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 host Radio Frequency Identification (RFID) device, comprising:
 a subsystem for estimating power consumption thereof, the subsystem comprising
 a mechanism for tracking at least an amount of time the RFID device is in an active state; and 
 a mechanism for generating a value representing at least the amount of time the RFID 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 host RFID device of  claim 1 , wherein the mechanism for tracking an amount of time the host RFID device is in the active state is a first oscillator 
   
   
       3 . The host RFID device of  claim 2 , wherein the first oscillator operates at a fraction of a rate of a primary oscillator of the host RFID device. 
   
   
       4 . The host RFID device of  claim 3 , wherein the first oscillator operates at no greater than one sixteenth the rate of the primary oscillator of the host RFID device. 
   
   
       5 . The host RFID device of  claim 2 , wherein the first oscillator is idle when the host RFID device is in an inactive state. 
   
   
       6 . The host RFID device of  claim 2 , wherein the first oscillator operates at a first frequency when the host RFID device is in the active state, wherein the first oscillator operates at a second frequency when the host RFID device is in a state other than the active state. 
   
   
       7 . The host RFID device 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 RFID device. 
   
   
       8 . The host RFID device of  claim 2 , wherein a frequency of the first oscillator is calibrated. 
   
   
       9 . The host RFID device of  claim 1 , wherein a reference current source is calibrated. 
   
   
       10 . The host RFID device of  claim 1 , wherein a rate that the value increases varies independently of a data transmission rate of the host RFID device, wherein the mechanism for tracking the amount of time is dependent upon a rate of a primary oscillator of the host RFID device. 
   
   
       11 . The host RFID device of  claim 1 , wherein a rate that the value increases varies depending on a power dissipation rate of the host RFID device. 
   
   
       12 . The host RFID device of  claim 1 , wherein the mechanism for generating the value representing the amount of time the host RFID device is in the active state is a counter, the value being a cumulative count stored in the counter. 
   
   
       13 . The host RFID device of  claim 12 , wherein the speed of the counter is digitally controlled. 
   
   
       14 . The host RFID device of  claim 1 , wherein the mechanism for tracking an amount of time the host RFID 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 RFID device is in the active state, wherein the first oscillator operates at a second frequency for tracking an amount of time the host RFID device is in a state other than the active state. 
   
   
       15 . The host RFID device of  claim 14 , wherein the frequency of the first oscillator is controlled by an analog control signal. 
   
   
       16 . The host RFID device of  claim 14 , wherein the oscillator operates continuously. 
   
   
       17 . The host RFID device of  claim 1 , wherein the mechanism for tracking an amount of time the host RFID 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. 
   
   
       18 . The host RFID device of  claim 17 , further comprising a calibration matrix of digitally controlled diodes for calibrating a bias current of the oscillator. 
   
   
       19 . The host RFID device of  claim 18 , wherein the calibration matrix is automatically calibrated upon detection of an event. 
   
   
       20 . The host RFID device of  claim 18 , wherein the subsystem self-calibrates from a single reference frequency. 
   
   
       21 . The host RFID device of  claim 20 , wherein the reference frequency is derived from a signal from the remote device. 
   
   
       22 . The host RFID device of  claim 17 , wherein the oscillator operates continuously. 
   
   
       23 . The host RFID device of  claim 17 , wherein the oscillator operates on a current of less than about one microampere (μA). 
   
   
       24 . The host RFID device of  claim 17 , wherein the oscillator operates on a current of less than about 5 nanoamperes (nA). 
   
   
       25 . The host RFID device 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 RFID device is in the active state. 
   
   
       26 . The host RFID device of  claim 1 , wherein the mechanism for tracking an amount of time the host RFID 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 RFID device is in a state other than the active state. 
   
   
       27 . The host RFID device of  claim 1 , wherein the remote device uses the value to estimate usage of power in the host RFID device. 
   
   
       28 . A host Radio Frequency Identification (RFID) device having a subsystem for estimating power consumption thereof, the subsystem comprising:
 a mechanism for tracking at least an amount of time the RFID device is in an active state; and   a mechanism for generating a value representing at least the amount of time the RFID device is in the active state based on the tracking.   
   
   
       29 . A method for estimating power consumption, comprising:
 tracking an amount of time a host Radio Frequency Identification (RFID) device is in an active state;   generating a value representing the amount of time the host RFID device is in the active state; and   sending the value to a remote device.   
   
   
       30 . The method of  claim 29 , wherein the remote device uses the value to estimate power consumption in the host RFID device. 
   
   
       31 . 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,   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.   
   
   
       32 . 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.   
   
   
       33 . 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.