Abstract: An audio system including an audio power amplifier, a transducer electrically connected to the audio power amplifier, an enclosure coupled to the transducer, and a secondary resonant element coupled to the enclosure. An electrical feedback signal representative of the transducer current is negatively fed back to the audio power amplifier to synthesize a positive output impedance.

Abstract: A microphone unit includes a substrate. The substrate includes a first face formed with a first recess, a second face opposite to the first face, and a through hole communicating the second face to a bottom part of the first recess. A diaphragm unit includes a diaphragm, and at least a part of which is disposed in the first recess so that the diaphragm opposes the through hole.

Abstract: System for pulse-width-modulated class D audio amplifiers. In one preferred embodiment an adder is described to generate a difference signal responsive to an input signal and a feedback signal, a pulse-width-modulator coupled to the adder to compare the difference signal to a reference signal and produce a pulse-width-modulated signal based on the comparing, a filter coupled to an output of the pulse-width-modulator, and a loop filter having a first input coupled to the output of the filter and a second input coupled to the input of the filter, the loop filter to generate a feedback signal by applying transfer functions to signals at its inputs. The loop transfer function of the amplifier is minimum aliasing error transfer function. The minimum aliasing error properties provide low distortion and taking the feedback from the output of the filter reduces high frequency output impedance.

Abstract: To efficiently obtain two outputs including one at a normal level and the other at an excessive level. An input signal input to the negative input terminal of an operational amplifier (14) having a negative feedback path is amplified to output an output signal. Signal combining units (18, 20, 22) are provided for adding in a weighted manner a negative input terminal side signal obtained by combining the input signal input to the negative input terminal of the operational amplifier (14) and a feedback signal from the negative feedback path and the output signal from the operational amplifier to output a combined signal, so that two signals, namely the output signal from the operational amplifier (14) and the combined signal, are obtained.

Abstract: Distortion caused in the voltage of an audio signal due to a back electromotive force generated due to loads in a speaker is detected, the detected distorted voltage is eliminated from the voltage of the audio signal, and the audio signal without the distorted voltage is amplified and given to the speaker.

Abstract: Disclosed are a sound card and a method for limiting inputs to and outputs from that computer sound card. Specifically, the voltage of a feedback connection between the input and output of a sound card amplifier is increased from minimum voltage until an over-saturation condition occurs. This finds the “output voltage limit.” Thereafter, the output voltage of the amplifier is restricted to the output voltage limit. The feedback connection is then terminated and the voltage of the signal being supplied to the amplifier is increased from minimum voltage until the over-saturation condition again occurs. This finds the “input voltage limit.” Thereafter, the input supplied to the amplifier is restricted to the input voltage limit.

Abstract: A self-biased electrecret microphone amplifier with phantom biasing is using only standard devices implemented in a digital Complementary Metal Oxide Semiconductor (CMOS) process. The stable gain is provided open loop with a self-biased linear transconductance amplifier device that does not require large external components for filtering.

Abstract: An audio processing system is provided. The audio processing system comprises a transducer, a gain stage, a capacitor network, and a preamplifier. The transducer transduces a sound signal to a voltage signal. The gain stage comprises an input coupled to the transducer and an output. The capacitor network, coupled between the output of the gain stage and the transducer, provides an equivalent capacitance. The preamplifier coupled to the transducer amplifies the voltage signal.

Abstract: An ear tip for a sound device. The ear tip has an asymmetrical arrangement which more closely aligns with a user's ear canal. The ear tip includes an ear tip base, ear tip shaft, and a first group of low-profile flanges. The ear tip is arranged along an ear tip central axis. The ear tip has a sound tube connection and a sound channel which extends through the ear tip base and ear tip shaft. The first group of low-profile flanges are spaced along an ear tip shaft axis, and extend radially from the ear tip shaft in perpendicular alignment to the ear tip shaft axis. A first flange, a second flange and an intermediate flange are provided. Each flange is constructed of a flat roof with a downwardly transitioning radial wall. There is a space between each of the flanges. The flanges seal against the ear wall to attenuate sound and reduce resonance.

Abstract: An audio system performing a class-D amplification includes a first pulse width modulation (PWM) signal generation unit and a second PWM signal generation unit. The first PWM signal generation unit generates a first switching signal based on a first audio signal. The second PWM signal generation unit generates a second switching signal based on a second audio signal. The second switching signal has a frequency difference with respect to the first switching signal such that a harmonic frequency component generated by interference between the first switching signal and the second switching signal is removed. Accordingly, the audio system performing the class-D amplification may improve a signal to noise ratio by minimizing influence of the harmonic frequency components on the first and second switching signals.

Abstract: An n-channel integrated circuit device (n is an integer of 1 or greater) for muting an audio signal includes a control circuit configured to generate a control signal and a delayed control signal, a charging and discharging circuit configured to charge and discharge a time constant control terminal according to the control signal and the delayed control signal, an N-th voltage-to-current converting circuit (N is an integer from 1 to n) configured to generate a (2N?1)-th current corresponding to a voltage on the time constant control terminal and a (2N)-th current corresponding to an intermediate voltage, a (2N?1)-th mirror circuit configured to copy the (2N?1)-th current to generate (4N?3)-th and (4N?2)-th intermediate currents, a (2N)-th mirror circuit configured to copy the (2N)-th current to generate (4N?1)-th and (4N)-th intermediate currents, a (2N?1)-th selecting and combining circuit configured to combine a (2N?1)-th mute control current using the (4N?3)-th intermediate current and the (4N?1)-th interm

Abstract: Various embodiments of the present invention are directed to methods and systems that reduce acoustic echoes in audio signals in accordance with changing conditions at first and second locations that are linked together in a communication system. In one embodiment of the present invention, a first digital signal encoding sounds produced at the first location is output from the first location, and a second digital signal encoding an acoustic echo and sounds produced at the second location is output from the second location. The method computes a control state that depends on the signals transmitted between the first and the second locations and computes an approximate acoustic echo based on the control state.

Abstract: An operational amplifier capable of compensating offset voltage includes an input stage circuit having a positive input end, a negative input end, a first current output end, and a second current output end, for outputting current corresponding to voltage received by the positive and negative input ends, an output stage circuit coupled to the first current output end and the second current output end of the input stage circuit, for outputting voltage according to current outputted from the first current output end and the second current output end, and an trimming device coupled between the input stage circuit and the output stage circuit, for adjusting current of the first current output end or the second current output end for compensating offset voltage.

Abstract: An audio output circuit includes an on-chip left channel amplifier module, an on-chip center channel amplifier module, and an on-chip right channel amplifier module. A left channel IC pin is operably coupled to an output of the on-chip left channel amplifier module. A right channel IC pin is operably coupled to an output of the on-chip right channel amplifier module. A center channel IC pin is operably coupled to an output of the on-chip center channel amplifier module. A center channel feedback IC pin is operably coupled to an input of the on-chip center channel amplifier module to provide a feedback loop. A left jack connection is operably coupled to the left channel IC pin. A right jack connection is operably coupled to the right channel IC pin. A jack return connection coupled to the center feedback IC pin. An inductor has a first node coupled to the jack return connection and a second node coupled to the center channel IC pin.

Abstract: Direct current (DC) offset in and audio driver can cause a constant drain on power even when there is no sound. Furthermore it can cause an audible pop when the audio driver is enabled. A scaled replica output stage can be employed to perform DC offset cancellation offline during a sampling phase. Once DC offset cancellation is achieved, the audio driver uses a full scale output stage during the operation phase.

Abstract: The invention concerns an audio system comprising a microphone, audio signal processing means, an output transducer and mans for detecting a possible feedback tone and the corresponding frequency of the feedback tone in the audio system between the output transducer and the microphone. According to the invention means for counteracting feedback are provided. Further, mans are provided for changing the phase of the audio signal at a given frequency.

Abstract: A speaker system for a musical instrument that detects the displacement of a voice coil of a speaker and provides feedback processing. The speaker system has a preamp that alters the frequency characteristics of the an electrical signal that has been input to an input terminal, and a power amplifier that amplifies the electrical signal. A speaker is driven by the power amplifier and a feedback unit detects the displacement of the speaker and provides a feedback signal to the power amplifier. The power amplifier amplifies the electrical signal in conformance with the output of the preamp and the feedback signal.

Abstract: An audio processing apparatus includes an amplification unit to receive and amplify an audio signal, a power source unit to provide power source to the amplification unit, and a signal processing unit to adjust the power source level provided to the amplification unit based on audio signal level and power source level. Accordingly, high-quality audio may be reproduced.

Abstract: There is provided an audio amplifier circuit (200), comprising: an input, for receiving an input signal; an amplifier (205) for receiving a modified input signal and outputting an amplified signal; and a feedback loop (245) comprising digital circuitry for feeding back the amplified signal and combining a feedback signal with the input signal to generate the modified input signal. The feedback loop (245) comprises: a low-pass filter (220) for filtering the amplified signal; a comparator (225) for comparing the filtered signal with a threshold value and outputting a comparison signal; and an integrator (230) for integrating the comparison signal and outputting the feedback signal. According to another embodiment, the feedback loop comprises an integrator and a sigma-delta modulator.

Abstract: The present disclosure describes an apparatus and a system for generating electrical signals for a loudspeaker. The loudspeaker may include one or more piezoelectric actuators configured to deflect a diaphragm of the loudspeaker in response to an input signal. The apparatus may be configured to receive the input signal and to drive the piezoelectric actuators to deflect the diaphragm based on the received input signal.

Abstract: A condenser microphone employs a wide band stop filter, having improved resistance to electrostatic discharge. This includes providing a condenser microphone used for a multi-band by comprising a wide band stop filter capable of efficiently blocking a wide band signal including low frequency and radio frequency used in a mobile communication. A condenser microphone includes: an acoustic module for converting sound pressure into an electric signal; an FET for amplifying the electric signal; and a wide band stop filter for blocking a wide band signal including low frequency and radio frequency output from the FET. The filter is realized by resistors and/or capacitors which are connected selectively according to the radio frequency band between the drain and the source of the FET. The range capable of removing EM noise is widened, an excellent filtering effect of noise is obtained, and resistance of electrostatic discharge applied from outside is improved.

Abstract: An audio power amplifier provides a virtual ground to reduce power on/off noise and a method for processing a signal in the audio power amplifier. The audio power amplifier includes a switching amplifier to amplify a small output pulse width modulation (PWM) signal so as to generate a large output PWM signal, a pulse generating unit to generate a pulse signal having the same level as that of the PWM signal level, a first low pass filter to allow the large output PWM signal amplified by the switching amplifier to be low-pass filtered so as to restore the PWM signal to an audio signal, and a second low pass filter to allow the pulse signal generated by the pulse signal generating unit to be low-pass filtered so as to convert the pulse signal into a virtual ground voltage with respect to the restored audio signal.

Abstract: A method and apparatus for selecting and mixing electronic signals. The circuit has an operational amplifier and two or more ganged, tapped-resistors in which the tap divides the resistance into a first and a second resistance. The tapped-resistors are connected so that either the first or the second resistance provides the effective input resistance for that signal at the operational amplifier. The second resistance of one of the tapped-resistors provides the output resistance for all signals at operational amplifier. As the tapped resistors are equivalent and their taps ganged, when the signals are mixed, those signals whose effective input resistance at the operational amplifier is selected to be the second resistance have unit gain, while those signals whose effective input resistance at the operational amplifier is selected to be the first resistance have a gain equal to the second resistance divide by the first resistance.

Abstract: The present invention utilizes switching power amplifier technology to improve the performance of self-amplified speaker system. In contrast to analog Class A and Class AB amplifiers, the present invention utilizes a digital class D amplifier. Class D amplifiers are a pulse width modulated or digital switching amplifier configuration. The Class D amplifiers of the present invention includes 2-pole compensation feedback and power supply tracking that improves stability and total harmonic distortion over conventional power amplifiers. Class D amplifiers have an average electrical efficiency value of at least 65%. This level of electrical efficiency leads to reduction in the amount of power lost in the device or systems that result in heat generation.

Abstract: A miniature speaker device includes a housing, a speaker mounted on the housing, a passive radiator mounted on the housing and vibrating in resonance with vibration of the speaker and having no driving system and a low frequency range amplification circuit for amplifying sound pressure in frequency components of a low frequency range of a single audio signal input in the speaker.

Abstract: A dynamic contoured-sound/subwoofer-synthesis system including an adjustable high pass filter coupled to the input terminal, the high pass filter being designed to provide a variety of frequency response shapes in response to adjustments thereof. A primary amplifier is coupled to receive one of the variety of frequency response shapes from the adjustable high pass filter and includes a main operational amplifier (op-amp) with the inverting input coupled to the adjustable high pass filter through a series connected input capacitor and input resistor. The primary amplifier provides low frequency signal gain and shaping of the received frequency response shape. A high frequency signal shaping circuit includes a feedback op-amp coupled to the inverting input of the main op-amp through a feedback resistor and a feedback capacitor.

Abstract: A solid stage audio power amplifier comprises of two output stages with one generating the real output signal that drives the real loud speaker load and the other mimicking the real output stage and generating a dummy output signal that drives a dummy resistor load. A frequency dependent feedback selection network, denoted as Feedback-Shifting network hereafter, is implemented between the two outputs and the input of the amplifier to fulfill a unique global feedback loop. In a particular embodiment, the Feedback-Shifting network can be constructed so that it receives more feedback information from the real output node than from the dummy output node at low frequencies, but less feedback information from the real output node than from the dummy output node at mid to high frequency bands.

Abstract: The invention relates to a class-D audio amplifier. The class-D audio amplifier is configured in a current feedback mode as a voltage-controlled current source and a passive inductor/capacitor (LC) reconstruction filter. A portion of the passive LC reconstruction filter is situated in a feedback loop to an error amplifier.

Abstract: A data transfer apparatus is composed of a transmitter and a receiver. The transmitter includes an output buffer developing a differential signal in response to a data signal, and an amplitude controller. The receiver includes an input buffer converting the differential signal into a single-end signal, and an amplitude detector developing a feedback signal in response to the single-end signal. The amplitude controller controls an amplitude of the differential signal in response to the feedback signal.

Abstract: Differential dynamic content delivery including providing a session document for a presentation, wherein the session document includes a session grammar and a session structured document; selecting from the session structured document a classified structural element in dependence upon user classifications of a user participant in the presentation; presenting the selected structural element to the user; streaming presentation speech to the user including individual speech from at least one user participating in the presentation; converting the presentation speech to text; detecting whether the presentation speech contains simultaneous individual speech from two or more users; and displaying the text if the presentation speech contains simultaneous individual speech from two or more users.

Abstract: System for pulse-width-modulated class D audio amplifiers. In one preferred embodiment an adder is described to generate a difference signal responsive to an input signal and a feedback signal, a pulse-width-modulator coupled to the adder to compare the difference signal to a reference signal and produce a pulse-width-modulated signal based on the comparing, a filter coupled to an output of the pulse-width-modulator, and a loop filter having a first input coupled to the output of the filter and a second input coupled to the input of the filter, the loop filter to generate a feedback signal by applying transfer functions to signals at its inputs. The loop transfer function of the amplifier is minimum aliasing error transfer function. The minimum aliasing error properties provide low distortion and taking the feedback from the output of the filter reduces high frequency output impedance.

Abstract: An amplifier includes an amplifying block (26) for receiving an input signal to drive a speaker (23), and a power supply block (25) for supplying an output voltage to the amplifying block. The amplifying block (26) includes a PWM-signal generation circuit (4) which converts the input signal into a PWM signal, a speaker driving circuit (20) which drives the speaker based on the PWM signal, and a duty detection circuit (8) which outputs a time difference signal proportional to a difference between the pulse width and the pulse interval of the PWM signal. The power supply block (25) controls the output voltage thereof based on the time difference signal. If the volume of a speaker (23) is loud, the amplifier increases the drive voltage of the speaker (23) to suppress distortion of the volume.

Abstract: Embodiments of the present invention provide methods and devices for controlling a command signal applied to a load. In embodiments of the invention, current through and voltage across a load are determined and the values of both are used to generate a hybrid control signal. For example, in some embodiments the hybrid control signal is generated by taking a weighted summation of the current and voltage control signals. In other embodiments, a percentage of the difference between the current and voltage control signals is added to one of the current or voltage control signals to generate the hybrid control signal. In one embodiment, a potentiometer is used to generate the hybrid control signal.

Abstract: An audio system performing a class-D amplification includes a first pulse width modulation (PWM) signal generation unit and a second PWM signal generation unit. The first PWM signal generation unit generates a first switching signal based on a first audio signal. The second PWM signal generation unit generates a second switching signal based on a second audio signal. The second switching signal has a frequency difference with respect to the first switching signal such that a harmonic frequency component generated by interference between the first switching signal and the second switching signal is removed. Accordingly, the audio system performing the class-D amplification may improve a signal to noise ratio by minimizing influence of the harmonic frequency components on the first and second switching signals.

Abstract: An audio system including an audio power amplifier, a transducer electrically connected to the audio power amplifier, an enclosure coupled to the transducer, and a secondary resonant element coupled to the enclosure. An electrical feedback signal representative of the transducer current is negatively fed back to the audio power amplifier to synthesize a positive output impedance.

Abstract: A method of, and apparatus for, limiting inputs to and outputs from a computer sound card forms a feedback connection between the input and output of the sound card amplifier. The voltage of the feedback connection is increased from minimum voltage until an over-saturation condition occurs. This finds the “output voltage limit.” Thereafter, the output voltage of the amplifier is restricted to the output voltage limit. The feedback connection is then terminated and the voltage of the signal being supplied to the amplifier is increased from minimum voltage until the over-saturation condition again occurs. This finds the “input voltage limit.” Thereafter, the input supplied to the amplifier is restricted to the input voltage limit.

Abstract: In the present invention, in parallel with a resistor which determines an amplification rate being fed back from an output to an input of an output stage OP amp in an audio amplifier circuit, providing a first diodes connected bi-directionally together with a first switch circuit, the output voltage of the output stage OP amp is limited to a voltage, when the first diodes are turned ON. The limit voltage of the first diodes corresponds to a speaker having a low withstand voltage. Accordingly, through ON/OFF of the first switch circuit, a power output from the output stage OP amp can be selected depending on the withstand voltage of a speaker to be connected.

Abstract: An audio apparatus is constructed for use in negative drive of a loudspeaker having an internal impedance to perform a desired amplitude-frequency characteristic. In the audio apparatus, an amplifier device drives the loudspeaker with a driving voltage. A feedback device performs a positive feedback of a signal corresponding to the driving voltage of the loudspeaker to the amplifier device with a variable feedback gain, thereby causing the amplifier device to generate a negative impedance effective to negate the internal impedance of the loudspeaker. An adjustment device decreases the variable feedback gain of the feedback device as a level of the driving voltage of the loudspeaker increases, thereby adjusting the amplitude-frequency characteristic of the amplifier device.

Abstract: An audio signal amplifier circuit includes an external output terminal of an IC to which an output line of a power amplifier circuit is connected, a first resistor connected between a certain terminal of the IC other than the external output terminal and a feedback input of a differential amplifier circuit, a first capacitor connected between the external output terminal and a loud speaker, a second capacitor between the certain terminal of the IC and a wiring line between the external output terminal and the loud speaker, a filter circuit provided on a signal input side of the differential amplifier circuit and including a second resistor and a third capacitor for attenuating signal components having frequencies in a middle and high frequency ranges and voltage follower means provided between an input stage and an output stage of the audio signal amplifier circuit, wherein the first capacitor is a small capacitor having a capacitance value in the order of 30 &mgr;F or smaller and an attenuation characteristi

Abstract: An automatic gain control circuit for use with a motorcycle radio and headset features an adjustable control for setting the maximum signal allowed to reach the headset, while allowing normal signal levels below that point to be controlled at the motorcycle radio. The circuit may be easily incorporated for use with a previously installed radio as well as an enhancement for new radio designs. Isolation transformers on both the input and output of the circuit eliminate the necessity to ground the circuit. Bass boost and internal gain circuits compensate for internal losses and headphone loading characteristics to provide near-transparent signal transfer below the set maximum signal level.

Abstract: A transimpedance amplifier (18) receives an audio signal from a power audio amplifier (14) and provides a variable power level to a loudspeaker (16). A first variable gain amplifier (28) receives the audio signal and provides a variable gain to a power amplifier (40). The output signal of the power amplifier drives the loudspeaker. A sense amplifier (52) subtracts a voltage representative of current flowing through the loudspeaker from a voltage applied to the loudspeaker and provides a difference signal. A second variable gain amplifier (70) receives the difference signal and provides a variable gain to a load amplifier (80). The gains of the first and second variable gain amplifiers are inversely proportional. A resistive element (84) having a real impedance is coupled between an output of the load amplifier and the input of the transimpedance amplifier to maintain the complex impedance of the loudspeaker at the output of the power audio amplifier.

Abstract: Systems and methods for reducing crosstalk in power amplifiers driving low impedance loads are provided. A low impedance power amplifier includes a first power amplifier and a second power amplifier. The first power amplifier amplifies a first signal and the second power amplifier amplifies a second signal. A mid-rail component is connected to the first power amplifier and the second differential amplifier in order to provide a DC bias for the amplified signals. The first and second differential amplifiers drive a low impedance load (e.g., headphone speakers). A common ground of a low impedance load is connected to a mid-rail component that compensates for mid-rail component variations in the amplified signals facilitating the reduction of crosstalk.

Abstract: A circuit for widening the stereobase in the reproduction of stereophonic sound signals contains one amplifier (10, 34) each for the stereo signals assigned to the right-hand and left-hand channel. Each amplifier (10, 34) comprises a non-inverting input (16, 36) for the corresponding stereo signal and an inverting input (18, 42) for an output signal fed back via a first resistor (R1, R5) from the amplifier output (20, 40). An ON/OFF connection is provided between the inverting inputs (18, 42) of both amplifiers (10, 34). The connection between the inverting inputs (18, 42) of the two amplifiers (10, 34) is formed by two amplifiers (48, 50) circuited in antiparallel as voltage followers and a second resistor (R8, R9) connected in series with the output of each amplifier (48, 50).

Abstract: In a dual bridge amplifier (1) for processing two input signals (Iin1; Iin2) and providing two amplified output signals (VL1; VL2) into two separate loads, comprising two signal amplifiers (10; 20) and one common buffer amplifier (30), the channel separation is improved by utilizing a feedback coupling over the load.

Abstract: An output stage for a power amplifier comprises an amplifying device T1 connected in series with a variable current sink T2 between positive and negative supply rails +/−V. A loudspeaker S is connected between the zero volt rail OV and a point intermediate the amplifying device T1 and the variable current sink T2. A feedback loop A1,A2 is provided for increasing the amount of current required by the variable current sink T2 as the amount of current delivered to the loudspeaker s by the amplifying device T1 falls. Thus, in one half cycle of the input signal Vin, the loudspeaker S is provided with current through the amplifying device T1 and in the other half cycle the variable current sink T2 draws current through the loudspeaker S. When no input is applied, the variable current sink T2 draws a low current and thus the output stage has an improved efficiency compared with conventional class A amplifiers.

Abstract: An apparatus (Z) having controllable impedance is inserted from output (22) to ground (23) of an audio-signal amplifier (20). Typically, the apparatus comprises a switch-chain (50) having multiple switches (52, 53, and so on); the first switch (52) is connected to one terminal (62) of the apparatus. A capacitor (82, 84, and so on) is connected from each switch to a second terminal (61). The network formed by the switch-chain (50) and the capacitor network (80) is called a matrix (60C). To bypass audio frequencies away from the chopping effect of the switches, an inductor (31) parallels the matrix. To prevent shorting of audio signals to ground, a larger capacitor (30) is in series with the inductor. An unstable voltage at output will see increasing capacitance as more switches are closed. The changing of capacitive impedance in relation to the amplitude of the unstable voltage is designed such that the unstable voltage cannot grow too large. More complex matrices further reduce voltage fluctuations.

Abstract: A PWM amplifier comprising a comparator and an integrator is known to amplify, for example, audio signals. One drawback of the known PWM amplifiers is the maximally achievable loop gain is low. To overcome the disadvantages of the prior art PWM amplifiers, a PWM amplifier is provided with a second integrator in the feedback loop.

Abstract: A remotely controlled microphone amplifier has a first amplifier stage with a variable gain circuit operatively connected in the overall feedback loop of the first stage for controlling the gain in first increments. A unity gain second amplifier stage has variable attenuator operatively coupled between the output of the first amplifier stage and the input of the second amplifier stage. The variable attenuator controls the input to the second stage in second increments less than the first increments. The overall gain is linearly adjustable and varies in equal increments.

Abstract: The present invention is directed to a circuit for performing volume expansion on an audio signal. The circuit includes an amplifier that has an input side and an output side. Further, the amplifier amplifies the audio signal at a first amplification to produce an amplified signal at the output side of the amplifier. The circuit also includes a shunting element coupled across the input side and output side of the amplifier. The shunting element includes a variable impedance device for changing the first amplification of the amplifier to a second amplification if the amplified signal reaches a predetermined threshold.

Abstract: A self-biased electret microphone amplifier with phantom powering which avoids the need for JFETs and depletion mode devices, both of which are not standard devices when using BiCMOS fabrication processes. Feedback is included to provide enhanced gain, dynamic range, linearity and temperature stability, without requiring filtering, large resistances or external components. A self-biased, phantom powered, differential MOSFET amplifier receives and pre-amplifies the microphone signal. Further amplification and feedback is provided by a differential amplifier and bipolar output amplifier which operates as a common emitter amplifier for the amplified microphone output signal and as an emitter follower amplifier for the feedback signal.