regulated sensor or waveform generator)
Self-tracking sources VDCS, VDCC (125...250 mV)
for differential current signals of photodiode arrays
Table 13: S/C-Channel Offset Reference Source
VDCS
VDCC
Code
0x00
0x01
...
0x20
...
0x3F
Notes
Adr 0x07, bit 4:0; Adr 0x06, bit 7
Adr 0x08, bit 6:1
VDCi = (1 − k) · VPi + k · VNi
k = 1/3
k = 0.3386
k = 1/3 + 1/3 · Code/63
k = 0.5026 (center setting)
...
k = 2/3
Adjustment is required only if VOSSC = 0x3.
The calibration range for the S/C offset is dependent
on the selected VOSSC source and is set using ORS
and ORC. Both sine and cosine signals are then cali-
brated using factors OFS and OFC. The calibration tar-
get is reached when the DC fraction of the differential
signals PCHx versus NCHx is zero.
ORS
ORC
Code
00
01
10
11
Adr 0x09, bit 0; Adr 0x08, bit 7
Adr 0x0A, bit 5:4
Range
x1
x2
x6
x12
Table 15: S/C-Channel Offset Range
OFS
OFC
Code
0x00
0x01
...
0x7F
Adr 0xA, bit 3:0; Adr 0x9, bit 7:4
Adr 0xC, bit 0; Adr 0xB, bit 7:1
Factor
Code
Factor
0
0x00
0
0.0079
0x01
-0.0079
...
...
...
1
0xFF
-1
Table 16: S/C-Channel Offset Factors
S/C Phase Correction
If the phase shift between the sine and cosine signal
deviates from the ideal 90^◦ this can be compensated
for using parameter PHSC. Following this the calibra-
tion of the amplitude compensation, intermediate po-
tentials and offset voltages may have to be corrected.
PHSC
Code
0x00
0x01
...
0x1F
Adr 0xD, bit 2:0; Adr 0xC, bit 7:5
Correction angle Code
Correction angle
+0^◦
0x20
-0^◦
+ 0.65 ^◦
0x21
- 0.65 ^◦
...
...
...
+ 20.2 ^◦
0x3F
- 20.2 ^◦
Table 17: Phase Correction
Table 14: S/C-Channel Intermediate Voltages