Abstract: A ratiometric circuit (40) includes a differential capacitive sensor (42) for sensing a change in capacitance, a differential capacitive detector (46) operatively connected to the differential capacitive sensor for detecting a change in the capacitance of the differential capacitve sensor, an error voltage generator (48) operatively connected to the differential capacitve detector for generating a corrective voltage in response to the detected change in capacitance, and a bias circuit (50) operatively connected to the differential capacitive sensor for generating a bias voltage inversely proportional to and independent of a supply voltage for maintaining the ratiometricity between an output voltage of the differential capacitive sensor and the supply voltage.

Abstract: A pressure sensor circuit (10A) is disclosed which preferably utilizes a piezoresistive pressure transducer (11A) having a substantial temperature coefficient of resistance to provide an inherent temperature variation which is used to implement offset temperature compensation for the circuit. Two operational amplifiers (OA1, OA2) are configured along with selectable resistors (R.sub.1, R.sub.9, R.sub.7, R.sub.8, R.sub.5, R.sub.6 and R.sub.4) to implement four adjustments of the circuit (10A) to adjust span (gain), offset and temperature variation of both span and offset to achieve a desired result. All this is achieved while implementing a common mode gain for the circuit (10A) which is less than 5 and preferably no more than 2.

Abstract: In a calibration circuit for calibration of the output of a differential sensor, signals adjustable in gain for calibration are summed with potentiometrically derived signals for offset calibration to provide a single ended output. Additionally, a signal dependent upon a parameter in respect of which the sensor is unwantedly dependent is summed so that the unwanted response may be compensated. This additional signal is also arranged for calibration in gain and offset so that the unwanted response is calibrated out. The range of calibration includes a null point where there is no response in respect of one parameter to permit calibration in respect of another without interaction.

Abstract: A mass fluid flow sensor is disclosed which utilizes a sensing bridge circuit to develop a sense (control) signal related to fluid flow. A fluid temperature variable resistor, separate from said bridge circuit, is utilized to implement temperature compensation so that a desired output signal is a function of sensed fluid flow, but is less dependent on fluid temperature than the sense (control) signal provided by the bridge circuit. A resistor in the bridge circuit is selected such that the sense (control) signal provided by the bridge circuit has a rate of change as a function of flow rate substantially independent of fluid temperature, but this sense signal still varies as a function of fluid temperature. This permits fluid temperature compensation of the bridge sense signal in a noncomplex and cost effective manner. An improved adjustable circuit (36-41) is provided for producing a desired temperature variable output signal (V.sub.os).

Abstract: A mass fluid flow sensor is disclosed which utilizes a sensing bridge circuit to develop a sense (control) signal related to fluid flow. A fluid temperature variable resistor, separate from said bridge circuit, is utilized to implement temperature compensation so that a desired output signal is a function of sensed fluid flow, but is less dependent on fluid temperature than the sense (control) signal provided by the bridge circuit. A resistor in the bridge circuit is selected such that the sense (control) signal provided by the bridge circuit has a rate of change as a function of flow rate substantially independent of fluid temperature, but this sense signal still varies as a function of fluid temperature. This permits fluid temperature compensation of the bridge sense signal in a noncomplex and cost effective manner.

Abstract: A method and apparatus are described for converting variations in a measured variable (such as pressure) to corresponding variations in an electrical output signal. The preferred method utilizes a capacitive sensor whose capacitance changes to reflect changes in the measured variable. The changes in capacitance are preferably used to vary the gain of a switched-capacitor amplifier whose signal input receives a relatively constant DC reference voltage. The amplifiers' output may be sampled and further amplified to provide an output signal which is indicative of the value of the measured variable.