Abstract:
An apparatus and method for powering headphone electronics over a standard audio signal cable without interfering with the normal audio transmission or playback of transmitted audio signals. A software application resides on a cell/smart phone or other mobile device that combines the nominal audio output of such a mobile device, like music or spoken word, with a high frequency audio signal to produce a dual component signal. The high frequency component is decoded and rectified outside of the mobile device, either in a connector or on the structure of the headphones themselves, to produce a direct current (“DC”) that powers the headphones. The music or other audible signal component transferred over the audio cable is decoded in parallel and sent to the headphone speakers for normal playback. The invention provides an alternative power source to headphone electronics such as active noise cancelling headphones over the audio cable.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to headphone power systems. In greater particularity, the present invention relates to headphone powering systems for actively powered headphones, such as noise cancelling headphones. In even greater particularity, the present invention relates to the conversion of high frequency signals into direct current power for powering electronics, such as headphones. 
       BACKGROUND OF THE INVENTION 
       [0002]    Noise cancelling and white noise generating headphones have become popular in the last 10 years for actively controlling the output of headphone sound. In particular, noisy environments, such as airplane travel environments, demand active control over audio output in headphones in order to dynamically adjust to varied user environments. However, actively controlling headphone output requires electronics powered within the headphone system. Currently, such electronics cannot be powered by the audio signal that is received by the headphones without unacceptable degradation of the audio signal so such headphones incorporate either a separate power supply, necessitating a separate power wire, or a good set of batteries. 
         [0003]    Batteries in headphones add weight and either must be replaced with new batteries or replaced with freshly recharged batteries. Some headphones have attempted to reduce the weight of battery load by using smaller batteries, but this necessitates more frequent chargings, and less available power. And while having a separate power line for headphones is possible, the additional wire is usually unacceptable to the user. 
         [0004]    In concert with the advent of powered and active headphones, cell phones and mobile devices, like the iPad and iPod, have become much more powerful, both computationally and in battery strength. Applications can now be written for these platforms in a matter of days with reliable outcomes. Moreover, the dominant music source for music entertainment today is a user&#39;s mobile phone, or similar mobile device. Coincidentally, the protocol or format for outputting music through an audio port in a phone or mobile device is standardized. In other words, even though some variation in diameter still exits for mobile device audio ports, the pin configuration and electrical design specifications are universally accepted. 
         [0005]    Hence, what is needed is a system and method for using the standardized audio output port in mobile electronics, such as a cell phone, to transfer power to a pair of audio headphones without interfering with the primary purpose of those headphones—for faithful reproduction of music and other audio signals coming from the mobile device. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention consists of a software application that resides on a cell phone or other mobile device that combines the nominal audio output of such a mobile device, like music or spoken words, with a high frequency audio signal to produce a dual component signal. The high frequency component is decoded and rectified outside of the mobile device, either in a connector or on the structure of the headphones themselves, to produce a direct current (“DC”) that powers the headphones. The music or audible component is decoded and sent to the speakers in the headphones to reproduce the audible component for the user of the headphones. By producing a DC current for the headphones, power may be supplied to either power electronics on the headphones, such as noise cancelling electronics, or rechargeable batteries may be supplied with power for recharging. An alternate embodiment of the invention provides a module that may be plugged into a standard electrical wall outlet to provide power in the same manner as above using the same audio cable. 
         [0007]    Other features and objects and advantages of the present invention will become apparent from a reading of the following description as well as a study of the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A headphone power system incorporating the features of the invention is depicted in the attached drawings which form a portion of the disclosure and wherein: 
           [0009]      FIG. 1  is a diagram showing the general configuration of the invention; 
           [0010]      FIG. 1A  is a diagram showing the general configuration of another embodiment of the invention; 
           [0011]      FIG. 2  a wave form graph showing the frequency distribution for the electronic signals of the invention in which music is streamed; 
           [0012]      FIG. 2A  a wave form graph showing the frequency distribution for the electronic signals of the invention in which a telephone conversation is streamed; 
           [0013]      FIG. 3  is a process flow diagram for converting the electrical signal into direct current; 
           [0014]      FIG. 4  is a schematic diagram showing the DC conversion circuitry of the invention; 
           [0015]      FIG. 5  is a process flow diagram for converting the electrical signal into direct current for another embodiment of the invention; and, 
           [0016]      FIG. 6  is a schematic diagram showing the circuitry for generating an audio signal from another embodiment of the invention instead of using an iPod to generate the signal. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]      FIG. 1  shows a general configuration of the invention when configured to work with an iPod®, iPod Touch®, iPhone®, or similar mobile electronic device. The Invention  10  works in conjunction with the standard capabilities of mobile devices that are capable of outputting audio signals listened to by a user. All such mobile devices have software applications that are either resident in firmware memory and may be loaded for execution into the mobile device&#39;s random access memory (“RAM”), or applications that are transferred from outside the device and retained in static RAM or miniature hard drives and transferred into dynamic RAM (“DRAM”) for execution by one or more processors or processing cores. Such applications are routinely downloaded from virtual application stores on the Internet, such as Apple&#39;s Apps Store®, and transferred from a synchronization program from a PC such as iTunes® or other program. Further description of the process of the downloading applications and the running of those applications on mobile devices shall be omitted as the mechanics and technology associated with such processes is well known and not necessary for a complete understanding of the herein described invention. 
         [0018]    Electronic device  11  includes the capability to play music or the spoken word through a software application  13  as part of its nominal functionality, with the control and generation of such output being controlled through a touch screen user interface  12 . The output of the application  13  is streamed through audio jack or port  14 . Headphones  21  are connected to port  14  through audio connector  17  and wire  18 , and a miniaturized electronics enclosure  26  mounted on headphones support  24 . Support  24  also connects right and left speakers  22 R,  22 L, and optionally supports a battery enclosure  27 . 
         [0019]    As shown in  FIG. 1A , an alternate embodiment of the herein described invention  30  uses all of the above described elements of embodiment  10  except that in place of a mobile device having a processor, a software application, and a user interface, an electronic module  31  is substituted containing signal generating electronics. The module  31  is inserted into a standard household electrical outlet  32  with the usual electrical plugs  33  to power the internal electronics. Audio cable  18  with connector  17  is inserted into an audio jack  14  as with above embodiment  10 . However, module  31  has internal electronics only for generating an electrical signal representing an audio tone above the human hearing range, typically 20 kHz to 23 kHz, over cable  18 . Essentially, module  31  is providing a charging stimulus from the household AC voltage source. The tone or signal is converted into power in the same manner as with invention  10  through conversion electronics  26 . Suitable electronics for module  31  are shown in  FIG. 6 . 
         [0020]    Referring now to  FIG. 2 , it may be seen a frequency distribution graph  35  of a typical audio music signal as it is transferred to a pair of headphones using the herein described invention  10 . The y or vertical axis  41  of the graph  35  is the measure of decibels relative to full scale, commonly abbreviated “dBFS,” and the x or horizontal axis  42  is the signal frequency in hertz as shown. Audio signal A ( 36 ) is comprised of two signal components or signal portions B ( 44 ) and C ( 39 ). Signal B ( 43 ) represents the audio spectrum of a music signal spanning from approximately 20 Hz to 20 kHz, and a power signal C ( 39 ) that spans frequencies from approximately 20 kHz to 23 kHz. Audible threshold  46  separates the two signal components  44  and  39  at 20 kHz, and is a lower threshold for power signal  38 . Power signal  38  also has an upper threshold  48  of 23 kHz, although the inventor fully contemplates using higher frequencies to increase power transfer efficiency. 
         [0021]    The graph  50   FIG. 2A  is similar to  FIG. 2  except that audio signal  43  has a limited band region D ( 51 ) of from approximately 300 Hz to 3400 Hz, and power signal  38  has been shifted to a frequency range F ( 52 ) just above the audio threshold  46 . 
         [0022]    A process  55  for transferring the dual component signal A ( 36 ) and extracting power from it may be seen in  FIG. 3 . The signal  36  is received 57 by electronics  26  and using low-pass  58  and high-pass  59  filters to separate the audio signal component B ( 44 ) and the power signal component C ( 39 ). After component B ( 44 ) is extracted, it can simply be passed  61  to headphone speakers  22 L,R for conversion into a human recognized waveform. 
         [0023]    Power signal C ( 39 ) is rectified  62  and the voltage regulated  63  to meet the needs of the headphone electronics. The voltage produced at  63  can then be used for charging  64  a battery, such as a lithium ion battery  66 , or simple connected to the power bus or rail  67  to power noise cancelling electronics for the headphones  21 . Because the power signal portion C ( 39 ) is above the audible threshold  46 , filters  59  and  58  may precisely isolate the power signal  38  and, thereby, not interfere with the accurate reproduction of the audio signal  43 . 
         [0024]    Electronics suitable for filtering out the two component signals B ( 44 ) and C ( 39 ) are shown in  FIG. 4  and disclose element values suitable for the preferred embodiment. Right and left channel lines  71 , 72  receive the right and left channels of audio signal  43  and pass it to a low pass filter  73 . Low pass filter elements, namely resistors  74  and capacitors  76 , filter out the power signal which is generally above the human audible hearing range of 20 kHz such that the audio signal component B ( 44 ) is passed via left and right channel lines  75  to headphone speakers  21 , or to other headphone sound generating electronics such as noise cancelling electronics also connected to the speakers  21 . 
         [0025]    A high pass filter comprised of a capacitor circuit  77  allows power signal component C ( 39 ) to be propagated through power generation circuit  78 , thereby screening out audible audio signal component B ( 44 ). Power generation circuit  78  includes for each audio channel a micro-transformer  79  for stepping up the voltage of signal component C ( 39 ) by approximately 20 times the typically audio voltage. The signal is then rectified with an FET bridge  81  and Schottky diode  82 , as shown. Capacitor  83  then acts as a filter DC voltage reservoir to connector  86 , that combines the current source capability of each channel to produce a suitable power rail  87  that powers the electronics for headphone  21 . The voltages generated by circuit  78  are expected to be in the range of 1.8V to 4V depending on the source input level and the specific mobile device implementation. 
         [0026]    Referring to  FIG. 5 , power generation circuit  78  may be utilized with a wall mounted power generation module  31  adapted to generate a power signal  38  to power headphones  21  pursuant to process  91 . Power generation circuit  78  is unchanged from process  55  shown in  FIG. 3 , except that high pass filter elements  77  of  78  are not needed because no low frequency signal component B ( 44 ) is transmitted from module  31  to headphones  21 . Therefore, process  91  requires no changes to the existing electronics shown in  FIG. 4 . 
         [0027]    A circuit implementation of module  31  shown in  FIG. 5  may be seen in  FIG. 6 , preferably with circuit elements having values as shown in the figure. With module  31  inserted into a household power outlet, sub-circuit  97  takes nominal household 120 Volt AC power and converts it into usable 5 volt DC power. Sub-circuit  98  then uses the generated DC to transmit an audio tone to the electronics  26  located in the headphones  21  for powering the headphones  21 . 
         [0028]    Sub-circuit  99  in circuit  97  utilizes a standard LinkSwitch™ II monolithic integrated circuit  102  having a high-voltage power MOSFET, oscillator, simple ON/OFF control scheme, a high-voltage switched current source, frequency jittering, with cycle-by-cycle current limit and thermal shutdown circuitry. The IC  102  is manufactured by Power Integrations of San Jose, Calif. House plug connections  103  supply 120 VAC to circuit  99  and is rectified by diodes D 1  ( 104 ) through D 4  ( 107 ), and is filtered by the bulk storage capacitors C 1  ( 109 ) and C 2  ( 111 ). Inductor L 1  ( 112 ), with capacitors C 1  and C 2 , form pi (π) filters to attenuate conducted differential-mode EMI noise. The LinkSwitch-II device U 1  ( 102 ) allows sufficient voltage margins in universal input AC applications and the circuit  97  is self-powered from a bypass pin via the decoupling capacitor C ( 113 ), the value of which programs the cable-drop voltage compensation. In the preferred embodiment, a 10 μF capacitor gives the 350 mV (7% of VNO), the compensation needed for a nominal #24 AWG cable, with 0.35Ω impedance. A bias circuit consists of elements D 6  ( 117 ), C 5  ( 114 ), and R 4  ( 116 ) to increase efficiency and to reduce no-load input power to less than 150 mW. The rectified and filtered input voltage is then applied to one end of the transformer T 1  ( 126 ) primary winding. The other side of the transformer&#39;s primary winding is driven by the internal MOSFET of U 1  ( 102 —LS-II). An RCD-R clamp consisting of D 5  ( 108 ), R 2  ( 123 ), R 3  ( 124 ), and C 3  ( 122 ) limits drain voltage spikes caused by leakage inductance. Resistor R 2  ( 123 ) has a relatively large value to prevent any excessive ringing on the drain voltage waveform caused by leakage inductance. The LS-II IC ( 102 ) samples the feedback winding each cycle, 2.5 μs is after turn-off of its internal MOSFET. 
         [0029]    Transformer T 1 &#39;s ( 126 ) secondary winding is rectified by D 7  ( 127 ), a Schottky barrier-type diode, and filtered by C 7  ( 131 ) and C 8  ( 132 ). In this application, C 7  and C 8  have sufficiently low ESR characteristics to allow meeting the output voltage ripple requirement without adding an LC post filter. However, post filter L 3  ( 134 ), C 9  ( 136 ) was employed to reduce ripple less than 100 mV. Resistor R 7  ( 129 ) and capacitor C 6  ( 128 ) dampen high-frequency ringing and reduce the voltage stress on D 7  ( 127 ). It will be noted that bias winding  139  is used to sense the output voltage of circuit  99 , and feedback resistors R 5  ( 118 ) and R 6  ( 119 ) are selected using standard 1% resistor values to center both the nominal output voltage and constant current regulation thresholds. Resistor R 8  ( 133 ) provides a minimum load to maintain output regulation when the output is an unloaded state. The resultant voltage (Vcc) at connector  138  is 5.0 Volts DC at 1 amp, ±0.25 volts. 
         [0030]    Sub-circuit  98  takes regulated DC voltage generated by sub-circuit  97  at connector  138  and produces an audio tone via an operational amplifier  141 . Essentially, circuit  98  is a tuned oscillator. The circuit  98  uses two T-filters tuned to a discrete frequency as shown using the specified element values, preferably in this case optimized for 21 kHz. The audio signal is transferred over a standard 3.5 mm audio cable  18  via connectors  142 . In the headphones  21 , the 21 kHz signal is rectified and regulated using the same electronics  78  shown in  FIG. 4 . This allows a user to simply plug in the headphones into wall module  31  using the standard headphone audio cable  18  and charge or power the headphones  24  without adding additional electronics to the headphone pursuant to  FIG. 1A . 
         [0031]    While I have shown my invention in one form, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications without departing from the spirit thereof.