iC-NQC: 13-bit real-time encoder interpolation now with BiSS C for uninterrupted measurement
iC-NQC: high-resolution sine interpolation provides memory expansion for sensor ID plate and OEM data via the serial BiSS C Interface
For the first time ever high-resolution sine-to-digital converter iC-NQC provides the microelectronics industry with a BiSS slave in C protocol that enables bidirectional data exchange with the existing device memory at the same time as the cyclic output of measurement data. Using normed addresses device information is available that indexes the relevant standard device profile or a description file. An optional electronic ID plate can also be used to describe the measurement application.
In essence, iC-NQC is an interpolation circuit with signal error compensation for sinusoidal sensor signals, such as those generated by optical or magnetic position sensors, for example. Both decimal and binary resolutions of up to 8,192 angle steps per signal period can be set; these can be output as an absolute value via a BiSS Interface at clock rates of up to 10 MHz or incrementally as encoder quadrature signals with A/B and an index Z.
The sine-to-digital converter iC-NQC is suitable for a number of different sensor setups, such as magnetoresistive sensor bridges for linear or angle measurement and optoelectronic scanners, for instance. Front-end instrumentation amplifiers permit sensor bridges to be connected directly without the need for any additional components. The signal gain is programmable in stages for standard sensor signals of between 20 mVpp and to 1.5 Vpp; the device can be adapted for photocurrents using external resistors.
A signal conditioning unit is integrated to correct typical sensor errors; this unit intercepts the analog signal path via several D/A converters. As iC-NQC can compensate for offset, amplitude and phase errors, interpolation results are considerably improved, with an accuracy of 10 bits or an angle error of +/- 0.35° maximum per signal period achievable. Special analog and digital test signals support this calibration process.
Sine-to-digital conversion with response times of under 250 ns is more or less achieved in real time, with a programmable vector follower guaranteeing no missing codes. Binary resolutions of between 8 and 8,192 angle steps or decimal resolutions from 25 to 2,000 angle steps can be selected. Here, the user has various ways of influencing the temporal behavior of the converter. For incremental output, the maximum tracking rate and minimum transition distance can be stipulated; for the output of an absolute angle via the serial interface an automatic resolution adaptation feature can be activated in order to trail high input frequencies of up to 250 kHz. A scalable 24-bit period counter also enables signal periods to be tracked.
A patented signal conditioning unit provides glitch-free incremental signals that always keep to the preselected minimum transition distance and can be reliably counted and processed by the follow-on system. At the same time the sensor signals are digitally deglitched, with regular, legitimate signals not subject to the disadvantage of delays from a low-pass filter.
A synchronized zero signal at a selectable angle position supplements the incremental signal when enabled by the assigned zero signal comparator inputs. The frequency and level of the sensor signal are monitored so that fractured cables, short circuits, override or dirt and ageing can be signaled as an alarm.
One new feature of this device is the serial data interface; this enables triggered measurement value acquisition in either SSI or BiSS C protocol. During the output of cyclic data, with clock rates of up to 10 MHz, BiSS C now also simultaneously permits bidirectional communication with the registers. It is no longer necessary to switch modes or use coded PWM data, considerably easing emulation of the protocol by a controller with an SPI interface. The storage addresses for the device ID, serial number, OEM data and EDS, an optional ID plate, have also been normed.
An integrated I2C interface provides access to an external EEPROM with 2 to 16 kbit that can store the CRC-checked configuration and ca. 1 kilobyte for other application data. On startup iC-NQC automatically reads the setup and checks the CRC or waits for the configuration from BiSS.
Typical applications include: – Incremental and absolute encoders for BiSS and SSI – Magnetic linear position measurement systems – Optical linear scales – Synchronous evaluation of sine encoders for inverters – PC measuring cards for 1 V, 11 A and TTL encoder signals
With a single supply of +5 V the device operates within the industrial operating temperature range of -20 to +85°C. As an option, it can also be supplied for operating temperatures of -40 to +125°C.
iC-NQC comes as a space-saving 20-pin TSSOP package, taking up just 6.4 x 6.4 mm on the circuit board. It comes with the new NQ6D demo board that can be queued up in a chain, various BiSS PC adapters and a PC user program for evaluation purposes. The programming of resources by the customer can be supported by a device DLL.