Wake up device for a communications system

A communications system having reduced power consumption, comprising:

• a) a master receiver for receiving data, said master receiver comprising:
• i. at least a first and a second mode of operation, said second mode using substantially less power than said first mode;
• ii. a substantially low power receiver for receiving a wake up signal, said wake up signal having a predetermined frequency and at least a first rate of data transmission, said low power receiver comprising:
• (1) means for detecting a characteristic of said wake up signal;
• and
• (2) a switch for switching between at least said first and said second modes in response to said detecting means;
• and
• b) a transmitter for transmitting data to said master receiver during said first mode and for transmitting said wake up signal to said low power receiver during said second mode.

A communications system for use in an identification system having reduced power consumption, comprising:

• a) a master receiver for receiving data having at least an active mode and a sleep mode of operation;
• b) a transmitter for transmitting data to said master receiver during said active mode and for transmitting a wake up signal during said sleep mode, said wake up signal having a predetermined frequency and rate of data transmission;
• and
• c) a switch for switching said master receiver between said active mode and said sleep mode, said switch comprising a wake up receiver for receiving said wake up signal, said switch being enabled in response to said wake up signal, said wake up receiver using substantially less power than said master receiver, said wake up receiver comprising:
• i. a frequency detector for detecting said frequency of said wake up signal, said frequency detector comprising:
• (1) a first bandpass filter having a first bandwidth, said first bandwidth being substantially narrow;
• and
• (2) a first envelope detector coupled to said first bandpass filter;
• ii. a data rate detector for detecting said rate of data transmission of said wake up signal, said data rate detector having an output and comprising:
• (1) a second bandpass filter having a second bandwidth, said second bandwidth being substantially narrow;
• and
• (2) a second envelope detector coupled to said second bandpass filter;
• and
• iii. a comparator for comparing said output of said data rate detector with a reference voltage, thereby enabling said switch when said frequency detector detects said frequency of said wake up signal and said data rate detector detects said data rate of transmission of said wake up signal.

A method for reducing the consumption of energy in operating a communications system, said communications system comprising a transmitter, a master receiver and a wake up receiver, said master receiver having at least an active mode and a sleep mode of operation, said wake up receiver using substantially less power than said master receiver, comprising the steps of:

• transmitting data to said master receiver during said active mode and a wake up signal to said wake up receiver during said sleep mode, said wake up signal having a predetermined frequency, and a predetermined rate of data transmission;
• detecting said wake up signal;
• and
• enabling up said master receiver in response to said detecting.