Abstract: A preamplifier having extremely high input impedance amplifies the electrical signal output from an electret condenser microphone (ECM) without suffering from the effects of a DC leakage current at the input. The preamplifier circuit includes a pair of cross-coupled PN junction diodes setting the input impedance, a PMOS device, and a load resistor configured similarly to a conventional preamplifier. A capacitor is placed between the input and the cross-coupled diodes such that a DC path no longer exists to bias the cross-coupled diodes. Therefore, leakage currents are prevented from upsetting the DC operating point of the preamplifier and biasing the cross-coupled diodes. Consequently, small signal gain distortion, excessive demodulation products and increased noise can be avoided.

Abstract: A preamplifier having extremely high input impedance amplifies the electrical signal output from an electret condenser microphone (ECM) without suffering from the effects of a DC leakage current at the input. The preamplifier circuit includes a pair of cross-coupled PN junction diodes setting the input impedance, a PMOS device, and a load resistor configured similarly to a conventional preamplifier. A capacitor is placed between the input and the cross-coupled diodes such that a DC path no longer exists to bias the cross-coupled diodes. Therefore, leakage currents are prevented from upsetting the DC operating point of the preamplifier and biasing the cross-coupled diodes. Consequently, small signal gain distortion, excessive demodulation products and increased noise can be avoided.

Abstract: A microelectric position sensor wherein an assembly of magnetic field sensitive elements assume first and second states when subjected to a magnetic field having an intensity below or above first or second predetermined values respectively. A magnet is selectively movable relative to the assembly, so that the elements are selectively subjected to the magnetic field. The magnet has focusing tongues for focusing the magnetic field at a region including substantially only one of the elements, so that the magnetic field within the region has an intensity above the second value, and the magnetic field outside the region has an intensity below the first value.

Abstract: The invention concerns a Switched MAGFET (MAGnetic field sensitive Field Effect Transistor). A preferred SMAGFET embodiment consists of a MAGFET structure with two equal sized drain contacts (3, 4), a gate area consisting of two equal sized and electrically isolated gate regions G1 and G2 (5, 6) separated by a third isolated gate region Gc (7) placed along the symmetry line of the device and slightly overlapping G1 and G2. The SMAGFET has a common source (1). By varying the gate voltage on Gc (with reference to the common source contact), the magnetic sensitivity of the SMAGFET may be controlled. By applying a first voltage on Gc, exchange of carriers from the channels beneath G1 and G2 is blocked. In case of an applied magnetic field, this will prevent Lorentz deflected carriers to cross symmetry line and redistribute the drain currents, i.e. the magnetic field sensitivity is virtually zero as the drain currents will remain unaffected by the magnetic induction.