Piezoelectric resonator and FM detection circuit incorporating the same

A piezoelectric resonator made of a piezoelectric material and sealed by a packaging resin, wherein the temperature coefficient εTC of the capacitance of the piezoelectric material, the bandwidth ratio Δf/fo, the temperature coefficient FrTC of the resonance frequency, the temperature coefficient FaTC of the anti-resonance frequency, the temperature coefficient RfoTC of the center frequency associated with a stress of the packaging resin, and a target value α for the temperature coefficient of the center frequency satisfy the following expression:

• |(FrTC+FaTC)/2+K×εTC×(Δf/fo)+RfoTC|≦α
• where
• K=a coefficient determined according to the impedance at the midpoint between Fr and Fa;
• εTC=A×(the amount of change in capacitance in a measured temperature range)/(the capacitance at a reference temperature×the measured temperature range);
• Δf/fo=(Fa at the reference temperature−Fr at the reference temperature)/(fo at the reference temperature);
• FrTC=A×(the amount of change in Fr in the measured temperature range)/(Fr at the reference temperature×the measured temperature range);
• FaTC=A×(the amount of change in Fa in the measured temperature range)/(Fa at the reference temperature×the measured temperature range);
• and
• A=a coefficient of +1 for a positive temperature coefficient and −1 for a negative temperature coefficient.