Method and apparatus for low current RF signal detection
First Claim
1. A signal detection circuit for indicating whether an radio frequency (RF) input signal is a valid predetermined input signal, said signal detection circuit comprising:
- a comparator receiving the RF input signal and generating an output baseband signal;
a counter circuit receiving the baseband signal from the comparator, said counter circuit counting predetermined edges of the baseband signal and providing a counter output signal indicating a number of counted edges;
an oscillator, said oscillator applying a clock signal to the counter circuit, wherein the clock signal is asynchronous with respect to the RF input signal; and
a threshold circuit receiving the counter output signal, said threshold circuit comparing the number of counted edges to a threshold range of counts, and providing a threshold output signal when the number of counted edges is within the threshold range of counts, thereby indicating that the RF input signal is valid.
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Accused Products
Abstract
A low signal detection circuit for use in an electronic tolling system which wakes up a receiver circuit associated with the tolling system based upon the type of signal received. An RF signal transmitted by the electronic tolling system is Manchester encoded and will therefore have a frequency within predetermined values. The system will detect the incoming RF signals or count the rising and falling edges of the baseband signal and apply the counts to a threshold circuit which will compare the number of counts to a predetermined value. If the number of counts falls within a predetermined range, then a signal indicating the presence of a valid RF signal will be output from the wake-up circuit. A power management circuit receives a clock signal from an oscillator circuit and provides a power signal which will wake up the detection circuitry for only a minimum predetermined period of time.
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Citations
15 Claims
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1. A signal detection circuit for indicating whether an radio frequency (RF) input signal is a valid predetermined input signal, said signal detection circuit comprising:
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a comparator receiving the RF input signal and generating an output baseband signal; a counter circuit receiving the baseband signal from the comparator, said counter circuit counting predetermined edges of the baseband signal and providing a counter output signal indicating a number of counted edges; an oscillator, said oscillator applying a clock signal to the counter circuit, wherein the clock signal is asynchronous with respect to the RF input signal; and a threshold circuit receiving the counter output signal, said threshold circuit comparing the number of counted edges to a threshold range of counts, and providing a threshold output signal when the number of counted edges is within the threshold range of counts, thereby indicating that the RF input signal is valid. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of detecting an input signal, said method comprising the steps of:
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applying the input signal to a comparator, wherein the comparator generates an output baseband signal; providing a counter circuit which receives the output baseband signal from the comparator, said counter circuit counting predetermined edges of the output baseband signal and providing a counter output signal indicating a number of counted edges; providing an oscillator, said oscillator applying a clock signal to the counter circuit, the clock signal being asynchronous with respect to the input signal; and providing a threshold circuit which receives the counter output signal, said threshold circuit comparing the number of counted edges to a threshold range of counts and providing a threshold output signal when the number of counted edges is within the threshold range of counts to indicate that the input signal is a valid predetermined input signal. - View Dependent Claims (9, 10, 11, 12)
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13. A signal detection circuit for indicating whether an input signal is a valid predetermined Manchester encoded signal, said signal detection circuit comprising:
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a comparator receiving the input signal and generating a baseband signal; an oscillator generating a clock signal, the clock signal being asynchronous with respect to the input signal; a power management circuit receiving the clock signal and applying a power management signal to the comparator at predetermined time intervals defined by the clock signal; a counter circuit receiving the baseband signal from the comparator and the clock signal from the oscillator, said counter circuit counting predetermined edges of the baseband signal and providing a counter output signal indicating a number of counted edges; and a threshold circuit receiving the counter output signal, said threshold circuit comparing the number of threshold range of counts and providing a threshold output signal to indicate the input signal is valid and Manchester encoded when the number of counted edges is within the threshold range of counts. - View Dependent Claims (14, 15)
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Specification