A hearing aid that is compact and efficient and that provides a high degree of control over its frequency response and also over its output level versus input level characteristic. The frequency response control includes an adjustable four pole high pass filter and an adjustable four pole low pass filter, to define the pass band, and an adjustable slope filter, to define the slope within the pass band. The control over the output level versus input level characteristic includes an input AGC system with well defined, independent control of compression threshold and compression ratio, an adjustable peak clipper, and a selectable output AGC system that tracks the peak clipper setting. The hearing aid incorporates a number of novel circuits including a state variable filter with adjustable corner frequency, a filter that can be continuously adjusted from a single pole low pass characteristic to a single pole high pass characteristic, a circuit to provide a range of reference voltages to accurately set the range of control currents used to control the corner frequencies of the state variable filters, a compansion system surrounding the filter network to effectively increase its limited dynamic range, a differential voltage threshold detector, a differential voltage controlled current source with an exponential relationship of output current to differential input voltage, an adjustable clipping circuit, a voltage clamp to prevent voltage excursions from going substantially below a substrate voltage, and bias compensation circuit to supply the input bias current of a transistor.

A fully differential non-linear amplifier includes an operational amplifier (12), a first input resistor (R1), a second input resistor (R2), a first feedback resistor (R3), a second feedback resistor (R4), a first clamping network (CN1), and a second clamping network (CN2). The first clamping network (CN1) is formed of a first P-channel clamping transistor (P10) and a first N-­channel clamping transistor (N10). The second clamping network (CN2) is formed of a second P-channel clamping transistor (P12) and a second N-channel clamping transistor (N12). The gates of the first and second P-­channel clamping transistors (P10, P12) are connected to receive a P-bias signal. The gates of the first and second N-channel clamping transistors (N10, N12) are connected to receive a N-bias signal. The non-linear amplifier clamps its differential output signal to a constant voltage level independent of variations in process and temperature.

Die Anordnung in einer integrierten Schaltung benützt Spannungsfolger mit zwei Eingängen, um in sehr ökono­mischer Weise Halbwellengleichrichter und Amplituden­begrenzer zu realisieren.

Ein Halbwellengleichrichter (Fig. 1) benötigt einen Spannungsfolger (10) und eine Gleichspannung Null (V12), ein Amplitudenbegrenzer (Fig. 2) kommt mit zwei Spannungsfolgern (20P, 20N) und zwei Gleich­spannungen (V22, V26) aus.

Diese Anordnungen zur Erzeugung nichtlinearer Funk­tionen sind wesentlich einfacher als bekannte Prob­lemlösungen in Switched Capacitor-Technik.

A hearing aid that is compact and efficient and that provides a high degree of control over its frequency response and also over its output level versus input level characteristic. The frequency response control includes an adjustable four pole high pass filter and an adjustable four pole low pass filter, to define the pass band, and an adjustable slope filter, to define the slope within the pass band. The control over the output level versus input level characteristic includes an input AGC system with well defined, independent control of compression threshold and compression ratio, an adjustable peak clipper, and a selectable output AGC system that tracks the peak clipper setting. The hearing aid incorporates a number of novel circuits including a state variable filter with adjustable corner frequency, a filter that can be continuously adjusted from a single pole low pass characteristic to a single pole high pass characteristic, a circuit to provide a range of reference voltages to accurately set the range of control currents used to control the corner frequencies of the state variable filters, a compansion system surrounding the filter network to effectively increase its limited dynamic range, a differential voltage threshold detector, a differential voltage controlled current source with an exponential relationship of output current to differential input voltage, an adjustable clipping circuit, a voltage clamp to prevent voltage excursions from going substantially below a substrate voltage, and bias compensation circuit to supply the input bias current of a transistor.

A current-limiting circuit for a differential amplifier includes a voltage generator (V_LS) which is switched in prallel with a signal-current-generating impedance RM connected between the emitters of the differential amplifier transistors (Q₁, Q₂) whenever an input signal exceeds the voltage of the voltage generator (VLS). A practical embodiment for limiting the current in either direction for opposite-polarity input signals includes a pair of voltage generators cross-coupled from a respective differential amplifier transistor base to the opposite transistor emitter via transistor switches (Q₃, Q₄)

A vehicle audio system (100) is presented, comprising a user interface unit (101) and a volume control unit (104). The volume control unit is configured to store a first maximum volume level (201). The user interface unit (101) is configured to allow setting a second maximum volume level (203) that is less than or equal to the first maximum volume level (201). The volume control unit (104) is configured to limit a volume level of an audio signal of the vehicle audio system (100) to the second maximum volume level (203).

Die Erfindung betrifft eine Begrenzerschaltung umfassend einen HF-Eingang (E) und einen HF-Ausgang (A), wobei zwischen dem HF-Eingang (E) und dem HF-Ausgang (A) eine NIP- Diode (1) und eine PIN-Diode (2) geschaltet sind, wobei der Kathodenanschluss (K1) der PIN-Diode (1) und der Anodenanschluss (A2) der NIP-Diode (2) mit Masse (M) verbunden sind und wobei der Anodenanschluss (A1) der PIN-Diode (1) und der Kathodenanschluss (K2) der NIP-Diode (2) miteinander verbunden sind und über jeweils eine Kapazität (C1, C2) mit dem HF-Eingang (E) und dem HF-Ausgang (A) verbunden sind.

Die Erfindung betrifft eine Begrenzerschaltung umfassend einen HF-Eingang (E) und einen HF-Ausgang (A), wobei zwischen dem HF-Eingang (E) und dem HF-Ausgang (A) eine NIP- Diode (1) und eine PIN-Diode (2) geschaltet sind, wobei der Kathodenanschluss (K1) der PIN-Diode (1) und der Anodenanschluss (A2) der NIP-Diode (2) mit Masse (M) verbunden sind und wobei der Anodenanschluss (A1) der PIN-Diode (1) und der Kathodenanschluss (K2) der NIP-Diode (2) miteinander verbunden sind und über jeweils eine Kapazität (C1, C2) mit dem HF-Eingang (E) und dem HF-Ausgang (A) verbunden sind.

An automatic input-gain control circuit of an audio amplifier and a method thereof are provided. If an acoustic signal exceeds a dynamic range, a gain of the acoustic signal can be automatically attenuated based on a pre-set limit level to minimize a distortion of the acoustic signal caused by clipping of the acoustic signal and limit an over-input so as to input the acoustic signal within the dynamic range. Thus, an original form of an over-input signal on a specific level or more can be maintained but only a gain of the over-input signal can be attenuated. As a result, a distortion of an output waveform caused by clipping of the output waveform can be minimized, and a harmonic distortion and a stepped high frequency noise occurring during clipping can be simultaneously removed.

An input signal (IN) and a threshold signal (Vt) are coupled to an output terminal (2) via the base-emitter paths of first (Q1) and second (Q2) transistors having respective collector electrodes connected to a supply voltage source (3). The output terminal (2) is coupled to a source of reference potential (4) via a first resistor (Re) and is coupled via a second resistor (Rd) to a selected plate of a capacitor (C1) that is connected between the collector and base electrodes of the second transistor (Q2). Circuit impedances are scaled such that Re>Rd>R1 wherein Re and Rd are the values of the first and second resistors, respectively, and R1 is a component of the output impedance of the threshold signal source (5).