Microphone Preamplifiers for Hearing Aids
A microphone pre-amplifier boosts signals, typically to line-level (the level needed to transmit analog signals point-to-point, between devices.) Further amplification may be necessary. The noise performance of a pre-amp is critical since the final signal-to-noise ratio of downstream amplifiers can be magnified. For an audio input application, such as microphones, the pre-amp is physically mounted near the sensor that feeds it, to reduce noise and interference.
Audio Codecs for Hearing Aids
A codec is a device that can encode and/or decode a digital data signal. A codec encodes data for transmission and/or decodes it for playback. Essentially, a codec has one or more Digital-to-Analog data converters (DAC) and Analog-to-Digital converters (ADC) in a single package. A codec is essential for the use of Digital Signal Processors (DSPs) in audio applications, since it can convert real-world analog signals (like sound) to digital signals for the DSP, and back again from digital to analog for the human ear.
Audio Amplifiers for Hearing Aids
A power or audio amplifier is typically used to greatly increase the signal strength, or amplitude, of a current or voltage signal. In audio applications, late stage "power" amplifiers in a signal chain can be used to increase the power output of a signal such that the signal can physically move, or drive, the diaphragms in a loud speaker.
DSPs for Hearing Aids
A digital signal processor (DSP) is a specialized microprocessor usually with a modified Harvard architecture and a single cycle multiply-and-accumulate required for the fast operational needs of processing and for mathematically manipulating real-world signals like voice, audio, and video. In a noise cancellation application, the DSP examines the characteristics of the input noise waveform. The DSP then generates the anti-noise waveform which effectively negates the input noise waveform. The human ear then hears less "white" noise as the cancellation occurs in real, or near-real time.
RF Interfaces for Hearing Aids
An RF, or Radio Frequency interface, is a wireless method to transmit information via high frequency radio waves, through the air. Wireless technology enables the transfer of information over short or very long distances without cables. Wireless communication is possible using a wireless transmitter and corresponding receiver. If both devices are in the same package it is called a transceiver. A wireless receiver refers to the receiving end of the information transfer and requires less energy to operate than the active transmitting portion where the transfer originates.
Power Management for Hearing Aids
Power management for a hearing aid is a crucial technology element. Size must be as small as possible and nothing can produce heat that will injure the wearer. Power management objectives include: small size, low heat, ultra low power so the device is long lasting on a single coin-sized battery, and overall reliability and low noise introduction from collective systems.
AC/DC Adapters for Hearing Aids
An AC/DC adapter is a type of external power supply, often enclosed in what looks like an over-sized AC wall-plug. Other names include power adapter, power converter, plug-in adapter, adapter block, domestic mains adapter, line power adapter, or simply AC adapter. AC adapters are used with electrical devices that require DC power but do not have the internal circuitry to accomplish the conversion of AC to DC. Medical-grade power supplies are designed to meet the IEC60601-1 medical equipment safety standard and may include typical output voltages of 3.3 to 48 Vdc, a variety of package style (open-frame, enclosed, encapsulated, etc.), mounting options, thermal management, and environmental features, among others.
Battery Chargers for Hearing Aids
Battery charging circuits are used to recharge batteries and are available in linear or switching topologies. They can be completely autonomous in operation or used with a microcontroller. Generally speaking, integrated chip charging technology can produce charge currents in a range from around 625 nA, up to around 4.5A. Battery charger ICs often do more than just charge; they can protect from overcharging, regulate voltage, and manage charging from irregular sources such as energy harvesters or very low voltage sources. In portable technology, battery chargers are indispensable.
Fuel Gauges for Hearing Aids
A battery fuel gauge, or state-of-charge (SOC) indication, has evolved from a simple warning to a more complex system level use of the information, such as soft shutdown to prevent data loss. Considerations that affect accurate accounting for remaining battery charge include the effects of aging, self discharge and temperature variations. The value for full capacity is obtained and algorithms are used to calculate the remaining capacity. The drawback of this approach is that self-discharge is difficult to model since it is a function of aging and temperature.