Analysis and design of two-device sensors with high-gain feedback enforced matching and linear digital output
Is Version Of
A technique to analyze and design different types of sensors and references is presented. Many well-known circuits, such as the bandgap reference, Widlar current reference and threshold-voltage-based temperature sensors, can be analyzed and modified thanks to the insight obtained with the method proposed. This systematic approach to the study of these circuits has the advantage of naturally leading to self-biased circuits, which are more insensitive to perturbations. High-gain feedback is employed to ensure matching of electrical variables of the circuit. This feedback loop allows embedding an Analog-to-Digital conversion as part of the system. As a result, a digital representation of the physical quantity of interest can be obtained. Moreover, this type of feedback loop is more flexible, since the controlled variable can be any kind of electrical parameter or design parameter that is controllable by a Digital-to-Analog circuit.
As an example of application, a variation of the Inverse Widlar temperature sensor is designed. By means of this technique, the sensor can be implemented without the need of devices with different threshold voltages, thus improving device matching. Also, the output is readily available as a digital code that is mathematically a linear function of the temperature to be measured.