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.   
   
   
       2 . 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. 
   
   
       3 . The system of  claim 2 , wherein the first oscillator operates at a fraction of a rate of a primary oscillator of the host device. 
   
   
       4 . The system of  claim 3 , wherein the first oscillator operates at no greater than one sixteenth the rate of the primary oscillator of the host device. 
   
   
       5 . The system of  claim 2 , wherein the first oscillator is idle when the host device is in an inactive state. 
   
   
       6 . The system of  claim 2 , 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. 
   
   
       7 . The system of  claim 2 , wherein a frequency of the first oscillator is calibrated. 
   
   
       8 . The system of  claim 1 , wherein a rate that the value increases varies independently of a data transmission rate of the host device, wherein the mechanism for tracking the amount of time is dependent upon a rate of a primary oscillator of the host device. 
   
   
       9 . The system of  claim 1 , wherein a rate that the value increases varies depending on a power dissipation rate of the host device. 
   
   
       10 . The system of  claim 1 , wherein the mechanism for generating the value representing the amount of time the host device is in the active state is a counter, the value being a cumulative count stored in the counter. 
   
   
       11 . The system of  claim 10 , wherein the speed of the counter is digitally controlled. 
   
   
       12 . 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. 
   
   
       13 . The system of  claim 12 , wherein the oscillator operates on a current of less than about one microampere (μA). 
   
   
       14 . The system of  claim 12 , wherein the oscillator operates on a current of less than about 5-nanoamperes (nA). 
   
   
       15 . The system of  claim 1 , wherein the remote device uses the value to estimate usage of power in the host device. 
   
   
       16 . The system of  claim 1 , wherein the system is embodied on a Radio Frequency Identification (RFID) tag. 
   
   
       17 . A method for estimating power consumption, comprising:
 tracking an amount of time a host device is in an active state;   generating a value representing the amount of time the host device is in the active state; and   sending the value to a remote device.   
   
   
       18 . The method of  claim 17 , wherein the remote device uses the value to estimate power consumption in the host device. 
   
   
       19 . The method of  claim 17 , wherein the method is performed by a radio frequency identification (RFID) system. 
   
   
       20 . 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.   
   
   
       21 . The system of  claim 20 , 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. 
   
   
       22 . The system of  claim 20 , wherein the host device has a battery, wherein a remote device calculates an estimation of a remaining battery life of the host device based on the power consumption value. 
   
   
       23 . The system of  claim 20 , wherein the frequency of the oscillator is digitally controlled. 
   
   
       24 . The system of  claim 20 , wherein the oscillator operates on a current of less than about one microampere (μA). 
   
   
       25 . The system of  claim 20 , wherein the oscillator operates on a current of less than about 5 nanoamperes (nA). 
   
   
       26 . The system of  claim 20 , 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. 
   
   
       27 . The system of  claim 20 , wherein a frequency of the oscillator varies depending on the state of the host device. 
   
   
       28 . The system of  claim 20 , wherein the system is embodied on a Radio Frequency Identification (RFID) tag. 
   
   
       29 . A method for estimating power consumption of a host device, comprising:
 generating a first tracking signal at a first frequency when a host device is in a first state;   generating a second tracking signal at a second frequency when the host 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 device.   
   
   
       30 . A method for estimating power consumption of a host device, comprising:
 generating a tracking signal at a constant frequency when a host device is in a first or second state;   dividing the frequency of the tracking signal when the host device is in the second state; and   storing a count of the frequency.   
   
   
       31 . A method for calibrating a current by linking the current to a first oscillator and adjusting the current such that the first oscillator frequency approximates the frequency of an external reference oscillator. 
   
   
       32 . A method for simultaneously calibrating a plurality of integrated circuit devices, comprising:
 supplying a reference frequency to all devices; and   commanding all devices to self-calibrate using the reference frequency.   
   
   
       33 . A system for frequency-based calibration, comprising:
 a mechanism for linking calibration parameters to an internal frequency; and   a mechanism for linking the internal frequency to an external frequency.   
   
   
       34 . The system of  claim 33 , wherein the mechanism for linking calibration parameters to the internal frequency is a voltage controlled oscillator. 
   
   
       35 . The system of  claim 33 , wherein the mechanism for linking the internal frequency to an external frequency is a phase locked loop oscillator. 
   
   
       36 . A real time clock, comprising:
 a real time clock operating at a first frequency;   a wireless receiver for receiving a reference frequency; and   a mechanism for calibrating the real time clock frequency using the external reference frequency.   
   
   
       37 . An RFID system, comprising:
 an RFID tag implementing the system of  claim 1 ; and   an RFID reader in communication with the RFID tag.   
   
   
       38 . An RFID system, comprising:
 an RFID tag implementing the system of  claim 20 ; and   an RFID reader in communication with the RFID tag.