One inductive sensor is configured to maintain a fixed frequency in a resonant circuit. One apparatus includes an inductance-to-digital converter (LDC). The LDC includes a digital filter to measure an inductance change of a sensor and convert the inductance change to a digital value. The LDC further includes a digital control loop to maintain a fixed frequency in the sensor. The sensor forms an oscillator in the digital control loop. An output of the digital control loop is representative of the inductance change of the sensor.

One inductive sensor is configured to maintain a fixed frequency in a resonant circuit. One apparatus includes an inductance-to-digital converter (LDC). The LDC includes a digital filter to measure an inductance change of a sensor and convert the inductance change to a digital value. The LDC further includes a digital control loop to maintain a fixed frequency in the sensor. The sensor forms an oscillator in the digital control loop. An output of the digital control loop is representative of the inductance change of the sensor.

Maintaining a fixed frequency in a resonant circuit of an inductive sensor circuit is described. In one embodiment, an apparatus includes an inductance-to-digital converter (LDC). The LDC includes a digital filter to measure an inductance change of a sensor and convert the inductance change to a digital value. The LDC further includes a digital control loop to maintain a fixed frequency in the sensor. The sensor forms an oscillator in the digital control loop. An output of the digital control loop is representative of the inductance change of the sensor.

A method for detecting an open line (10) of a receiver coil (17; 18) of a resolver (16) comprisesproviding a pull-up resistor (R.sub.1; R.sub.3) and a pull-down resistor (R.sub.2; R.sub.4) at the terminals (7a, 7b; 8a, 8b) on a control device (1) for the signal lines (13a, 13b; 14a, 14b) of the receiver coil (17; 18);measuring the voltage between the two signal line terminals (7a, 7b; 8a, 8b) of the receiver coil at two sampling times provided symmetrically at the middle of the excitation period;calculating an offset value by calculating an average value that comprises the measured values measured at the two sampling times in an excitation period; andidentifying an open line (10) if the offset value exceeds a threshold value.

A rotation angle sensor system for an optical system including a rotor and a stator, for determining a rotation angle and/or an orientation between the rotor and the stator. The system includes a coil system that is stator-based and attached in a rotatably fixed manner to the stator as a sensor element for receiving a magnetic alternating field, and has a target that is rotor-based and attached in a rotatably fixed manner to the rotor for generating a magnetic alternating field, and in which the coil system and the target are attached to the stator and to the rotor in such a way that different overlaps and/or spatial proximities occur between the coil system and the target as a function of the rotation angle and/or of the orientation between stator and rotor with a correspondingly different effect on the magnetic alternating field of the target on the coil system.

Front-end circuits that combine inductive and capacitive sensing are described. In one embodiment, an apparatus includes a plurality of inductive elements, an inductive measurement circuit, and a frequency divider circuit. The inductive measurement circuit is to output a first signal with a first frequency. The first signal is associated with an inductance change of one of the inductive elements. A feedback circuit can maintain the sinusoidal operation of the first signal. The frequency divider circuit can generate a second signal with a second frequency that is lower than the first frequency.

A method for detecting an open line (10) of a receiver coil (17; 18) of a resolver (16) comprisesproviding a pull-up resistor (R.sub.1; R.sub.3) and a pull-down resistor (R.sub.2; R.sub.4) at the terminals (7a, 7b; 8a, 8b) on a control device (1) for the signal lines (13a, 13b; 14a, 14b) of the receiver coil (17; 18);measuring the voltage between the two signal line terminals (7a, 7b; 8a, 8b) of the receiver coil at two sampling times provided symmetrically at the middle of the excitation period;calculating an offset value by calculating an average value that comprises the measured values measured at the two sampling times in an excitation period; andidentifying an open line (10) if the offset value exceeds a threshold value.

Front-end circuits that combine inductive and capacitive sensing are described. In one embodiment, an apparatus includes a plurality of inductive elements, an inductive measurement circuit, and a frequency divider circuit. The inductive measurement circuit is to output a first signal with a first frequency. The first signal is associated with an inductance change of one of the inductive elements. A feedback circuit can maintain the sinusoidal operation of the first signal. The frequency divider circuit can generate a second signal with a second frequency that is lower than the first frequency.