Battery monitor

Abstract

A circuit tracks the total amount of time that a host device has spent in its high power “activated” state (an optionally idle and hibernate states) and thereby can estimate the total power consumed by the tag. A remote device can query the state of a counter storing a value representing this time to accurately determine how much of the energy has been consumed by the host device and how much time is left and/or how many more operations can be performed before the host device's battery is exhausted.

1 . A system for estimating power consumption of a host device, comprising:
 a mechanism for tracking at least an amount of time a host device is in an active state;   a mechanism for generating a value representing at least the amount of time the host device is in the active state based on the tracking; and   a mechanism for sending the value or derivative thereof to a remote device;   wherein the mechanism for tracking an amount of time the host device is in the active state is a first oscillator;   wherein the first oscillator operates at a first frequency when the host device is in the active state, wherein the first oscillator operates at a second frequency when the host device is in a state other than the active state.   
   
   
       2 . The system of  claim 1 , wherein the first oscillator is a voltage controlled oscillator, a frequency of the first oscillator varying depending on a power dissipation of the host device. 
   
   
       3 . The system of  claim 1 , wherein a frequency of the first oscillator is calibrated. 
   
   
       4 . The system of  claim 1 , wherein a reference current source is calibrated. 
   
   
       5 . The system of  claim 1 , wherein the mechanism for tracking an amount of time the host device is in the active state is a first oscillator, the first oscillator operating at least two frequencies, wherein the first oscillator operates at a first frequency for tracking the amount of time the host device is in the active state, wherein the first oscillator operates at a second frequency for tracking an amount of time the host device is in a state other than the active state. 
   
   
       6 . The system of  claim 5 , wherein the frequency of the first oscillator is controlled by an analog control signal. 
   
   
       7 . The system of  claim 5 , wherein the oscillator operates continuously. 
   
   
       8 . The system of  claim 1 , wherein the mechanism for tracking an amount of time the host device is in the active state is an oscillator, the oscillator operating at about a constant frequency, wherein at least one frequency divider operates between the oscillator and the mechanism for generating the value; and
 further comprising a calibration matrix of digitally controlled diodes for calibrating a bias current of the oscillator.   
   
   
       9 . The system of  claim 8 , wherein the calibration matrix is automatically calibrated upon detection of an event. 
   
   
       10 . The system of  claim 8 , wherein the system self-calibrates from a single reference frequency. 
   
   
       11 . The system of  claim 10 , wherein the reference frequency is derived from a signal from the remote device. 
   
   
       12 . The system of  claim 8 , wherein the oscillator operates continuously. 
   
   
       13 . The system of  claim 8 , wherein the oscillator operates on a current of less than about one microampere (μA). 
   
   
       14 . The system of  claim 8 , wherein the oscillator operates on a current of less than about 5-nanoamperes (nA). 
   
   
       15 . The system of  claim 1 , further comprising a switched capacitor precision resistor for controlling a bias current to the mechanism for tracking the amount of time the host device is in the active state. 
   
   
       16 . The system of  claim 1 , wherein the mechanism for tracking an amount of time the host device is in the active state is a first oscillator, and further comprising a second oscillator, the second oscillator tracking an amount of time the host device is in a state other than the active state. 
   
   
       17 . A system for estimating power consumption of a host device, comprising:
 an oscillator for tracking at least an amount of time a host device is in a first state;   a counter receiving output from the oscillator for generating a value representing a power consumption of the host device based on output from the oscillator, wherein the counter operates at different speeds depending on the state of the host device; and   wherein the frequency of the oscillator is controlled by an analog control signal.   
   
   
       18 . The system of  claim 17 , further comprising a calibration matrix of digitally controlled diodes for calibrating a bias current of the oscillator. 
   
   
       19 . The system of  claim 18 , wherein the calibration matrix is automatically calibrated upon detection of an event. 
   
   
       20 . The system of  claim 18 , wherein the system self-calibrates from a single reference frequency. 
   
   
       21 . The system of  claim 20 , wherein the reference frequency is derived from a signal from a remote device. 
   
   
       22 . The system of  claim 17 , further comprising a switched capacitor precision resistor for controlling a bias current to the oscillator. 
   
   
       23 . The system of  claim 17 , wherein the oscillator operates continuously. 
   
   
       24 . The system of  claim 17 , wherein the oscillator operates on a current of less than about one microampere (μA). 
   
   
       25 . The system of  claim 17 , wherein the oscillator operates on a current of less than about 5 nanoamperes (nA).