Stmicroelectronics Gmbh

Sgs-thomson Microelectronics Limited

Jorg Schambacher

Peter Kirchlechner

Jurgen Lubbe

A method for offset compensation of a signal processing circuit in whose signal path a circuit configuration with offset is disposed, wherein the circuit configuration with offset is temporarily decoupled from the signal path of the signal processing circuit and meanwhile held strictly in a dc mode; a compensating dc voltage is added to the output dc voltage occurring at the output of the circuit configuration with offset in the dc mode, said compensating dc voltage being varied until the cumulative value of output dc voltage and compensating dc voltage has became zero; the circuit configuration with offset is then coupled into the signal path again; and

Method and apparatus for offset compensation of a signal processing

An audio signal processor is disclosed which has at least one audio signal input and at least one audio signal output as well as at least one control input, and an audio signal processing unit connected between audio signal input and audio signal output, the audio signal processing unit having a programmable indicator tone generator circuit to be driven via the control input and whose indicator tone signal is switched to the audio signal output in accordance with the state of the control input.

Audio signal processor

For eliminating the emphasis given an audio signal in the transmitter, an audio signal processor of an audio device (e.g., a car radio) contains a low-pass filter. In order to attenuate the spurious higher-frequency signal fractions in case of poor reception and accordingly low received field strength, the cutoff frequency of the low-pass filter is shifted in the direction of lower frequencies in accordance with a received field strength signal when the field strength becomes lower. In order to avoid external adjusting components and save pins on the IC chip, the field strength signal is supplied to an analog-to-digital converter and the latter supplies a digital signal to a low-pass filter whose cutoff frequency is variable. For this purpose the low-pass filter contains a number of integrated components one of which is connected or disconnected by a digit place of the digital signal in each case.

Device for varying the cutoff frequency of a low-pass filter

An electric signal processing circuit with an operational amplifier having a signal input, a feedback input and a signal output, and a nonlinear circuit device having a characteristic with a distortion-producing nonlinearity and located in the input signal circuit or in the feedback circuit of the operational amplifier, wherein a compensating circuit device having a characteristic with generally the same nonlinearity as the characteristic of the nonlinear circuit device is disposed in the feedback circuit or in the input signal circuit of the operational amplifier for compensating the distortion of the nonlinear circuit device.

Nonlinearity compensation in an electric signal processing circuit

A filter circuit adjustably decreases or increases the amplitude of audio signals in a predetermined frequency range. The filter circuit includes a filter module having an RC network with at least one frequency-response-determining RC member whose resistor component R is realized in SC technology. A setting device is connected to the filter module such that its setting determines the frequency response of the SC filter. The setting device renders possible a neutral setting in which the effective audio signal path of the filter circuit circumvents the filter module so that no decrease or increase of the amplitude of individual frequency portions takes place. Furthermore, an audio signal processor comprises at least one audio signal input, at least one audio signal output, and at least one control input. The audio signal processor also comprises an audio signal processing unit connected between the audio signal input and the audio signal output, with the audio signal processing unit having at least one such filter circuit.

Filter circuit and audio signal processor provided therewith

In a stereo decoder, channel separation takes place with the aid of a demodulator to acquire signals for stereo operation. At low received field strength there is a continuous switchover to mono operation for each channel in the demodulator. For this purpose a switch is located in a signal path between input and output of the demodulator and driven by a PWM signal whose pulse-width repetition rate determines whether solely mono operation, solely stereo operation or a mixture of the two takes place. For generating the PWM signal, the field strength signal is compared with a triangular signal. To permit the switchover points between stereo and mono operation to be aligned by the manufacturer in accordance with the amplitude of the field strength signal, the apparatus contains two limit storage registers in which digital limit signals are set from outside. These limit signals are converted by a digital-to-analog converter into analog voltages which fix upper and lower limits the triangular signal, thereby determining the behavior of the triangular signal and thus also the pulse-width repetition rate of the PWM signal in accordance with the field strength signal.

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Munchen, Germany

Jorg Schambacher