A gyrator for AC signals was developed. This gyrator comprises a Hall effect material, means for permeating this Hall effect material with a magnetic field that is perpendicular to the plane or surface of the material, at least one input port for coupling an alternating current (I.sub.1; I.sub.2) into the Hall effect material, and at least one output port for outcoupling an output voltage (U.sub.2; U.sub.1) which is a measure of the Hall voltage generated by the incoupled alternating current. Each of these ports has at least two terminals, which are connected to the outside. At least one terminal of each port is connected to a connecting electrode, which is electrically insulated from the Hall effect material and forms a capacitor together with the Hall effect material. The alternating current is thus capacitively coupled into the Hall effect material, and the output voltage is capacitively coupled out of the Hall effect material. The capacitive coupling of the connecting electrodes provides boundary conditions for the potential in the interior of the Hall effect material, which do not necessarily force potential jumps there. The development of hot spots, at which energy is dissipated, in the region of potential jumps can thereby advantageously be reduced or even entirely suppressed.

A gyrator for AC signals comprises a Hall effect material, means for coupling an alternating current (I.sub.1; I.sub.4) into the Hall effect material, means for permeating a Hall effect material with a magnetic field that is perpendicular to the plane or surface of the material, and means far converting a current (I.sub.3; I.sub.2), which was generated by the current I.sub.1 perpendicularly to the electric field generated by I.sub.1 in the Hall effect material, into an output voltage (U.sub.4; U.sub.1). A transformer is provided between at least one conductor loop (1a; 2a) made of a normal-conducting or semi-conducting material and at least one conductor loop (1; 2) made of the Hall effect material for coupling the current (I.sub.1; I.sub.4) into the Hall effect material and/or for converting the current (I.sub.3; I.sub.2) in the Hall effect material into the output voltage (U.sub.4; U.sub.1). It was found that eliminating an inefficient galvanic coupling of the Hall effect material to metallic or semi-conducting conductors minimizes the dissipative losses that occur during the conversion of the input current (I.sub.1; I.sub.4) into the output voltage (U.sub.4; U.sub.1). The gyrator can thus also be used for highly sensitive experiments in quantum information processing at low temperatures.

A drive loop circuit for a MEMS resonator. The circuit comprises a closed loop circuit to detect and amplify a signal of the MEMS resonator, a phase shifting circuit to phase shift the detected and amplified signal, and a feedback circuit to feed the detected, amplified and phase shifted signal as a feedback signal back to the MEMS resonator. The phase shifting circuit can include a low pass filter of at least 2.sup.nd order.

Disclosed are example embodiments of a circuit comprising a first inductor-capacitor (LC) loop, a second LC loop having at least one of a series connection or parallel connection to the first LC loop, and a gyrator coupled between the first LC loop and the second LC loop. In an example, the first LC and the second LC loop each include an inductive element (L) and a capacitive (C) element coupled to each other in series. In another example, the first LC and the second LC loop each include an inductive element (L) and a capacitive (C) element coupled to each other in parallel.