TUNED RESONANT CIRCUITS

• US 20110241750A1
• Filed: 10/20/2009
• Published: 10/06/2011
• Est. Priority Date: 11/14/2008
• Status: Active Grant

• Current Assignee: SureFlap Ltd.
• Original Assignee: Cambridge Resonant Technologies Ltd. (Merck & Co., Inc.)
• Inventors: Hill, Nicholas Patrick Roland
• Granted Patent: US 8,576,021 B2
• Time in Patent Office: Days
• US Class Current: 327/306
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• 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 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• CPC Class Codes: H03J 1/0008 using a central processing unit, e.g. a microprocessor digital tuning in general H03J5/0245

Abstract

A circuit block which comprises a non-linear capacitor with two different values of capacitance dependent on a value of a voltage of a resonant signal on the capacitor; a plurality of second capacitors each coupled to a respective switch to enable a said second capacitor to be switched in or out of parallel connection with the nonlinear capacitor; and a tuning control, coupled to the second capacitor switches, and sensing an amplitude of the resonant signal. The tuning control circuit is configured to control the second capacitor switches to successively switch the second capacitors in/out of parallel connection with the non-linear capacitor dependent on the amplitude of the resonant signal until the non-linear capacitor has substantially a single one of two different values, such that in a resonant circuit the circuit block then behaves as a fixed value capacitor.

Claims

1-31. -31. (canceled)

32. A circuit block for a resonant circuit, the circuit block having a pair of connections for connection of the circuit into the resonant circuit as a capacitor, the circuit block comprising:

a first, non-linear capacitor, said first, non-linear capacitor having two different values of capacitance dependent on a value of a voltage of a resonant signal on the nonlinear capacitor;

a power supply circuit coupled to said non-linear capacitor to provide a power supply for the circuit block;

a plurality of second capacitors each coupled to a respective second capacitor switch to enable a said second capacitor to be switched in or out of parallel connection with said first, non-linear capacitor; and

a tuning control circuit powered by said power supply, coupled to said second capacitor switches, and having an input to sense an amplitude of said resonant signal; and

wherein said tuning control circuit is configured to control said second capacitor switches to successively switch said second capacitors in or out of said parallel connection with said first, non-linear capacitor dependent on said amplitude of said resonant signal until said first, non-linear capacitor has substantially a single one of said two different values such that in said resonant circuit said circuit block then appears to behave substantially as a fixed value capacitor.

33. A circuit block as claimed in claim 32 wherein said first, non-linear capacitor comprises a pair of series coupled capacitors with a transistor coupled across one of the pair.

34. A circuit block as claimed in claim 33 wherein said transistor is a field effect transistor, and further comprising a gate capacitor coupled to a gate of said field effect transistor, and a circuit to charge said gate capacitor to change an effective average capacitance value of said first, non-linear capacitor to increase an amplitude of said resonant signal towards a target amplitude, and wherein said tuning control circuit is configured successively to add or remove a said second capacitor from said parallel connection with said first, non-linear capacitor when a threshold amplitude is reached.

35. A circuit block as claimed in claim 34 wherein said tuning control circuit is configured to switch said second capacitor in or out of said parallel connection with said first, non-linear capacitor until said field effect transistor is substantially either fully on or fully off.

36. A circuit block as claimed in claim 32 wherein a said second capacitor switch is coupled in series with a said second capacitor, wherein a said second capacitor switch comprises a field effect transistor, and wherein each said series connected said second capacitor and second capacitor switch is coupled across said first, non-linear capacitor.

37. A circuit block as claimed in claim 32 wherein said second capacitors comprise non-linear capacitors.

38. A circuit block as claimed in claim 37 wherein a said second capacitor comprises a pair of series coupled capacitors with a transistor coupled across one of the pair, and wherein a said second capacitor switch is configured to control a gate voltage of the transistor coupled across one of the pair of series coupled capacitors.

39. A circuit block as claimed in claim 38 wherein said first, non-linear capacitor and said second, non-linear capacitors each comprise a respective field effect transistor with an associated gate capacitor, the circuit comprising a plurality of current mirrors to mirror a charge current of said gate capacitor of said first, non-linear capacitor to charge said gate capacitors of said second, non-linear capacitors.

40. A circuit block as claimed in claim 32 wherein said tuning control circuit is configured to force said first, non-linear capacitor to have substantially a single said value when all of said second capacitors have been switched in or out of said parallel connection with said first, non-linear capacitor.

41. A circuit block as claimed in claim 32 wherein said single one of said two different values is a maximum one of said two different values.

42. A resonant circuit comprising the circuit block of claim 32.

43. An RFID tag including the resonant circuit of claim 42.

44. A method of using a self-adaptive reactive element in a resonant circuit, said self-adaptive reactive element having a reactive impedance which automatically adjusts to a frequency of a signal applied to said resonant circuit to bring a resonant frequency of said resonant circuit into alignment with said frequency of said applied signal, said reactive impedance of said self-adaptive reactive element varying between a maximum and a minimum value, the method comprising:

deriving a power supply from said resonant circuit; and

using said power supply to switch additional reactive impedance in or out of said resonant circuit until said maximum or minimum value of said reactive impedance of said self-adaptive reactive element is reached, such that said self-adaptive element behaves substantially as a non-adaptive reactive element.

45. A controller for a self-adaptive reactive element, said self-adaptive reactive element having a reactive impedance which automatically adjusts to a frequency of a signal applied to said resonant circuit to bring a resonant frequency of said resonant circuit into alignment with said frequency of said applied signal, said reactive impedance of said self-adaptive reactive element varying between a maximum and a minimum value, the controller comprising:

a circuit to derive a power supply from said resonant circuit; and

a circuit to use said power supply to switch additional reactive impedance in or out of said resonant circuit until said maximum or minimum value of said reactive impedance of said self-adaptive reactive element is reached, such that said self-adaptive element behaves substantially as a non-adaptive reactive element

46. A tuned circuit component comprising:

a first capacitor;

a first MOSFET;

at least one second MOSFET;

a second capacitor (C3) coupled in series with said first MOSFET, said series coupled second capacitor and first MOSFET being coupled in parallel with said first capacitor; and

at least one fourth capacitor coupled in series with said at least one second MOSFET, said series combination of said fourth capacitor and said second MOSFET being coupled in parallel with said first capacitor.

47. A tuned circuit component as claimed in claim 46 further comprising a third capacitor (C2), said third capacitor being coupled in parallel with said first MOSFET.

48. A tuned circuit component as claimed in claim 46 comprising a plurality of said fourth capacitors each coupled in series with a respective said second MOSFET, each said series combination of said fourth capacitor and said second MOSFET being coupled in parallel with said first capacitor.

49. A tuned circuit component as claimed in claim 46, further comprising at least one fifth capacitor coupled across the or each said second MOSFET.

50. A tuned circuit component as claimed in claim 49 further comprising a gate capacitor coupled to a gate of the or each said second MOSFET.

51. A tuned circuit component as claimed in claim 46 further comprising a gate capacitor coupled to a gate of said first MOSFET to store a gate voltage for said first MOSFET.

52. A tuned circuit component as claimed in claim 51 further comprising a charge circuit coupled to said first capacitor to charge said first MOSFET gate capacitor.

53. A tuned circuit component as claimed in claim 52 further comprising an amplitude detect circuit coupled to detect an amplitude of a signal on said first capacitor, and a charge inhibit circuit coupled to said amplitude detect circuit to inhibit said charging when said amplitude exceeds a first threshold amplitude.

54. A tuned circuit component as claimed in claim 53 further comprising a capacitor select circuit coupled to said amplitude detect circuit to control a said second MOSFET to switch a said fourth capacitor in or out of said parallel coupling with said first capacitor when said amplitude exceeds a second said threshold amplitude.

55. A tuned circuit component as claimed in claim 54 wherein said capacitor select circuit includes a delay circuit to inhibit said switching of one said fourth capacitor in or out of said parallel coupling until a delay interval after switching a previous said fourth capacitor in or out of said parallel coupling.

56. A self-powered resonant circuit, the circuit comprising:

at least one self-adaptive resonant circuit, said self-adaptive resonant circuit having a resonant frequency which automatically tunes to a frequency of a signal applied to said self-adaptive resonant circuit;

a power supply circuit to coupled to said self-adaptive resonant circuit to derive a power supply from a resonant signal in said self-adaptive resonant circuit;

a plurality of switched reactive elements each coupled to said self-adaptive resonant circuit; and

a controller to selectively switch said switched reactive elements into said selfadaptive resonant circuit until said self-adaptive resonant circuit has reached substantially a limit of a range of said automatic tuning.

57. A tuned circuit comprising a series coupled pair of capacitors, a first MOSFET coupled across one of said pair of capacitors, a system to change a gate voltage of said first MOSFET dependent on an amplitude of a signal in said tuned circuit, a system to inhibit said changing when a threshold said amplitude is reached, and a system to switch in or out reactive impedance of said tuned circuit when said threshold is reached until said first MOSFET is either substantially fully on or substantially fully off.

58. A tuned circuit as claimed in claim 57 wherein said system to switch in or out reactive impedance of said tuned circuit is configured to switch said reactive impedance in or out stepwise with a delay between successive steps.

59. A tuned circuit as claimed in claim 57 wherein said system to switch in or out reactive impedance of said tuned circuit is configured to switch in said reactive impedance until said first MOSFET is substantially fully on.

60. A tuned circuit as claimed in claim 57, wherein said reactive impedance comprises series coupled pairs of capacitors across each capacitor of a said pair of which is connected a MOSFET.

61. A tuned circuit as claimed in claim 57, wherein said reactive impedance comprises pairs of series coupled capacitors and MOSFETs.

62. An RFID tag including a tuned circuit as claimed in claim 57.