iC-TW2 8-BIT SIN/COS INTERPOLATION IC
WITH INTEGRATED EEPROM
Rev D3, Page 17/30
CALIBRATION
In order to facilitate system gain and offset calibration, Oscillator and index window calibration
two calibration modes can be enabled by either setting When calibration mode 2 is enabled, the output of the
bit CALIB1 of register 0x01 or CALIB2 of register 0x0C. index comparator is driven on pin B_V. In conjunc-
tion with the actual index output on pin Z_W, the gat-
ing window can be centered around the output pulse.
Fine offset adjustment applied to the input of the in-
dex comparator is possible through OFSZ(3:0) which is
sign magnitude encoded. This is beneficial when using
small amplitude index sources such as an MR sensor.
Simultaneously, the oscillator frequency fosc/32 can be
observed on pin A_U. Register CLOCK(4:0) is used to
tune the oscillator to its desired frequency.
CALIB2
CALIB1
CALIB2;1
00
Addr. 0x0C; bit 0
R/W
Addr. 0x01; bit 5
R/W
Function, defaults to eeprom setting
Normal operation, no calibration
A/B gain and index calbration
Oscillator and index window calibration
Not permitted
01
10
11
Table 18: Calibration mode
OFSZ(3:0)
Code
1111
1110
1001
...
Addr. 0x0B; bit 7:4
R/W
A/B gain and offset calibration
Function, defaults to eeprom setting
In calibration mode 1 the SIN/COS input is directly
passed through two zero-cross comparators to output
pin A and B respectively. In addition, the sum of the
input signals
maximum negative adjust, -10.5 mV
-9 mV
-1.5 mV
...
SIN + COS
1000
0000
0001
...
no correction
√
2
no correction
1.5 mV
is also fed through a comparator and driven on pin Z.
...
0110
0111
1
9 mV
The actual calibration process must be carried out in
several steps.
10.5 mV
calibration mode 2 activated
1. Select proper coarse gain by programming register
GC(2:0). Set GFA(1:0) and GFB(1:0) to 0.
Table 19: Index comparator offset control
2. Adjust offset register OFSA(5:0) and OFSB(5:0) un-
til output A and B are 50% duty cycle.
CLOCK(4:0)
Addr. 0x0A; bit 4:0
R/W
Code
00000
...
Function, defaults to eeprom setting
Slowest clock
...
3. Adjust fine gain register GFA(1:0) and GFB(1:0) until
output Z is equidistant between output A and B.
11111
fastest clock
4. Repeat step 1 and 2 until no more improvement can
be achieved.
Table 20: Oscillator tuning
ICHAUS [ IC-HAUS GMBH ]
