Speedy Sine Evaluation at x1000 Interpolation Factor

For optical and magnetic length gauges featuring decimal gratings, iC-MQF offers a sine resolution of up to 4000 edges. The circuit incorporates a signal conditioning analog front end, a vector-tracking converter for real-time conversion without latency, as well as fault-tolerant RS422 driver stages which output the incremental signals. Reverse polarity protection is also embedded and covers all cable connections.

Differential or referenced input signals from a few millivolts upwards can be connected up, such as those coming from MR bridge sensors or photo sensors, for which alternatively also a low impedance can be selected.

Excellent interpolation accuracy is obtained from analog signal corrections: offsets, amplitude mismatches and phase errors can be compensated. After initial adjustment, a controlled current source output maintains the measurement accuracy during operation by tracking the sensor’s excitation. For example, the LED current of an optical encoder or the supply of a magnetic sensor bridge is regulated, so that temperature and aging effects are automatically compensated for.

All of the chip's major functions are monitored and can be configured for alarm indication. Typical sensor errors, such as loss of signal due to wire breakage, short circuits, dirt or aging, are recognized. Further operational errors, such as exceeding the permissible operating temperature, exceeding the permissible input frequency through fast movements, or a line count error of the scale are detected.

The mode of error handling is extensively configurable; an alarm can be displayed at the error output by an LED, can set the output drivers to tristate, or can be transmitted to the error memory for later diagnosis.

The encoder signals are supplemented by a generated index signal whose position, width and logic can be set as required. At the same time a patented signal conditioning unit provides glitch-free quadrature signals with hysteresis which always maintain a preset minimum transition distance. This enables counting errors to be avoided and enhances the circuit’s EMI tolerance with sensor applications.

iC-MQF is pin-compatible to the iC-MSB/iC-MQ device family and also available as a 20-pin TSSOP, taking a board space of just approx. 6.4 x 6.4 mm. It is configured using the integrated I2C multi-master interface, either by a microcontroller or a serial EEPROM.

With a single supply of +5 V the device functions within an operating temperature range of -40 to +100 degree Celsius. Using an integrated protection switch iC-MQF also protects the connected sensor circuit against a reversed supply voltage.

A ready-to-operate demo board with a GUI (PC software) is available for sampling; a device DLL is optional to support production tools. Production volume is available at $9.79 in 1ku volumes through the sales channels.

Further information is available at www.ichaus.com/mqf

White Paper on Sine/Cosine Interpolation at: www.ichaus.de/wp7_whitepaper_HighPrecision_SinC[...]