Abstract: A CMOS low frequency oscillator circuit comprising an amplifier (10) and an interface for connecting a first and a second terminal of an external crystal oscillator (14) in a feedback path of the amplifier (10). In one aspect, the oscillator circuit further comprises a regulated current source (24) supplying a regulated current to the amplifier (10) controlled by the voltage swing across the external crystal oscillator (14); and a constant current source (32) supplying a minimum constant current to the amplifier (10) independent of the voltage swing across the external crystal oscillator (14).

Abstract: A CMOS analog switch is provided that can handle negative input polarity. The semiconductor substrate wherein the analog switch is formed has a substrate area of n-conductivity type. First and second p-channel transistors are formed in the n-conductivity substrate area and each have a gate, a source connected to the input terminal and a drain connected to the output terminal. The analog switch further has a comparator for comparing a voltage level at the input terminal with ground level, a switch driven by an output of the comparator to selectively connect the n-conductivity area with the signal input terminal for a positive input voltage level or to ground for a negative input voltage level, and control circuitry providing gate control signals for the first and second p-channel transistors. The inherent substrate diodes are effectively kept from becoming conductive.

Abstract: A transponder (1) comprising an antenna (4), a demodulator (5) and a signal processing circuit (6) which converts a modulated signal received via the antenna (4) into a signal suitable for processing in the demodulator (5). The signal processing circuit (6) comprises an amplifier (7) with a predefined amplification factor and a closed loop control circuit (8) serving to maintain the voltage swing of the processed signal applied at the input of the demodulator (5) substantially constant. In a preferred embodiment the closed loop control circuit comprises a capacitor which is continually discharged and differingly charged as a function of the strength of the output signal of the amplifier of the signal processing circuit, the voltage resulting across the capacitor controlling a controllable resistor connected in parallel to the input of the signal processing circuit and forming with a coupling capacitor a voltage divider.

Abstract: A comparator with hysteresis which achieves fast switching despite a low current consumption. The comparator comprises a first transistor (M1) and a second transistor (M2) whose gates form the inputs of the comparator. The main current paths of both transistors are connected to each other at one end, with a third transistor (M3) and a fourth transistor (M4) being provided. The gate of the third transistor is connected to the gate of the first transistor and its main current path is circuited between the one end of the main current paths of the first and second transistor and is connected via the main current path of the fourth transistor to the other end of the main current path of the second transistor. The gate of the fourth transistor is connected to the output signal or inverted output signal of the comparator. The comparator in accordance with the invention may be put to use e.g. in an ASK demodulator such as those used in RFID transponders.

Abstract: A CMOS analog switch is provided that can handle negative input polarity. The semiconductor substrate wherein the analog switch is formed has a substrate area of n-conductivity type. First and second p-channel transistors are formed in the n-conductivity substrate area and each have a gate, a source connected to the input terminal and a drain connected to the output terminal. The analog switch further has a comparator for comparing a voltage level at the input terminal with ground level, a switch driven by an output of the comparator to selectively connect the n-conductivity area with the signal input terminal for a positive input voltage level or to ground for a negative input voltage level, and control circuitry providing gate control signals for the first and second p-channel transistors. The inherent substrate diodes are effectively kept from becoming conductive.

Abstract: A voltage follower comprising a first field-effect transistor (MN1) whose gate forms the input of the voltage follower. Further provided is a second field-effect transistor (MN2) whose drain connected to the gate forms the output of the voltage follower. The sources of the two field-effect transistors (MN1, MN2) are connected to each other and to the drain of a third field-effect transistor (MN3) serving as current source and to the gate of which a predefined bias voltage is applied. The invention employs in addition a fourth field-effect transistor (MN4) whose source-drain path is circuited between the output of the voltage follower and the drain of the third field-effect transistor (MN3) and whose gate is connected to the gate of the third field-effect transistor (MN3). As compared to prior art voltage followers the voltage follower in accordance with the invention comprises a wider voltage range in which it can be put to use. This can be made use of e.g.

Abstract: A transponder (1) comprising an antenna (4), a demodulator (5) and a signal processing circuit (6) which converts a modulated signal received via the antenna (4) into a signal suitable for processing in the demodulator (5). The signal processing circuit (6) comprises an amplifier (7) with a predefined amplification factor and a closed loop control circuit (8) serving to maintain the voltage swing of the processed signal applied at the input of the demodulator (5) substantially constant. In a preferred embodiment the closed loop control circuit comprises a capacitor which is continually discharged and differingly charged as a function of the strength of the output signal of the amplifier of the signal processing circuit, the voltage resulting across the capacitor controlling a controllable resistor connected in parallel to the input of the signal processing circuit and forming with a coupling capacitor a voltage divider.

Abstract: A voltage follower comprising a first field-effect transistor (MN1) whose gate forms the input of the voltage follower. Further provided is a second field-effect transistor (MN2) whose drain connected to the gate forms the output of the voltage follower. The sources of the two field-effect transistors (MN1, MN2) are connected to each other and to the drain of a third field-effect transistor (MN3) serving as current source and to the gate of which a predefined bias voltage is applied. The invention employs in addition a fourth field-effect transistor (MN4) whose source-drain path is circuited between the output of the voltage follower and the drain of the third field-effect transistor (MN3) and whose gate is connected to the gate of the third field-effect transistor (MN3). As compared to prior art voltage followers the voltage follower in accordance with the invention comprises a wider voltage range in which it can be put to use. This can be made use of e.g.

Abstract: A comparator with hysteresis which achieves fast switching despite a low current consumption. The comparator comprises a first transistor (M1) and a second transistor (M2) whose gates form the inputs of the comparator. The main current paths of both transistors are connected to each other at one end, with a third transistor (M3) and a fourth transistor (M4) being provided. The gate of the third transistor is connected to the gate of the first transistor and its main current path is circuited between the one end of the main current paths of the first and second transistor and is connected via the main current path of the fourth transistor to the other end of the main current path of the second transistor. The gate of the fourth transistor is connected to the output signal or inverted output signal of the comparator. The comparator in accordance with the invention may be put to use e.g. in an ASK demodulator such as those used in RFID transponders.

Abstract: An analog switch includes two complementary MOS field-effect transitors (10, 12) whose source-drain circuits are located in parallel between the input terminal (18) and the output terminal (20) of the switch. A control signal for controlling the switch is applied to the gate of the MOS field-effect transistor (12) of the one channel type directly and to the gate of the MOS field-effect transistor (10) of the other channel type via a negator (16). Between the input terminal (18) and output terminal (20) of the switch the series source-drain circuits of three MOS field-effect transistors (22, 24, 26) are inserted, whereby the MOS field-effect transistor (24) located in the middle of the series circuit has a channel type opposite that of the other two MOS field-effect transistors (22, 26). The gates of all MOS field-effect transistors of the other channel type are each interconnected.

Abstract: A demodulator circuit for demodulating a signal ASK-modulated with modulation pulses equal in duration, and having a small depth of modulation and large dynamic range comprises an amplitude limiter (10) through which an amplitude-dependent current flows when the amplitude of the signal to be demodulated exceeds its limiting threshold value. Furthermore comprised is an envelope detector (12) to the input of which the signal to be demodulated is applied, as well as a differentiating network (14) configured so that it differentiates the output signal of the envelope detector (12) and outputs a signal pulse only when the change in amplitude of this output signal is in one direction. A bandpass filter (18) in the demodulator circuit passes, from a signal derived from an amplitude-dependent current from the amplitude limiter (10), the frequency component attributed to the duration of the modulation pulses.

Abstract: An improved damping modulation circuit (140) for a transponder (14) receives energy transmitted from a transmitter/receiver antenna (16) to produce a unique recognition signal in the transponder. The improved damping modulation circuit (140) includes a high fieldstrength circuit (152, 160, 174) that protects full-duplex transponder (14) from over-voltage through the use of voltage limiters (132), while still providing power to transponder (14). Low fieldstrength circuit (152) activates only minimal circuitry to provide the highest possible amount of power to full-duplex transponder (14). Medium fieldstrength circuit (152, 160) increases the fieldstrength in full-duplex transponder (14) for establishing a sufficient amount of current flow for proper modulation using only a medium amount of transponder (14) circuit elements.

Abstract: A circuit arrangement is described with the aid of which a control signal can be generated in dependence upon the occurrence of an extreme value of a sinusoidal oscillation. The circuit arrangement (10) includes a storage member (22) which is adapted to be charged via a diode (20) to one of the extreme values of the sinusoidal oscillation. A discharge path (26) for the storage member (22) is present, the time constant of which is so dimensioned that within the period duration of the sinusoidal oscillation an appreciable discharge of the storage member (22) takes place. A switch element (24) controllable by the charge voltage of the storage member (22) furnishes the control signal at its output (14) for the period of time during which the charge voltage at the storage member (22) is smaller than the extreme value of the sinusoidal oscillation. The circuit arrangement can be used in maintaining the oscillations of a resonance circuit stimulated to oscillate by means of a momentary HF carrier wave pulse.

Abstract: Analog AC to digital signal converter includes a sampling circuit which cyclically samples the analog AC signal to form analog sampling values, and an analog-digital converter for converting the analog sampling values to digital sampling values. A sign integrator integrates the sign of the digital sampling values, and a compensating voltage generator generates a compensating voltage in dependence upon the integration result. A combination circuit combines the compensating voltage with the analog sampling value from the sampling means and applies the combination result to the analog-digital converter. The circuit compensates any DC voltage component contained in the analog AC signal and avoids interferences resulting from such DC voltage component.