Dialog Semiconductor Gmbh

Edgar Sexauer

Klaus Graef

Gary Hague

Markus Engelhardt

A circuit, which is enabling the superpositioning of different audio signals such as voice, music or ringer signals in a audio output device is achieved. The individual superpositioning can be activated and performed by a combination of resistors and switches without the need of an additional mixing amplifier as in prior art. One common output stage is used for all the signals activated and superpositioned. The adjustment of the amplitude of the output signal, which can be used for the volume adjustment of a loudspeaker, is provided by a precise amplitude setting via the gain control stages of an inverting voltage amplifier through a current-voltage conversion. Said current-voltage conversion is performed by a string of resistors activated by a string of correspondent switches. This circuit reduces the power consumption, the chip area required and the offset and improves the power supply rejection rate (PSSR).

Audio superpositioning

A circuit where the same amplifiers and the same volume adjustment circuitry are used for the ringer mode as well as for the audio mode of a mobile phone is achieved. The volume adjustment in the audio and ringer mode is provided by a precise amplitude setting via the gain control stages of an inverting voltage amplifier used in a bridge circuit through a current-voltage conversion. This volume adjustment circuit avoids the high power dissipation of a volume control through pulse width modulation (PWM) and avoids the risk of over-and undershooting of the amplifier's output signal due to a high slew rate in combination with the inductance of the loudspeaker. The current-voltage conversion is performed by a series of resistors activated by a series of correspondent switches. High impedance current less sense paths are eliminating the parasitic effect of the resistance of low cost standard switches to adjust the volume of the loudspeaker in the audio and the ringer mode.

Combine audio and ringing mode

A system and methods to convert a digital bit stream to analog values without previous knowledge of the sample rate of the incoming digital bit stream has been achieved. The system comprises a sample rate measurement device being able to measure the sample rate out of the incoming digital bit stream. Another device is removing all bits, which are not required for the digital to analog conversion from the incoming bit stream. The measured and calculated sample rate is added to the 'cleaned' bit stream and a digital to analog conversion device is performing the conversion using the sample rate which has been added to the bit stream.

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Stuttgart, Germany

Edgar Sexauer