Olaf Machul

A smart pressure transducer with on-chip readout, calibration and nonlinear temperature compensation based on spline-functions

A smart pressure transducer with a piezo resistive pressure sensor microbridge, digitally controlled readout electronics, and a nonlinear temperature compensation based on spline functions, is integrated on a single CMOS chip. The chip also contains a temperature sensor and control hardware for test and calibration functions. The calibration process of the sensing and temperature compensation parameters has been optimized for high volume production. The smart pressure transducer is in standard 2 /spl mu/m n-well CMOS technology completed by anisotropic cavity etching.

A novel architecture for inductive proximity sensors using sigma delta modulation

This paper presents a novel architecture for inductive proximity sensors using sigma delta modulation. The LC-oscillator is included in the sigma delta control loop providing amplitude regulation and high precision analog-to-digital conversion in one block. The circuit consists of a new LC-oscillator suitable for clocked tail current injection, two SC integrators and a clocked comparator forming the sigma delta modulator and a PLL providing the clock for synchron amplitude sampling. The circuit was realized in a 0.8 mum CMOS technology of the Fraunhofer Institute for Microelectronic Circuits and Systems. Measurements show the capability of the system to distinguish even smallest differences in the target distance.

Readout electronics with calibration and on-line test for resistive sensor bridges

In this paper a digitally programmable readout electronics for resistive sensor bridges is presented together with an efficient method for calibration based on the principle of piecewise linear interpolation. The calibration enables a temperature compensation in the range between -40/spl deg/C and +120/spl deg/C. The architecture also allows an automatic calibration process with a minimum expenditure of external hardware. In addition the system contains an implemented function for monitoring the resistive sensor bridge condition during operation. For automotive applications an integrated voltage regulator is available so that the chip can optionally operate either at a stabilized 5 V power supply voltage or use an unregulated voltage in the range between 7.5 V and 16 V.

Nonlinear function generation using oversampled /spl Sigma//spl Delta/-modulators

In this paper we present a technique for nonlinear function generation which uses a novel sparse look-up table approach. This novel approach can be derived from the simple look-up table concept and utilizes the interpolating properties of oversampled /spl Sigma//spl Delta/-modulators. We show that the approximation process with oversampled /spl Sigma//spl Delta/-modulators can be generally understood as a weighted sum of piecewise-continuous polynomial B-splines. The weights are digitally stored in a sparse look-up table memory which can be used for the nonlinear function mapping. The shape of the polynomial B-splines depends on the order of the loop-filter which is used in the /spl Sigma//spl Delta/-modulator topology. Derailed investigations of the approximation behaviour show that a spectrum of linear, square, and cubic piecewise-continuous interpolation can be achieved if we use up to 3rd order /spl Sigma//spl Delta/-modulators. With the increased order of modulator topology the approximation quality is also improved under the assumption that we use the same weight set for function mapping. The fact that polynomial B-splines delivers only nonzero values within a limited range of input arguments makes this approximation method much less sensitive to local errors than classical approximation methods like Lagrange or Newton interpolation.

Detection of defective sensor elements using ΣΔ -modulation and a matched filter

We present an integrable solution for detection of defective sensor elements using sigma-delta-(Σ∆)modulation and a matched filter. The sensor element is stimulated using a pseudo random binary sequence (PRBS). The sensor signal is read out and the analog output is digitized using a Σ∆-modulator. The binary pulse density stream of the Σ∆-modulator is the output of the sensor system and thus should ideally contains the PRBS. A matched filter has the task of detecting the pseudo random sequence in the pulse density stream and its sampled output is compared to a threshold thus making it possible to judge the functionality of the sensor element. By evaluating the magnitude of the matched filter output it is also possible to measure the sensor sensitivity. We present a discrete solution of this method, but an integrated chip using a standard 1.2μm CMOS-process has been designed and is being fabricated.

Detection of defective sensor elements using /spl Sigma//spl Delta/-modulation and a matched filter

We present an integrable solution for the detection of defective sensor elements using sigma-delta-(/spl Sigma//spl Delta/)-modulation and a matched filter. The sensor element is stimulated using a pseudo random binary sequence (PRBS). The sensor signal is read out and the analog output is digitized using a /spl Sigma//spl Delta/-modulator. The binary pulse density stream of the /spl Sigma//spl Delta/-modulator is the output of the sensor system and thus should ideally contain the PRBS. A matched filter has the task of detecting the pseudo random sequence in the pulse density stream and its sampled output is compared to a threshold thus making it possible to judge the functionality of the sensor element. By evaluating the magnitude of the matched filter output it is also possible to measure the sensor sensitivity. We present a discrete solution of this method, but an integrated chip using a standard 1.2 /spl mu/m CMOS process has been designed and is being fabricated.

A Single-Chip Smart Pressure Sensor Family with 2 Dimensional Calibration

We present a single-chip CMOS solution for a pressure transducer reaching an 1% accuracy over the temperature range between -40°C and 125°C after calibration that delivers a ratiometric analog output voltage and a pulse density digital output. Two on-chip sensors are cointegrated: a surface-micromachined capacitive pressure sensor and temperature sensor using parasitic bipolar transistors. The surface-micromachined capacitive pressure sensor is fully compatible to a standard CMOS-process and therefore cost-optimized when compared to piezoresistive sensor elements. The sensor signal processing covers the sensor readout, the linearization, and the temperature sensor based compensation of the temperature sensitivity. A highly efficient parallel and automated calibration based on ∑△-modulators requires only a few calibration points for full pressure and temperature range. The two-dimensional calibration procedure has been optimised for parallel processing and allows efficient mass production. The sensor chip family has been fabricated in an 1.2 μm CMOS-process with surface micromachining extension and occupies a chip area of 11.8 mm.2 The power consumption of the sensor chip is 6 mW using a 5 V power supply.