Abstract:
The disclosure discloses a method for extending the length of time over which a cordless telephone system can operate without an external source of power. The method involves detecting a power supply outage, determining that a telephone call is not currently being handled, placing the portable unit into a mode of reduced power consumption, and placing the base unit into a mode of reduced power consumption. After a period of time, the base unit resumes functionality, determines whether a call is being initiated, and handles any such calls. If the system is not active, the base unit re-enters its mode of reduced power consumption, and the cycle is repeated.

Description:
BACKGROUND OF THE INVENTION 
     Cordless telephones have become a common fixture in the modern household, to the extent that many consumers now have few, if any, conventional corded telephones. While the convenience, mobility, and high sound quality of cordless telephones have attracted many consumers, one of their drawbacks is that they consume more power than can be provided by a conventional telephone line. Consequently, modern cordless telephones must be plugged into a power outlet for operation. 
     One significant drawback of wall-powered cordless telephones is that such telephones commonly become inoperative during a power outage. If the telephone consumer does not also own a conventional corded telephone that operates on telephone line power, the consumer is then unable to place a telephone call reporting the power outage, or other emergencies. As a result, consumers must either keep an unwanted conventional telephone in service, or risk elimination of telephone services in the event of a power outage. Even if a consumer does keep a corded telephone in service, they will be inconvenienced by having to locate and utilize the corded telephone while power is out. 
     Some prior art cordless telephone designs have addressed this problem by including a rechargeable battery pack in the cordless telephone base unit, which can temporarily provide power to the base unit when the wall power supply fails. However, the effectiveness of this solution is limited by the significant power consumption of a typical cordless telephone system, resulting in limited battery life. 
     It is therefore an object of this invention to maximize cordless telephone utilization time following a power outage by placing the system into a sleep mode, during which power consumption is reduced. 
     It is another object of this invention to periodically check for incoming or outgoing calls such that the system retains functionality during the power outage. 
     It is yet another object of this invention to control the frequency with which the system checks for call activity based upon the power level remaining in the rechargeable batteries. 
     SUMMARY OF THE INVENTION 
     The invention involves a cordless telephone system, including a base unit and a portable unit, each capable of operating from a rechargeable battery pack as a power source. The base unit is further capable of operating on power supplied by an external source, such as a wall outlet and AC-to-DC converter. 
     In accordance with the method of the invention, the base unit detects when the external source of power fails. If the telephone system is not currently handling a call, the portable unit is placed into a mode in which its power consumption is reduced. The base unit is also placed into a mode of reduce power consumption, during which time calls cannot be processed. The length of the sleep period can be fixed at a predetermined interval. Alternatively, the period length can vary based on the amount of power remaining in the base unit battery. In one embodiment, the sleep period is interrupted immediately upon receipt of an incoming call on the telephone line to which the base unit is connected. 
     After sleeping for a period of time, the base unit circuits are awakened. The base unit then determines whether the telephone system is active. The telephone system will be deemed active if, for example, a telephone call is being placed by a user of the handset, or an incoming call is being received on the telephone line into which the base unit is connected. If the telephone system is active, the base unit handles the call. 
     Finally, when the telephone system is not active, and power is still not being supplied by the external power source, the base unit is placed back into the state of reduced power consumption, and the cycle is repeated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 of the drawings is a schematic diagram of one embodiment of the invention. 
     FIG. 2 of the drawings is a flowchart describing the operation of one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While this invention is susceptible to embodiment in many forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to embodiments illustrated. 
     The present invention comprises a method and apparatus for extending the duration over which a cordless telephone can operate after its external power source has failed. The invention places both the base unit and portable unit of the cordless telephone into a low-power mode while inactive and operating on battery power. 
     In the embodiment of FIG. 1, a primary external power source is applied to the base unit at the external power source input, Vunreg. In this embodiment, approximately +9 VDC is applied to Vunreg, typically converted from a wall outlet AC voltage by an AC-to-DC converter, which can be either internal to the base unit or external. During normal operation, regulator U 1  converts the Vunreg voltage level to +5 VDC. Regulator U 2  then regulates the voltage level down to +3 VDC for distribution to the remaining active components in the base unit. 
     The external power source also charges batteries B 1  and B 2 . Base unit battery B 1  is charged through current limiting resistor R 1  and diode D 1 . Diode D 1  prevents the reverse flow of current from battery B 1  to Vunreg in the event of a failure of the primary power source. The external power source charges portable unit battery B 2  when the portable unit is electrically engaged with the base unit. Current flows from Vunreg, through diode D 2  and current limiting resistor R 6 , into B 2 . Diode D 2  prevents the reverse flow of current from battery B 2  to Vunreg in the event of a failure of the primary power source. 
     Comparator U 4 , in combination with resistors R 7 , R 8 , R 9 , and R 10 , detects failure of the primary power source by comparing the Vunreg voltage to the voltage at battery B 1 . When the primary power source fails, the output of U 4  transitions from high to low. The state of the comparator U 4  output is detected by microcontroller U 3 . 
     Transistors Q 1 , Q 2 , and Q 3 , along with resistors R 2 , R 3 , R 4 , and R 5 , form a power switch circuit which automatically provides power to the base unit circuitry from Vunreg when Vunreg is present, and from battery B 1  if Vunreg fails. As was stated, during normal operation Vunreg supplies current to regulators U 1  and U 2  for distribution to the base unit circuitry. Vunreg also biases resistors R 2  and R 3 , turning on transistor Q 3 . Q 3  pulls the base of Q 2  low, thereby turning Q 2  off. When Q 2  is off, it draws no current from the base of Q 1 , thereby turning transistor Q 1  off. Because Q 1  is off, the battery B 1  is disconnected from the rest of the circuitry during normal operation. 
     When Vunreg fails, Q 3  is turned off. Battery B 1  biases the base of Q 2 , causing Q 2  to turn on Q 1 . Therefore, current flows from battery B 1  through transistor Q 1 , for regulation by U 2  and subsequent distribution to the base unit circuitry  100 . 
     The embodiment of FIG. 1 further includes circuitry for charging the battery of the portable unit when the portable unit and the base unit are engaged and the primary power source has failed. If battery B 2  nears depletion while base unit battery B 1  has power remaining, microcontroller U 3  can temporarily close switch SW 1  to transfer energy between batteries B 1  and B 2  through current-limiting resistor R 11 . 
     The operation of the invention when the primary power source has failed is explained in the flow chart of FIG.  2 . When the primary power source fails and a call is not in progress, step  10 , the base unit sends a sleep command to the handset, step  11 . The base unit then places its own circuitry into a sleep mode in step  12 . The sleep mode constitutes a mode of operation in which power consumption is decreased, while the functionality of many circuits is suspended or reduced. In the preferred embodiment, the transmitter and receiver circuits are powered off. Microcontrollers are either placed into a steady state, or operated with clock frequencies reduced from, for example, 8 MHz to 32 kHz. When a devices awakens from a sleep mode, its circuits typically resume their normal functionality. 
     During the sleep mode, both the base unit and the portable unit awaken periodically. In one embodiment, each unit awakens once every 1.5 seconds. The precise time between awakenings can be varied to suit particular design goals. As the period increases, energy use is reduced, but unit responsiveness is also reduced, forcing a user to wait as much as a full period before the handset responds to an incoming call, or the base responds to the user&#39;s attempt to initiate a call. In another embodiment, the period varies in accordance with the level of energy remaining in the backup battery. While the battery is highly charged, the sleep period may be comparatively short, such as 0.5 seconds, thereby providing a high level of responsiveness to the user during shorter power outages. As the battery charge falls, the period between awakenings increases to avoid complete operation outage. 
     In step  13 , the base unit starts a timer during which duration the base unit circuits remain insleep mode. An interrupt is provided by step  14 , such that if the base detects an incoming telephone call on the telephone line to which the base unit is connected, the base unit circuits are awoken immediately, step  18 , and the call is handled, step  19 . Otherwise, after the timer has completed its duration, step  15 , the base unit circuits are awoken in step  16 . 
     When the base unit awakens from the power-conserving mode of operation, its receiver scans for radio transmissions emanating from the portable unit which would indicate that the portable unit is initiating a telephone call, or engaging in some other communication which requires base unit participation. Similarly, when the portable unit awakens, its receiver scans for radio transmissions emanating from the base unit that would indicate a telephone call is being received. This sleep mode operation of the portable unit may differ from conventional power-conserving handset operation in that the time period between awakenings can be increased from the typical 0.5 seconds or less to match the base unit and further reduce power consumption. 
     In step  17 , the base unit receiver then scans for radio transmissions emanating from the portable unit which would indicate that the portable unit is paging the base unit to initiate a telephone call, or engaging in some other communication which requires base unit participation, such as an intercom connection. If the base unit detects paging by the handset, the base unit handles the call, step  19 . If the base unit does not detect any paging by the handset in step  17 , the base unit returns to the start of the power-failure operation cycle of FIG.  2 . 
     The foregoing descriptions and drawings merely explain and illustrate the invention and the invention is not limited thereto except insofar as the appended claims are so limited, as those skilled in the art who have the disclosure before them will be able to make modifications or variations therein without departing from the scope of the invention.