Compensation circuit for an automotive ignition sensing system
First Claim
1. In a vehicle having an engine and an ignition system providing an ignition voltage signal to the engine, an ignition sensing circuit for providing a signal indicative of the ignition voltage to a device, the sensing circuit comprising:
- an input for receiving the ignition voltage signal;
an active filter element electrically connected between said input and a first output node, said filter element configured to filter the ignition voltage signal;
an active compensation element electrically connected between said first output node and ground, wherein said compensation element is physically proximate said filter element and has substantially the same electrical performance characteristics as said filter element; and
means for providing a compensated ignition voltage signal to the device by subtracting the voltage drop across said compensation element from the voltage at said first output node.
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Abstract
In a vehicle having an engine and an ignition system, a sensing circuit is provided for sensing the ignition voltage and providing this sensed signal to various operating modules of the vehicle. The sensing circuit includes a diode/resistor filter that provides a filtered voltage signal at a first output node. A compensation circuit is provided that compensates voltage errors introduced by the filter circuit. The compensation circuit includes a second diode that has substantially identical electrical performance characteristics as the first diode, and that is preferably mounted on a common substrate. A voltage signal at a second output node between the second diode and the filter circuit is indicative of the voltage drop across the second diode, which is further representative of the voltage error introduced by the filter circuit. In one embodiment, the operating module receiving the ignition voltage signal is configured to receive voltage signals at the first and second output nodes. The operating module can include a microprocessor that receives the A/D converted voltage signals and subtracts the signal at the second output node from the signal produced by the filter circuit according to a predetermined relationship. The result of this subtraction is then utilized by other software functions of the operating module that depend upon the ignition voltage signal.
148 Citations
13 Claims
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1. In a vehicle having an engine and an ignition system providing an ignition voltage signal to the engine, an ignition sensing circuit for providing a signal indicative of the ignition voltage to a device, the sensing circuit comprising:
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an input for receiving the ignition voltage signal;
an active filter element electrically connected between said input and a first output node, said filter element configured to filter the ignition voltage signal;
an active compensation element electrically connected between said first output node and ground, wherein said compensation element is physically proximate said filter element and has substantially the same electrical performance characteristics as said filter element; and
means for providing a compensated ignition voltage signal to the device by subtracting the voltage drop across said compensation element from the voltage at said first output node. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
a second output node electrically connected between said first output node and said compensation element, wherein said voltage drop across said compensation element is equivalent to the voltage at said second output node.
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3. The ignition sensing circuit according to claim 2, in which the device includes a microprocessor having a first input connected to an A/D converter and a second input connected to an A/D converter, wherein:
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said first output node is connected to the first input of the microprocessor;
said second output node is connected to the second input of the microprocessor; and
said means for providing a compensated voltage signal includes subtraction means implemented by the microprocessor for subtracting a second A/D converted value for the voltage at said second output node from a first A/D converted value for the voltage at said first output node.
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4. The ignition sensing circuit according to claim 1, further comprising:
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a first resistance element connected in series between said filter element and said first output node; and
a second resistance element connected in series between said first output node and said compensation element.
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5. The ignition sensing circuit according to claim 4, wherein said first resistor element and said second resistor element are mounted on a common substrate.
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6. The ignition sensing circuit according to claim 4, wherein said means for providing a compensated ignition voltage signal includes:
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a second output node electrically connected between said second resistance element and said compensation element, wherein said voltage drop across said compensation element is equivalent to the voltage at said second output node.
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7. The ignition sensing circuit according to claim 6, in which the device includes a microprocessor having a first input connected to an A/D converter and a second input connected to an A/D converter, wherein:
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said first output node is connected to the first input of the microprocessor;
said second output node is connected to the second input of the microprocessor; and
said means for providing a compensated voltage signal includes subtraction means implemented by the microprocessor for subtracting a second A/D converted value for the voltage at said second output node from a first A/D converted value for the voltage at said first output node.
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8. The ignition sensing circuit according to claim 7, wherein:
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said first resistance element has a resistance value 3R and said second resistance element has a resistance value 1R; and
said subtraction means implemented by the microprocessor is operable to divide the second A/D converted value by two (2) prior to subtracting from the first A/D converted value.
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9. The ignition sensing circuit according to claim 8, wherein said subtraction means implemented by the microprocessor is operable to multiply the result of said subtraction by four (4).
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10. The ignition sensing circuit according to claim 1, wherein both said filter element and said compensation element are diodes.
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11. The ignition sensing circuit according to claim 10, wherein both said filter element and said compensation element are forward biased.
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12. The ignition sensing circuit according to claim 1, wherein said filter element and said compensation element are mounted on a common substrate.
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13. The ignition sensing circuit according to claim 1, wherein both said filter element and said compensation element include dual diode rectifiers.
Specification