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.

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.

A bulk acoustic wave resonator, a method for manufacturing the same and an electronic device are provided, and belong to the field of communication technology. The bulk acoustic wave resonator includes: a base substrate, a first electrode, a piezoelectric layer, and a second electrode. The bulk acoustic wave resonator further includes: a first bias resistance layer on a side of the first electrode close to the base substrate, and a first electric isolation layer between the first bias resistance layer and the first electrode; the first bias resistance layer is made of a material with a high resistivity; and/or a second bias resistance layer on a side of the second electrode away from the base substrate, and a second electric isolation layer between the second bias resistance layer and the second electrode; and the second bias resistance layer is made of a material with a high resistivity.

An acoustic transformer in a transmitter chain is disclosed. In one aspect, a differential power amplifier may produce a differential signal that is provided to a first transformer. A differential output of this first transformer is provided to an acoustic transformer that provides a single-ended output signal for use by an acoustic filter. By making the second transformer an acoustic transformer, the second transformer may be integrated into the same circuitry that forms the acoustic filter, thereby simplifying the die. Further, the acoustic transformer may be tuned if ferroelectric resonators are used, which provides strong out-of-band signal cancelation.

The present disclosure relates to filter circuitry, which includes a first node and a second node, a series resonator coupled between the first node and the second node, and a compensation circuit coupled in parallel with the series resonator and located between the first node and the second node. Herein, the compensation circuit includes a tunable acoustic resonator with at least one transduction structure. The at least one transduction structure includes at least one ferroelectric material, and polarization of the at least one ferroelectric material varies with an electric field across the at least one ferroelectric material. Upon adjusting a direct current voltage applied to the tunable acoustic resonator, the compensation circuit is capable of providing a variable negative equivalent capacitance to at least partially cancel out an equivalent capacitance presented by the series resonator between the first node and the second node.