Monitoring method, circuit and system

Abstract

A monitoring circuit for use with a monitored circuit having a power supply input and a load output. The monitoring circuit having a biasing module, a reference generator coupled to the power supply input and the biasing module, a comparator coupled to the monitored circuit and the reference generator and an output device coupled to the load output and activated at a predetermined signal threshold.

We claim: 
     
       1. A monitoring circuit for use with a monitored circuit, the monitoring circuit having an input connected to a power supply and an output connected a load, the monitoring circuit comprising:
 an undervoltage decision circuit coupled to a positive terminal of the power supply, the undervoltage decision circuit including an undervoltage decision output and configured to adjust a logic level of the undervoltage decision output based on a voltage of the positive terminal; 
 an undervoltage level shifter receiving the undervoltage decision output and configured to couple or decouple the power supply and the load based on the logic level of the undervoltage decision output; 
 an overvoltage decision circuit coupled to the positive terminal of the power supply, the overvoltage decision circuit including an overvoltage decision output and configured to adjust a logic level of the overvoltage decision output based on the voltage of the positive terminal; and 
 an overvoltage level shifter receiving the overvoltage decision output and configured to couple or decouple the power supply and the load based on the logic level of the overvoltage decision output. 
 
     
     
       2. The monitoring circuit of  claim 1 , wherein the undervoltage decision circuit includes an undervoltage reference generator and a comparator, such that the comparator compares the voltage of the positive terminal to a voltage of the undervoltage reference generator and asserts a logic high on the undervoltage decision output when the voltage of the positive terminal is greater than the voltage of the undervoltage reference generator and a logic low when the voltage of the positive terminal is less than the voltage of the undervoltage reference generator. 
     
     
       3. The monitoring circuit of  claim 2 , wherein the power supply is coupled to the load when the voltage of the positive terminal is greater than the voltage of the undervoltage reference generator, and the power supply is decoupled from the load when the voltage of the positive terminal is less than the voltage of the undervoltage reference generator. 
     
     
       4. The monitoring circuit of  claim 1 , wherein the overvoltage decision circuit includes an overvoltage reference generator and a comparator, such that the comparator compares the voltage of the positive terminal to a voltage of the overvoltage reference generator and asserts a logic high on the undervoltage decision output when the voltage of the positive terminal is greater than the voltage of the undervoltage reference generator and a logic low when the voltage of the positive terminal is less than the voltage of the undervoltage reference generator. 
     
     
       5. The monitoring circuit of  claim 4 , wherein the power supply is coupled to the load when the voltage of the positive terminal is less than the voltage of the overvoltage reference generator, and the power supply is decoupled from the load when the voltage of the positive terminal is greater than the voltage of the overvoltage reference generator. 
     
     
       6. A system for reducing offline power consumption comprising:
 a voltage reference coupled to a power source;   a comparator coupled to the voltage reference and the power source; and   a pass device coupled to the power source and the comparator, wherein the comparator is configured to disconnect the pass device from a load when a voltage of the power source is less than a voltage of the voltage reference, wherein the voltage reference comprises a floating n-gate transistor.    
     
     
       7. The system of claim 6 wherein the power source comprises a battery power source.  
     
     
       8. The system of claim 6 wherein the comparator comprises an additional comparator configured for use only during an increase of the voltage of the power source during a transition from an “OFF” state to an “ON” state.  
     
     
       9. The system of claim 6 wherein the comparator comprises a transistor.  
     
     
       10. The system of claim 6 wherein the pass device comprises a transistor.  
     
     
       11. The system of claim 6 wherein the power source comprises a plurality of batteries.  
     
     
       12. The system of claim 6 wherein the voltage reference comprises an overvoltage reference and an undervoltage reference.  
     
     
       13. The system of claim 6 wherein the comparator comprises a plurality of comparators.  
     
     
       14. A system for reducing offline power consumption comprising:
 a voltage reference coupled to a power source;   a comparator coupled to the voltage reference and the power source;   a pass device coupled to the power source and the comparator, wherein the comparator is configured to disconnect the pass device from a load when a voltage of the power source is less than a voltage of the voltage reference; and   a level shifter coupled to the comparator and configured to generate a level-shifted output signal.    
     
     
       15. The system of claim 6 further comprising a selectable hysteresis circuit coupled to the comparator.  
     
     
       16. The system of claim 15 wherein the selectable hysteresis circuit comprises one or more transistors and a plurality of resistors.  
     
     
       17. A system for reducing offline power consumption comprising:
 a voltage reference coupled to a power source;   a comparator coupled to the voltage reference and the power source; and   a pass device coupled to the power source and the comparator, wherein the comparator is configured to disconnect the pass device from a load when a voltage of the power source is less than a voltage of the voltage reference, wherein the voltage reference comprises a plurality of overvoltage references and a plurality of undervoltage references, the power source comprises a plurality of batteries, the comparator comprises a plurality of comparators, and further comprising a plurality of level shifters, each coupled to one of the plurality of comparators.    
     
     
       18. A system for reducing offline power consumption comprising:
 a voltage reference coupled to a power source;   a comparator coupled to the voltage reference and the power source;   a pass device coupled to the power source and the comparator, wherein the comparator is configured to disconnect the pass device from a load when a voltage of the power source is less than a voltage of the voltage reference;   a plurality of transistors coupled in series to the voltage reference and configured to reduce current consumption by the system; and   a plurality of resistors coupled to the plurality of transistors.