IC-TW4 Datasheet, PDF (7/14 Pages) IC-Haus GmbH – PROGRAMMABLE INTERPOLATOR WITH AUTOMATIC OFFSET CORRECTION

iC-TW4 PROGRAMMABLE INTERPOLATOR
WITH AUTOMATIC OFFSET CORRECTION
INPUT STAGE
Rev D1, Page 7/14
Programmable Gain Amplifier
A programmable gain amplifier (PGA) with output re-
ferred offset adjustment is used as input stage, shown
in Figure 2. The gain is common for both channel A
and B and is programmed through pin CFG2.
matically and continuously. Amplifier offset and sensor
offset are both eliminated offering a true plug-and-play
system. Additional device or sensor calibration is not
required as the iC-TW4 does all calibration automati-
cally. In addition, the effect of temperature dependent
offset drift of both the amplifier and the sensor is elim-
inated.
Consider the Table 5 regarding the relationship be-
tween input signal peak-to-peak differential amplitude
and resulting offset correction range. The sensor input
signal offset must satisfy the requirement of Equation
1 as well as the limits set by Table 5. The sensor offset
cannot lie outside of the correction range. Otherwise,
the tracking engine is not able to converge.
Equation 1:
V _AOFS2
+
V
2
BOFS
<
V _R2
Figure 2: Input stage
Automated Offset Adjustment
Offset adjustment is provided at the output of the in-
put amplifier. The offset correction is performed auto-
Parameter Description
Unit
V_AOFS
V_BOFS
V_IN
V_R
Sensor offset input A
mV
Sensor offset input B
mV
Sensor input amplitude peak-peak differential mV
V_R = V_IN/2 - 12 mV
mV
Table 4: Parameters of equation
CFG2 configuration Input signal range Max allowed sensor offset*
0
800 mV - 1.5 V ±400 mV
1
400 mV - 800 mV ±232 mV
2
200 mV - 400 mV ±112 mV
3
100 mV - 200 mV ±50 mV
4
50 mV - 100 mV ±19 mV
5
25 mV - 50 mV ±3.5 mV
6
10 mV - 25 mV [out of range]
* Notes: the values are based on amplifier input offset of ±12 mV.
Table 5: Input amplifier gain and offset
Limits of Automated Offset Adjustment
The Automated Offset Adjustment function is immune to monotonic acceleration (resp. deceleration) - i.e.
changes in input frequency - over multiple (> 2) periods. Motion profiles with short steps or vibrations within
up to 2 periods may accumulate offset and occasionally reduce accuracy to 1/8 of the period, which is +/-45
deg.