The MAX1457 is a highly integrated analog-sensor signal processor optimized for piezoresistive sensor calibration and compensation. It includes a programmable current source for sensor excitation, a 3-bit programmable-gain amplifier (PGA), a 12-bit ADC, five 16-bit DACs, and an uncommitted op amp. Achieving a total error factor within 0.1% of the sensor's repeatability errors, the MAX1457 compensates offset, full-span output (FSO), offset TC, FSO TC, and full-span output nonlinearity of silicon piezoresistive sensors.
The MAX1457 calibrates and compensates first-order temperature errors by adjusting the offset and span of the input signal via digital-to-analog converters (DACs), thereby eliminating quantization noise. If needed, residual higher-order errors are then compensated using linear interpolation of the first-order coefficients stored in a look-up table (in external EEPROM).
The MAX1457 integrates three traditional sensor-manufacturing operations into one automated process:
- Pretest: Data acquisition of sensor performance under the control of a host test computer.
- Calibration and Compensation: Computation and storage (in an external EEPROM) of calibration and compensation coefficients determined from transducer pretest data.
- Final Test: Verification of transducer calibration and compensation, without removal from a pretest socket.
Analog outputs are provided for both pressure and temperature. A general-purpose, uncommitted op amp is also included on-chip to increase the overall circuit gain, or to facilitate the implementation of a 2-wire, 4-20mA transmitter. The serial interface is compatible with MICROWIRE™ and SPI™, and directly connects to an external EEPROM. Additionally, built-in testability features of the MAX1457 facilitate manufacturing and calibration of multiple sensor modules, thus lowering manufacturing cost.
Although optimized for use with piezoresistive sensors, the MAX1457 may also be used with other resistive sensor types (i.e., accelerometers and strain gauges) with the addition of a few external components.