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).

Description

RELATED APPLICATIONS[0001]The present application is a continuation-in-part of application PCT / EP2011052887, filed on 28 Feb. 2011, in Europe, and published as WO 2012116720 A1.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This application relates to hearing aids. More specifically, it relates to hearing aids comprising digital output stages for driving acoustic output transducers. The invention further relates to a method for driving a digital output stage of a hearing aid.[0004]In this context, a hearing aid is defined as a small, battery-powered device, comprising a microphone, an audio processor and an acoustic output transducer, configured to be worn in or behind the ear by a hearing-impaired person. By fitting the hearing aid according to a prescription calculated from a measurement of a hearing loss of the user, the hearing aid may amplify certain frequency bands in order to compensate the hearing loss in those frequency bands. In order to provide an accurat...

AI Technical Summary

Benefits of technology

[0018]It is a feature of the present invention to devise an output stage for a hearing aid having an output converter capable of providing the benefits of a three-stage output converter without having the capacitive noise and interference problems associated with output converters of the prior art, regardless of having long wires connecting the output stage to the loudspeaker of the hearing aid.

Problems solved by technology

However, it also has some inherent drawbacks, which will be explained in greater detail in the following.

This radiation results in increased crosstalk to nearby surroundings, such as telecoils or wireless transmission receiver coils typically present in the hearing aid.

The wireless receiver coil, however, suffers a very considerable reduction in signal-to-noise ratio from the capacitive interference resulting from this crosstalk phenomenon, often to a degree where reliable signal reception becomes impossible.

This capacitive interference emanates mainly from electrically exposed parts of the output circuit, primarily the wires connecting the output pads of the electronic circuit chip of the hearing aid to the input terminals of the acoustic output transducer.

The voltage pulses are presented to the output transducer at a frequency of 1-2 MHz, and the resulting noise components may thus disturb the operation of electronic circuits sensitive to capacitive interference at high frequencies.

In cases where the afflicted electronic equipment incorporates a wireless remote control for the hearing aid the problems caused by electromagnetic interference are exceptionally severe, as the effective operating range of the wireless remote control is limited considerably by the capacitive interference emanating from the output stage and masking the remote control signals from proper reception.

If, for example, a hearing aid housing and circuitry may be adapted for use with a range of different loudspeakers having different impedance values, e.g. for treating different degrees of hearing loss, a loudspeaker having an integrated output driver would not be well suited for this configuration.

In cases where this type of flexibility is desired, long wires between the output stage terminals of the hearing aid circuit and the terminals of the loudspeaker of the hearing aid are unavoidable.

An extra set of long wires for the signal from the loudspeaker to the feedback circuit would also be required by the prior art output driver, which would further increase capacitive interference noise.

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