Method and circuit intended for high-frequency communication between an interrogator and a smart tag

• US 20130003712A1
• Filed: 06/28/2012
• Published: 01/03/2013
• Est. Priority Date: 06/29/2011
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: ams AG (Ams-Osram AG), IDS doo (Ams-Osram AG)
• Inventors: Kunc, Vinko, Stiglic, Maksimilijan, Vodopivec, Andrej
• Granted Patent: US 8,774,157 B2
• Time in Patent Office: Days
• US Class Current: 370/345
• CPC Class Codes: H04B 5/45 Transponders
• CPC Class Codes: H04W 52/242 taking into account path loss
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range

Abstract

When communicating with a traditional interrogator of passive smart tags, an actively transmitting smart tag of the invention, even within a data frame being transmitted, observes a first phase (Φi) being a phase of a voltage induced in a tag'"'"'s antenna by an interrogator'"'"'s high-frequency carrier signal and transmits wave packets in that it excites the antenna with a voltage having a phase (Φt), which is always set at the beginning of transmission of each said wave packet shifted with respect to said first phase (Φi) by the same phase angle (ΔΦ). At ΔΦ=180° an amplitude of voltage across an interrogator'"'"'s antenna, when some of said wave packets influence this antenna, attains the largest attainable interference rise. Miniature actively transmitting smart tags are enabled to wirelessly communicate with said traditional interrogator and a communication range of pocket-sized tags is herewith increased.

Claims

1. A method intended for high-frequency communication between an interrogator and a smart tag,

a circuit of said smart tag being galvanically coupled with a voltage source and,

according to which method the smart tag observes a first phase (Φ

i),

which is a phase of a voltage induced in a tag'"'"'s antenna by a high-frequency carrier signal generated by the interrogator,

characterized in

that the smart tag observes the first phase (Φ

i) in those time intervals located even within a data frame being transmitted,

in which time intervals, according to a communication protocol, the smart tag does not transmit packets of high-frequency radio waves,

and that the smart tag transmits said high-frequency wave packets,

in that it excites its own antenna with a voltage,

the phase of which voltage, being a second phase (Φ

t),

is set, at the beginning of transmitting each said high-frequency wave packet,

each time shifted with respect to said observed first phase (Φ

i)

by the same phase angle (Δ

Φ

)

being determined by a relation Δ

Φ

=Φ

t−

Φ

i.

2. The method as recited in claim 1, characterized in

that the smart tag observes the first phase (Φ

i) in the time intervals

with a duration according to the communication protocol being long enough that the smart tag can match the second phase (Φ

t) with a phase,

which is shifted by the phase angle (Δ

Φ

) with respect to the first phase (Φ

i).

3. The method as recited in claim 2, characterized in

that said time intervals of the phase observation are placed closely before the instants,

in which, according to the communication protocol,

the smart tag starts transmitting said high-frequency wave packets.

4. The method as recited in claim 3, characterized in

that said time intervals of the phase observation are placed

in a time window with no tag'"'"'s transmission

even within the duration of bits,

in which bits, according to the communication protocol,

the smart tag transmits said high-frequency wave packets.

5. The method as recited in claim 4, characterized in

that the smart tag transmits said high-frequency wave packets,

in that it excites its own antenna with a simple harmonic voltage,

the phase of which voltage, being a second phase (Φ

t),

is set, at the beginning of transmitting each said high-frequency wave packet,

shifted each time by the same said phase angle (Δ

Φ

).

6. The method as recited in claim 4, characterized in

that the smart tag transmits said high-frequency wave packets,

in that it excites its own antenna with a voltage

having a shape of a pulse group and,

the phase of which voltage, being a second phase (Φ

t),

is set, at the beginning of transmitting each said high-frequency wave packet,

shifted each time by the same phase angle (Δ

Φ

).

7. The method as recited in claim 5, characterized in

that the frequency (ft) of the radio waves in said tag'"'"'s high-frequency wave packets

is equal to the frequency (fi) of the interrogator'"'"'s carrier signal

and that said phase angle (Δ

Φ

) is such

that an amplitude of voltage across an interrogator'"'"'s antenna each time

when some of said wave packets influence this antenna

always attains the largest attainable interference rise or

the largest attainable interference drop.

8. The method as recited in claim 7, characterized in

that the largest attainable interference rise in the amplitude of the voltage across the interrogator'"'"'s antenna is attained by setting said second phase (Φ

t) shifted with respect to said observed first phase (Φ

i) by the phase angle being Δ

Φ

=180°

.

9. The method as recited in claim 7, characterized in

that the largest attainable interference drop of the amplitude of the voltage across the interrogator'"'"'s antenna is attained by setting said second phase (Φ

t) shifted with respect to said observed first phase (Φ

i) by the phase angle being Δ

Φ

=0.

10. The method as recited in claim 1, characterized in

that the smart tag should set said second phase (Φ

t)

with respect to said observed first phase (Φ

i)

with an accuracy better than 20° and

preferably 10°

.

11. The method as recited in claim 8, characterized in

that the smart tag selects a value of said phase angle (Δ

Φ

) and

said second phase (Φ

t) is then set automatically.

12. The method as recited in claim 11, characterized in

that in said time intervals of the phase observation

the smart tag digitizes a signal (rs′

),

which the interrogator'"'"'s carrier signal induces in the tag'"'"'s antenna

and is then amplified,

and that said digitized received signal (drs) is used

as a reference signal for a phase-frequency comparator.

13. The method as recited in claim 12, characterized in

that the phase-frequency comparator is connected into a phase-locked loop,

whose voltage-controlled oscillator operates

at the frequency (fi) of the interrogator'"'"'s high-frequency carrier signal and

whose output signal is shifted by the phase angle Δ

Φ

+90° and

is amplified and

conducted to the tag'"'"'s antenna through a capacitor as a simple harmonic signal to be transmitted in the form of high-frequency wave packets.

14. The method as recited in claim 12, characterized in

that the phase-frequency comparator is connected into a phase-locked loop

whose voltage-controlled oscillator operates at a frequency,

which is a multiple of the frequency (fi) of

the interrogator'"'"'s high-frequency carrier signal,

and an output signal of said voltage-controlled oscillator is conducted through

a digital-to-analogue converter or a digital divider,

where the phase is shifted by the phase angle Δ

Φ

+90° and

is amplified and

conducted to the tag'"'"'s antenna through a capacitor as a simple harmonic signal to be transmitted in the form of the high-frequency wave packets.

15. The method as recited in claim 14, characterized in

that the voltage-controlled oscillator operates at a frequency,

which is an eighthfold, preferably a sixteenthfold

of the frequency (fi) of the interrogator'"'"'s high-frequency carrier signal.

16. The method as recited in claim 13, characterized in

that the phase-locked loop opens

while the interrogator interrupts transmitting the high-frequency carrier signal.

17. The method as recited in claim 13, characterized in

that in said time interval of the phase observation

the smart tag observes a first amplitude (Ai),

which is an amplitude of the voltage

induced in the tag'"'"'s antenna by the interrogator'"'"'s high-frequency carrier signal,

and that the phase-locked loop opens

whenever said first amplitude (Ai) drops below a certain value.

18. The method as recited in claim 13, characterized in

that the phase-locked loop opens closely before the instants,

in which, according to the communication protocol,

the smart tag starts transmitting said high-frequency wave packets.

19. The method as recited in claim 16, characterized in

that the smart tag uses the output signal of said voltage-controlled oscillator as a clock signal,

which oscillator at that time operates either in the closed phase-locked loop mode or in the open phase-locked loop mode.

20. The method as recited in claim 1, characterized in

that the smart tag observes the first amplitude (Ai),

which is an amplitude of the voltage

induced in the tag'"'"'s antenna by the interrogator'"'"'s high-frequency carrier signal,

and that the smart tag transmits high-frequency wave packets

in that it excites its own antenna with the voltage,

an amplitude of which voltage is essentially constant during transmitting each said high-frequency wave packet

and as a second amplitude (At) it is mainly set with respect to

the first amplitude (Ai) observed by then

so that the second amplitude (At) is inversely proportional to the first amplitude (Ai).

21. The method as recited in claim 20, characterized in

that the smart tag observes the first voltage amplitude (Ai) in time intervals,

in which, according to the communication protocol,

the smart tag does not transmit said high-frequency wave packets.

22. The method as recited in claim 21, characterized in

that the tag'"'"'s antenna is excited by the voltage,

whose second amplitude (At) is automatically set to a highest value (Atmax)

when the first amplitude (Ai) is below its reference value (Airef),

and that the tag'"'"'s antenna is excited by the voltage,

whose second amplitude (At) is automatically set to a value,

which is determined by an expression Atmax·

Airef/Ai

when the first amplitude (Ai) is above its reference value (Airef).

23. The method as recited in claim 22, characterized in

that the reference value (Airef) of the first amplitude (Ai) is determined as

a twofold to fivefold of such minimum value (Aimin) of the first amplitude (Ai),

which the interrogator'"'"'s magnetic field induces in the tag'"'"'s antenna

at a lowest value, as required by the standard,

of the magnetic field density at a position of the tag'"'"'s antenna.

24. The method as recited in claim 1, characterized in

that the resonance frequency (fi) of the interrogator'"'"'s antenna circuit equals 13.56 MHz.

25. The method as recited in claim 24, characterized in

that the length of duration of said high-frequency wave packets equals the length of duration, as required by the standard,

of a load-modulation of antenna'"'"'s impedance in passive smart tags.

26. A circuit intended for high-frequency communication between

an interrogator and a smart tag

a circuit of said smart tag being galvanically coupled with a voltage source and

a received signal (rs) induced in a tag'"'"'s antenna (A)

being conducted to an input of a variable-gain amplifier (VGA) and

an output of said variable-gain amplifier (VGA) being connected through a digitizer (Dig) or directly

to a reference input of a phase-matched signal generator (PhMSG;

PhMSG′

) and

the smart tag transmitting high-frequency radio wave packets,

which are generated out of a phase-matched signal (ts′

)

from an output of the phase-matched signal generator (PhMSG;

PhMSG′

),

characterized in

that each time at the beginning of transmitting each said wave packet

said phase matched signal (ts′

),

whose phase is a second phase (Φ

t) increased by 90°

,

gets phase-matched in the phase-matched signal generator (PhMSG;

PhMSG′

) with said received signal (rs),

which an interrogator'"'"'s high-frequency carrier signal induced in the tag'"'"'s antenna (A) and whose phase as a first phase (Φ

i) is observed

in said phase-matched signal generator (PhMSG;

PhMSG′

),

so that the second phase (Φ

t) is shifted with respect to said observed first phase (Φ

i)

by the same phase angle (Δ

Φ

)

being determined by a relation Δ

Φ

=Φ

t−

Φ

i,

wherein the second phase (Φ

t) is a phase of a voltage exciting the tag'"'"'s antenna (A)

to transmit said high-frequency wave packets,

that the output of the phase-matched signal generator (PhMSG;

PhMSG′

)

is connected to the tag'"'"'s antenna (A) through an output amplifier (OA) and a capacitor,

which output amplifier sets an amplitude of the voltage across the tag'"'"'s antenna (A)

as a second amplitude (At) to form said high-frequency wave packets,

and that, in order to form said high-frequency wave packets,

the phase-matched signal generator (PhMSG;

PhMSG′

) and the output amplifier (OA)

are controlled by a transmit-on signal (tos)

defining the start and end of tag'"'"'s transmitting.

27. The circuit as recited in claim 26, characterized in

that a frequency (ft) of the radio waves in said tag'"'"'s high-frequency wave packets is equal to a frequency (fi) of the interrogator'"'"'s high-frequency carrier signal

and that said phase angle (Δ

Φ

) is such

that an amplitude of the voltage at an interrogator'"'"'s antenna at the time

when some of said wave packets influence this antenna

always attains the largest attainable interference rise or

the largest attainable interference drop.

28. The circuit as recited in claim 26,

characterized in

that the phase-matched signal generator (PhMSG)

comprises a phase-frequency comparator (PhFC),

to whose reference input a digitized received signal (drs) is conducted and

whose output is conducted to a phase-locked voltage-controlled oscillator (VCO),

which operates at the frequency (fi) of the interrogator'"'"'s high-frequency carrier signal and

whose output is connected to a phase shifter (PhSh),

which shifts the phase of an input signal by said phase angle (Δ

Φ

) increased by 90° and

whose output signal is said phase matched signal (ts′

),

wherein the phase-frequency comparator (PhFC), the voltage-controlled oscillator (VCO)

and the phase shifter (PhSh) are controlled by said transmit-on signal (tos).

29. The circuit as recited in claim 26, characterized in

that the phase-matched signal generator (PhMSG′

)

comprises a phase-frequency comparator (PhFC),

to whose reference input a digitized received signal (drs) is conducted and

whose output is conducted to a phase-locked voltage-controlled oscillator (HFVCO) with a frequency divider (FDiv),

which voltage-controlled oscillator (HFVCO)

operates at an eighthfold, preferably a sixteenthfold of the frequency (fi) of the interrogator'"'"'s high-frequency carrier signal and

whose output is connected

either to an input of a digital-to-analogue converter (DAC)

or to an input of a digital divider (DigDiv),

wherein by a digital presetting of the digital-to-analogue converter (DAC)

or the digital divider (DigDiv)

the phase of an input signal is shifted by said phase angle (Δ

Φ

) increased by 90°

, and

whereby said phase matched signal (ts′

) is generated,

wherein the phase-frequency comparator (PhFC),

the voltage-controlled oscillator (HFVCO)

and the digital-to-analogue converter (DAC) or the digital divider (DigDiv)

are controlled by said transmit-on signal (tos).

30. The circuit as recited in claim 28, characterized in

that the generator (PhMSG;

PhMSG′

) of the phase-matched signal (ts′

)

sets said second phase (Φ

t) with respect to said observed first phase (Φ

i)

with an accuracy better than 20° and

preferably 10°

.

31. The circuit as recited in claim 30, characterized in

that a phase-shift control signal (pscs) is conducted to

a control input of the phase shifter (PhS) or

a control input of the digital-to-analogue converter (DAC) or

the digital divider (DigDiv).

32. The circuit as recited in claim 31, characterized in

that an amplitude measuring circuit (AMC) observes

an amplitude of the received signal (rs) as a first amplitude (Ai),

which is an amplitude of the voltage induced in the tag'"'"'s antenna (A)

by the interrogator'"'"'s high-frequency carrier signal, and

with its first output signal (ays) representing a measured amplitude value controls said output amplifier (OA) in a way

that said second amplitude (At),

which is the amplitude of the voltage across the tag'"'"'s antenna (A)

to form a new wave packet,

is set with respect to first amplitude (Ai) as observed each time by then and

with its second output signal (ads) representing the measured amplitude-decrease value

controls said phase-frequency comparator (PhFC) in a way

that said phase-locked loop opens

whenever said first amplitude (Ai) drops below the predetermined value.

33. The circuit as recited in claim 32, characterized in

that the smart tag sets a gain of the variable-gain amplifier (VGA) by means of a gain control signal (gcs).

34. The circuit as recited in claim 33, characterized in

that the variable-gain amplifier (VGA) and the amplitude measuring circuit (AMC) are connected to the tag'"'"'s antenna (A)

through an attenuator and a DC voltage defining circuit (Att/DC)

and that said attenuator and DC voltage defining circuit (Att/DC) is controlled

by means of said transmit-on signal (tos)

defining the start and end of the tag'"'"'s transmission

so that said circuit attenuates the signal from the tag'"'"'s antena (A)

while the smart tag transmits the high-frequency wave packets

and sets up a DC voltage level

while the smart tag does not transmit the high-frequency wave packets.