Low noise sensing circuit with cascaded reference

Abstract

This disclosure provides cascaded reference circuits and low amplitude signal sensing circuits that are useful in applications where high sensitivity, low noise measurements are needed. Such embodiments may be especially useful in health and fitness wearable devices. Systems incorporating the circuits, as well as methods for using these circuits to determine quantities and qualities of a person's moods, such as how much and what kinds of stress they experience. The provided devices are useful on limbs and appendages, such as in a smart watch that is worn on the wrist. Methods are provided for using the devices of this disclosure to privately alert wearers to an increase in bad stress in the moment when they can take actions to reduce their stress and physiological stress responses. These devices are useful for measuring and increasing the effectiveness of relaxation techniques. As a result of using methods and devices of this disclosure, people are healthier, they make more response-able decisions, and relationships improve.