Interpolator iC-MQF is a non-linear A/D converter which digitizes sine/cosine sensor signals using a count-safe tracking conversion principle with selectable resolution and hysteresis. The angle resolution per sine period can be set using SELRES; up to 4000 angle steps are possible (see page 27). The angle position is output incrementally by differential RS422 drivers as an encoder quadrature signal with a zero pulse or, if selected, as a counter signal for devices compatible with 74HC191 or 74HC193. The zero pulse is generated electronically when an enable has been set by the X1/X2 inputs. This pulse can be configured extensively: both in its relative position to the input signal with regard to the logic gating with A and/or B and in its width from 90° to 360° (1/4 to 1 T).
A preselectable minimum transition distance ensures glitch-free output signals and prevents counting errors which in turn boosts the noise immunity of the position encoder. Programmable instrumentation amplifiers with selectable gain levels allow differential or single-ended, referenced input signals; a external reference can be used via input X2 as reference voltage for the offset correction. The modes of operation differentiate between high impedance (V modes) and low impedance (I modes). This adaptation of the iC to voltage or current signals enables MR sensor bridges or photosensors to be directly connected up to the device. The optical scanning of low resolution code discs is also supported by the reference function of input X2; these discs do not evaluate tracks differentially but in comparison with a reference photodiode.
The integrated signal conditioning unit allows signal amplitudes and offset voltages to be calibrated accurately and any phase error between the sine and cosine signals to be corrected. The channel for the zero signal can be configured separately. A control signal is generated from the conditioned signals which can track the transmitting LED of optical encoders via the integrated 50mA driver stage (output ACO). If MR sensors are connected this driver stage can also track the power supply of the measuring bridges. By tracking the sensor energy supply any temperature and aging effects are compensated for, the input signals stabilized and the exact calibration of the input signals is maintained. This enables a constant accuracy of the interpolation circuit across the entire operating temperature range. If control limits are reached, these can be indicated at the maskable error pin ERR. Faults such as overdrive, wire breakage, short circuiting, dirt or aging,
for example, can be logged.
iC-MQF includes extensive self-test and system diagnosis functions which check whether the sensor is working properly or not. For all error events the user can select whether the fault is indicated at the pin ERR or whether the outputs should shutdown. At the same time errors can be stored in the EEPROM to enable failures to be diagnosed at a later stage. For encoder applications the line count of the code disc, the sensor signal regarding signal level and frequency and the operating temperature can be monitored, for example, the latter using an adjustable onchip sensor. Display error pin ERR is bidirectional; a system fault
recognized externally can be recorded and also registered in the error memory.
iC-MQF is protected against reverse polarity and offers its monitored supply voltage to the external circuit, thus extending the protection to the system (for load currents up to 20 mA). Reverse polarity protection also covers the short-circuit-proof line drivers so that an unintentional faulty wiring during initial operation is tolerated. On being activated the device configuration is loaded via the serial configuration interface from an external EEPROM and verified with a CRC. A microcontroller can also configure iC-MQF; the implemented interface is multimaster-competent and allows direct RAM access.