Abstract:
An active-noise-reduction (ANR) headset includes at least one auxiliary connection to an output of at least one device, such as a personal communications, computing, and/or entertainment device. An exemplary headset also includes a primary connection to an aircraft two-way radio or public-address system and circuitry for automatically suppressing or muting the volume of an auxiliary input signal relative to that of a primary input signal. Other exemplary features include a headset power supply, a microphone, a microphone preamplifier, and a device-detection circuit. The device-detection circuit selectively couples the power supply to the microphone preamplifier, enabling it to provide audio signals to the microphone input of the auxiliary device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/018,910 filed Feb. 1, 2011, which is a continuation of U.S. application Ser. No. 11/735,704 filed Apr. 16, 2007, now U.S. Pat. No. 7,907,721, which is a continuation of U.S. patent application Ser. No. 10/624,906, filed Jul. 22, 2003, now U.S. Pat. No. 7,215,766, which claims priority under 35 U.S.C. 119(e) to co-pending and co-owned U.S. provisional application 60/397,888, filed Jul. 22, 2002, which applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention concerns headphones or headsets and related circuits and methods. 
     BACKGROUND 
     Headsets are used in a variety of applications to facilitate one- or two-way audio communications between users and/or devices. For example, many aircraft pilots wear headsets to enable them to communicate via two-way radio with other aircraft and air-traffic controllers as well as via a public-address system with passengers. Additionally, some headsets are worn to facilitate hands-free usage of mobile telephones, while others facilitate private listening to devices, such as computers, stereos, disk players, etc. 
     One problem that the present inventor recognized is that conventional headsets lack means for successfully integrating more than one audio source, despite their proximity to multiple sources of audio signals. Accordingly, there is a need for headsets that facilitate use of more than one signal source. 
     SUMMARY 
     To address this and/or other needs, the present inventor devised one or more devices, circuits, and methods related to simultaneous connection of at least two audio input signals to a headset. For example, in one embodiment, an active-noise-reduction (ANR) headset includes at least one auxiliary port for connection to an output of at least one device, such as a personal communications, computing, and/or entertainment device. This exemplary headset also includes a primary port for connection to a two-radio or public-address system and circuitry for automatically suppressing or muting the volume of an auxiliary input signal relative to that of a primary input signal. 
     Other exemplary features include a headset power supply, a microphone, a microphone preamplifier, and a device-detection circuit. The device-detection circuit detects connection of the auxiliary port to a microphone input and couples the power supply to the microphone preamplifier, enabling it to provide audio signals to the microphone input. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary system  100  corresponding to one or more embodiments of the present invention. 
         FIG. 2  is a flow chart of an exemplary method of operating one or more portions of system  100 , which corresponds to one or more embodiments of the present invention. 
         FIG. 3  is an electrical schematic of one or more exemplary circuits in system  100 , each corresponding to one or more embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description, which references and incorporates the attached Figures, describes and illustrates one or more specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art. 
       FIG. 1  shows an exemplary system  100  incorporating teachings of the present invention. Specifically, system  100  includes a primary audio communication device  110 , a secondary audio communications device  120 , and an automatic-noise-reduction (ANR) headset  130 . 
     Primary communications device  110  includes, among other items not shown, a headphone output jack  112  and a microphone jack  114  coupled to internal circuitry not shown. In the exemplary embodiment, device  110  takes the form of a two-way aircraft radio, with headphone jack  112  being a 0.250-inch female stereo plug connector and microphone jack  114  being a 0.206-inch, female stereo plug connector. In some embodiments, device  110  includes a public-address or intercom capability. 
     Secondary communications device (or system)  120  includes, among other items (not shown), an audio output jack  122  and an external microphone jack  124 . In the exemplary embodiment, communications device  120  takes the form of a cellular telephone, with output jack  122  and microphone jack  124  coupled to interface circuitry (not shown) which supports use of a conventional hands-free mobile-phone headset, which includes a microphone and an ear-piece (or headphones). (Hands-free headsets typically include an unbuffered electret microphone that is powered by interface circuitry (not shown) in the cell phone or other type secondary device. In the exemplary embodiment, this interface circuitry is not suitable for boom microphones in aviation headsets.) In some other embodiments, device  120  takes the form of a two-way radio, laptop computer, or other audio source or audio output device, such as a music or video player or other personal listening device. In still other embodiments, device  120  includes or is coupled to an input/output port of a larger multiport distribution network that distributes audio signals, for example, throughout an airliner. 
     ANR headset  130  includes, among other things, an earpiece  132 , a boom microphone  134 , and a controller  136 . Earpieces  132 , which each take the exemplary form of a circumaural earcup in this embodiment, fit over a respective ear of a user (not shown). However, in other embodiments, the earpiece takes the form of superaural, in-the-ear, or behind-the-ear devices. Specifically, earpiece  132  includes ANR control circuitry  1321 , an ANR microphone  1322 , an ANR speaker  1323 , and a non-ANR speaker  1324 . 
     Boom microphone  134  includes a boom  1341  which extends from one of earpieces  132 , and a microphone  1342  positioned at an end of the boom. Other embodiments use other forms of microphones. Earpiece  132  and boom microphone  134  are both coupled to controller  136 . 
     Controller  136  includes secondary-device detector  1361 , a boom microphone preamplifier  1362 , a comm-priority module  1363 , a battery box  1364 , and user controls  1365 . In the exemplary embodiment, the controller is provided as a box or module separate from the earpieces; however, in some embodiments, all, or one, or portions of the controller are incorporated into one or more of the earpieces. For example, some embodiments place one or more of the controller input jacks directly on one of the earpieces. 
     Secondary-device detector  1361  is coupled to microphone jack  124  of secondary communications device  120 , microphone preamplifier  1362 , and battery box  1364 . Microphone preamplifier  1362 , in the exemplary embodiment, is designed to operate using a 5-10 VDC voltage source and a 600-2000 ohm resistor. Comm-priority module  1363  is coupled to headphone jack  122  of primary communications device  110  and to audio output jack  122  of the secondary communication device. Manual controls  1365  include on-off switch, left-right volume controls, stereo-mono switch, mode-programming switches, and bass and treble controls (all not shown separately). 
     In general operation, secondary device detector  1361 , which includes an audio input jack coupled to microphone jack  124  of secondary communications device  120 , senses or detects connection or activation of device  120  to headset  130  and in response couples power derived from battery box  1364  to boom microphone preamplifier  1362 . Comm-priority module  1363 , which is coupled to the headphone jack of the primary communications device and to an audio output jack of the secondary communication device, provides an automatic muting or attenuation function that reduces the volume or amplitude of an audio or electrical signal derived from the secondary communication device relative to the volume or amplitude of an audio or electrical signal derived from the primary communications device. Detector  1361  also senses decoupling or deactivation of device  120  and in turn decouples battery box  1364  from boom microphone preamplifier  1362 . 
     More particularly,  FIG. 2  shows a flow chart  200  of one or more exemplary methods of operating system  100 , particularly in relation to control module  136 . Flow chart  200  includes process blocks  210 - 280 , which are arranged and described serially for clarity. However, two or more of the blocks, in whole or in part, can be executed in parallel. Additionally, some embodiments may alter the process sequence by omitting or adding one or more blocks or provide different functional partitions to achieve analogous results. Moreover, still other embodiments implement one or more of the blocks using a processor or programmable logic device and an electronic, magnetic, or optical storage medium bearing machine-executable instructions for execution or facilitating execution of one or more portions of the exemplary method. Thus, the exemplary process flow applies to software, hardware, firmware, and other implementations beyond those exemplified here. 
     At block  210 , exemplary execution begins with determining whether a secondary device, such as secondary communications device  120 , is coupled to headset  130 , or more precisely control module  136 . In the exemplary embodiment, this entails using detector  1361  to detect or sense a preamplifier bias signal from secondary communications device  120 . In some embodiments, the preamplifier bias signal is a 2.5VDC signal, which is generally incompatible with the bias signal used in most aviation-grade ANR headsets. Other embodiments may use the state of a switch to determine connection of a secondary device. If the determination is that a secondary device is coupled to the headset, execution advances to block  220 . 
     In block  220 , detector  1361  couples power derived from battery box  1364  to microphone preamplifier  1362 , thereby enabling the headset to self-power its boom microphone rather than relying on power from the primary communications device. This self-powering feature allows one to use the headset with the secondary communications device independent of any connection to the primary communications device. One benefit of this feature is that it allows the secondary device to be used in a noisy environment with no other electronics or power beyond the headset itself. Execution of the exemplary method continues at block  230 . 
     Block  230  entails headset  130  receiving audio signals from one or the other or both of the primary and the secondary communications devices  110  and  120 . In the exemplary embodiment, these audio signals are received at comm-priority module  1363  via headphone jack  112  and/or audio output  122 . Execution then proceeds to block  240 . 
     Block  240  entails determining whether to alter the relative amplitude of the primary and secondary audio signals. In the exemplary embodiment, this entails comparing the primary audio signal (more precisely the voltage at headphone jack  112 ) to a threshold voltage. If the comparison indicates that the primary audio signal is greater than the threshold voltage, execution advances to block  250 ; otherwise execution branches to block  260 . 
     Block  250  entails altering the relative amplitude of the primary and secondary audio signals. In the exemplary embodiment, this alteration entails reducing the amplitude (or volume) of the secondary audio signal relative to that of the primary audio signal. Some embodiments may increase the amplitude or volume of the primary audio signal to be greater than that of secondary audio signal. Some embodiments may additionally output a notification signal, such as high-pitched tone or beep, to indicate presence of a primary audio signal in excess of the threshold. 
     Block  260  entails mixing the primary and secondary audio signals. In the exemplary embodiment, this mixing entails mixing the primary audio signal, or more precisely any voltage present on headphone jack  112  with the reduced or unreduced secondary audio signal. 
     Block  270  entails outputting the mixed primary and secondary audio signals to one or both of earpieces  132 . In the exemplary embodiment, the mixed signals are output to speaker  1324  and to ANR circuitry  1321 . Some embodiments, however, may omit or bypass the ANR circuitry. Execution then returns back to block  210 . 
     Block  210  determines whether there is still a secondary device coupled to the headset. If the determination is that a device is still coupled to the headset, execution continues to block  220 , as previously described. However, if the determination is that there is no secondary device (or that the secondary device has been deactivated, for example, as evidenced by failure to receive a microphone bias voltage from the device), then execution advances to block  280 , which entails decoupling of the headset battery from the boom microphone preamplifier to conserve battery power. 
       FIG. 3  shows circuitry  300 , which includes a detector circuit  310  that represents an exemplary implementation of secondary-device detector  1361  and a comm-priority circuit  320  that represents an exemplary implementation of comm-priority module  1363 . In the figure, incoming signals from the secondary device are received at secondary inputs Aux_R and Aux_L, and incoming signals from the primary device are received at COM_AUD TIP and COM_AUD GND. Battery terminals (shown in the lower left-hand corner) are labeled Bat+ and Bat−. 
     Detector circuit  310  detects the presence of an external bias signal at an audio input jack (denoted cell_mic in the figure) via a transistor Q 6 , which turns on the current source comprising a transistor Q 10 . Activation of the current source provides a bias current for the boom microphone preamplifier. The current source has a compliance of over 10VDC for undistorted communications at high-sound pressures. Notably, this implementation does not interfere with normal operation of the boom microphone preamplifier, if it is connected to a radio or intercom bias circuit because it is a current source realizing a high Thevinin equivalent impedance. Although not preferred, some embodiments may use a source with a low Thevinin equivalent impedance. 
     Comm-priority circuit  320  treats the Com_L input as the primary input to the headset and compares this signal to a threshold voltage via comparator circuitry that includes operational amplifier U 1 B. If the signal at the Com_L input exceeds the trigger threshold (set by resistors R 1  and R 2 , voltage V+, and processor output pin  11 ), then the output of operational amplifier U 1 B output goes high, saturating transistor Q 8  and causing this transistor to rapidly discharge capacitor C 1 . In response to this discharge, operational amplifier U 1 C produces a low voltage at its output, which is coupled to a pulse-width-modulation (PWM) circuit comprising oscillator U 4  and PWM comparator U 3 . 
     In turn, the PWM circuit reduces the duty cycle of its output signal. This output signals controls analog switch U 11  (4053), which is part of a chopping circuit, causing it to attenuate the auxiliary inputs Aux_L and Aux_R. U 1 A and U 1 D denote summing amplifiers that sum or mix the primary and secondary inputs, and also provide a reconstruction filter for the chopped signal. The outputs of summing amplifiers U 1 A and U 1 D are then passed up to the earpieces for transduction into acoustic signals. 
     When the primary audio input stops exceeding the trigger threshold, capacitor C 1  slowly starts to charge up via resistor R 3 , thus increasing the duty cycle of the signal output from the PWM circuit and the gain level of the secondary audio input. The exemplary embodiment increases this gain linearly until it reaches its original level. (Non-linear restoration of the secondary signal is also feasible.) Microprocessor U 5  is programmable via control inputs CONTROL 1  and CONTROL 2  to disable communications priority by setting processor output pin  11  to a high logic state and thereby moving the trigger threshold for initiating attenuation of the secondary input to a high value. 
     Other implementations could assign priority to the secondary inputs or allow the user to select which inputs have priority. The comm-priority functionality is selectable and controlled through microprocessor U 5  using a combination of pushes of a button on a separate control module, such as module  136 . Other embodiments place this control with controls on one or more of the earcups, the bridge between the earcups, or other convenient location. 
     CONCLUSION 
     The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which encompasses all ways of practicing or implementing the concepts of the invention, is defined by the following claims and their equivalents.