Patent ID: 6950640

Claim:
An FM detector circuit comprising: a discriminator defining a phase shifter and including a piezoelectric material, wherein the following equation is satisfied: |( Fr TC +Fa TC )/2 +K×ε TC ×(Δ f/fo )+ Cfo TC |≦α where ε TC represents a temperature characteristic of a capacitance of the piezoelectric material of the discriminator, Δf/fo represents a specific frequency bandwidth of the FM detector, Fr TC represents a temperature characteristic of a resonance frequency of the FM detector, Fa TC represents a temperature characteristic of an antiresonance frequency of the FM detector, Cfo TC represents a temperature characteristic of the FM detector circuit excluding the discriminator, and α represents a target value of temperature characteristic of the center frequency of the FM detector circuit, wherein K represents a coefficient determined by an impedance at an intermediate point between Fr and Fa, ε TC equals A×(a range of variation of capacitance of the piezoelectric material within a range of measurement temperature)/{(the capacitance of the piezoelectric material at a reference temperature)×(the range of measurement temperature)}, Δf/fo equals {(Fa at the reference temperature)−(Fr at the reference temperature)}/(fo at the reference temperature), Fr TC equals A×(a range of variation of Fr within the range of measurement temperature)/{(Fr at the reference temperature)×(the range of measurement temperature)}, Fa TC equals A×(a range of variation of Fa within the measurement temperature)/{(Fa at the reference temperature)×(the range of measurement temperature)}, Cfo TC equals A×(the temperature characteristic of the FM detector circuit excluding the discriminator), and A is a coefficient which equals +1 if the temperature characteristic is positive in trend, or equals −1 if the temperature characteristic is negative in trend.