Radio frequency temperature sensor and method of calibrating temperature therefor

#This application claims the priority benefit of Taiwan application serial no.92136368, filed on Dec. 22, 2003.

#1. Field of the Invention

#The present invention relates to a radio frequency measuring device, and more particularly to a radio frequency temperature sensor and a method of calibrating temperature therefor.

#FIG. 1 is a block diagram showing an active radio frequency temperature sensor according to an embodiment of the present invention.

#FIG. 2 is a drawing showing a ring oscillator according to an embodiment of the present invention.

#FIG. 3 is an operation waveform of the radio frequency transmission interface 140 of the present invention when the card reader is reading data.

#FIG. 1 is a block diagram showing an active radio frequency temperature sensor according to an embodiment of the present invention. Referring to FIG. 1, the radio frequency temperature sensor 100 comprises a ring oscillator 110, a memory 120, such as a non-volatile memory, and a frequency counter 130 for measuring temperature. The measuring principle is described below.

#First, the ring oscillator 110 is adapted to generate an oscillating signal Clock_in frequency corresponding a measured temperature. The oscillating signal serves as the clock pulse of the frequency counter 130. FIG. 2 is a drawing showing a ring oscillator according to an embodiment of the present invention. Referring to FIG. 2, the ring oscillator 110 comprises a thermal resistor 210, a capacitor 220, a Schmitt inverter 230, an inverter 240 and a NAND gate 250.

#Referring to FIG. 2, the thermal resistor 210 comprises a first terminal and a second terminal. The capacitor 220 comprises a first terminal and a second terminal, the first terminal of the capacitor 220 coupled to the second terminal of the thermal resistor 210, and the second terminal of the capacitor 220 grounded. The Schmitt inverter 230 has an input terminal coupled to the second terminal of the thermal resistor 210, and an output terminal. The inverter 240 has an input terminal coupled to the output terminal of the Schmitt inverter 230, and an output terminal. The NAND gate 250 has a first input terminal, a second input terminal and an output terminal. The first input terminal of the NAND gate 250 is adapted to receive an enable signal En. The output terminal is coupled to the first terminal of the thermal resistor 210 forming a ring circuit. The second input terminal is coupled to the output terminal of the inverter 240 and adapted to output the oscillating signal Clock_In frequency corresponding to the measured temperature. The variation of the frequency of the oscillating signal Clock_In results from RC delay of the circuit by the variation of the resistance of the thermal resistor 210 in response to temperature.