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Signal conditioner IC enhances car sensor accuracy

Posted: 24 Nov 2006 ?? ?Print Version ?Bookmark and Share

Keywords:ZMD AG? ZMD31150? signal conditioner? automotive? bridge sensors?

ZMD AG has introduced a high-speed automotive signal conditioner IC with advanced on-chip diagnostics for use with all types of wheat stone bridge sensors. Called the ZMD31150, the new device is designed for all sensing applications in automotive environments, such as fuel injection, ABS, power steering, air induction, fuel tank, air conditioning and occupant classification.

"In some applications, speed is of the essence," says Frank Schulze, business line manager for automotives at ZMD. "For optimum safety in a car crash, the car must sense the size, weight and orientation of the front-seat occupants quickly in order to control the airbag's deployment. The ZMD31150 is two to seven times faster than other signal-conditioning chips with comparable accuracy and its diagnostic features mean increased reliability when it's needed most."

Sensor signal conditioner
Sensor inaccuracy or failure is a leading cause of unscheduled service for modern automobiles. A sensor signal conditioner (SSC) must either give a known-correct response, or report an error code. Enhanced real-time diagnostics in the ZMD31150 detect faulty connections, shorts and power loss events. An error-correcting function in the EEPROM insures uncorrupted content and increased MTBF. This is backed up with an EEPROM signature check that detects severe multibit failures. To enhance hardware reliability, the output is protected against short-circuits, reverse-polarity and voltages as high as 33V.

The ZMD31150 promises highly accurate amplification and sensor-specific digital correction of bridge sensor signals. An analog pre-amp gain of 420 accommodates bridge outputs as low as 1mV/V and an extended sensor offset. A 16bit ADC with an integrating input characteristic gives a 7.8KHz sample rate, so the whole system delivers a comparable analog bandwidth of 4KHz. Accuracy and flexibility is further enhanced by selectable internal or external temperature sensors. This allows more precise temperature compensation of sensor readings.

Signal conditioning is done by an internal digital signal processor running a correction algorithm based on calibration coefficients stored in the on-chip EEPROM. By calibrating the chip to a specific sensor digitally, users gain the benefits of speed and accuracy, while eliminating the cost associated with trimming methods using lasers and/or external devices. Calibration is accomplished easily with a simple PC-based program using the ZMD31150's serial interface. Additional EEPROM bytes allow storage of a serial number or other product-traceability data. Because it is re-programmable, sensors can be recalibrated as often as desired. This makes field replacement of sensors easier, more accurate and less expensive, the company said.

Excellent accuracy
The measured and corrected bridge values are provided at the output pin, which can be configured as an analog voltage output with 12bit resolution, or ZMD's ZACwire one-wire digital output, or as an I?C bus signal. A built-in programmable digital filter helps fit the sensor system response to the required output behavior. The output levels also have programmable digital clipping levels. All together, this promises excellent accuracy: 0.1 percent FSO from -25C to 85C, 0.25 percent FSO from -40C to 125C and 0.5 percent FSO from -40C to 150C.

Accurate fuel-system pressure monitoring is essential for the Gasoline Direct Injection (GDI) and diesel common-rail injection engines. The ZMD31150's wide temperature range (-40C to 150C), high accuracy and sophisticated diagnostics fit well in this application.

A development kit supports the ZMD31150 evaluation and experimental calibration. The kit includes PCBs, samples, software and technical documentation.

The ZMD31150 is available in an SSOP14 package at a unit cost of $3.42 for 1,500 units, or as a die at a unit cost of $2.12 for 1,700 units. Support for industrial mass calibration is available, as is quick circuit customization for large production volumes.

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