Relaxation oscillator for transponder
First Claim
1. An RF transponder comprising:
- a measurement current source for providing a measurement current to a relaxation oscillator, the relaxation oscillator comprising a measurement switching circuit, a set-reset circuit having a first phase path and a second phase path, and an output, characterized by;
a logic circuit;
a measurement capacitor disposed in the measurement switching circuit;
a first transistor, controlled by the logic circuit, for directing the measurement current to the measurement capacitor for charging the measurement capacitor; and
a current mirror having transistors controlled by the logic circuit, for mirroring the measurement current in a second transistor, for discharging the measurement capacitor;
wherein the logic circuit provides measurement control signals for combining signals indicative of a phase of the set-reset circuit with signals from a timing generator for controlling alternating charging and discharging of the measurement capacitor according to the phase of the set-reset circuit.
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Accused Products
Abstract
A relaxation oscillator for a transponder capable of measuring one or more parameters (e.g., temperature, pressure) in an object and transmitting a data stream to an external reader/interrogator. The transponder typically operates in a passive mode, deriving its power from an RF interrogation signal received by an antenna system, but c=also operate in a battery-powered active mode. The transponder includes memory for storing measurements, calibration data programmable trim settings, transponder ID and the like. Measurement readings comprise counting oscillations of a measurement signal during a fixed time window. The measurement signal is generated by a relaxation oscillator driven by the alternating charging and discharging of measurement capacitors. wherein the capacitor charging rate is a function of current, and of capacitance. By using a mirror measurement current lo discharge the measurement capacitors, the discharge rate is made approximately equal to the charge rate. The measurement current can be scaled according to programmed trim settings to independently optimize readings for the different measured parameters.
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Citations
25 Claims
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1. An RF transponder comprising:
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a measurement current source for providing a measurement current to a relaxation oscillator, the relaxation oscillator comprising a measurement switching circuit, a set-reset circuit having a first phase path and a second phase path, and an output, characterized by; a logic circuit; a measurement capacitor disposed in the measurement switching circuit; a first transistor, controlled by the logic circuit, for directing the measurement current to the measurement capacitor for charging the measurement capacitor; and a current mirror having transistors controlled by the logic circuit, for mirroring the measurement current in a second transistor, for discharging the measurement capacitor; wherein the logic circuit provides measurement control signals for combining signals indicative of a phase of the set-reset circuit with signals from a timing generator for controlling alternating charging and discharging of the measurement capacitor according to the phase of the set-reset circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An RF transponder comprising:
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a measurement current source for providing a measurement current to a relaxation oscillator, the relaxation oscillator comprising a set-reset circuit having a first phase path and a second phase path, and an output, characterized by; a first measurement switching circuit having an output and a second measurement switching circuit having an output; a logic circuit; a first measurement capacitor disposed at the output of the first measurement switching circuit; a first switch, controlled by the logic circuit, for connecting the output of the first measurement switching circuit to the set-reset circuit; a second measurement capacitor disposed at the output of the second measurement switching circuit; a second switch, controlled by the logic circuit, for connecting the output of the second measurement switching circuit to the set-reset circuit; a first transistor, controlled by the logic circuit, for directing the measurement current to the first measurement capacitor for charging the first measurement capacitor; a first current mirror, having transistors controlled by the logic circuit, for mirroring the measurement current in a second transistor, for discharging the first measurement capacitor; wherein the logic circuit provides first measurement control signals for combining signals indicating a phase of the set-reset circuit with signals from a timing generator for controlling alternating charging and discharging of the first measurement capacitor according to the phase of the set-reset circuit; a third transistor, controlled by the logic circuit, for directing the measurement current to the second measurement capacitor for charging the second measurement capacitor; a second current mirror, having transistors controlled by the logic circuit, for mirroring the measurement current in a fourth transistor, for discharging the second measurement capacitor; wherein the logic circuit provides second measurement control signals for combining signals indicating the phase of the set-reset circuit with signals from the timing generator for controlling alternating charging and discharging of the second measurement capacitor according to the phase of the set-reset circuit; and wherein the logic circuit provides capacitor selection signals for combining signals from the timing generator for controlling the opening and closing of the first and second switches. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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21. A method of generating an oscillating measurement signal in an RF transponder, the RF transponder comprising a relaxation oscillator having at least one measurement switching circuit, wherein the frequency of the oscillating measurement signal is indicative of a measured parameter;
- the method characterized by;
providing a measurement current to the at least one measurement switching circuits; providing a measurement capacitor in each one of the at least one measurement switching circuits; and alternately directing the measurement current to the measurement capacitor for charging the measurement capacitor and directing a mirrored measurement current to the measurement capacitor for discharging the measurement capacitor. - View Dependent Claims (22, 23, 24, 25)
- the method characterized by;
Specification