Abstract: A circuit having a first input and a second input configured to apply an alternating voltage, a first output and a second output configured to supply a rectified and regulated voltage, a rectifier bridge circuit having a current return circuit, a third transistor and a fourth transistor, and a controller configured to regulate the voltage between the first and the second output to a constant value. The current return circuit is connected to the first input, the second input and to the second output. The third transistor is configured as a series voltage regulator and is connected to the first input and the first output. The fourth transistor is configured as a series voltage regulator and is connected to the second input and the first output. The controller is coupled to a control input of the third transistor and to a control input of the fourth transistor. Further, a method for rectifying and regulating voltages of a circuit is provided. The circuit and the method can be used in a contactless chip card.

Abstract: A transponder circuit arrangement including antenna contacts to which an antenna signal can be applied. The antenna signal includes at least one signal in one transmission band of a plurality of transmission bands. The transponder circuit arrangement also includes a detector adapted to detect whether the antenna signal includes a signal in a predetermined transmission band, and a demodulator adapted to demodulate the signal in the predetermined transmission band when the signal has been detected therein, and otherwise to demodulate a signal in another transmission band.

Abstract: Transponder circuit arrangement having antenna connections for application of a voltage signal, a load-reduction modulation device, which is coupled to the antenna connections and is designed to modulate the applied, unmodulated voltage signal, which is at a first level, and a voltage conversion device, which is coupled to the load-reduction modulation device and is designed to provide a supply voltage, the magnitude of whose level is greater than the first level.

Abstract: A device for providing a supply voltage and a load modulation in a transponder with a unit having a resistance controllable by a control signal at a control input thereof, a unit for applying a load modulation signal to the control input, and a unit for applying a voltage limitation control signal to the control input.

Abstract: The present invention pertains to an oscillator arrangement for carrying out a frequency modulation process, wherein an oscillator (1) with automatic amplitude control (5, 6, 7) is provided. The shift keying is not realized with reconnectable capacitances in the oscillator (1) that determine its oscillator frequency, but rather by suitably influencing (6) the feed current of the oscillator in dependence on the modulation signal (FSK), namely with the aid of the amplitude control (5, 6, 7). Undesirable charge injections do not occur in the proposed oscillator arrangement because reconnectable capacitances are no longer required for achieving the desired frequency deviation.