iC-TW28: Latency Free Interpolation Circuit with Error Correction at the push of a button

10-bit Sine-To-Digital Converter With Automatic Signal Correction

The 3 V interpolation circuit iC-TW28 helps to evaluate magnetic and optical sensors that generate sine and cosine signals. A simple touch of the button is enough to adjust the required signal gain and to correct signal errors, e.g. for the assembly of MR sensors or optical incremental encoders.

Furthermore, a permanent auto-correction then minimizes the angular error, so that the RS422 output drivers always provide high-quality quadrature signals, at interpolation factors of x1 up to x256, and at a negligible constant delay of only 1.5 µs. Additional UVW signals with an adjustable pulse count are also available for the commutation of brushless motors with up to 32 pole pairs.

Download text and photo at http://www.ichaus.de/iC-Haus_TW28_newsrelease_en
The device iC-TW28 contains a 3-channel analog front-end with differential PGA inputs that easily accepts typical sine or cosine signals of magnetic sensors with 50 mV, or of encoders with 1 Vpeak-peak, and automatically adjusts itself to the provided signals, even in the index channel. MR, GMR, TMR, linear and switching Hall sensors can be connected as reference marks sensor.

Fast A/D converters track the inputs at up to 700 kHz what allows a very high revolution speed or linear velocity for position encoders. The implemented algorithms and special filters ensure a constant latency of only 1.5 µs or 600 ns with an optional correction respectively.

There is no need for measuring equipment to benefit from the converter's accuracy - just a touch of a button! The device automatically learns the required signal corrections for offset, amplitude and phase errors and secures them in the on-chip EEPROM. If the start values are not sufficient, e.g. in case of enduring amplitude changes or an offset drift over temperature, permanent auto-corrections can be selected.

The input angle is resolved with 10 bit and available as absolute data over SPI, approximately in real time due to a minimum grid of only 20 ns, or as incremental data over encoder quadrature outputs in a flexible resolution of up to 256 periods per input cycle. The integrated RS422 drivers can allow up to 12 MHz, but to guarantee a fail-safe counting at the receiver, the output frequency can be limited to enlarge the edge distance.

For controller applications, the evaluation is simplified by the integrated SPI interface: A 24-bit position register supplies 14 bit for the revolutions tracked by the cycle counter and 10 bit for the angle value within the current sine cycle. Additionally, for the evaluation of distance-coded reference marks in linear systems, a second register captures the cycle count when a zero signal is detected.

The device iC-TW28 provides several options for configuration. A subset of pre-configured functions and interpolation factors can be selected by pins, and the auto-calibration is easily available at the push of a button - the commissioning does not require any programming. In addition, the full range of functions can be achieved if the serial SPI interface is used: an AB output divider for fractional interpolation, filter settings for jitter reduction and configurable monitoring of errors and signal quality.

If the application would require a different function or an update of the calibration, for instance after the encoder mounting position has been changed, the integrated Encoder Link interface can be activated to access configuration registers using the output cable.
Typical applications are:
* magnetic motor position encoders
* optical encoders with higher resolution by interpolation
* programmable magnetic or optical incremental encoders
* general evaluation of Hall sensors for angular measurement
* general evaluation of sine or cosine signals up to high frequencies (e.g. PC measuring cards for 1 Vpp)

iC-TW28 is operated at a single-sided supply of +3.1 V to 3.6 V and allows a temperature range of -40 to +125 degrees Celsius. Only a few external components are required, for example a voltage regulator and a protection diode against a reversed supply voltage.
iC-TW28 is housed in a space-saving 32-pin QFN package that takes only 5 x 5 mm on the PCB. For sampling, a PC operating program (GUI) and a ready-to-play evaluation board that can also serve as programming adapter are available.

Further information is provided at www.ichaus.com/tw28

Introducing iC-Haus
iC-Haus GmbH is a leading, independent German manufacturer of standard iCs (ASSP) and customized ASiC semiconductor solutions with worldwide representation. The company has been active in the design, production, and sales of application-specific iCs for industrial, automotive, and medical applications for more than 30 years.
The iC-Haus cell libraries in CMOS, bipolar, and BCD technologies are specifically suited to realize the design of sensor, laser/opto, and actuator ASiCs, amongst others. The iCs are assembled in standard plastic packages or using the iC-Haus chip-on-board technology to manufacture complete microsystems, multichip modules, and optoBGA/QFN in conjunction with sensors.
Further information is available at
For more information, please contact:

iC-Haus GmbH
Am Kuemmerling 18, 55294 Bodenheim, Germany
Tel. +49 6135/9292-0
Fax +49 6135/9292-192

January 2018

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