An acoustic wave filter includes a substrate, a first resonator disposed on the substrate, a second resonator disposed on the substrate to be spaced apart from the first resonator, a connector electrically connecting the first and second resonators, and a variable capacitor formed in the connector to tune a pass band frequency of the acoustic wave filter.

A method for the batch production of acoustic wave filters comprises: synthesizing N theoretical filters, each filter defined by a set of j theoretical resonator(s) having a triplet C.sub.0ij,eq, .sub.rij,eq and .sub.aij,eq, these parameters grouped into subsets; determining a reference resonator structure for each subset, naturally having a resonant frequency .sub.r,ref, where .sub.aij,eq<.sub.r,ref<.sub.rij,eq; determining, for each theoretical resonator, an elementary building block comprising an intermediate resonator R.sub.ij, a parallel reactance Xp.sub.ij and/or a series reactance Xs.sub.ij, the intermediate resonator R.sub.ij having a triplet C.sub.0ij, .sub.r,ref and .sub.a,ref, the parameters C.sub.0ij, Xpij and/or Xs.sub.ij defined so the elementary building block has a triplet: C.sub.0ij,eq, .sub.rij,eq and .sub.aij,eq; determining the geometrical dimensions of the actual resonators R.sub.ij of the filters so they have a capacitance C.sub.0ij; producing each actual resonator; associating series and/or parallel reactances with actual resonators in order to form the elementary building blocks.

A crystal unit includes: a capacitor body in which a plurality of light-transmitting dielectrics and a plurality of internal electrodes are alternately stacked; a crystal piece arranged above the capacitor body and having excitation electrodes on both surfaces thereof; an external electrode formed on a surface of the capacitor body; and a first conductor portion formed in an inner layer of the capacitor body, and including one end electrically coupled to a first internal electrode among the plurality of internal electrodes, and the other end electrically coupled to the external electrode.

An acoustic wave filter includes a substrate, a first resonator disposed on the substrate, a second resonator disposed on the substrate to be spaced apart from the first resonator, a connector electrically connecting the first and second resonators, and a variable capacitor formed in the connector to tune a pass band frequency of the acoustic wave filter.

In wireless communications, many radio frequency bands are used. For each frequency band, there are two frequencies, one for transmitting and the other for receiving. As the band widths are small and separation between adjacent bands is also small, many band pass filters with different band pass frequencies are required for each communication unit such as mobile handset. The invention provides tunable film bulk acoustic resonators TFBARs containing semiconducting piezoelectric layers and methods for tuning and adjusting the resonant properties. When a DC biasing voltage is varied, both the depletion region thickness and neutral region thickness associated in the semiconducting piezoelectric layers varies leading to changes in equivalent capacitances, inductance and resistances and hence the resonance properties and frequencies. A plurality of the present TFBARs are connected into a tunable oscillator or a tunable and selectable microwave filter for selecting and adjusting of the bandpass frequency by varying the biasing voltages.

In one embodiment, a transducer controller is configured to form a drive signal with a first frequency to drive a transducer. The drive signal has a period and a half-period and drives the transducer for a first portion of the half-period. The transducer controller is configured to, for a second portion of the half-period, sense a voltage formed by the transducer, measure portions of the voltage and estimate a phase error between the first frequency and a resonant frequency of the transducer, and to adjust the first frequency to a second frequency that reduces the phase error.

In one embodiment, a transducer controller is configured to form a drive signal with a first frequency to drive a transducer. The drive signal has a period and a half-period and drives the transducer for a first portion of the half-period. The transducer controller is configured to, for a second portion of the half-period, sense a voltage formed by the transducer, measure portions of the voltage and estimate a phase error between the first frequency and a resonant frequency of the transducer, and to adjust the first frequency to a second frequency that reduces the phase error.

A method for the batch production of acoustic wave filters comprises: synthesizing N theoretical filters, each filter defined by a set of j theoretical resonator(s) having a triplet C.sub.0ij,eq, .sub.rij,eq and .sub.aij,eq, these parameters grouped into subsets; determining a reference resonator structure for each subset, naturally having a resonant frequency .sub.r,ref, where .sub.aij,eq<.sub.r,ref<.sub.rij,eq; determining, for each theoretical resonator, an elementary building block comprising an intermediate resonator R.sub.ij, a parallel reactance Xp.sub.ij and/or a series reactance Xs.sub.ij, the intermediate resonator R.sub.ij having a triplet C.sub.0ij, .sub.r,ref and .sub.a,ref, the parameters C.sub.0ij, Xpij and/or Xs.sub.ij defined so the elementary building block has a triplet: C.sub.0ij,eq, .sub.rij,eq and .sub.aij,eq; determining the geometrical dimensions of the actual resonators R.sub.ij of the filters so they have a capacitance C.sub.0ij; producing each actual resonator; associating series and/or parallel reactances with actual resonators in order to form the elementary building blocks.

A resonant circuit comprises an input terminal and an output terminal and at least: a group of N resonators, where N1, the resonators having the same resonance frequency and the same antiresonance frequency; a first and a second impedance matching element having a non-zero reactance, the first element being in series with the group of resonators, and the second element being in parallel with the group of resonators, the resonant circuit comprising: first means for controlling the group of resonators, enabling the static capacitance of the group to be fixed at a first value; second control means, enabling the impedance of the first impedance matching element and that of the second element to be fixed at second values; the first and second values being such that the triplet of values composed of the static capacitance of the group, the impedance of the first element, and the impedance of the second element can be used to determine the following triplet of parameters: the characteristic impedance Z.sub.c of the assembly formed by the group, the first impedance matching element and the second matching element; the resonance frequency .sub.r of the assembly; the antiresonance frequency .sub.a of the assembly, in order to stabilize the impedance of the circuit at a chosen characteristic impedance.

A crystal unit includes: a capacitor body in which a plurality of light-transmitting dielectrics and a plurality of internal electrodes are alternately stacked; a crystal piece arranged above the capacitor body and having excitation electrodes on both surfaces thereof; an external electrode formed on a surface of the capacitor body; and a first conductor portion formed in an inner layer of the capacitor body, and including one end electrically coupled to a first internal electrode among the plurality of internal electrodes, and the other end electrically coupled to the external electrode.