All The Claims

1. A system configured to:
issue, to at least one node of a plurality of nodes, a respective certificate, the respective certificate configured to enable the associated node to authenticate itself to other nodes in a communication system;
store the respective certificate at a second node of the plurality of nodes that is not the associated node;
determine that a first certificate, of the respective one or more certificates, that is associated with a first node should be revoked; and
responsive to determining that the first certificate associated with the first node should be revoked, write an indicator of the first certificate’s revocation to at least one location at a node of the plurality of nodes, wherein the at least one location at a node is external to the system, the first node associated with the revoked certificate, and the second node.
2. A system as claimed in claim 1, wherein the system is further configured to transmit the indicator of the first certificate’s revocation for storage at the at least one location effective to not permit the first node associated with the revoked certificate to write to the location in which the indicator is stored.
3. A system as claimed in claim 1 further configured to, responsive to determining that the certificate should be revoked, issue a new certificate to the first node associated with the revoked certificate.
4. A system as claimed in claim 1, wherein the indicator identifies a certificate that is the valid certificate most recently issued to the first node associated with the revoked certificate.
5. A system as claimed in claim 4, wherein the indicator comprises a serial number associated with the valid certificate most recently issued to the first node associated with the revoked certificate.
6. A system as claimed in claim 1, wherein the system is further configured to enable storing the indicator of the certificate’s revocation on multiple nodes of the plurality of nodes, each node of the multiple nodes being different than the first node associated with the certificate and external to the system.
7. A system as claimed in claim 1, wherein the system is further configured to enable periodically distributing, to the plurality of nodes, an update indicating the validity of the respective one or more certificates associated with the respective nodes of the plurality of nodes.
8. A system as claimed in claim 7, wherein the update comprises a compressed representation of the validity of one or more certificates of the one or more respective certificates associated with the respective nodes of the plurality of nodes effective to prevent a node from unambiguously determining from the update whether or not a particular certificate is valid.
9. A system as claimed in claim 8, wherein the system is further configured to enable each of the plurality of nodes to, if said each node cannot unambiguously determine from the update whether or not a particular certificate is valid, obtain an indicator corresponding to that certificate effective to determine from the indicator whether or not the certificate is valid.
10. A system as claimed in claim 7, wherein the system is further configured to enable generating the update by:
forming a data set identifying which certificates of the one or more certificates are valid and which of the one or more respective certificates are invalid; and
generating the update by applying a lossy compression algorithm to the data set.
11. A system as claimed in claim 10, wherein the system is further configured to enable forming the data set as a bitmap comprising a number of entries at least as great as the number of the one or more respective certificates.
12. A system as claimed in claim 10, wherein the system is further configured to enable generating the update as a bitmap comprising a number of entries fewer than the number of the one or more respective certificates.
13. A system as claimed in claim 10, wherein the system is further configured to enable generating the update by applying a Bloom filter to the data set.
14. The communications system as recited in claim 1, wherein the communications system is further configured to determine one or more locations of the indicator by applying a mathematical function to a username associated with said revoked certificate effective select at least one node out of the plurality of nodes.
15. A certificate authority node for operating in a communication system comprising a plurality of nodes, the certificate authority node configured to:
issue to each of the plurality of nodes a respective certificate effective to enable each node to authenticate itself to other nodes in the communication system;
store each respective certificate at a node of the plurality of nodes that is external to the node to which the certificate was issued, and external to the certificate authority node;
determine that a first certificate associated with a first node of the plurality of nodes should be revoked;
responsive to that determination, write an indicator of the first certificate’s revocation to a location in the communication system that is external to the certificate authority node, external to the first node associated with the revoked certificate, and to which the first node associated with the revoked certificate is not permitted to write; and
transmit the indicator of the first certificate’s revocation to at least one storage node for storage, wherein the at least one storage node comprises at least one node of the plurality of nodes that is external to:
the certificate authority node;
the node storing the first certificate; and
the first node associated with the revoked certificate,

wherein the location is determined based, at least in part, on a username associated with the first certificate.
16. A certificate authority node as claimed in claim 15 further configured to transmit the indicator of the first certificate’s revocation to a plurality of storage nodes to which the revoked certificate is not associated with for storage on each of the plurality of storage nodes.
17. A certificate authority node as claimed in claim 15 further configured to, responsive to the determination that the first certificate should be revoked, issue a new certificate to the first node associated with the revoked certificate.
18. A certificate authority node as claimed in claim 15, wherein the indicator comprises an identifier that identifies a valid certificate most recently issued to the first node associated with the revoked certificate.
19. A certificate authority node as claimed in claim 15, wherein the indicator comprises a serial number associated with a valid certificate most recently issued to the first node associated with the revoked certificate.
20. A certificate authority node as claimed in claim 15 further configured to periodically distribute to the plurality of nodes an update indicating the validity of the respective certificates issued to the plurality of nodes.
21. A certificate authority node as claimed in claim 20, wherein the update comprises a compressed representation of the validity of one or more respective certificates issued to the plurality of nodes effective to prevent a node from unambiguously determining from the update whether or not a particular certificate is valid.
22. A certificate authority node as claimed in claim 21 further configured to:
form a data set identifying which certificates of the one or more respective certificates are valid and which of the one or more respective certificates are invalid; and
generate the update by applying a lossy compression algorithm to the data set.
23. A certificate authority node as claimed in claim 22, wherein the data set comprises a bitmap that includes a number of entries at least as great as the number of the one or more respective certificates.
24. A certificate authority node as claimed in claim 22, wherein the update comprises a bitmap that includes a number of entries fewer than the number of the one or more respective certificates.
25. A certificate authority node as claimed in claim 20 further configured to generate the update by applying a Bloom filter to the data set.
26. A certificate authority node as claimed in claim 15, wherein the authentication node is further configured to:
generate one or more certificates for each node of the plurality of nodes; and
responsive to generating the one or more certificates, generate status data associated with each one or more generated certificates.
27. A node for operating in a communication system comprising a plurality of nodes, each of the plurality of nodes being issued a certificate effective to enable said each node to authenticate itself to other nodes in the communication system, the node configured to:
receive, using the node, an indicator of a certificate’s revocation from an authentication node that issued the certificate to a first node that is external to the authentication node and external to the node;
store, using the node, the indicator at a location within the node; and
prevent, using the node, the first node issued the revoked certificate to write to the location in which the indicator is stored.
28. A node as claimed in claim 27, wherein the node is further configured to permit only the authentication node to write to the location in which the indicator is stored.
29. A node as claimed in claim 27, wherein the node is further configured to:
receive from another node a request to update the another node whenever an indicator corresponding to a particular certificate changes; and
responsive to the indicator corresponding to the particular certificate changes, transmit an indication of that change to the another node.
30. A node as claimed in claim 29, wherein the node is further configured to, responsive to receiving a new indicator corresponding to the particular certificate, transmit the new indicator to the another node.
31. A node for operating in a communication system comprising a plurality of nodes, each node of the plurality of nodes being issued a certificate effective to enable said each node of the plurality of nodes to authenticate itself to other nodes in the communication system, the node configured to:
receive, from a first node in the plurality of nodes, a certificate issued to a second node in the plurality of nodes, by a certificate authority node in the plurality of nodes, the certificate authority node being a different node from the node, the first node and the second node;
obtain, from at least a third node in the plurality of nodes, a first indicator of that certificate’s validity, the third node being a different node from the node, the certificate authority node, the first node, and the second node;
obtain, from at least a fourth node in the plurality of nodes, a second indicator of that certificate’s validity, the fourth node being a different node from the node, the certificate authority node, the first node, the second node, and the third node;
compare the second indicator from the at least fourth node to the first indicator from the at least third node;
determine a validity of the certificate based, at least in part, on said comparison of the second indicator and the first indicator; and
authenticate the second node in dependence on the certificate and at least the first indicator.
32. A node as claimed in claim 31, wherein the node is further configured to request an update from the at least third node whenever an indicator corresponding to the certificate changes, wherein the certificate is not issued to the at least third node.
33. A node as claimed in claim 31, wherein the node is further configured to authenticate the second node in dependence on an update received from an authentication node that indicates the validity of the certificates issued to the plurality of nodes.
34. A node as claimed in claim 33, wherein the node is further configured to, responsive to being unable to unambiguously determine from the update whether or not a particular certificate is valid, obtain an indicator corresponding to the particular certificate and determine from the indicator whether or not the particular certificate is valid.
35. A node as claimed in claim 31, wherein the node is further configured to determine the certificate is invalid based, at least in part, on the first indicator and second indicator comprising contradictory information.
36. At least one computer-readable storage memory embodying computer-executable instructions which, responsive to execution by at least one processor, implement, at least in part, an authentication node for operating in a communication system comprising a plurality of nodes, the authentication node configured to:
issue each node of the plurality of nodes a respective certificate effective to enable each said respective node to authenticate itself to other nodes in the communication system;
store each respective certificate on a respective node that is external to the authentication node and external to the respective node issued the certificate;
determine that a certificate associated with a respective node should be revoked; and
responsive to determining the certificate associated with the respective node should be revoked, write an indicator of that certificate’s revocation to a location in the communication system that is external to the authentication node, the respective node to which the certificate is issued, and the respective node storing the certificate, wherein the respective node to which said revoked certificate is issued is not permitted to write to the location.
37. At least one computer-readable storage memory embodying computer-executable instructions which, responsive to execution by at least one processor, implement, at least in part, a node for operating in a communication system comprising a plurality of nodes, each node of the plurality of nodes being issued a certificate effective to enable said each node of the plurality of nodes to authenticate itself to other nodes in the communication system, the node configured to:
receive an indicator of a certificate’s revocation from an authentication node that issued the certificate to a first node that is external to the authentication node and external to the node;
store that indicator at a location within the node; and
prevent the first node from writing to the location in which the indicator is stored.
38. The at least one computer-readable storage memory of claim 37, wherein the node is further configured to:
receive, from another node of the plurality of nodes, a request for the indicator of the certificate’s revocation; and
send, to the another node, the indicator of the certificates revocation.
39. The at least one computer-readable storage memory of claim 38, wherein the node, the another node, the authentication node, and the first node are all different nodes in the plurality of nodes.
40. The at least one computer-readable storage memory of claim 37, wherein the indicator comprises information associated with a valid certificate issued to the first node.
41. The at least one computer-readable storage memory of claim 37, wherein the information comprises a serial.
42. At least one computer-readable storage memory embodying computer-executable instructions which, responsive to execution by at least one processor, implement, at least in part, a node for operating in a communication system comprising a plurality of nodes, each node of the plurality of nodes being issued a certificate effective to enable said each node of the plurality of nodes to authenticate itself to other nodes in the communication system, the node configured to:
receive, from a first node in the plurality of nodes, a certificate issued to another node by a certificate authority node in the plurality of nodes;
obtain, from at least a second node, a first indicator of that certificate’s validity;
obtain, from at least a third node, a second indicator of that certificate’s validity;
compare the second indicator from the at least third node to the first indicator from the at least second node;
determine a validity of the certificate based, at least in part, on said comparison of the second indicator the first indicator; and
authenticate the another node in dependence on the certificate and at least the first indicator,
wherein the node, the another node, the certificate authority node, the first node, the second node, and the third node are all different nodes in the plurality of nodes.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.

1. An apparatus comprising a demodulator of an electrical signal frequency-modulated about a carrier frequency with a modulation frequency, said demodulator comprising an acquisition terminal for receiving the frequency-modulated signal, a rendering terminal for rendering the frequency-demodulated electrical signal, a radiofrequency oscillator comprising a magnetoresistive device within which there flows a spin-polarized electrical current to produce an oscillating signal at an output electrode, the magnetoresistive device being formed by a stack of magnetic layers and non-magnetic layers, the layers having a resistance whose amplitude varies as a function of frequency of the oscillating signal at the output electrode, at least one of a current source to cause a continuous current of electrons to flow perpendicularly through said layers and a magnetic field generator configured for generating a continuous magnetic field, field lines of which cross a free layer of the magnetoresistive device with an intensity greater than or equal to 1 Oersted, the at least one of a current source and a continuous magnetic field generator being set so that, under identical conditions of operation, the radiofrequency oscillator is synchronized with oscillations at a first frequency and, in alternation, with oscillations at a second frequency, where the first and second frequencies are used in the frequency-modulated signal to encode respective pieces of information, and a synchronization terminal for synchronizing the frequency of the oscillating signal with the frequency of the signal received at the synchronization terminal, the synchronization terminal being connected to the acquisition terminal, and a low-pass filter having a \u22123 dB cut-off frequency that is strictly lower than the carrier frequency and higher than the modulation frequency, said low-pass filter being connected to the output electrode of the magnetoresistive device to filter the oscillating signal, and to the rendering terminal to provide, as a demodulated electrical signal, the filtered signal, the low-pass filter.
2. The apparatus of claim 1, wherein the magnetoresistive device comprises: an input electrode by which a direct electrical current is injected, a reference layer for spin-polarizing the electrical current, the reference layer having a magnetization having a fixed direction, wherein the magnetization of the free layer can oscillate when the free layer is crossed by the spin-polarized current, a non-magnetic spacer layer interposed between the reference layer and the free layer to form one of a tunnel junction and a spin valve, a cross-section of at least one of the layers of the stack having a diameter of less than 300 nanometers, and wherein at the output electrode, there is produced a signal oscillating at an oscillating frequency as a function of one of an intensity of the direct current and an amplitude of the continuous magnetic field, field lines of which cross the free layer.
3. The apparatus of claim 1, wherein the radiofrequency oscillator is configured to produce a signal oscillating at a scaled first frequency when the oscillator is synchronized with oscillations at the first frequency and to produce a signal oscillating at a scaled second frequency when the oscillator is synchronized with oscillations at the second frequency, wherein the first and second scaled frequencies are obtained by scaling the first and second frequencies by a scale factor that is strictly greater than one.
4. The apparatus of claim 1, wherein the radiofrequency oscillator comprises a magnetic field generator equipped with the synchronization terminal, the magnetic field generator being configured for generating an alternating magnetic field having a frequency that is a function of the frequency of the signal received at the synchronization terminal, and wherein the alternating magnetic field comprises field lines that cross the free layer so that the frequency of the oscillating signal is synchronized with the frequency of the signal received at the synchronization terminal.
5. The apparatus of claim 2, wherein the radiofrequency oscillator comprises a summing element equipped with the synchronization terminal, the summing element being configured for adding the electrical signal received at the synchronization terminal to the direct current that perpendicularly crosses the layers so that the frequency of the oscillating signal is synchronized with the frequency of the signal received at the synchronization terminal.
6. A method for demodulating an electrical signal frequency-modulated about a carrier signal having a carrier frequency and a modulation frequency, the method comprising receiving the modulated electrical signal at an acquisition terminal, rendering the demodulated signal at a rendering terminal, synchronizing a radiofrequency oscillator, under identical conditions of operation, with oscillations at a first frequency and, in alternation, with oscillations at a second frequency, wherein the first and second frequencies are frequencies used in the frequency-modulated signal to encode respective pieces of information, the radiofrequency oscillator comprising a magnetoresistive device within which there flows a spin-polarized electrical current to produce an oscillating signal at an output electrode, the magnetoresistive device being formed by a stack of magnetic layers and non-magnetic layers, the layers having a resistance whose amplitude varies as a function of the frequency of the oscillating signal at the output electrode, at least one of a current source to cause a continuous current of electrons to flow perpendicularly through the layers and a magnetic field generator configured for generating a continuous magnetic field, field lines of which cross a free layer of the magnetoresistive device with an intensity greater than or equal to 1 Oersted, the at least one of a current source and a continuous magnetic field generator being set so that, under identical conditions of operation, the radiofrequency oscillator is synchronized with oscillations at a first frequency and, in alternation, with oscillations at a second frequency, and a synchronization terminal for synchronizing the frequency of the oscillating signal with the frequency of the signal received at the synchronization terminal, the synchronization terminal being connected to the acquisition terminal, filtering, using a low-pass filter having a \u22123 dB cut-off frequency that is strictly lower than the carrier frequency and higher than the modulation frequency, the oscillating signal generated at the output electrode, and providing the filtered signal to the rendering terminal as a demodulated electrical signal.
7. The method of claim 6, wherein the direct continuous current andor a continuous magnetic field are set so that a free frequency of oscillation of the oscillation signal produced in the absence of a signal at the synchronization terminal is between first and second scaled frequencies, where the first and second frequencies are respectively the lowest and the highest of the frequencies used in the frequency-modulated signal to encode a piece of information, and wherein the first and second scaled frequencies are obtained by scaling the first and second frequencies by a rational number.
8. The method of claim 7, further comprising amplifying the frequency-modulated electrical signal so that an extent of the range, about the carrier frequency, of the frequencies with which the radiofrequency oscillator is synchronized is strictly greater than an absolute value of a difference between the first and second frequencies.
9. The method of claim 8, further comprising amplifying the frequency-modulated electrical signal to have an amplitude at the synchronization terminal that is greater than 10% of the intensity of the direct continuous current or that corresponds to an alternating magnetic field, the intensity of which is greater than 1 Oersted within the free layer when converted into a magnetic field by a generator.
10. The method of claim 6, wherein the modulation frequency is strictly lower than a frequency corresponding to a rate of relaxation of amplitude of the magnetoresistive device.

1. A discharge lamp ballast comprising:
an inverter circuit including first and second pairs of four switching elements in a full bridge configuration, and a resonant circuit having a resonant frequency connected between output terminals of the switch pairs, the inverter circuit further adapted to output AC power for driving a discharge lamp; and
a control circuit adapted to control switch states of the switching elements and thereby to generate the output AC power,
wherein the control circuit during a starting operation is adapted to control the inverter switching elements for a predetermined time so as to make an operating frequency of the output AC power sufficiently close to the resonant frequency of the resonant circuit, wherein a high voltage is generated for igniting the discharge lamp, and
the control circuit is further adapted to control the inverter switching elements in the starting operation so as to periodically and alternately repeat a state of
turning on the switching elements in one of the first or second sets of switching elements, respectively, and
turning off the switching elements in the other set, respectively, and a state of turning on only one of the switching elements in the other set and turning off the remaining three switching elements, respectively,

wherein a DC component is generated in the output voltage during the starting operation.
2. The discharge lamp ballast of claim 1, wherein the control circuit at a predetermined point during the starting operation is adapted to interchange switching operations between the first and second sets of switching elements, and
the control circuit is further adapted to control the inverter in a transient operation between each interchange of switching operations, each transient operation further comprising gradually lowering the output voltage for a predetermined period of time.
3. The discharge lamp ballast of claim 2, wherein the transient operation further comprises alternately and periodically turning on the first and second sets of switching elements, and an on-duty of one of the respective sets of switching elements is made higher than an on-duty of the other set of respective switching elements.
4. The discharge lamp ballast of claim 2, wherein the transient operation further comprises periodically and cyclically repeating a state of turning on the switching elements in one of the sets of switching elements and turning off the switching elements in the other set, a state of turning on the switching elements in the other set and turning off the respective switching elements in the one set, and a state of turning on one of the switching elements in the other set and turning off the remaining three switching elements, respectively.
5. The discharge lamp ballast of claim 2, wherein the transient operation further comprises turning off the switching elements in one of the sets of switching elements, maintaining one of the switching elements in the other set in an ON state and periodically turning on and off the other of the switching elements in the other set.
6. The discharge lamp ballast of claim 1, wherein the control circuit is adapted to control the inverter in the starting operation so as to periodically and cyclically repeat a state of turning on the switching elements in one of the first or second sets of switching elements, respectively, and turning off the switching elements in the other set, respectively, a state of turning on only one of the switching elements in the one set and turning off the remaining three switching elements, respectively, and a state of turning on only one of the switching elements in the other set and turning off the remaining three switching elements, respectively.
7. The discharge lamp ballast of claim 1, wherein the control circuit is adapted to gradually change the operating frequency of the inverter within a predetermined sweep frequency range including the resonant frequency of the resonant circuit in the starting operation.
8. The discharge lamp ballast of claim 7, wherein the control circuit is adapted to gradually decrease the operating frequency of the inverter from an upper limit frequency of the sweep frequency range to a lower limit frequency thereof in the starting operation.
9. The discharge lamp ballast of claim 7, wherein the control circuit is adapted to change the operating frequency of the inverter a plurality of times in the starting operation, and between each of the plurality of changes in the operating frequency the control circuit is further adapted to maintain the operating frequency of the inverter at a frequency lower than the upper limit frequency of the sweep frequency range and higher than the lower limit frequency of the sweep frequency range for a predetermined period of time.
10. The discharge lamp ballast of claim 7, wherein the control circuit is adapted to control the inverter so as to invert the polarity of the DC component of the output voltage at least once during the starting operation.
11. The discharge lamp ballast of claim 7, wherein the control circuit is adapted to detect lighting of the discharge lamp and subsequently to control the inverter to superimpose spike components on the output current.
12. A method of operating a discharge lamp ballast comprising an inverter circuit having four switches arranged in a full bridge configuration, a resonant circuit having a resonant frequency and a control circuit, the method comprising:
(a) adjusting the operating frequency of the inverter switching elements within a predetermined sweep frequency range during a starting operation having a predetermined time duration, the frequency range including the resonant frequency of the resonant circuit wherein a high voltage is generated near the resonant frequency for igniting the discharge lamp during the starting operation; and
(b) further during the starting operation, periodically and alternately repeating a state of turning on a first set of the four switching elements positioned diagonally with respect to each other, and turning off a second set of the four switching elements positioned diagonally with respect to each other, and a state of turning on only one of the second set of switching elements and turning off the remaining three switching elements, respectively, so as to generate a DC component in the output voltage during the starting operation.
13. The method of claim 12, further comprising the step of:
(c) interchanging the switching operations in step (b) between the first and second sets of switching elements at a predetermined time during the starting operation.
14. The method of claim 13, wherein step (b) comprises:
periodically and cyclically repeating a state of turning on the switching elements in one of the first or second sets of switching elements, respectively, and turning off the switching elements in the other set, respectively, a state of turning on only one of the switching elements in the one set and turning off the remaining three switching elements, respectively, and a state of turning on only one of the switching elements in the other set and turning off the remaining three switching elements, respectively.
15. The method of claim 14, further comprising the step of:
(d) performing a transient operation between each interchange of switching operations, each transient operation further comprising gradually lowering the output voltage for a predetermined period of time by alternately and periodically turning on the first and second sets of switching elements, and making an on-duty of one of the respective sets of switching elements higher than an on-duty of the other set of respective switching elements.
16. The method of claim 14, further comprising the step of:
(d) performing a transient operation between each interchange of switching operations, each transient operation further comprising periodically and cyclically repeating a state of turning on the switching elements in one of the sets of switching elements and turning off the switching elements in the other set, a state of turning on the switching elements in the other set and turning off the respective switching elements in the one set, and a state of turning on one of the switching elements in the other set and turning off the remaining three switching elements, respectively.
17. The method of claim 14, further comprising the step of:
(d) performing a transient operation between each interchange of switching operations, each transient operation further comprising turning off the switching elements in one of the sets of switching elements, maintaining one of the switching elements in the other set in an ON state and periodically turning on and off the other of the switching elements in the other set.
18. A light fixture comprising:
a lamp housing adapted to secure a discharge lamp;
a discharge lamp ballast further comprising an inverter circuit having four switches arranged in a full bridge configuration, a resonant circuit having a resonant frequency and a control circuit; and
a main housing adapted to secure said discharge lamp ballast,
wherein said control circuit of said discharge lamp ballast is adapted during a starting operation having a predetermined time duration to adjust an operating frequency of the inverter switches within a predetermined sweep frequency range including the resonant frequency of the resonant circuit, wherein a high voltage is generated near the resonant frequency for igniting the discharge lamp during the starting operation, and
said control circuit further adapted during the starting operation to periodically and alternately repeat a state of turning on a first set of switching elements positioned diagonally with respect to each other and turning off a second set switching elements positioned diagonally with respect to each other, and a state of turning on only one of the second set of switching elements and turning off the remaining three switching elements, respectively, so as to generate a DC component in the output voltage during the starting operation.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.

What is claimed is:

1. An ignition system with an ion current detecting circuit, the system comprising:
an ignition circuit that has an energy accumulating coil, a first switching device disposed in series to the energy accumulating coil for controlling a current therethrough, an ignition coil having a primary coil disposed in parallel to the first switching device and a secondary coil that supplies a secondary current to a spark plug, and a second switching device disposed in series to the primary coil for turning on and off a primary current therethrough;
a current detecting means for detecting a current flowing through the spark plug and outputting a signal indicative of the detected current;
an extracting means for extracting a component within a specific frequency range from the signal detected by the current detecting means; and
a knock detecting means for detecting the knock based on the component extracted by the extracting means.
2. The ignition system with the ion current detecting circuit according to claim 1, wherein the extracting means extracts the component including a higher harmonic component indicative of the knock.
3. The ignition system with the ion current circuit according to claim 1, wherein the extracting means extracts a component at least within 10 to 14 kHz.
4. The ignition system with the ion current detecting circuit according to claim 1, further comprising a current path where the current detected by the current detecting means flows, the current path has a resonance frequency that substantially coincides with a frequency that is extracted by the extracting means.
5. The ignition system with the ion current detecting circuit according to claim 1, wherein the secondary coil has inductance less than 10 henries (H).
6. The ignition system with the ion current detecting circuit according to claim 1, further comprising a control circuit which drives the first and second switching devices so as to provide a multi-spark ignition.
7. The ignition system with the ion current detecting circuit according to claim 6, wherein the control circuit drives the first and second switching devices so that the switching devices turn on and off periodically in an opposed manner.
8. The ignition system with the ion current detecting circuit according to claim 7, wherein the ignition circuit further comprises a condenser disposed in parallel with the first switching device.
9. An ignition system with an ion current detecting circuit for an engine, comprising:
an ignition circuit which has an ignition coil and a driving circuit for driving the ignition coil according to a multi-spark ignition sequence; and
an ion current detecting circuit for detecting an ion current indicative of a knock of the engine, wherein the ignition coil has inductance less than 10 henries (H), and the ion current detecting circuit detects at least a component of the ion current that has a second or higher harmonic frequency of the knock.
10. The ignition system with the ion current detecting circuit for the engine according to claim 9, wherein components providing the ignition circuit and the ion current detecting circuit are designed so that a current path where the ion current flows has a resonance frequency that substantially coincides with the second or higher harmonic frequency detected by the ion current detecting circuit.
11. The ignition system with the ion current detecting circuit for the engine according to claim 9, wherein components providing the ignition circuit and the ion current detecting circuit are designed so that a Q-value of the current path is greater than 1.