A resin composition having excellent impact resistance and heat resistance, comprising a poly-3-hydroxybutyrate, and a core-shell latex rubber comprising an acrylic rubber andor silicone-acrylic rubber copolymer as a core component and polymethyl methacrylate as a shell component, or a specific thermoplastic polyurethane, is disclosed. The connecting device has a housing arrangement which forms an outer conductor. Optionally, to reduce harmonic distortions and to further stabilize the output common mode voltage of the amplifier, current is controllably supplied to the intermediate stage of the amplifier. In one alternative aspect of the invention, the switch at the switch-out end of the waveguide resonator is a plasma switch, employing at least one dielectric window positioned in the resonator guide to have minimum effect on the resonator Q. The common-mode level adjust circuit alters a common-mode level of a differential input signal to be substantially equal to a desired common-mode level and the tuning circuit provides a compensation voltage to the common-mode level adjust circuit based on a difference between the common-mode levels.