Hearing aid with an H-bridge output stage and a method of driving an output stage

Abstract

A digital, three-level output driver ( 7 ) of the H-bridge variety for a hearing aid ( 20 ) obtains a reduced capacitive interference by providing a primary voltage ( 3 ) and a secondary voltage ( 8 ) for the output driver ( 7 ) and applying the secondary voltage ( 8 ) to both sides of the output driver ( 7 ) whenever the middle level of the three-level output driver ( 7 ) is present in the input signal for the output driver ( 7 ). The output driver ( 7 ) may be controlled from a pulse-width modulated signal, a sigma-delta pulse-density modulated signal, or a combination of those signals. The output driver ( 7 ) produces a clocked output signal consisting of a positive level, a negative level, and a zero level for driving an acoustic output transducer of the hearing aid ( 20 ). The invention provides a hearing aid ( 20 ) and a method of driving an output stage ( 7 ) of a hearing aid ( 20 ).

We claim: 
     
       1. A hearing aid comprising an input transducer, an analog-to-digital converter, a digital signal processor, a three-level output modulator connected to a three-level output driver, a first voltage source providing a first voltage, a second voltage source providing a second voltage different from said first voltage, a common voltage node and an acoustic output transducer, wherein the output driver comprises an H-bridge output stage configured to control the connection of a first and a second terminal of the acoustic output transducer, the H-bridge being configured to connect the first voltage source to the first terminal of the acoustic output transducer and the common voltage node to the second terminal of the acoustic output transducer when the output modulator generates a first level, to connect the second voltage source to both the first and the second terminal of the acoustic output transducer when the output modulator generates a second level, and to connect the first voltage source to the second terminal of the acoustic output transducer and the common voltage node to the first terminal of the acoustic output transducer when the output modulator generates a third level. 
     
     
       2. The hearing aid according to  claim 1 , wherein the second voltage source is configured to provide a voltage level of substantially half the voltage level of the first voltage source. 
     
     
       3. The hearing aid according to  claim 1 , wherein the output modulator is a sigma-delta modulator. 
     
     
       4. The hearing aid according to  claim 1 , wherein the output modulator is a pulse-width modulator. 
     
     
       5. The hearing aid according to  claim 1 , wherein the output modulator is a combined pulse-width modulator and sigma-delta modulator. 
     
     
       6. A method of driving an output stage of a hearing aid, said method comprising
 providing a single-bit digital signal representing an audio signal to be reproduced by the hearing aid, 
 providing a first voltage source for generating a first voltage, 
 providing a second voltage source for generating a second voltage different from said first voltage, 
 providing an acoustic output transducer, 
 converting the single-bit digital signal into a three-level control signal comprising a positive level, a negative level, and a zero level, 
 connecting the first voltage source to a first terminal of the acoustic output transducer, and connecting a second terminal of the acoustic output transducer to ground, whenever the control signal produces a negative level, 
 connecting the first voltage source to the second terminal of the acoustic output transducer, and connecting the first terminal of the acoustic output transducer to ground, whenever the control signal produces a positive level, and 
 connecting the second voltage source to both the first terminal and the second terminal of the acoustic output transducer whenever the control signal produces a zero level. 
 
     
     
       7. The method according to  claim 6 , wherein the voltage level of the second voltage source is substantially half the voltage of the first voltage source. 
     
     
       8. The method according to  claim 6 , wherein the connections controlled by the control signal are provided by semiconductor elements. 
     
     
       9. The method according to  claim 6 , wherein the voltage of the second voltage is derived from the first voltage. 
     
     
       10. An output driver receiving a three-level bit stream as input and driving an acoustic output transducer, and comprising:
 a first voltage source, 
 a second voltage source configured to provide a voltage level of substantially half the voltage level of the first voltage source, 
 a common voltage node, and 
 an H-bridge output stage configured to control the connection of a first and a second terminal of the acoustic output transducer, the H-bridge being configured
 to connect the first voltage source to the first terminal of the acoustic output transducer and the common voltage node to the second terminal of the acoustic output transducer when the output modulator generates a first level, 
 to connect the second voltage source to both the first and the second terminal of the acoustic output transducer when the output modulator generates a second level, and 
 to connect the first voltage source to the second terminal of the acoustic output transducer and the common voltage node to the first terminal of the acoustic output transducer when the output modulator generates a third level.