EP1695592B1

EP1695592B1 - Integrated circuit for hearing aids including a magnetic field sensor

Info

Publication number: EP1695592B1
Application number: EP03819164A
Authority: EP
Inventors: Steven E. Boor; Paris Tsangaris
Original assignee: Knowles Electronics LLC
Current assignee: Knowles Electronics LLC
Priority date: 2003-12-16
Filing date: 2003-12-16
Publication date: 2011-04-13
Anticipated expiration: 2023-12-16
Also published as: CN1887028A; AU2003297233A1; WO2005062669A1; DK1695592T3; DE60336766D1; EP1695592A1

Abstract

A system and method for assisting listening wherein an integrated circuit selects one or more audio sources from among a plurality audio sources to be presented to a signal processing circuit. Selection of the audio source can be automatically executed in response to detection of an external magnetic field, such as from a telephone handset, or manually controlled by a user input.

Description

Technical Field

This patent relates to assisted-listening systems. More specifically, this patent relates to an integrated circuit for an assisted-listening device capable of determining and adapting to surrounding environmental conditions.

Background

Assisted-listening devices, e.g. hearing aids and the like, should be capable of operating in, and being adaptable to, several environmental conditions. For example, the assisted-listening device should be capable of automatically selecting amongst various audio sources, e.g., telecoil, microphone, or auxiliary. One commercially available hearing aid utilizes a magnetic reed switch to provide magnetic field detection and automatic transducer mode selection. Unfortunately, there are a number of limitations associated with utilizing the magnetic reed switch. Frequently, the reed switch lacks the sensitivity to operate with many types of telephones and often requires placing an external magnet onto the telephone handset earpiece. Additionally, the reed switch requires use of a portion of the communicate device, such as a very limited space within the hearing aid. Furthermore, the reed switch may be susceptible to damage or performance changes if the hearing aid is dropped or subjected to extremely high magnetic fields - thus undermining the effective reliability of the assisted-listening system. Another shortcoming involves the added costs that are incurred to implement the reed switch into the assisted-listening system due to the additional components and manufacturing effort required.
US - A - 20030059073 describes the coupling of multiple sources which are directed to a signal processing unit by the operation of a switch.

Brief Description of the Drawings

FIG. 1 is a schematic block diagram of an integrated circuit in accordance with one of the described embodiments;
FIG. 2 is a schematic block diagram of an integrated circuit in accordance with another of the described embodiments; and,
FIG. 3 is a schematic block diagram of an integrated circuit in accordance with still another of the described embodiments.

Detailed Description

The present invention is defined by the appended claims.
The output of the magnetic field threshold comparator may comprise a first signal and a second signal and be determined in response to the comparison of the sensed external magnetic field and the magnetic field threshold value wherein the first signal is presented to the signal processing circuit when the magnetic field threshold value exceeds the sensed external magnetic field and the second signal is presented to the signal processing circuit when the sensed external magnetic field exceeds the magnetic field threshold value.
Although the following text sets forth a detailed description of numerous different embodiments of the invention, it should be understood that the legal scope of the invention is defined by the words of the claims set forth at the end of this patent.
FIG. 1 depicts an integrated circuit 10, shown in dotted lines, operably disposed between a plurality of audio sources 13 and a signal processing circuit 14. H The integrated circuit 10 includes a magnetic field sensor 16, a magnetic field sensor amplifier 17 and a gate 18. The gate 18, preferably a multiplexer, is operably responsive to the output from the magnetic field sensor amplifier 17. The magnetic field sensor 16 may include a threshold comparator 26 wherein detection of a magnetic field is based upon whether the magnetic field strength detected is above or below a threshold level. The threshold level 19 can be fixed or adjustable. The magnetic field sensor amplifier 17 provides an output signal to the gate 18 to ensure desired operation.
The gate 18 includes a plurality of inputs 20 for receiving the outputs of transducers or auxiliary audio sources, e.g., magnetic (telecoil) 12 via coupled magnetic telecoil amplifier 28, acoustic (microphone) 13. A gate output 22 is coupled to the signal processing circuit 14 wherein one of the plurality of inputs 20 is selected to be output to the signal processing circuit in response to detection of an external magnetic field.
FIG. 2 depicts an alternate embodiment of an integrated circuit 10'. Circuit design preferences, manufacturing constraints, etc., are only a few of the many parameters that may influence whether certain devices, e.g., gate 18, are to be included in the configuration of the integrated circuit.
The integrated circuit 10' includes a magnetic field sensor 16' that integrates therewith the magnetic field sensor amplifier 17'. An output of the magnetic field sensor 16' is coupled to a threshold comparator 26 which also couples threshold value input 19'. The output of the threshold comparator 26 is then coupled to the gate 18. The threshold level again may be fixed or adjustable. FIG. 3 depicts an alternate embodiment of an integrated circuit 10" including a magnetic field sensor 16" having a magnetic field sensor amplifier 17", similar to that illustrated in FIG. 2 as integrated circuit 10'. As shown in FIG. 3, signal shaping devices 29, e.g., biasing elements, amplifiers, filters, rectifiers, etc., and other circuit devices may also be incorporated in the design of the integrated circuit 10".
The embodiments of the integrated circuit 10, 10' and 10" include a manual override 24, which allows one or more than one of the plurality of inputs 20 to be manually selected and presented to the signal processing circuit 14.
Several techniques may be utilized to detect the presence of the external magnetic field - often referred to as a B-field - for the control of the gate 18, e.g., microphone-telecoil multiplexer (MT MUX) in presenting a signal to the signal processing circuit 14. Some B-field detection methods include, but are not limited to:

Detection of a static B-field above or below a certain threshold level (the detection level can be hysteretic to guard against oscillatory behaviour);
detection of the AC EMF generated by the telecoil when merely bringing the telephone handset into close proximity of the telecoil;
detection of the AC EMF generated by the telecoil in response to the audio signal transmitted by a telephone handset or a room loop; or,
any combination of the above.

The static B-field detection method may be preferred because it is more robust in the presence of electromagnetic interference (EMI) - either environmental or man-made. The other external B-field detection methods are susceptible to "false" B-field detection from EMI, which may result in an undesirable transducer mode selection change that would require user intervention to correct. Although all three detection methods may initially respond unfavorably to EMI, the first method is capable of automatically reverting back to proper transducer mode operation without user intervention once the EMI event has subsided.
Another advantage of the static B-field detection method is that it can be configured with amplifiers which operate only at low frequencies, i.e., a very low bandwidth requirement, on the order of 10 Hz. This is very advantageous for the development of a detector and control circuit which operate with minimum power consumption.
There are several possible semiconductor, e.g., solid-state silicon, devices that could be utilized as detectors for the static B-field of a telephone handset. The silicon external B-field detectors may include: a lateral bipolar magnetotransistor (LBMT), a split-drain MAGFET, or a micro-electromechanical system (MEMS) type device. A standard Hall effect sensor may also be utilized.
Advantages of using the LBMT are: it is a very sensitive silicon device for the detection of B-fields; it is less noisy than the MAGFET device; and, it detects B-fields that are tangential to the silicon surface - which would be in the same direction as the maximum sensitivity of the telecoil, when using standard mounting methods to attach the IC to the body of the telecoil. Unlike the LBMT, the MAGFET and standard Hall effect sensor are sensitive to B-fields that are perpendicular to the silicon surface. This is a potential disadvantage for the LBMT that may require non-standard mounting techniques to attach the IC to the telecoil body to ensure that the telecoil has the same maximum B-field sensitivity orientation direction as the sensor device.
For assisted-listening device applications, power consumption of the B-field sensor should be 100 microwatts or less to extend the battery life of the hearing aid as much as possible. At this power level, it is possible that the MAGFET may also provide adequate sensitivity for use as a B-field sensor since LBMTs are routinely operated at milliwatt power levels to obtain high B-field detection sensitivity. However, the LBMT could be operated at a low duty cycle to save power, since the B-field detection circuitry does not require continuous operation.
Because both the LBMT and the split-drain MAGFET can be utilized to generate a differential current output that is proportional to the B-field strength, either device could be readily integrated into the same silicon integrated circuit with a telecoil preamplifier commonly incorporated in assisted-listening devices. The other amplifier circuitry needed to convert the detector differential current output into a digital signal — utilized to control the transducer selection mode needed for MT MUX operation — could also be easily integrated into the same silicon IC with all of the above circuitry. Note that a standard Hall effect sensor operates in voltage mode, so an alternative voltage based signal processing architecture would be necessary to generate the desired control signal for MT MUX operation.
In addition, an override switch can be utilized to control MT MUX operation and provide a user the ability to manually select a mode of operation that allows both the telecoil and microphone outputs — or other audio sources — to be presented simultaneously to the signal processing circuit of an assisted-listening device. This feature is desirable in listening environments such as churches, auditoriums, and classrooms that are often wired with magnetic room loops to assist the hearing impaired wherein hearing aid users can simultaneously utilize the magnetic and the acoustic audio information supplied in these situations.
As discussed above, many of the limitations of today's assisted-listening devices are addressed by the described embodiments. For example, each of the embodiments is capable of being readily incorporated with telecoil preamplifier electronics in "active telecoil" transducers at very low cost onto the same integrated circuit. Additional benefits that may include:

providing the ability to automatically detect whether a telephone handset is in close proximity;
providing the ability to automatically select the appropriate audio source, i.e., microphone output, to be output to the signal processing circuitry of an assisted-listening device when the external magnetic field strength is less than a predetermined threshold level;
providing the ability to automatically select the appropriate audio source, i.e, telecoil output, to be output to the signal processing circuitry of an assisted-listening device when the external magnetic field strength is greater than a predetermined thresholds level;
providing improved assisted-listening device reliability through an integrated circuit design that is more resilient and less susceptible to damage or performance shifts;
efficiently utilizing existing available space within the assisted-listening device; and,
reducing the complexity and cost of the assembly process for assisted-listening device manufacturers by reducing the number of device components.

Claims

An integrated circuit (10) for being operably disposed between a plurality of audio sources (12, 13) and a signal processing circuit (14), the integrated circuit (10) comprising:
a magnetic field sensor (16) selected from one of a lateral bipolar magnetotransistor, a split-drain MAGFET, a Hall effect sensor or a micro-mechanical system (MEMS) device;

a magnetic field threshold comparator (26) and a magnetic field threshold value (19), the magnetic field threshold comparator (20) being operably coupled to the magnetic field sensor (16) and the magnetic field threshold value (19);

a gate (18) being operably responsive to the magnetic field threshold comparator (26), the gate (18) including a plurality of gate inputs (20) and a gate output (22), the plurality of gate inputs (20) for receiving respective ones of the plurality of audio sources (12, 13), and the gate output (22) for being operably coupled to the signal processing circuit (14), wherein one of the plurality of audio sources (12, 13) is selected to be fed to the signal processing circuit in response to the magnetic field threshold comparator output characterized in that the integrated circuit further comprises a manual override (24), operable to couple one or more of the plurality of audio sources to the signal processing circuit, and wherein the magnetic field sensor (16) has a power consumption of substantially 100 µ W or less.
A circuit including the integrated circuit (10) of Claim 1 and a signal shaping device (29) selected from the group consisting of biasing, amplifying, filtering, and rectifying devices to which the integrated circuit is coupled.