Detection of an RFID device by an RF reader unit operating in a reduced power state

• US 6,476,708 B1
• Filed: 03/20/1998
• Issued: 11/05/2002
• Est. Priority Date: 03/20/1998
• Status: Expired due to Term

• Current Assignee: Assa Abloy AB
• Original Assignee: HID Corporation (Assa Abloy AB)
• Inventors: Johnson, David A.
• Primary Examiner(s): Holloway, III, Edwin C.
• Application Number:
  US09/045,860
• Time in Patent Office: 1,691 Days
• Field of Search: 340/10.34, 340/10.33, 340/10.3, 340/10.1, 340/5.31, 340/5.61, 340/5.62, 340/5.63, 340/10.42, 340/572.1, 340/572.2, 340/572.4
• US Class Current: 340/10.34
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device

Abstract

A method is provided for operating an RF transponder system to detect the presence of an RFID device in the proximal space of an RF reader unit having an excitation signal generator circuit and an RFID device detection circuit. The excitation signal generator circuit unit initially operates in a reduced power state, generating ring signals in response to a reduced electrical current and transmitting the ring signals into the proximal space. The RFID device detection circuit evaluates the ring signals to determine variations in an RFID device detection parameter. When the variations pass a variation threshold level due to the presence of the RFID device, the ring signals are terminated and the excitation signal generator circuit switches to an increased power state, wherein the excitation signal generator circuit generates an RF excitation signal which is transmitted to the RFID device.

Claims

1. A method for detecting an RFID device in the presence of an RF reader unit comprising:

a) providing an RF reader unit having an excitation signal generating function, a pulse generating function, a sample timing function, and a ring signal sampling function, wherein each function has an operative mode, and wherein said pulse generating function and said ring signal sampling function is each selectively transitionable between a power consumption state and a power conservation state when in said operative mode, and further wherein said excitation signal generating function, said pulse generating function and said ring signal sampling function is each selectively transitionable between said operative mode and an inoperative mode;

b) generating first and second ring-generating pulses while said pulse generating function of said RF reader unit is in said operative mode and said excitation signal generating function of said RF reader unit is in said inoperative mode, wherein said second ring-generating pulse is generated only after a time interval has elapsed from generation of said first ring-generating pulse, and wherein said first and second ring-generating pulses each have a pulse width corresponding to a ring-generating pulse time, said time interval being long relative to said ring-generating pulse time and said pulse generating function being in said power conservation state throughout said time interval except for the duration of said ring-generating pulse time when said pulse generating function is in said power consumption state;

c) applying said first and second ring-generating pulses to an antenna, wherein said first ring-generating pulse generates a first ring signal series in said antenna exhibiting a first decay rate of said first ring-generating pulse and said second ring-generating pulse generates a second ring signal series in said antenna exhibiting a second decay rate of said second ring-generating pulse, each succeeding ring signal in said first ring signal series having a lower energy level than each preceding ring signal and each succeeding ring signal in said second ring signal series having a lower energy level than each preceding ring signal;

d) generating first and second sample pulses while said sample timing function is in said operative mode, wherein generation of said first and second sample pulses is each delayed a delay time after generation of said first and second ring-generating pulses, respectively, and wherein said first and second sample pulses each has a sample length corresponding to a sample pulse time, said time interval being long relative to said sample pulse time;

e) obtaining a first sample signal series from said first ring signal series in said antenna and obtaining a second sample signal series from said second ring signal series in said antenna while said ring signal sampling function is in said operative mode, wherein said first sample signal series is obtained in correspondence with generation of said first sample pulse and has said sample pulse time and said second sample signal series is obtained in correspondence with generation of said second sample pulse and has said sample pulse time, said ring signal sampling function being in said power conservation state throughout said time interval except for the duration of said sample pulse time when said ring signal sampling function is in said power consumption state;

f) comparing each succeeding sample signal in said first sample signal series to a preceding sample signal in said first sample signal series to determine said first decay rate and comparing each succeeding sample signal in said second sample signal series to a preceding sample signal in said second sample signal series to determine said second decay rate; and

g) comparing said first and second decay rates and transitioning said pulse generating function to said inoperative mode and said excitation signal generating function to said operative mode when a difference between said first and second decay rates series exceeds a threshold level caused by the presence of an RFID device in a proximal space of said RF reader unit while maintaining said pulse generating function in said operative mode and said excitation signal generating function in said inoperative mode when said difference between said first and second decay rates does not exceed said threshold level caused by the absence of said RFID device in said proximal space.

2. The method of claim 1, wherein said second ring-generating pulse has substantially identical properties to said first ring-generating pulse.

3. The method of claim 1, wherein said RF reader unit has a duty cycle and said duty cycle is substantially lower when said pulse generating function is in said operative mode and said excitation signal generating function is in said inoperative mode than when said pulse generating function is in said inoperative mode and said excitation signal generating function is in said operative mode.

4. The method of claim 1 further comprising transmitting an RF excitation signal to said RFID device in said proximal space when said excitation signal generating function is in said operative mode and processing said RF excitation signal in a transponder circuit of said RFID device.

5. The method of claim 4 further comprising generating an RF response signal in said RFID device in response to said RF excitation signal, transmitting said RF response signal to said RF reader unit and reading said RF response signal.

6. The method of claim 5 further comprising transitioning said pulse generating function to said operative mode and said excitation signal generating function to said inoperative mode after reading said RF response signal.

7. The method of claim 1 further comprising in step d) generating first and second timing pulses corresponding to said first and second ring-generating pulses, respectively, and generating said first and second sample pulses in response to said first and second timing pulses, respectively, wherein generation of said first sample pulse is delayed said delay time after said first timing pulse and generation of said second sample pulse is delayed said delay time after said second timing pulse.

8. The method of claim 1 further comprising:

repeating steps a)-d) to generate a third ring-generating pulse, a third ring signal series, and a third sample pulse and to obtain a third sample signal series when said difference between said first and second decay rates does not exceed said threshold level;

comparing each succeeding sample signal in said third sample signal series to a preceding sample signal in said third sample signal series to determine a third decay rate of said third ring-generating pulse; and

comparing said second and third decay rates and transitioning said pulse generating function to said inoperative mode and said excitation signal generating function to said operative mode when a difference between said second and third decay rates exceeds said threshold level caused by the presence of said RFID device in said proximal space while maintaining said pulse generating function in said operative mode and said excitation signal generating function in said inoperative mode when said difference between said second and third decay rates does not exceed said threshold level caused by the absence of said RFID device in said proximal space.

9. The method of claim 1, wherein said delay time is less than said time interval.

10. A method for detecting an RFID device in the presence of an RF reader unit comprising:

a) providing an RF reader unit having a pulse generating function, a ring signal sampling function, and a sample timing function;

b) generating first and second ring-generating pulses with said pulse generating function, wherein said second ring-generating pulse is generated only after a time interval has elapsed from generation of said first ring-generating pulse, and wherein said first and second ring-generating pulses each has a pulse width corresponding to a ring-generating pulse time, said time interval being long relative to said ring-generating pulse time;

c) applying said first and second ring-generating pulses to an antenna, wherein said first ring-generating pulse generates a first ring signal series in said antenna exhibiting a first decay rate of said first ring-generating pulse and said second ring-generating pulse generates a second ring signal series in said antenna exhibiting a second decay rate of said second ring-generating pulse, each succeeding ring signal in said first ring signal series having a lower energy level than each preceding ring signal and each succeeding ring signal in said second ring signal series having a lower energy level than each preceding ring signal;

d) generating first and second timing pulses with said sample timing function, wherein said first and second timing pulses correspond to said first and second ring-generating pulses, respectively, and generating first and second sample pulses in response to said first and second timing pulses, respectively, wherein generation of said first and second sample pulses is each delayed a delay time after said first and second timing pulse, respectively, and wherein said first and second sample pulse each has a sample length corresponding to a sample pulse time, said time interval being long relative to said sample pulse time;

e) obtaining a first sample signal series from said first ring signal series in said antenna and obtaining a second sample signal series from said second ring signal series in said antenna with said ring signal sampling function, wherein said first sample signal series is obtained in correspondence with generation of said first sample pulse and has said sample pulse time and said second sample signal series is obtained in correspondence with generation of said second sample pulse and has said sample pulse time;

f) comparing each succeeding sample signal in said first sample signal series to a preceding sample signal in said first sample signal series to determine said first decay rate and comparing each succeeding sample signal in said second sample signal series to a preceding sample signal in said second sample signal series to determine said second decay rate; and

g) comparing said first and second decay rates and transitioning said pulse generating function to said inoperative mode when a difference between said first and second decay rates exceeds a threshold level caused by the presence of an RFID device in a proximal space of said RF reader unit while maintaining said pulse generating function in said operative mode when said difference between said first and second decay rates does not exceed said threshold level caused by the absence of said RFID device in said proximal space.

11. The method of claim 10, wherein said RF reader unit has an excitation signal generating function, said method further comprising transitioning said excitation signal generating function to an operative mode when said difference between said first and second decay rates exceeds said threshold level while maintaining said excitation signal generating function in an inoperative mode when said difference between said first and second decay rates does not exceed said threshold level.

12. The method of claim 10 further comprising:

repeating steps a)-d) to generate a third ring-generating pulse, a third ring signal series, a third timing pulse, and a third sample pulse and to obtain a third sample signal series when said difference between said first and second decay rates does not exceed said threshold level;

comparing each succeeding sample signal in said third sample signal series to a preceding sample signal in said third sample signal series to determine a third decay rate of said third ring-generating pulse; and

comparing said second and third decay rates and transitioning said pulse generating function to said inoperative mode when a difference between said second and third decay rates exceeds said threshold level caused by the presence of said RFID device in said proximal space while maintaining said pulse generating function in said operative mode when said difference between said second and third decay rates does not exceed said threshold level caused by the absence of said RFID device in said proximal space.

13. A method for detecting an RFID device in the presence of an RF reader unit comprising:

a) generating first and second ring-generating pulses, wherein said second ring-generating pulse is generated only after a time interval has elapsed from generation of said first ring-generating pulse, and wherein said first and second ring-generating pulses each has a pulse width corresponding to a ring-generating pulse time, said time interval being long relative to said ring-generating pulse time;

b) applying said first and second ring-generating pulses to an antenna, wherein said first ring-generating pulse generates a first ring signal series in said antenna exhibiting a first decay rate of said first ring-generating pulse and said second ring-generating pulse generates a second ring signal series in said antenna exhibiting a second decay rate of said second ring-generating pulse, each succeeding ring signal in said first ring signal series having a lower energy level than each preceding ring signal and each succeeding ring signal in said second ring signal series having a lower energy level than each preceding ring signal;

c) generating first and second sample pulses, wherein generation of said first and second sample pulses is each delayed a delay time after generation of said first and second ring-generating pulse, respectively, and wherein said first and second sample pulses each has a sample length corresponding to a sample pulse time, said time interval being long relative to said sample pulse time;

d) obtaining a first sample signal series from said first ring signal series in said antenna and obtaining a second sample signal series from said second ring signal series, wherein said first sample signal series is obtained in correspondence with generation of said first sample pulse and has said sample pulse time and said second sample signal series is obtained in correspondence with generation of said second sample pulse and has said sample pulse time;

e) comparing each succeeding sample signal in said first sample signal series to a preceding sample signal in said first sample signal series to determine said first decay rate and comparing each succeeding sample signal in said second sample signal series to a preceding sample signal in said second sample signal series to determine said second decay rate; and

f) comparing said first and second decay rates and terminating generation of subsequent ring-generating pulses when a difference between said first and second decay rates exceeds a threshold level caused by the presence of an RFID device in a proximal space of an RF reader unit while repeating steps a)-d) to generate a third ring-generating pulse, a third ring signal series, a third sample pulse, and a third sample signal series when said difference between said first and second decay rates does not exceed said threshold level caused by the absence of said RFID device in said proximal space.

14. The method of claim 13 further comprising:

comparing each succeeding sample signal in said third sample signal series to a preceding sample signal in said third sample signal series to determine a third decay rate of said third ring-generating pulse; and

comparing said second and third decay rates and terminating generation of subsequent ring-generating pulses when a difference between said second and third decay rates exceeds said threshold level caused by the presence of said RFID device in said proximal space.

15. An RF reader unit comprising:

means for generating ring-generating pulses, wherein each succeeding ring-generating pulse is generated only after a time interval has elapsed from generation of a preceding ring-generating pulse, and wherein each ring-generating pulse has a pulse width corresponding to a ring-generating pulse time, further wherein said time interval is long relative to said ring-generating pulse time, said ring-generating pulse generating means is selectively transitionable between an operative mode and an inoperative mode and is selectively transitionable between a power consumption state and a power conservation state when in said operative mode, said ring-generating pulse generating means being in said power conservation state throughout said time interval except for the duration of said ring-generating pulse time when said ring-generating pulse generating means is in said power consumption state;

means for applying said ring-generating pulses to an antenna, wherein each ring-generating pulse generates a ring signal series in said antenna exhibiting a decay rate of said ring-generating pulse, thereby generating a plurality of ring signal series each exhibiting a decay rate of a ring-generating pulse, and wherein each succeeding ring signal in each ring signal series has a lower energy level than each preceding ring signal;

means for generating sample pulses, wherein generation of each sample pulse is delayed a delay time after generation of each ring-generating pulse, and wherein each sample pulse has a sample length corresponding to a sample pulse time, said time interval being long relative to said sample pulse time;

means for obtaining a first sample signal series from a first ring signal series in said antenna and obtaining a second sample signal series from a second ring signal series in said antenna, each sample signal in said first or second sample signal series obtained in correspondence with generation of each sample pulse and each sample signal in said first or second sample signal series having said sample pulse time, wherein said sample obtaining means is selectively transitionable between an operative mode and an inoperative mode and selectively transitionable between a power consumption state and a power conservation state when in said operative mode, said sample obtaining means in said power conservation state throughout said time interval except for the duration of said sample pulse time when said sample obtaining means is in said power consumption state;

means for comparing each succeeding sample signal in said first sample signal series to a preceding sample signal in said first sample signal series to determine said decay rate of said first ring-generating pulse, comparing each succeeding sample signal in said second sample signal series to a preceding sample signal in said second sample signal series to determine said decay rate of said second ring-generating pulse, and comparing said decay rates of said first and second ring-generating pulses; and

means for transitioning said ring-generating pulse generating means to said inoperative mode when a difference between said decay rates of said first and second ring-generating pulses exceeds a threshold level caused by the presence of an RFID device in a proximal space of said RF reader unit while maintaining said ring-generating pulse generating means in said operative mode when said difference between said decay rates of said first and second ring-generating pulses does not exceed said threshold level caused by the absence of said RFID device in said proximal space.

16. The RF reader unit of claim 15 further comprising means for generating an excitation signal selectively transitionable between an operative mode and an inoperative mode, wherein said transitioning means transitions said excitation signal generating means to said operative mode when said difference between said decay rates of said first and second ring signal series exceeds said threshold level while maintaining said excitation signal generating means in said inoperative mode when said difference between said decay rates of said first and second ring signal series does not exceed said threshold level.