Audio superpositioning

#(1) Field of the Invention

#The invention relates to a audio output device circuit, and more particularly, to superpositioning of different audio input channels as voice, music and ringer signals wherein said different audio signals are using a common output stage and can be heard together or separately as required.

#(2) Description of the Prior Art

#In the accompanying drawings forming a material part of this description there is shown:

#FIG. 1 Prior art illustrates a typical circuit for superpositioning of 2 different audio signals.

#FIG. 2 illustrates a schematic illustration of a receive path of a wireless phone.

#The preferred embodiments disclose a novel circuit enabling the superpositioning of different audio signals in the signal processing module of a audio output device as e.g. mobile phone. FIG. 2 shows a schematic illustration of a receive path of a mobile phone. In the shown conception of an embodiment the receive path of a mobile phone comprises the antenna 20, an RF receiver 21, a signal processing module 22 and a speaker 23. Said novel circuit of the invention enabling the superpositioning of audio signals is located in said signal processing module 22.

#FIG. 3 illustrates a preferred embodiment of the invention. 31 and 32 represent two different audio input signals as e.g. music and voice, 33 and 34 represent a pair of parallel resistors, in an actual embodiment they have a resistance in the magnitude of 10 KΩ. A pair of parallel switches 35 and 36 can activate either one or both of said input audio signals. The input signal xx, the resistor yy and the switch zz represent a multitude of possible input stages of any number. In one implementation three input stages are being used for speech, music and any other audio sequence. Said three input stages can be activated at the option of the user of said audio output device. The resistance of the switches being typically in the magnitude of 100-150 Ω is small compared to the resistance of said entry resistors. The point 37 is the summation point of the different input signals for superpositioning. The resistor 38 is the entry resistor of the output stage.

#The string of resistors 41 and the string of switches 42 shown in FIG. 3 represent a multitude of n resistors and related switches used for the amplitude setting of the output signal 43. Said number n of resistors and switches is much higher in reality than shown in FIG. 3. The output stage is comprising said string of resistors 41, a correspondent string of resistive gain switches 42, an inverted amplifier 40, a reference voltage 44 and the output voltage 43. Said output voltage can drive a loudspeaker (not shown in the drawing). One resistive gain switch 42 is assigned to each resistor 41.