IC-TW4QFN24 参数 Datasheet PDF下载

iC-TW4

PROGRAMMABLE INTERPOLATOR

WITH AUTOMATIC OFFSET CORRECTION

Rev D1, Page 7/14

INPUT STAGE

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

AOFS 2

+

V

BOFS 2

<

V

R 2

Figure 2: Input stage

Automated Offset Adjustment

Parameter

V

AOFS

V

BOFS

V

IN

V

R

Description

Sensor offset input A

Sensor offset input B

Sensor input amplitude peak-peak differential

V

R

= V

IN

/2 - 12 mV

Unit

mV

mV

mV

mV

Offset adjustment is provided at the output of the in-

put amplifier. The offset correction is performed auto-

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 4: Parameters of equation

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.