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US 6,950,640 B2Granted
FM detector circuit
AssigneeMurata Manufacturing Co., Ltd.
InventorsYoshihiro Ikeda, Kunio Sawai
Life of this patent
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Abstract
An FM detector circuit includes a bridge circuit having four sections with a discriminator connected as one of the four sections. An FM intermediate frequency is applied across one pair of diagonally opposed nodes of the bridge circuit and an output is picked up across the other pair of diagonally opposed nodes of the bridge circuit. The discriminator includes a piezoelectric material that is selected to produce stable overall temperature characteristics.
Claims20
An FM detector circuit comprising:
- a discriminator defining a phase shifter and including a piezoelectric material, wherein the following equation is satisfied:
- |(FrTC+FaTC)/2+K×εTC×(Δf/fo)+CfoTC|≦α
- where εTC 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, FrTC represents a temperature characteristic of a resonance frequency of the FM detector, FaTC represents a temperature characteristic of an antiresonance frequency of the FM detector, CfoTC 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, εTC 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), FrTC equals A×(a range of variation of Fr within the range of measurement temperature)/{(Fr at the reference temperature)×(the range of measurement temperature)}, FaTC equals A×(a range of variation of Fa within the measurement temperature)/{(Fa at the reference temperature)×(the range of measurement temperature)}, CfoTC 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.
An FM detector circuit comprising:
- a discriminator defining a phase shifter;
- a resin mold encapsulating the discriminator;
- wherein
- the following equation is satisfied:
- |(FrTC+FaTC)/2+K×εTC×(Δf/fo)+RfoTC+CfoTC|≦α
- where εTC represents a temperature characteristic of a capacitance of a piezoelectric material of the discriminator, Δf/fo represents a specific frequency bandwidth of the FM detector, FrTC represents a temperature characteristic of a resonance frequency of the FM detector, FaTC represents a temperature characteristic of an antiresonance frequency of the FM detector, RfoTC represents a temperature characteristic of a center frequency responsive to stress in the resin mold, CfoTC represents a temperature characteristic of the FM detector circuit excluding the discriminator, and α represents a target value of temperature characteristic of a center frequency of the FM detector circuit, wherein K represents a coefficient determined by the impedance at an intermediate point between Fr and Fa, εTC equals A×(a range of variation of the capacitance of the piezoelectric material within a range of measurement temperature)/{(a 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), FrTC equals A×(a range of variation of Fr within the range of measurement temperature)/{(Fr at the reference temperature)×(the range of measurement temperature)}, FaTC equals A×(a range of variation of Fa within the measurement temperature)/{(Fa at the reference temperature)×(the range of measurement temperature)}, CfoTC 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.
3 more elements
Dependencies are inferred from the claim text.