Source: https://patents.google.com/patent/US8203429B2/en
Timestamp: 2019-10-21 21:44:04
Document Index: 546109277

Matched Legal Cases: ['Application No. 61', 'Application No. 07251386', 'Application No. 07251386', 'Application No. 07251386', 'Application No. 2007201297', 'Application No. 07251385', 'Application No. 2007201297', 'Application No. 07251385', 'Application No. 07251385', 'Application No. 07251385', 'Application No. 07251386']

US8203429B2 - Switched capacitance method for the detection of, and subsequent communication with a wireless transponder device using a single antenna - Google Patents
Switched capacitance method for the detection of, and subsequent communication with a wireless transponder device using a single antenna Download PDF
US8203429B2
US8203429B2 US12/416,104 US41610409A US8203429B2 US 8203429 B2 US8203429 B2 US 8203429B2 US 41610409 A US41610409 A US 41610409A US 8203429 B2 US8203429 B2 US 8203429B2
US12/416,104
US20090251291A1 (en
Eric J. Borcherding
2008-04-01 Priority to US4135808P priority Critical
2009-03-31 Application filed by Assa Abloy AB filed Critical Assa Abloy AB
2009-03-31 Priority to US12/416,104 priority patent/US8203429B2/en
2009-06-26 Assigned to ASSA ABLOY AB reassignment ASSA ABLOY AB ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BORCHERDING, ERIC J.
2009-10-08 Publication of US20090251291A1 publication Critical patent/US20090251291A1/en
2012-06-19 Publication of US8203429B2 publication Critical patent/US8203429B2/en
239000003990 capacitor Substances 0 claims description 89
230000004044 response Effects 0 description 74
A transponder detector is provided with capabilities for detecting the presence and type of a transponder in its read range while operating at low power and also using a common antenna for detecting and executing data transactions with transponders.
This Application claims the benefit of U.S. Provisional Application No. 61/041,358, filed Apr. 1, 2008, the entire disclosure of which is hereby incorporated herein by reference.
Radio frequency identification (RFID) systems typically include at least one reader and a plurality of transponders, which are commonly termed credentials, cards, tags, or the like. Each transponder is an active or passive radio frequency communication device which is directly attached to or embedded in an article to be identified or otherwise characterized by the reader. Alternatively, the transponder is embedded in a portable substrate, such as a card, tag, or the like, carried by a person or an article to be identified or otherwise characterized by the reader.
An active transponder is powered up by its own internal power supply, such as an internal battery, which provides the operating power for the transponder circuitry. In contrast, a passive transponder is dependent on the reader for its power. The passive transponder typically consists of an integrated circuit (IC) chip coupled to a resonant LC circuit which has a capacitor and an inductive antenna in parallel or in series. The reader “excites” or powers up the passive transponder by transmitting excitation signals of a given frequency into the proximal space surrounding the reader. When the transponder resides in the proximal space, its inductive antenna receives the excitation signals which are converted into the operating power for the IC chip of the recipient transponder.
In any case, the transponder data signals are transmitted via the transponder antenna into the proximal space surrounding the reader in which the transponder resides. The reader contains its own LC circuit having a capacitor and an inductive antenna which is tuned to essentially the same resonant frequency as the transponder LC circuit, thereby rendering the reader and transponder compatible. The reader LC circuit receives the transponder data signals and is coupled to additional reader circuitry, which enable the reader to “read” the transponder data signals (i.e., extract the data from the transponder data signals). Accordingly, contactless communication is effected between the reader and the transponder in accordance with a specific communication protocol, which is likewise often unique to the particular manufacturer of the transponder and/or reader.
The excitation signal generating and transmitting functions and the transponder data signal receiving and reading functions performed by the reader as described above define a mode of reader operation termed a “data transaction mode.” The data transaction mode further encompasses reader data signal generating and transmitting functions, wherein information stored in the reader memory or otherwise generated by the reader is communicated to the transponder. The manner in which the reader communicates information to the transponder is essentially the same or similar to the manner in which the transponder communicates information to the reader. As such, the reader data signals are characterized by essentially the same carrier frequency as the transponder data signals.
Although a reader can continuously operate in the data transaction mode, the functions of the data transaction mode typically have a relatively high power demand, which can rapidly deplete the power supply of the reader. This condition is particularly undesirable when the reader is powered by a self-contained portable power supply, such as a small disposable or rechargeable battery, which has a finite life. It is generally more power efficient to operate the reader in the data transaction mode only when a transponder is within the read range of the reader and to operate the reader in an alternate mode having a relatively lower power demand at all other times. A preferred alternate lower power mode of operation is termed a detection mode, which is commonly enabled by a ping or impulse signal generator circuit and a transponder detection circuit provided within the reader. Traditional readers operate in the detection mode except when the transponder detection circuit detects a transponder within the read range of the reader. The reader then switches to the data transaction mode upon detection of a transponder, but only for a limited time sufficient to complete communication between the reader and transponder before switching back to the detection mode.
The detection or “ping” capacitance and antenna inductance/size may be adjusted so that the antenna impedance effectively matches the antenna driver. It can also be used, in part, to adjust the source to load coupling impedance, amplitude, tune to retain optimally low detector power use, and somewhat set the circuit Q (i.e., quality factor), as well as a shift of ping frequency upwards with respect to the transaction frequency. In other words, the frequency that the antenna is operated at during the detection mode may correspond to a higher frequency than that frequency which is used by the antenna during the transaction mode. Tuning of the circuit in this manner can also affect the detection and/or transaction range of the antenna. In other words, the range of the antenna should be larger during the transaction mode than during the detection mode. This is done by adjusting the ratio of the capacitance in the shifted ground and the capacitance on the real ground. It is one aspect of the present invention to affect a simulated ground of one of the parallel capacitors that allows the ping impulse to occur on the same antenna that is used during the transaction mode.
Additional details of the detection algorithm and associated software are described in U.S. patent application Ser. No. 11/396,291, filed on Mar. 31, 2006, the entire contents of which are incorporated herein by reference. The embedded software may be used to evaluate the voltage waveform received during the detection mode. Upon detecting a change (e.g., any sufficient and user definable delta) in this waveform due to the presence of something having an inductance in the RFID field can be interpreted as a “card hit”, which will cause the reader to enter the transaction mode.
The invention will be illustrated below in conjunction with an exemplary reader device. Although well suited for use with, e.g., a system using access control readers and/or transponders, the invention is not limited to use with any particular type of access control system or configuration of system elements. Those skilled in the art will recognize that the disclosed techniques may be used in any RF system n which it is desirable to minimize power consumption of the reader.
The transponder 12 comprises a number of functional elements including a transponder integrated circuit (IC) 12 a and a transponder antenna 12 b. The transponder IC 12 a embodies the processing and memory capabilities of the transponder 12. The transponder antenna 12 b is coupled to the transponder IC 12 a and is a conventional inductive antenna coil termed a “dual-function antenna coil” which performs both the receiving and transmitting functions of the transponder 12. Alternatively, two separate receiving and transmitting antenna coils (not shown) can be substituted for the single dual-function antenna coil in the transponder 12. The transponder 12 also preferably includes an external transponder tuning capacitor (not shown) coupled to the transponder IC 12 a and to each antenna coil of the transponder antenna 12 b. The term “external” is used above with respect to the transponder 12 to designate electronic components which are not physically or functionally included within the transponder IC 12 a.
The term “tuning capacitor” is used herein to describe a capacitor preferably having a fixed capacitance which, in cooperation with the transponder antenna 12 b, establishes the transponder frequency of the transponder 12. The term “tuned resonant frequency” is used herein to describe a resonant frequency of the transponder LC circuit which is typically fixed at the time of transponder manufacture by selection of a specific transponder antenna and a specific cooperative tuning capacitor. Thus, the tuned resonant frequency of the transponder LC circuit in the transponder 12 is preferably non-adjustable after manufacture of the transponder. The term “transponder frequency” corresponds to the tuned resonant frequency of the transponder LC circuit in the transponder 12 and likewise to the carrier frequency of the transponder 12.
The reader 14 has at least two modes of operation, namely, a low power detection mode and a high power data transaction mode (alternately referred to as a “read mode”). The detection mode is the initial operating mode of the reader 14, wherein the wakeup unit 26 functions as a transponder detector to actively seek any transponders 12 residing in the surrounding space proximal to the reader 14, i.e., within the read range of the reader 14. Since the ER circuit 22 and main controller 24 are characterized as having a high power demand when performing read mode functions, the reader 14 is configured to deactivate most or all of the components and functions associated with the ER circuit 22, main controller 24 and I/O interface 28 during the detection mode. Substantial power savings are achieved by using the wakeup unit 26 as the sole or primary operating unit for performing the transponder detection function during the detection mode because the wakeup unit 26 is characterized as having a low power demand. Although the wakeup unit 26 is shown herein as being structurally and functionally integral with the reader 14, it is apparent to the skilled artisan applying the teaching herein that the wakeup unit 26 can alternately be constructed and/or adapted to function as a stand-alone transponder detector apart from the reader 14.
Referring to FIG. 4, an embodiment of a wakeup unit of the present invention is shown and designated 26 a. Elements of FIG. 4 which are specific embodiments of elements shown generally in FIG. 1 are designated by the same reference character, but with the suffix “a” added. The wakeup unit 26 a is configured to generate a serial progression of detection signals at a plurality of different frequencies. The wakeup unit 26 a comprises a detection signal generator circuit 40 a, a response signal receiver circuit 42 a, and a wakeup controller 44 a. In addition a cooperative antenna assembly 20 a is associated with the wakeup unit 26 a. The wakeup controller 44 a is provided with OP_AMP and DONE inputs 50, 52 to receive OP_AMP and DONE input signals, respectively. The wakeup controller 44 a is further provided with TAGREC, PING, SELECT1, SELECT2, and DETCLR outputs, 54, 56, 58, 59, 60 to send TAGREC, PING, SELECT1, SELECT2, and DETCLR output signals, respectively, which are generated by the wakeup controller 44 a.
The wakeup controller 44 a of the present embodiment is shown having two select signal outputs, i.e., SELECT1 output 58 and SELECT2 output 59, for purposes of illustration. It is within the scope of the present invention, for the wakeup controller 44 to have any integer number N of select signal outputs. Accordingly, each select signal output of the wakeup controller 44 is generally designated SELECTX output, on which a SELECTX output signal generated by the wakeup controller 44 is sent, wherein X=1, 2, 3 . . . N. The precise value of X for a given embodiment of the wakeup controller 44 is determined by the number of switched resistor/capacitor pairs in the detection signal generator circuit 40 a as described below.
A second capacitor 90 is connected between the inverter 82 and the parallel capacitance. The parallel capacitance is coupled to ground 84 and the antenna assembly 20 a via an antenna input/output node 92. Thus, the antenna assembly 20 a is connected in parallel with the first unswitched parallel capacitor 72, first switched parallel capacitor 74, and second switched parallel capacitor 78. As such, the output of the parallel capacitance (and correspondingly the input to the antenna assembly 20 a) is the antenna input/output node 92. Although the inverter 82 is shown herein as a single element, any suitable number of inverter elements may be included within the inverter 82 to achieve a desired power and/or range of the detection signal for a particular antenna assembly 20 a.
The detection signal generator circuit 40 a further comprises first, second, third and fourth resistors 94, 96, 98, 100, first and second diodes 102, 104, first and second transistors 106 and 108, an operational amplifier 110, a third capacitor 112, and a second voltage source (+Vdd) 114. The input to the first resistor 94 is the antenna input/output node 92. The base of the first transistor 106 is connected between the first diode 102 and the second resistor 96. The opposite end of the second resistor 96 is connected to ground 116. The emitter of the first transistor 106 is connected to the third resistor 98 and the collector of the first transistor 106 is connected to the second voltage source 114 via the second diode 104. The emitter of the second transistor 108 is connected to ground 118, the collector of the second transistor 108 is connected to the non-inverting input of the operational amplifier 110, and the base of the second transistor 108 is connected to the DETCLR output 60 via the fourth resistor 100 to receive the DETCLR (detection clear) output signal from the wakeup controller 44 a.
The operational amplifier 110 is connected between the second voltage source 114 (which preferably has a voltage value less than the first voltage source 88) and ground 118. As noted above, the noninverting input of the operational amplifier 110 is connected to the collector of the second transistor 108. The output of the operational amplifier 110 is connected to its inverting input and to the OP_AMP input 50, enabling the wakeup controller 44 a to receive analog OP_AMP input signals from the operational amplifier 110.
The wakeup controller 44 a initiates a serial progression of detection signals by periodically generating and sending a plurality of preferably identical PING output signals (also termed pulse signals) via the PING output 56. Each PING output signal is routed in series through the first capacitor 86, series resistance, inverter 82, series capacitance, and antenna input/output node 92 to the antenna assembly 20 a, thereby producing a ring signal (i.e., detection signal) on the coil of the antenna assembly 20 a. The inverter 82 preferably shapes each PING output signal to a selected width and amplitude, wherein the pulse width is preferably selected as a function of the tuned frequency of the LC circuit of the ER circuit 22 and the tuned frequency of the LC circuits of any transponders expected within the read range of the reader 14. An exemplary selected pulse width is 36.9 nanoseconds, which produces a wavy detection signal in the form of a decaying sine wave at 13.56 MHz on the coil of the antenna assembly 20 a.
The detection signal generator circuit 40 a employs the series resistance and parallel capacitance, which are responsive to specific SELECT1 and SELECT2 output signals, to selectively raise or lower the frequency value of the detection signals generated by the detection signal generator circuit 40 a from a baseline or middle frequency value. In this manner, the detection signal generator 40 a is able to generate a progression of detection signals, wherein each detection signal in the progression has a different frequency value.
1) wakeup controller 44 is in SLEEP state;
2) timer 46 signals change of wakeup controller 44 to AWAKE state;
3) prior or initial reading of transponder detection parameter is cleared from memory of wakeup controller 44 by asserting DETCLR output signal;
4) DETCLR output signal is de-asserted;
5) SELECTX output signal is asserted then PING output signal is asserted and de-asserted;
6) brief time period expended to permit operational amplifier 110 to slew to a valid analog OP_AMP input signal
7) wakeup controller 44 clock rate is boosted to accelerate processing functions;
8) ADC 48 turned on and instructed to run;
9) brief time period expended for ADC 48 to perform analog to digital conversion of analog OP_AMP input signal;
10) ADC 48 shut off;
11) composite energy due to mutual coupling of the antenna assembly 20 and transponder 12 at a given frequency (e.g. 13.56 MHz) or a near beat frequency of the detection signal is sampled and recorded;
12) rolling sum average for the frequency of the detection signal is maintained, both long-term and short-term;
13) rolling sum average based on a time interval allowing the wakeup unit 26 to adapt to metallic environments (metal reduces sensitivity of the wakeup unit 26, yet is compensated for by wakeup unit 26);
14) if change is seen in the transponder detection parameter greater than the current sensitivity setting of the wakeup unit 26, a detect event has occurred;
15) detect events for a progression of detection signals are correlated and further discriminated to categorically determine the type of the transponder 12 detected;
16) processing rate of wakeup controller 44 reduced to a minimum;
17) transponder detection and type determination reported to main controller 24 by asserting TAGREC output signal (TAGREC output signal is a categorized table of pulses for a progression of detection signals);
18) DONE input signal asserted to signal application is complete;
19) wakeup controller 44 returns to SLEEP state;
20) timer 46 signals change of wakeup controller 44 to AWAKE state.
The period of steps 1-20 above provides a basis for setting the rate that the PING output signals are generated by the wakeup unit 26. Thus, the time interval that the wakeup controller 44 is in the SLEEP state (i.e., the SLEEP time interval) is adjustable.
A) compare analog to digital conversion of analog OP_AMP input signal to a predetermined unsafe threshold level (typically substantially greater than the dynamic response threshold level)
B) if analog to digital conversion of analog OP_AMP input signal is below unsafe threshold level, proceed to step 11;
C) if analog to digital conversion of analog OP_AMP input signal exceeds unsafe threshold level, assert protected mode and periodically repeat steps 4, 7-10, and 3 until analog to digital conversion of analog OP_AMP input signal is below unsafe threshold level;
D) de-assert protected mode and proceed to step 2.
In summary, steps A-D comprise conveying the analog OP_AMP input signal to the wakeup controller 44 a where the ADC 48 converts the analog signal to a digital signal. The wakeup controller 44 a determines the amplitude of the digital signal and compares the amplitude value to a predetermined unsafe threshold level. The amplitude of the digital signal preferably represents a measure of radio frequency (RF) energy field strength present at the antenna assembly 20 a. If the amplitude of the digital signal is less than the predetermined unsafe threshold level, the response signal receiver circuit 42 a remains in the unprotected mode by continuing to de-assert the DETCLR output signal and the wakeup unit 26 a performs the transponder detection operations taught herein to actively seek a transponder 12 in the surrounding space of the reader 14.
If the amplitude of the digital signal is greater than the predetermined unsafe threshold level, the response signal receiver circuit 42 a switches to the protected mode by continuously asserting the DETCLR output signal to the base of the second transistor 108 which clamps one of the inputs (e.g., noninverting input) of the operational amplifier 110. The wakeup controller 44 a also preferably sends a signal to the main controller 24 indicating a high RF energy field strength at the antenna assembly 20 a. The main controller 24 preferably performs operations to protect sensitive components contained within the ER circuit 22 from incoming high voltage antenna signals in response to the high RF energy field strength signal from the wakeup controller 44 a.
Once in the protected mode, the response signal receiver circuit 42 a preferably remains in the protected mode for a specified (i.e., predetermined) or unspecified protected time period. Upon expiration of the protected time period, the wakeup controller 44 briefly de-asserts the DETCLR output signal which enables another determination of the amplitude of the digital OP_AMP output signal. If the amplitude of the digital OP_AMP output signal is still above the predetermined unsafe threshold level, the response signal receiver circuit 42 a remains in the protected mode. The protected time period can also be adjusted as a function of the newly determined value of the amplitude of the digital OP_AMP output signal. However, if the amplitude of the digital signal is less than the predetermined unsafe threshold level, the wakeup controller 44 a reinitiates the detection mode.
22. The reader of claim 20, wherein the first set of parallel capacitors includes at least a first parallel capacitance that is operated by an inverter adapted to control the operation of the at least a first parallel capacitance, wherein the inverter comprises at least one AND gate and a plurality of NOT gates which are used to condition the output voltage of the control circuitry to the rest of the tuning circuit.
US12/416,104 2008-04-01 2009-03-31 Switched capacitance method for the detection of, and subsequent communication with a wireless transponder device using a single antenna Active 2030-09-24 US8203429B2 (en)
US4135808P true 2008-04-01 2008-04-01
US12/416,104 US8203429B2 (en) 2008-04-01 2009-03-31 Switched capacitance method for the detection of, and subsequent communication with a wireless transponder device using a single antenna
US20090251291A1 US20090251291A1 (en) 2009-10-08
US8203429B2 true US8203429B2 (en) 2012-06-19
ID=40874613
US12/416,104 Active 2030-09-24 US8203429B2 (en) 2008-04-01 2009-03-31 Switched capacitance method for the detection of, and subsequent communication with a wireless transponder device using a single antenna
US (1) US8203429B2 (en)
EP (1) EP2107495B1 (en)
CA (1) CA2661121A1 (en)
ES (1) ES2396015T3 (en)
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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BORCHERDING, ERIC J.;REEL/FRAME:022880/0570