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:
 an oscillator for tracking at least an amount of time a host device is in a first state; and   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,   wherein the host device has a battery, wherein the host device calculates an estimation of a remaining battery life of the host device based on the power consumption value.   
   
   
       2 . The system of  claim 1 , wherein the frequency of the oscillator is controlled by an analog control signal. 
   
   
       3 . The system of  claim 1 , wherein the frequency of the oscillator is digitally controlled. 
   
   
       4 . The system of  claim 1 , further comprising a calibration matrix of digitally controlled diodes for calibrating a bias current of the oscillator. 
   
   
       5 . The system of  claim 4 , wherein the calibration matrix is automatically calibrated upon detection of an event. 
   
   
       6 . The system of  claim 4 , wherein the system self-calibrates from a single reference frequency. 
   
   
       7 . The system of  claim 6 , wherein the reference frequency is derived from a signal from a remote device. 
   
   
       8 . The system of  claim 1 , further comprising a switched capacitor precision resistor for controlling a bias current to the oscillator. 
   
   
       9 . The system of  claim 1 , wherein the oscillator operates continuously. 
   
   
       10 . The system of  claim 1 , wherein the oscillator operates on a current of less than about one microampere (μA). 
   
   
       11 . The system of  claim 1 , wherein the oscillator operates on a current of less than about 5 nanoamperes (nA). 
   
   
       12 . The system of  claim 1 , wherein a frequency of the oscillator is about constant, wherein at least one frequency divider operates between the oscillator and the mechanism for generating the value. 
   
   
       13 . The system of  claim 1 , wherein a frequency of the oscillator varies depending on the state of the host device. 
   
   
       14 . The system of  claim 1 , wherein the system is embodied on a Radio Frequency Identification (RFID) tag, the RFID tag being the host device. 
   
   
       15 . The system of  claim 1 , wherein a visual indication of the estimation of a remaining battery life of the host device is output to a user. 
   
   
       16 . An RFID system: comprising:
 an RFID tag implementing the system of  claim 1 , and   an RFID reader in communication with the RFID tag.   
   
   
       17 . A method for estimating power of a Radio Frequency Identification (RFID) device, comprising:
 generating a first tracking signal at a first frequency when a host RFID device is in a first state;   generating a second tracking signal at a second frequency when the host RFID device is in a second state different than the first state; and   processing the tracking signals for generating a value representing a power consumption of the host RFID device,   wherein a derivative of the value is generated for output to a user.