Temperature sensor

Abstract

In a temperature sensor, especially in a temperature sensor using a resonator, based on a frequency of one oscillator circuit (resonator), frequencies of the other one or more oscillator circuits (resonators) are measured, and frequency-temperature characteristics of a plurality of resonators are synthesized in order to realize an accurate temperature sensor which does not require an accurate frequency reference regardless of a temperature change, and has a linear characteristic and a wide measurable temperature range. Also, two oscillator circuits have two resonators respectively with quadratic characteristics in which quadratic coefficients are the same and linear characteristics are different from each other, and a difference between oscillation frequencies of both oscillator circuits is obtained.

What we claim is:  
     
         1 . A temperature sensor comprising: 
 two oscillator circuits using resonators having different temperature characteristics of resonance frequencies; and    a detection circuit for relatively obtaining, with a frequency of one oscillator circuit being made a reference, a frequency of the other oscillator circuit, for performing a predetermined calculation between both frequencies, and for outputting a calculation result as a temperature signal.    
     
     
         2 . The temperature sensor as claimed in  claim 1  wherein the detection circuit is composed of a reference counter for counting a predetermined time interval based on a frequency of one oscillator circuit, a temperature counter for counting an output of the other oscillator circuit during the predetermined time interval, and a calculating circuit for calculating a difference between values of the temperature counter and the reference counter.  
     
     
         3 . The temperature sensor as claimed in  claim 1  wherein the detection circuit is composed of a reference counter for counting a predetermined time interval based on a frequency of one oscillator circuit, a temperature counter for counting an output of the other oscillator circuit during the predetermined time interval, and a calculating circuit for calculating a ratio between values of the temperature counter and the reference counter.  
     
     
         4 . The temperature sensor as claimed in  claim 1 , further comprising one or more oscillator circuits using another resonator having a different temperature characteristic of a resonance frequency, 
 the detection circuit obtaining, with a frequency of a first oscillator circuit among the oscillator circuits being made a reference, frequencies of the remaining two or more second oscillator circuits, performing a predetermined calculation between all the frequencies, and outputting a calculation result as a temperature signal.    
     
     
         5 . The temperature sensor as claimed in  claim 4  wherein the detection circuit includes a reference counter for counting a predetermined time interval based on a frequency of the first oscillator circuit, a total counter for totalizing outputs of the remaining oscillator circuits either in an up direction or a down direction during the predetermined time interval to be counted, and a calculating circuit for calculating a difference between values of the total counter and the reference counter.  
     
     
         6 . The temperature sensor as claimed in  claim 4  wherein the detection circuit includes a reference counter for counting a predetermined time interval based on a frequency of the first oscillator circuit, a total counter for totalizing outputs of the remaining oscillator circuits either in an up direction or a down direction during the predetermined time interval to be counted, and a calculating circuit for calculating a ratio between values of the total counter and the reference counter.  
     
     
         7 . A temperature sensor comprising: 
 two oscillator circuits having two resonators respectively with quadratic characteristics in which quadratic coefficients are same and linear characteristics are different from each other; and    a detection circuit for detecting a difference between a frequency of one oscillator circuit and a frequency of the other oscillator circuit and for detecting a temperature corresponding to the difference.    
     
     
         8 . The temperature sensor as claimed in  claim 1  wherein the detection circuit multiplies or divides a frequency of at least one oscillator circuit.  
     
     
         9 . The temperature sensor as claimed in  claim 1  wherein the detection circuit further converts the temperature signal into a predetermined temperature value.  
     
     
         10 . The temperature sensor as claimed in  claim 4  wherein the resonator comprises an SAW resonator.  
     
     
         11 . The temperature sensor as claimed in  claim 10  wherein the SAW resonator is formed on a same substrate.  
     
     
         12 . The temperature sensor as claimed in  claim 11  wherein a propagation direction of one SAW resonator is angled with respect to a propagation direction of the other resonator.  
     
     
         13 . The temperature sensor as claimed in  claim 10  wherein at least one SAW resonator utilizes a Rayleigh wave, and at least another SAW resonator utilizes an SH wave.  
     
     
         14 . The temperature sensor as claimed in  claim 10  wherein the oscillator circuit has a separator for separating a Rayleigh wave from an SH wave of one SAW resonator, a mixer for mixing the separated Rayleigh wave and the SH wave, and two oscillation portions for respectively oscillating with frequencies of the Rayleigh wave and the SH wave.  
     
     
         15 . A VCTCXO device using the temperature sensor as claimed in  claim 1 .  
     
     
         16 . The temperature sensor as claimed in  claim 15  wherein an oscillator of a VCO portion and a resonator of the temperature sensor in the VCTCXO device are formed in one piece on a same substrate.  
     
     
         17 . The temperature sensor as claimed in  claim 7  wherein the detection circuit further converts a temperature signal into a predetermined temperature value.  
     
     
         18 . The temperature sensor as claimed in  claim 7  wherein the resonator comprises an SAW resonator.  
     
     
         19 . The temperature sensor as claimed in  claim 18  wherein the SAW resonator is formed on a same substrate.  
     
     
         20 . The temperature sensor as claimed in  claim 19  wherein a propagation direction of one SAW resonator is angled with respect to a propagation direction of the other resonator.  
     
     
         21 . The temperature sensor as claimed in  claim 18  wherein one SAW resonator utilizes a Rayleigh wave, and the other SAW resonator utilizes an SH wave.  
     
     
         22 . The temperature sensor as claimed in  claim 18  wherein the oscillator circuit has a separator for separating a Rayleigh wave from an SH wave of one SAW resonator, a mixer for mixing the separated Rayleigh wave and the SH wave, and two oscillation portions for respectively oscillating with frequencies of the Rayleigh wave and the SH wave.