Abstract: The invention relates to a resonator filter structure (10) for radio frequency (RF) filters, especially a bulk acoustic wave (BAW) filter structure. According to the invention, a resonator filter structure (10) is constructed with a BAW lattice filter section (20), in which all of the BAW resonator elements (20-1, 20-2, 20-3, 20-4) within the BAW lattice filter section (20) have substantially equal resonance frequencies. According to the invention, there are parallel capacitances (30-1, 30-2) connected in parallel to the BAW resonators (20-2, 20-3) of one branch type of the BAW lattice filter section (20). Thus, anti-resonance frequency of the respective BAW resonator (20-2, 20-3) is tuned. That results in a very narrow passband which corresponds approximately to the difference in anti-resonance frequencies between diagonal and horizontal branches of the lattice filter section (20). The parallel capacitances (30-1, 30-2) are used to tune the bandwidth: the smaller the capacitance, the smaller the bandwidth.

Abstract: An amplifier circuit contains a first and second current branch, each branch comprising an input transistor and a cascode transistor. Inputs of the amplifier are coupled to control electrodes of the input transistors in respective ones of the current branches. The control electrodes of the cascode transistors are coupled to each other. A high frequency coupling is provided between the control electrodes of the cascode transistors and a node of the common current source, to copy substantially common mode voltage changes of terminals of the main current channels of the input transistors to voltage changes at the control electrodes of the cascode transistors.