PATENT DOCUMENT

Publication Number: US-7769187-B1
Application Number: US-50300709-A
Country: US
Kind Code: B1

Title: Communications circuits for electronic devices and accessories

Abstract:
Hybrid circuits for electronic devices and accessories for electronic devices are provided. One or more pairs of hybrid circuits may convey audio signals, noise cancellation audio signals, microphone signals, control signals, and other signals between an electronic device and an accessory. The hybrid circuits may include a voltage controlled current source, a differential amplifier, separate signal and ground pins, multiple ground lines, an amplifier on a ground noise sense input line that can sense ground noise that may result from parasitic resistance, and other circuitry.

Claims:
1. An electronic device that supports communications with electronic equipment, comprising:
 an audio connector having four contacts including left channel and right channel audio contacts; 
 a first hybrid circuit having a common port coupled to the left channel audio contact and having a differential amplifier that receives a shared bias voltage; 
 a left channel audio output that transmits left channel analog audio signals through the first hybrid circuit; 
 a left channel microphone input that receives left channel microphone signals from the first hybrid circuit; 
 a second hybrid circuit having a common port coupled to the right channel audio contact and having a differential amplifier that receives the shared bias voltage; 
 a right channel audio output that transmits right channel analog audio signals through the second hybrid circuit; 
 a right channel microphone input that receives right channel microphone signals from the second hybrid circuit; and 
 a shared circuit that generates the shared bias voltage for the first and second hybrid circuits. 
 
     
     
       2. The electronic device defined in  claim 1  further comprising noise cancellation circuitry that reduces noise in speakers that receive the left and right channel audio signals using the left and right channel microphone signals, respectively. 
     
     
       3. The electronic device defined in  claim 1  further comprising ground noise sensing circuitry including an amplifier that is coupled to a ground contact in the audio connector. 
     
     
       4. The electronic device defined in  claim 3  further comprising audio codec circuitry that includes the left channel audio output, the right channel audio output, and a ground noise input coupled to the ground noise sensing circuitry, wherein the left channel audio output of the audio codec circuitry is coupled to the first hybrid circuit and wherein the right channel audio output of the audio codec circuitry is coupled to the second hybrid circuit. 
     
     
       5. The electronic device defined in  claim 1  further comprising power supply circuitry that generates a power supply voltage for the electronic equipment, wherein the power supply circuitry is coupled to a power contact in the audio connector. 
     
     
       6. An accessory comprising:
 an audio connector having a left channel audio contact, a right channel audio contact, a power contact, and a ground contact; 
 at least one hybrid circuit having a common node coupled to one of the audio contacts in the audio connector; 
 a wired path having a length between the audio connector and the hybrid circuit, wherein the length of the wired path between the audio connector and the hybrid circuit includes separate power ground and signal ground lines and wherein the power ground line and the signal ground line are both coupled to the ground contact in the audio connector; 
 a summing resistor coupled between the common node and the signal ground line; and 
 circuitry coupled to the power ground line. 
 
     
     
       7. The accessory defined in  claim 6  wherein the at least one hybrid circuit comprises a first hybrid circuit having a common node coupled to the left channel audio contact and a second hybrid circuit having a common node coupled to the right channel audio contact, the accessory further comprising:
 a left channel speaker that receives signals from the first hybrid circuit; and 
 a right channel speaker that receives signals from the second hybrid circuit. 
 
     
     
       8. The accessory defined in  claim 7  further comprising:
 a left channel microphone that detects left channel ambient noise signals to reduce noise in the left channel speaker; and 
 a right channel microphone that detects right channel ambient noise signals to reduce noise in the right channel speaker. 
 
     
     
       9. The accessory defined in  claim 6  wherein the at least one hybrid circuit comprises:
 a first hybrid circuit having a common node coupled to the left channel audio contact and having a differential amplifier that receives a shared bias voltage; and 
 a second hybrid circuit having a common node coupled to the right channel audio contact and having a differential amplifier that receives the shared bias voltage; the accessory further comprising a shared circuit that generates the shared bias voltage for the first and second hybrid circuits. 
 
     
     
       10. The accessory defined in  claim 6  wherein the at least one hybrid circuit comprises:
 a first hybrid circuit having a common node coupled to the left channel audio contact and having a differential amplifier that receives a shared bias voltage; and 
 a second hybrid circuit having a common node coupled to the right channel audio contact and having a differential amplifier that receives the shared bias voltage; the accessory further comprising:
 a first microphone that receives a common microphone bias signal; 
 a second microphone that receives the common microphone bias signal; and 
 a shared circuit that generates the shared bias voltage for the first and second hybrid circuits and that generates the common microphone bias signal for the first and second microphones. 
 
 
     
     
       11. The accessory defined in  claim 6  wherein the length of the wired path includes an additional signal ground line and wherein the at least one hybrid circuit comprises:
 a first hybrid circuit having a common node coupled to the left channel audio contact, wherein the first hybrid circuit includes circuitry coupled to the signal ground line; and 
 a second hybrid circuit having a common node coupled to the right channel audio contact, wherein the second hybrid circuit includes circuitry coupled to the additional signal ground line. 
 
     
     
       12. The accessory defined in  claim 11  further comprising:
 a left channel speaker that receives signals from the first hybrid circuit and that is coupled to the power ground line; and 
 a right channel speaker that receives signals from the second hybrid circuit and that is coupled to the power ground line. 
 
     
     
       13. An electronic device that supports communications with electronic equipment, comprising:
 an audio connector having a left channel audio contact, a right channel audio contact, a power contact, and a ground contact; 
 a first hybrid circuit having a common port coupled to the left channel audio contact; 
 a second hybrid circuit having a common port coupled to the right channel audio contact; 
 ground noise sensing circuitry including an amplifier that is coupled to the ground contact in the audio connector; and 
 audio codec circuitry having a left channel audio output coupled to the first hybrid circuit, a right channel audio output coupled to the second hybrid circuit, and a ground noise input coupled to the ground noise sensing circuitry. 
 
     
     
       14. The electronic device defined in  claim 13  wherein the first hybrid circuit has a differential amplifier that receives a shared bias voltage and wherein the second hybrid circuit has a differential amplifier that receives a shared bias voltage, the electronic device further comprising a shared circuit that generates the shared bias voltage for the first and second hybrid circuits. 
     
     
       15. The electronic device defined in  claim 13  comprising power supply circuitry that generates a power supply voltage for the electronic equipment, wherein the power supply circuitry is coupled to the power contact in the audio connector. 
     
     
       16. The electronic device defined in  claim 13  wherein the audio codec circuitry has a left channel audio input coupled to the first hybrid circuit and a right channel audio input coupled to the second hybrid circuit and wherein the audio codec circuitry includes noise cancellation circuitry that reduces noise in speakers that receive signals from the left and right channel audio outputs using signals received on the left and right channel audio inputs. 
     
     
       17. The electronic device defined in  claim 13  wherein the audio codec circuitry has a left channel audio input that receives left channel microphone signals from the first hybrid and a right channel audio input that receives right channel microphone signals from the second hybrid. 
     
     
       18. The electronic device defined in  claim 13  wherein the amplifier in the ground noise sensing circuitry has an output, a first input coupled to the ground contact, and a second input coupled to the output through a first resistor and wherein the second input is coupled to a ground in the electronic device through a second resistor.

Description:
BACKGROUND 
     Electronic devices such as computers, media players, and cellular telephones typically contain audio jacks. Accessories such as headsets have mating plugs. A user who desires to use a headset with an electronic device may connect the headset to the electronic device by inserting the headset plug into the mating audio jack on the electronic device. Miniature size (3.5 mm) phone jacks and plugs are commonly used IN electronic devices such as notebook computers and media players, because audio connectors such as these are relatively compact. 
     Audio connectors that are commonly used for handling stereo audio have a tip connector, a ring connector, and a sleeve connector and are sometimes referred to as three-contact connectors or TRS connectors. In devices such as cellular telephones, it is often necessary to convey microphone signals from the headset to the cellular telephone. In arrangements in which it is desired to handle both stereo audio signals and microphone signals, an audio connector typically contains an additional ring terminal. Audio connectors such as these have a tip, two rings, and a sleeve and are therefore sometimes referred to as four-contact connectors or TRRS connectors. 
     In a typical microphone-enabled headset, a bias voltage is applied to the microphone from the electronic device over the microphone line. The microphone in the headset generates a microphone signal when sound is received from the user (i.e., when a user speaks during a telephone call). Microphone amplifier circuitry and analog-to-digital converter circuitry in the cellular telephone can convert microphone signals from the headset into digital signals for subsequent processing. 
     Some users may wish to operate their cellular telephones or other electronic devices remotely. To accommodate this need, some modern microphone-enabled headsets feature a button. When the button is pressed by the user, the microphone line is shorted to ground. Monitoring circuitry in a cellular telephone to which the headset is connected can detect the momentary grounding of the microphone line and can take appropriate action. In a typical scenario, a button press might be used be used to answer an incoming telephone or might be used skip tracks during playback of a media file. 
     In conventional arrangements, it can be difficult or impossible to convey desired signals over an audio jack and plug. For example, it may not be possible to route signals from microphones in a headset to an audio circuit in an electronic device to implement noise cancellation functions. As another example, it may not be possible to convey desired signals from an electronic device to an accessory. Problems such as these can arise at least in part because conventional arrangements for coupling cellular telephones to headsets tend to be inflexible. 
     SUMMARY 
     Electronic devices and external equipment such as headsets and other accessories may operate in a variety of operating modes. Noise cancellation microphones and ambient noise reduction circuitry may be provided in the external equipment to reduce speaker noise and microphone noise. 
     Circuitry in the electronic device and external equipment may include one or more pairs of hybrid circuits associated with a wired link between the electronic device and external equipment. Each hybrid circuit may include a summing amplifier and a transconductance amplifier (e.g., a current source). When unidirectional operation is desired, to support operations such as the playback of right or left channel audio, the hybrid circuits can be bypassed. When bidirectional operation is desired, the hybrid circuit pairs may be switched into use. When a path is configured for bidirectional operation, analog output signals may be conveyed in one direction while analog input signals may be conveyed in the opposite direction. 
     The analog output signals that are conveyed over a bidirectional path may include analog right and left channel audio signals. The analog input signals may include microphone signals. The microphone signals may include voice microphone signals and ambient noise signals from one or more noise cancelling microphones for reducing voice microphone noise or speaker noise. 
     The wired link may include one or more ground paths between the electronic device and external equipment. With one suitable arrangement, the wired link may include two or more ground paths from the external equipment that converge into a single ground path near a connector that couples to the electronic device. The electronic device may include an amplifier coupled to a ground noise sensing line that is connected to the ground path. The electronic device may have circuitry that receives amplified ground noise signals from the amplifier. The circuitry may use the amplified ground noise signals to reduce noise over the wired link between the electronic device and external equipment. With one suitable arrangement, the electronic device may have an audio jack and the ground noise sensing line may be directly connected to a ground connector in the audio jack in the electronic device. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an illustrative electronic device in communication with an accessory such as a headset or other external equipment in a system in accordance with an embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing illustrative circuitry that may be used in an electronic device and an associated accessory or other external equipment in accordance with an embodiment of the present invention. 
         FIG. 3  is a circuit diagram showing how hybrid circuits may be used in a communications path between an electronic device and external equipment in accordance with an embodiment of the present invention. 
         FIG. 4  is a circuit diagram showing how pairs of hybrid circuits may be used in an electronic device and external equipment in an arrangement in which the hybrid circuits convey audio signals such as ambient noise signals and stereo audio signals in accordance with an embodiment of the present invention. 
         FIG. 5  is a diagram showing how a communications path between an electronic device and external equipment may include multiple ground lines that are connected together at one end of the communications path in accordance with an embodiment of the present invention. 
         FIG. 6  is a circuit diagram of illustrative circuitry that may be provided as part of an electronic device that can communicate with external equipment such as an accessory using hybrid circuits in accordance with an embodiment of the present invention. 
         FIG. 7  is a circuit diagram of illustrative circuitry that may be provided as part of an accessory or other electronic equipment that can communicate with an electronic device using hybrid circuits in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic components such as electronic devices and other equipment may be interconnected using wired and wireless paths. For example, a wireless path may be used to connect a cellular telephone with a wireless base station. Wired paths may be used to connect electronic devices to equipment such as computer peripherals and audio accessories. As an example, a user may use a wired path to connect a portable music player to a headset. 
     Electronic devices that may be connected to external equipment using wired paths include desktop computers and portable electronic devices. The portable electronic devices may include laptop computers, tablet computers, and small portable computers of the type that are sometimes referred to as ultraportables. The portable electronic devices may also include somewhat smaller portable electronic devices such as wrist-watch devices, pendant devices, and other wearable and miniature devices. 
     The electronic devices that are connected to external equipment using wired paths may also be handheld electronic devices such as cellular telephones, media players with wireless communications capabilities, handheld computers (also sometimes called personal digital assistants), remote controllers, global positioning system (GPS) devices, and handheld gaming devices. The electronic devices may be multifunction devices. For example, an electronic device may perform the functions of a cellular telephone and a music player while running additional applications such as email applications, web browser applications, games, etc. These are merely illustrative examples. 
     An example of external equipment that may be connected to such electronic devices by a wired path is an accessory such as a headset. A headset typically includes a pair of speakers that a user can use to play audio from the electronic device. The accessory may have a user control interface such as one or more buttons. When a user supplies input, the input may be conveyed to the electronic device. As an example, when the user presses a button on the accessory, a corresponding signal may be provided to the electronic device to direct the electronic device to take an appropriate action. Because the button is located on the headset rather than on the electronic device, a user may place the electronic device at a remote location such as on a table or in a pocket, while controlling the device using conveniently located headset buttons. 
     The external equipment that is connected by the wired path may also include equipment such as a tape adapter. A tape adapter may have an audio plug on one end and a cassette at the other end that slides into a tape deck such as an automobile tape deck. Equipment such as a tape adapter may be used to play music or other audio over the speakers associated with the tape deck. Audio equipment such as the stereo system in a user&#39;s home or automobile may also be connected to an electronic device using a wired path. As an example, a user may connect a music player to an automobile sound system using a cable with a three-pin or four-pin audio connector (e.g., TRS or TRRS connectors). 
     In a typical scenario, the electronic device that is connected to the external equipment with the wired path may produce audio signals. These audio signals may be transmitted to the external equipment in the form of analog audio (as an example). The external equipment may include a microphone. Microphone signals (e.g., analog audio signals corresponding to a user&#39;s voice or other sounds) may be conveyed to the electronic device using the wired path. The wired path may also be used to convey other signals such as power signals and control signals. Digital data may be conveyed if desired. The digital data may include, for example, control signals, audio, display information, etc. 
     If the electronic device is a media player and is in the process of playing a song or other media file for the user, the electronic device may be directed to pause the currently playing media file when the user presses a button associated with attached external equipment. As another example, if the electronic device is a cellular telephone with media player capabilities and the user is listening to a song when an incoming telephone call is received, actuation of a button on an accessory or other external equipment by the user may direct the electronic device to answer the incoming telephone call. Actions such as these may be taken, for example, while the media player or cellular telephone is stowed within a user&#39;s pocket. 
     Accessories such as headsets are typically connected to electronic devices using audio plugs (male audio connectors) and mating audio jacks (female audio connectors). Audio connectors such as these may be provided in a variety of form factors. Most commonly, audio connectors take the form of 3.5 mm (⅛″) miniature plugs and jacks. Other sizes are also sometimes used such as 2.5 mm subminiature connectors and ¼ inch connectors. In the context of accessories such as headsets, these audio connectors and their associated cables are generally used to carry analog signals such as audio signals for speakers and microphone signals. Digital connectors such as universal serial bus (USB) and Firewire® (IEEE 1394) connectors may also be used by electronic devices to connect to external equipment such as headsets, but it is often preferred to connect headsets to electronic devices using standard audio connectors such as the 3.5 mm audio connector. Digital connectors such as USB connectors and IEEE 1394 connectors can be of use where large volumes of digital data need to be transferred with external equipment such as when connecting to a peripheral device such as a printer. Optical connectors, which may be integrated with digital and analog connectors, may be used to convey data between an electronic device and an associated accessory, particularly in environments that carry high bandwidth traffic such as video traffic. If desired, audio connectors may include optical communications structures to support this type of traffic. 
     The audio connectors that may be used in connecting an electrical device to external equipment may have a number of contacts. Stereo audio connectors typically have three contacts. The outermost end of an audio plug is typically referred to as the tip. The innermost portion of the plug is typically referred to as the sleeve. A ring contact lies between the tip and the sleeve. When using this terminology, stereo audio connectors such as these are sometimes referred to as tip-ring-sleeve (TRS) connectors. The sleeve can serve as ground. The tip contact can be used in conjunction with the sleeve to handle a left audio channel and the ring contact can be used in conjunction with the sleeve to handle the right channel of audio (as an example). In four-contact audio connectors an additional ring contact is provided to form a connector of the type that is sometimes referred to as a tip-ring-ring-sleeve (TRRS) connector. Four-contact audio connectors may be used to handle a microphone signal, left and right audio channels, and ground (as an example). 
     Electrical devices and external equipment may be connected in various ways. For example, a user may connect either a pair of stereo headphones or a headset that contains stereo headphones and a microphone to a cellular telephone audio jack. Electrical devices and external equipment may also be operated in various modes. For example, a cellular telephone may be used in a music player mode to play back stereo audio to a user. When operated in telephone mode, the same cellular telephone may be used to play telephone call left and right audio signals to the user while simultaneously processing telephone call microphone signals from the user. Some headsets may have noise cancellation functionality. When operated in noise cancellation mode, ambient noise signals that are gathered by the headset may be processed locally or may be routed to the electronic device to implement noise reduction. 
     Electronic devices and external equipment may be provided with path configuration circuitry that allows the electronic devices and external equipment to be operated in a variety of different operating modes in a variety of different combinations. When, for example, a user connects one type of accessory to an electronic device, the path configuration circuitry may be adjusted to form several unidirectional paths between the electronic device and the accessory. When the user connects a different type of accessory to the electronic device or desires to operate the device and accessory in a different mode, the path configuration circuitry may be adjusted to form one or more bidirectional paths in place of one or more of the unidirectional paths. The path configuration circuitry may also be used to configure the wired path between an electronic device and attached external equipment to convey power signals or digital data in place of analog signals such as audio. Combinations of these arrangements may also be used. 
     An illustrative system in which an electronic device and external equipment with path configuration circuitry may communicate over a wired path is shown in  FIG. 1 . As shown in  FIG. 1 , system  10  may include an electronic device such as electronic device  12  and external equipment  14 . External equipment  14  may be equipment such as an automobile with a sound system, consumer electronic equipment such as a television or audio receiver with audio capabilities, a peer device (e.g., another electronic device such as device  12 ), or any other suitable electronic equipment. In a typical scenario, which is sometimes described herein as an example, external equipment  14  may be an accessory such as a headset. External equipment  14  is therefore sometimes referred to as “accessory  14 .” This is, however, merely illustrative. Accessory  14  may be any suitable electronic equipment if desired. 
     A path such as path  16  may be used to connect electronic device  12  and accessory  14 . In a typical arrangement, path  16  includes one or more audio connectors such as 3.5 mm plugs and jacks or audio connectors of other suitable sizes. Conductive lines in path  16  may be used to convey signals over path  16 . There may, in general, be any suitable number of lines in path  16 . For example, there may be two, three, four, five, or more than five separate lines. These lines may be part of one or more cables. Cables may include solid wire, stranded wire, shielding, single ground structures, multi-ground structures, twisted pair structures, or any other suitable cabling structures. Extension cord and adapter arrangements may be used as part of path  16  if desired. In an adapter arrangement, some of the features of accessory  14  such as user interface and communications functions may be provided in the form of an adapter accessory with which an auxiliary accessory such as a headset may be connected to device  12 . 
     Accessory  14  may be any suitable equipment or device that works in conjunction with electronic device  12 . Examples of accessories include audio devices such as audio devices that contain or work with one or more speakers. Speakers in accessory  14  may be provided as earbuds or as part of a headset or may be provided as a set of stand-alone powered or unpowered speakers (e.g., desktop speakers). Accessory  14  may, if desired, include audio-visual (AV) equipment such as a receiver, amplifier, television or other display, etc. Devices such as these may use path  16  to receive audio signals from device  12 . The audio signals may, for example, be provided in the form of analog audio signals that need only be amplified or passed to speakers to be heard by the user of device  12 . One or more optional microphones in accessory  14  may pass analog microphone signals to device  12 . For example, one microphone may be used to gather voice signals from a user, while one, two, or more than two additional microphones may be used to gather ambient noise signals to implement noise cancellation functions. Buttons or other user interface devices may be used to gather user input for device  12 . The use of these and other suitable accessories in system  10  is merely illustrative. In general, any suitable external equipment may be used in system  10  if desired. 
     Electronic device  12  may be a desktop or notebook computer, a portable electronic device such as a tablet computer or handheld electronic device that has wireless capabilities, equipment such as a television or audio receiver, or any other suitable electronic equipment. Electronic device  12  may be provided in the form of stand-alone equipment (e.g., a handheld device that is carried in the pocket of a user) or may be provided as an embedded system. Examples of systems in which device  12  may be embedded include automobiles, boats, airplanes, homes, security systems, media distribution systems for commercial and home applications, display equipment (e.g., computer monitors and televisions), etc. 
     In a typical scenario, device  12  may be, as an example, a handheld device that has media player and cellular telephone capabilities. Accessory  14  may be a headset with one or more microphones and a user input interface such as a button-based interface for gathering user input. Path  16  may be a four or five conductor audio cable that is connected to devices  12  and  14  using 3.5 mm audio jacks and plugs (as an example). 
     While paths such as path  16  may be based on commonly available digital connectors such as USB or IEEE 1394 connectors, it may be advantageous to use standard audio connectors such as a 3.5 mm audio connector to connect device  12  to accessory  14 . Connectors such as these are in wide use for handling audio signals. As a result, many users have a collection of headsets and other accessories that use 3.5 mm audio connectors. The use of audio connectors such as these may therefore be helpful to users who would like to connect their existing audio equipment to device  12 . Consider, as an example, a user of a media player device. Media players are well known devices for playing media files such as audio files and video files that contain an audio track. Many owners of media players own one or more headsets that have audio plugs that are compatible with standard audio jacks. It would therefore be helpful to users such as these to provide device  12  with such a compatible audio jack, notwithstanding the potential availability of additional ports such as USB and IEEE 1394 high speed digital data ports for communicating with external devices. 
     To accommodate different types of headsets and different types of operation, the circuitry in device  12  and accessory  14  may be configurable. For example, electronic device  12  and accessory  14  may include adjustable path configuration circuitry that can be configured to selectively connect different circuit components to the various contacts in the audio connectors as needed. 
     The path configuration circuitry may be adjusted to support different modes of operation. These different modes of operation may result from different combinations of accessories and electronic devices, scenarios in which different device applications are active, etc. With one suitable configuration, the path configuration circuitry may include hybrid circuits that can be selectively switched into use. When the hybrid circuits are not actively used, the communications line to which they are connected may be used primarily or exclusively for unidirectional analog signal communications (e.g., audio communications). When the hybrid circuits are switched into active use, the same communications line may be used to support bidirectional audio signals or other analog signals (e.g., an outgoing left or right audio channel in one direction and an incoming microphone signal in the opposite direction). 
     Because unidirectional paths may be selectively converted into bidirectional paths, it is possible to accommodate additional signals over the wired path between electronic device  12  and accessory  14 . These additional signals may include power signals (e.g., a power supply voltage that the external equipment provides to electronic device  12  to charge a battery in device  12  or a power supply voltage that device  12  supplies to external equipment  14  to power circuitry such as noise cancellation circuitry), data signals (e.g., analog or digital audio signals or signals for display or control functions), user input signals (e.g., signals from button presses or other user input activity), sensor signals, or other suitable signals. 
     A generalized diagram of an illustrative electronic device  12  and accessory  14  is shown in  FIG. 2 . In the  FIG. 2  example, device  12  and accessory  14  are shown as possibly including numerous components for supporting communications and processing functions. If desired, some of these components may be omitted, thereby reducing device cost and complexity. The inclusion of these components in the schematic diagram of  FIG. 2  is merely illustrative. 
     Device  12  may be, for example, a computer or handheld electronic device that supports cellular telephone and data functions, global positioning system capabilities, and local wireless communications capabilities (e.g., IEEE 802.11 and Bluetooth®) and that supports handheld computing device functions such as internet browsing, email and calendar functions, games, music player functionality, etc. Accessory  14  may be, for example, a headset with or without one or more microphones, a set of stand-alone speakers, audio-visual equipment, an adapter, an external controller (e.g., a keypad), a sound system such as an automobile stereo system, or any other suitable external equipment that may be connected to device  12 . 
     As shown in  FIG. 2 , device  12  may include power circuitry  170  and accessory  14  may include power circuitry  172 . Power circuitry  170  and  172  may include batteries such as rechargeable batteries, power adapter circuitry such as alternating current to direct current converter circuitry, battery charging circuitry, etc. 
     If desired, power circuitry  172  may supply power to device  12  over path  16  (e.g., to recharge a battery in device  12 .). Power circuitry  172  may, for example, be provided as part of the stereo system and other electronic equipment in an automobile. An audio cable may be used to connect device  12  to the automobile stereo system (e.g., using the audio cable to form path  16 ). When a user plugs device  12  into the automobile&#39;s electronics in this way, power circuitry  172  in the automobile may be used to deliver direct current (DC) power to power circuitry  170  in device (e.g., to recharge a battery in device  12  through one of the conductive lines in path  16 ). 
     In other arrangements, power may be delivered from device  12  to accessory  14  over one of the lines in path  16 . For example, a handheld electronic device battery in circuitry  170  of device  12  may supply power to circuitry  172  and to amplifier circuitry and other circuitry in an accessory  14  such as a headset. 
     By using path configuration circuitry, one or more of the lines in path  16  can be converted to power delivery lines in some situations (e.g., during certain modes of operation and when certain types of components are used) and may be converted to analog audio lines, digital data lines, or other types of lines in other situations. If desired, lines in path  16  may be used to deliver power (e.g., a relatively small amount of microphone bias power or a relatively larger amount of power for operating noise cancellation circuitry or other circuitry) while simultaneously conveying analog or digital signals (e.g., analog audio signals such as voice microphone signals or noise cancellation signals). For example, power may be delivered in one direction while analog or digital signals are conveyed in the opposite direction. 
     Device  12  and accessory  14  may include storage  126  and  144 . Storage  126  and  144  may include one or more different types of storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory), volatile memory (e.g., static or dynamic random-access-memory), etc. 
     Processing circuitry  128  and  146  may be used with storage  126  and  144  to control the operation of device  12  and accessory  14 . Processing circuitry  128  and  146  may be based on processors such as microprocessors and other suitable integrated circuits. These circuits may include application-specific integrated circuits, audio codecs, video codecs, amplifiers, communications interfaces, power management units, power supply circuits, circuits that control the operation of wireless circuitry, radio-frequency amplifiers, digital signal processors, analog-to-digital converters, digital-to-analog converters, or any other suitable circuitry. 
     With one suitable arrangement, processing circuitry  128  and  146  and storage  126  and  144  are used to run software on device  12  and accessory  14 . The complexity of the applications that are implemented depends on the needs of the designer of system  10 . For example, the software may support complex functionality such as internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, and less complex functionality such as the functionality involved in encoding button presses as ultrasonic tones. 
     To support communications over path  16  and to support communications with external equipment, processing circuitry  128  and  146  and storage  126  and  144  may be used in implementing suitable communications protocols. Communications protocols that may be implemented using processing circuitry  128  and  146  and storage  126  and  144  include internet protocols, wireless local area network protocols (e.g., IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol, protocols for handling 3 G communications services (e.g., using wide band code division multiple access techniques), 2G cellular telephone communications protocols, serial and parallel bus protocols, etc. In a typical arrangement, more complex functions such as wireless functions are implemented exclusively or primarily on device  12  rather than accessory  14 , but accessory  14  may also be provided with some or all of these capabilities if desired. 
     Input-output devices  130  and  148  may be used to allow data to be supplied to device  12  and accessory  14  and may be used to allow data to be provided from device  12  and accessory  14  to external destinations. Input-output devices  130  and  148  can include devices such as non-touch displays and touch displays (e.g., based on capacitive touch or resistive touch technologies as examples). Visual information may also be displayed using light-emitting diodes and other lights. Input-output devices  130  and  148  may include one or more buttons. Buttons and button-like devices may include keys, keypads, momentary switches, sliding actuators, rocker switches, click wheels, scrolling controllers, knobs, joysticks, D-pads (direction pads), touch pads, touch sliders, touch buttons, and other suitable user-actuated control interfaces. Input-output devices  130  and  148  may also include microphones, speakers, digital and analog input-output port connectors and associated circuits, cameras, etc. Wireless circuitry in input-output devices  130  and  148  may be used to receive and/or transmit wireless signals. 
     As shown schematically in  FIG. 2 , input-output devices  130  may sometimes be categorized as including user input-output devices  132  and  150 , display and audio devices  134  and  152 , and wireless communications circuitry  136  and  154 . A user may, for example, enter user input by supplying commands through user input devices  132  and  150 . Display and audio devices  134  and  152  may be used to present visual and sound output to the user. These categories need not be mutually exclusive. For example, a user may supply input using a touch screen that is being used to supply visual output data. 
     As indicated in  FIG. 2 , wireless communications circuitry  136  and  154  may include antennas and associated radio-frequency transceiver circuitry. For example, wireless communications circuitry  136  and  154  may include communications circuitry such as radio-frequency (RF) transceiver circuitry formed from one or more integrated circuits, power amplifier circuitry, passive RF components, antennas, and other circuitry for handling RF wireless signals. Wireless signals can also be sent using light (e.g., using infrared communications). 
     The antenna structures and wireless communications devices of devices  12  and accessory  14  may support communications over any suitable wireless communications bands. For example, wireless communications circuitry  136  and  154  may be used to cover communications frequency bands such as cellular telephone voice and data bands at 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, and 2100 MHz (as examples). Wireless communications circuitry  136  and  154  may also be used to handle the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz (also sometimes referred to as wireless local area network or WLAN bands), the Bluetooth® band at 2.4 GHz, and the global positioning system (GPS) band at 1575 MHz. 
     Although both device  12  and accessory  14  are depicted as containing wireless communications circuitry in the  FIG. 2  example, there are situations in which it may be desirable to omit such capabilities from device  12  and/or accessory  14 . For example, it may be desired to power accessory  14  solely with a low-capacity battery or solely with power received through path  16  from device  12 . In situations such as these, the use of extensive wireless communications circuitry may result in undesirably large amounts of power consumption. For low-power applications and situations in which low cost and weight are of primary concern, it may therefore be desirable to limit accessory  14  to low-power-consumption wireless circuitry (e.g., infrared communications) or to omit wireless circuitry from accessory  14 . Moreover, not all devices  12  may require the use of extensive wireless communications capabilities. A hybrid cellular telephone and media player device may benefit from wireless capabilities, but a highly portable media player may not require wireless capabilities and such capabilities may be omitted to conserve cost and weight if desired. 
     Transceiver circuitry  120  and  138  may be used to support communications between electronic device  12  and accessory  14  over path  16 . In general, both device  12  and accessory  14  may include transmitters and receivers. For example, device  12  may include a transmitter that produces signal information that is received by receiver  142  in accessory  14 . Similarly, accessory  14  may have a transmitter  140  that produces data that is received by receiver  124  in device  12 . If desired, transmitters  122  and  140  may include similar circuitry. For example, both transmitter  122  and transmitter  140  may include ultrasonic tone generation circuitry (as an example). Receivers  124  and  142  may each have corresponding tone detection circuitry. Transmitters  122  and  140  may also each have DC power supply circuitry for creating various bias voltages (which may be constant or which may be varied occasionally to convey information or to serve as a control signals), digital communications circuitry for transmitting digital data, analog signal transmission circuitry, or other suitable transmitter circuitry, whereas receivers  124  and  142  may have corresponding receiver circuitry such as voltage detector circuitry, analog components or receiver circuitry, digital receivers, etc. Symmetric configurations such as these may allow comparable amounts of information to be passed in both directions over link  16 , which may be useful when accessory  14  needs to present extensive information to the user through input-output devices  148  or when extensive handshaking operations are desired (e.g., to support advanced security functionality). 
     It is not, however, generally necessary for both device  12  and accessory  14  to have identical transmitter and receiver circuitry. Device  12  may, for example, be larger than accessory  14  and may have available on-board power in the form of a rechargeable battery, whereas accessory  14  may be unpowered (and receiving power only from device  12 ) or may have only a small battery (for use alone or in combination with power received from device  12 ). As another example, accessory  14  may be part of a relatively complex system, whereas device  12  may be formed in a small housing that limits the amount of circuitry that may be used in device  12 . In situations such as these, it may be desirable to provide device  12  and accessory  14  with different communications circuitry. 
     As an example, transmitter  122  in device  12  may include adjustable DC power supply circuitry. By placing different DC voltages on the lines of path  16  at different times, device  12  can communicate relatively modest amounts of data to accessory  14 . This data may include, for example, data that instructs accessory  14  to power its microphone (if available) or that instructs accessory  14  to respond with an acknowledgement signal. A voltage detector and associated circuitry in receiver  138  of accessory  14  may process the DC bias voltages that are received from device  12 . In this type of scenario, transmitter  140  in accessory  14  may include an ultrasonic tone generator that supplies acknowledgement signals and user input data (e.g., button press data) to device  12 . A tone detector in receiver  124  may decode the tone signals for device  12 . To support higher data rate transmissions between device  12  and accessory  14 , device  12  may include an ultrasonic tone generator in transmitter  122  that transmits ultrasonic tones to a corresponding ultrasonic tone receiver in receiver  142  of accessory  14 . If desired, patterns of tones may be transmitted by ultrasonic tone generators in transmitters  122  and  140  (e.g., patterns corresponding to particular commands or other information). These are merely illustrative examples. Device  12  and accessory  14  may include any suitable transceiver circuitry for communicating data using any suitable communications protocol if desired. 
     Applications running on the processing circuitry of device  12  may use decoded user input data as control signals. As an example, a cellular telephone application may interpret user input as commands to answer or hang up a cellular telephone call, a media playback application may interpret user input as commands to skip a track, to pause, play, fast-forward, or rewind a media file, etc. Still other applications may interpret user button-press data or other user input as commands for making menu selections, etc. 
     One illustrative circuit that may be used for one or more of the lines in path  16  is the circuitry of  FIG. 3 . Circuitry  216  of  FIG. 3  may include circuitry such as circuitry  180  that is located in device  12  and circuitry such as circuitry  182  that is located in accessory  14 . Line  218  may be one of the lines in path  16 . Ground node  198  may be provided with a ground voltage (e.g., from accessory  14  and/or from device  12 ). Node  198  and resistor  200  may be located in accessory  14  or in device  12 . For example, node  198  and resistor  200  may be located in accessory  14  and may be coupled to a ground voltage source such as a ground line in path  16 . As another example, node  198  may be located in device  12  and resistor  200  may be located in accessory  14 . 
     When configured as shown in  FIG. 3 , the circuitry of  FIG. 3  may support bidirectional communications. The signals that are conveyed over path  218  in  FIG. 3  may, for example, be analog signals such as microphone signals or left or right channel audio signals. Signals such as these typically lie in a frequency range of about 20 Hz to 20 kHz. If desired, ultrasonic signals (e.g., tones above 20 kHz in frequency such as 75 kHz to 300 kHz tones) may be conveyed over path  218 . Still other signals such as digital pulses or tones or other signals in normal audio frequency ranges may be conveyed if desired. 
     Circuitry  216  may include circuits  184  and  186  (sometimes referred to as “hybrids”). Circuit  184  has input port  188  and output port  190 . Common port  220  serves as both an input and an output for circuit  184 . Current source  196  is connected between line  194  and power supply  208  and is modulated by the input signal on input  188 . Circuit  186  has input port  212  and output port  214 . Common port  222  serves as both an input and an output for circuit  186 . Modulated current source  204  is connected between line  224  and power supply  210  and is controlled by the magnitude of the input signal on input  212 . 
     In the example of  FIG. 3 , circuit  184  receives an input voltage signal A on input  188  and circuit  186  receives an input voltage signal B on input  212 . In response, a current proportional to A flows through current source  196  and a current proportional to B flows through current source  204 . A resulting sum current that is proportional to A+B flows from node  202  to ground node  198  via resistor  200  and produces a voltage that is proportional to the sum of voltages A and B (i.e., the voltage at node  202  is proportional to A+B as shown in  FIG. 3 ). Because the voltage at node  202  is equal to the sum of A and B, a node such as node  202  may sometimes be referred to as a summing node and a resistor such as resistor  200  may sometimes be referred to as a summing resistor. Current sources  196  and  204  are controlled by input voltages and may therefore sometimes be referred to as transconductance amplifiers (i.e., amplifiers that receive input voltages and that produce corresponding output currents). 
     Circuit  184  has a summing circuit such as difference amplifier  192  with a negative input (−) and a positive input (+). This type of circuit may also be referred to as a summer, a differential amplifier circuit, a mixer, etc. The positive input of amplifier  192  receives the signal A from input  188  (e.g., from attenuator  176 ) while the negative input receives the common signal A+B from common input  220 . The resulting output of amplifier  192  is proportional to signal B and is provided to output  190 . In circuitry  186 , the negative input of amplifier  206  receives the common signal A+B from common input  222  while the positive input of amplifier  206  receives the signal B from input  212  (e.g., via attenuator  178 ). A corresponding output proportional to signal A is produced by amplifier  206  and is routed to output  214 , as shown in  FIG. 3 . 
     Optionally, circuit  184  may have an attenuator circuit such as circuit  176  and circuitry  186  may have an attenuator circuitry such as circuit  178 . With this type of arrangement, the gains of current sources  196  and  204  and the resistance of summing resistor  200  may be selected to match the attenuator circuits  176  and  178 . As one example, circuit  176  may reduce the voltage of signal A received by amplifier  192  by one-fourth and circuit  178  may reduce the voltage of signal B received by amplifier  206  by one-fourth. The gain (g m ) of current source  196  may be approximately equal to the gain (g m ) of current source  204  (e.g., the amount of current the current source produces as a function of the input voltage). In addition, the gain (g m ) of current sources  196  and  204  and the resistance (R) of resistor  200  may be configured such that the product of the gain (g m ) and the resistance (R) of resistor  200  is approximately equal to 0.25 (e.g., g m *R=¼). In this example, the common signal A+B on line  218  may be approximately equal to A/4+B/4 and the signals A and B on outputs  214  and  190  may be approximately equal to A/4 and B/4, respectively. 
     Device  12  and accessory  14  may, if desired, include path configuration circuitry such as switches and other configurable circuitry. The path configuration circuitry may be configured to selectively switch circuitry such as circuitry  216  of  FIG. 3  into use or out of use as desired. In situations in which the bidirectional nature of path  216  is desired, path configuration circuitry may be adjusted to switch circuits such as circuits  184  and  186  into use and thereby selectively form a directional path between device  12  and accessory  14 . In other situations, where only a unidirectional path is desired, the path configuration circuitry can be adjusted to switch circuits  184  and  186  out of use. 
     Circuitry  216  supports bidirectional (full duplex) communications. Device  12  may supply signal A to accessory  14  while accessory  14  simultaneously supplies signal B to device  12 . Signal A may sometimes be referred to herein as an output (OUT) signal as signal A is output by device  12  to accessory  14  and signal B may sometimes be referred to herein as an input (IN) signal as signal B is received by device  12  from accessory  14 . The signals that are transmitted in this way may be, for example, analog audio signals (e.g., analog signals in the audible frequency range of 20 Hz to 20 kHz), ultrasonic tones (e.g., tones at frequencies above 20 kHz that may be used alone or in patterns to represent control data or other signals), digital data, etc. The voltage that is supplied to power supply  210  may be conveyed over a separate power line in path  16 . If desired, the power line may also be used to bias a microphone in accessory  14  and to provide power to circuitry in accessory  14 . 
     Circuit pairs such as the pair of circuits of  FIG. 3  may be included in one of the lines in path  16 , in two of the lines in path  16 , or in more than two of the lines in path  16 . For example, circuitry  216  may include two pairs of hybrid circuits that provide two separate bidirectional communications paths. With this type of arrangement, circuitry  216  can simultaneously convey analog audio output (e.g., left and right channels of audio playback for accessory  14 ), ambient noise signals (e.g., signals from microphones in accessory  14  used by device  12  to produce noise cancellation signals in the analog audio output), and positive and ground power supply voltages (e.g., to power circuitry in accessory  14 ). With another implementation, circuitry  216  can simultaneously convey analog audio output (e.g., left and right channels of audio playback for accessory  14 ), microphone input (e.g., microphone signals and microphone ambient noise signals for device  12 ), and positive and ground power supply voltages (e.g., to power circuitry in accessory  14 ). 
       FIG. 4  shows an illustrative circuit configuration in which the left and right audio lines in path  16  have been provided with hybrid pairs. Audio connectors  46  may have four contacts each (i.e., tip, ring, ring, and sleeve contacts in a 3.5 mm connector pair). These contacts and the associated lines in the path  16  between device  12  and equipment  14  are labeled as L (left audio), R (right audio), PWR (power), and GND (ground). In the  FIG. 4  example, hybrids  236  and  264  form a first hybrid pair and hybrids  242  and  266  form a second hybrid pair. The first hybrid pair can be selectively switched into the left channel (L) audio path when it is desired to make the left channel path directional. When the first hybrid pair is not needed, a left channel bypass path may be switched into use. The second hybrid pair can likewise be selectively switched into the right channel (R) audio path when it is desired to make the right channel path bidirectional path. A right channel bypass path can be switched into use to bypass the second hybrid pair when the second hybrid pair is not needed. 
     The bidirectional paths formed by the first and second hybrid pairs can be used to convey any suitable signals between device  12  and accessory  14 . In the  FIG. 4  example, the bidirectional L and R paths are being used to route left and right audio from device  12  to accessory  14  while microphone signals are simultaneously being routed from accessory  14  to device  12 . The microphone signals may include, for example, voice microphone signals and noise cancellation microphone signals. 
     Device  12  may have one or more circuits such as circuit  226 . Circuit  226  may include storage and processing circuitry and may be implemented using one or more integrated circuits and other suitable circuit components. With one suitable arrangement, which is sometimes described as an example, circuit  226  may include an audio integrated circuit (sometimes referred to as a codec). Circuit  226  may generate right channel audio output (R_OUT) on right channel audio output  232  and can generate left channel audio output (L_OUT) on left channel audio output  244 . 
     Audio input can be received at audio inputs  238  and  240 . Analog-to-digital converter circuitry in circuit  226  can be used to digitize incoming audio signals. These signals can then be processed by the other storage and processing circuitry in device  12 . Circuit  226  may include active noise reduction circuits that use noise cancellation signals received using audio inputs  238  and  240  to remove noise from the left and right channel audio outputs (L_OUT and R_OUT). If desired, the active noise reduction circuits may include one or more differential amplifiers that can subtract the noise cancellation signals received using audio input  238  from the right channel audio output (R_OUT) and can subtract the noise cancellation signals received using audio input  240  from the left channel audio output (L_OUT). 
     The incoming audio signals on inputs  238  and  240  may correspond to microphone signals. Accessory  14  may have microphones such as microphones M 1  and M 2 . Accessory  14  may also have a right-channel speaker such as speaker SR and a left-channel speaker such as speaker SL. Microphones M 1  and M 2  may be mounted in the vicinity of speakers SL and SR, respectively. In this type of configuration, microphones M 1  and M 2  may pick up ambient noise in the vicinity of speakers SL and SR and may therefore serve as noise cancelling microphones for speakers SL and SR, respectively. As another example, microphone M 1  may be used to monitor the user&#39;s voice and microphone M 2  may be used to pick up ambient noise in the vicinity of microphone M 1 , so that the microphone signals from microphone M 2  can be used to reduce noise for microphone M 1 . 
     Noise cancellation operations can, in general, be implemented locally in accessory  14  or remotely in device  12 . In the  FIG. 4  arrangement, remote noise reduction for speakers SL and SR can be implemented using signals from noise reductions microphones M 1  and M 2  (e.g., using the hardware of device  12  such as circuit  226 ). Signals from microphone M 1  may be received by hybrid circuit  264  on input  268  and conveyed to hybrid circuit  236  over left channel audio path (L). Signals from microphone M 2  may be received by hybrid circuit  266  on input  270  and conveyed to hybrid circuit  242  over right channel audio path (R). While microphone signals are routed from microphone M 1  to input  240  over the left channel audio path (L) using hybrids  236  and  264 , audio output signals from the left channel audio output  244  may be routed in the opposite direction over the same path. Likewise, while microphone signals are routed from microphone M 2  to input  238  over the right channel audio path (R) using hybrids  242  and  266 , audio output signals from the right channel audio output  232  may be routed in the opposite direction over the same path. 
     When noise cancellation functions are implemented remotely in device  12 , circuit  226  can implement noise cancellation functions (e.g., subtraction functions in which ambient noise is removed from the voice microphone) using the relatively extensive processing capabilities available in circuit  226  and device  12 , thereby reducing the processing burden on the circuitry of accessory  14 . 
     While microphone signals from M 1  and M 2  are being conveyed from accessory  14  to device  12 , audio signals may be routed over the right and left channel audio lines to speakers SR and SL. The audio signals may be separate left and right channel audio signals or may be a mono signal that has been replicated on both channels. The audio signals may correspond to any suitable content such as a voice in a voice telephone call or a media file in a media playback operation. 
     The operation of the transconductance amplifiers and summers in the hybrids consumes power. Power can be conserved and high-quality audio playback can be obtained by bypassing the hybrid circuits when bidirectionality is not required. As an example, the hybrids may be bypassed when microphones M 1  and M 2  are not being used (e.g., when noise cancellation functions are disabled), but audio playback is still desired. With another example, the hybrids may be bypassed when supporting legacy accessories (i.e., accessories without extensive noise cancellation functions or other capabilities that draw larger amounts of power). Lower-power modes can also be used when it is desired to conserve battery power. In this type of example, the power (PWR) line in path  16  may provide a relatively high-impedance power supply voltage that can be used as a microphone bias signal. 
     The power (PWR) and ground (GND) lines in the path  16  may convey power supply signals between device  12  and accessory  14 . Accessory  14  may use the power supply signals on the power (PWR) and ground (GND) lines in path  16  to generate microphone bias signals and other power supply voltages in accessory  14 . The power supply signals from the power (PWR) and ground (GND) lines may be used to power left and right audio amplifiers (e.g., to amplify the L_OUT and R_OUT signals for the left and right speakers SL and SR), hybrid circuits, audio processing circuits, displays, and other circuits and components in accessory  14  (as examples). 
     With one suitable arrangement, the ground line (GND) in path  16  may include two or more separate ground lines that converge near the ground audio connector  46  as illustrated in the example of  FIG. 5 . As shown in  FIG. 5 , the ground line (GND) in path  16  may include a first signal ground line (SGND 1 ), a second signal ground line (SGND 2 ), and a power ground line (PGND) that run the length of path  16  and converge at (or just before) the ground connector  46  in path  16  that is used to connect to device  12 . As shown schematically in  FIG. 5 , each of the lines in path  16  may have an associated non-zero resistance  272 . 
     If desired, the power ground line (PGND) may serve as the ground line for relatively high power components in accessory  14  such as differential amplifiers, audio amplifiers, processing circuits, displays, etc. The signal ground lines (SGND 1  and SGND 2 ) may serve as the ground lines for relatively low power components in accessory  14 . In particular, the signal ground lines may serve as the ground lines for components that handle signals such as L_OUT, L_IN, R_OUT, and R_IN. This type of arrangement may help to reduce noise in components that use the signal ground lines. If desired, the first signal ground line (SGND 1 ) may be used in components that handle the left audio channel signals (L_IN and L_OUT) and the second signal ground line (SGND 2 ) may be used in components that handle the right audio channel signals (R_IN and R_OUT). This helps to reduce cross talk. 
     Device  12  may include circuitry that monitors ground signals on the ground audio connector  46  in device  12 . As one example, a ground detect line (GND_DET) may be connected to the ground audio connector  46  in device  12  as shown in  FIG. 5  to sense variations in the voltage on the ground lines in path  16 . 
       FIG. 6  shows an illustrative circuit configuration in device  12  in which a pair of hybrid circuits can be coupled to the left and right audio lines in path  16  to provide two bidirectional paths between device  12  and external equipment  14 . As shown in  FIG. 6 , hybrid circuit  236  of  FIG. 4  may be formed from circuit  276 , circuit  278 , and from shared circuit  274  (e.g., a circuit that produces a shared reference voltage such as reference voltage VB 1 ). Hybrid circuit  242  may be formed from circuit  280 , circuit  282 , and from shared circuit  274 . 
     Shared circuit  274  may generate one or more reference voltages such as reference voltage VB 1  for circuits  276  and  280  (as examples). With one arrangement, circuit  274  may receive a power supply voltage VDD 1  from device  12  and may generate the reference voltage VB 1 . As one example, the power supply voltage VDD 1  may be 3.0 volts. 
     Capacitors C 3  and C 4  in circuit  274  may help to reduce noise in circuit  274 . In general, capacitors C 3  and C 4  may have any suitable capacitances. The capacitances of capacitors C 3  and C 4  need not be equal. As one example, capacitors C 3  and C 4  may each have a capacitance of 1.0 microfarads (1.0 μF). 
     Zener diode U 4  may provide a reference voltage difference between VDD 1  and a node between resistors R 21  and R 22 . With one suitable arrangement, zener diode U 4  may be configured to have a breakdown voltage of approximately 1.225 volts (e.g., to maintain the node between resistors R 21  and R 22  within 1.225 volts of the voltage VDD 1 ). 
     Resistors R 22  and R 23  may form a voltage divider that provides the positive input to amplifier U 3 A in circuit  274 . In general, resistors R 22  and R 23  may have any suitable resistances. As one example, resistors R 22  and R 23  may have resistances of approximately 75.0 kilohms and 118.0 kilohms, respectively. Resistor R 21  may have a resistance of approximately 22.1 kilohms (as an example). With this type of arrangement, the voltage divider formed by resistors R 22  and R 23  may generate a voltage at VDD 1 −0.75 volts and may provide the voltage to the positive input of amplifier U 3 A. 
     Amplifier U 3 A may receive the voltage at VDD 1 −0.75 volts and may be configured as a voltage follower that generates an output at VDD 1 −0.75 volts (e.g., the negative input of the amplifier may be coupled to the output of the amplifier). The output of amplifier U 3 A may be fed into a voltage divider formed by resistors R 24  and R 25 . The output of the voltage divider may be a shared reference voltage VB 1  that is used by both circuits  276  and  280 . In general, resistors R 24  and R 25  may have any suitable resistances. Resistor R 24  may have a resistance that is half the resistance of resistor R 25 . As one example, resistors R 24  and R 25  may have resistances of 22.1 kilohms and 44.2 kilohms, respectively. With this type of arrangement, the output of the voltage divider formed by resistors R 24  and R 25  may be two-thirds of its input (e.g., ⅔*(VDD 1 −0.75) volts). 
     Circuit  276  may be a part of hybrid circuit  236 . In operation, circuit  276  may function as a current source (such as current source  196  of  FIG. 3 ) that produces a current on the left channel (L) audio line in path  16 . The current produced by circuit  276  may be proportional to the left channel audio signals (L_OUT) output by codec circuit  226 . Capacitor C 1  may help to reduce noise in circuit  276  and may have any suitable capacitance. As one example, capacitor C 1  may have a capacitance of 1.0 microfarads. Circuit  276  may have an amplifier U 1 A with a positive input connected to the power supply voltage VDD 1  through a resistor such as resistor R 1 . As one example, resistor R 1  may have a resistance of 7.5 kilohms. The amplifier U 1 A may be configured as a voltage follower with the negative input coupled to the output of the amplifier. With one suitable arrangement, the output and negative input of amplifier U 1 A may be coupled to the left audio output (L_OUT) of codec  226  through resistors R 2  and R 3 . Resistor R 2  may have a resistance that is half of the resistance of resistor R 3 . As one example, resistors R 2  and R 3  may have resistance of approximately 22.1 kilohms and 44.2 kilohms, respectively. The amplifier U 1 A may help to prevent current from power supply line VDD 1  from passing into and through resistor R 2  while providing the voltage of its positive input to resistor R 2 . 
     Differential amplifier U 1 B may have a positive input that receives the reference voltage VB 1  from circuit  274  and a negative input connected to a node between resistors R 2  and R 3 . With this type of arrangement, when the voltage on output  244  (i.e., L_OUT) is zero, the output of amplifier U 1 B may be at (VDD 1 −0.75−VBE(Q 1 )) volts and the output current of transistor Q 1  may be determined by dividing 0.75 volts by the resistance of resistor R 1 . VBE(Q 1 ) may represent the voltage drop across the base and emitter terminals of transistor Q 1 . When the voltage on output  244  is nonzero, the output of amplifier U 1 B may be reduced by a given factor equal to the voltage of output  244  multiplied by the resistance of R 2  divided by the resistance of R 3 . The output current of transistor Q 1  in this arrangement may be reduced by the given factor divided by the resistance of resistor R 1 . The output of circuit  276  (i.e., the current added to left channel audio line L in path  16 ) may therefore be proportional to the voltage of output  244  with an additional constant (DC) bias current (e.g., the current of transistor Q 1  when the voltage on output  244  is zero. 
     Circuit  278  may be another part of hybrid circuit  226 . In operation, circuit  278  may receive signals from the left channel audio line L in path  16  and from the output  244  of circuit  226  and may generate left audio channel input signals (L_IN) for input  240  of circuit  226 . Resistors R 5 , R 6 , and R 7  may form an attenuator (see, e.g., attenuator circuit  176  of  FIG. 3 ). In particular, resistors R 5 , R 6 , and R 7  may reduce the voltage of signals from output  244  to one-fourth and provide the reduced voltage to the negative input of amplifier U 1 D. In general, resistors R 5 , R 6 , and R 7  may have any suitable resistances. As one example, resistors R 5 , R 6 , and R 7  may have resistances of approximately 75.0 kilohms, 24.9 kilohms, and 22.1 kilohms, respectively. 
     Circuit  278  may include amplifier U 1 C coupled to the left audio path (L) in path  16 . Amplifier U 1 C may be configured as a voltage follower (e.g., amplifier U 1 C may have its negative input connected to its output). If desired, there may be a resistor such as resistor R 4  located between the left audio path (L) (e.g., the tip connector  45  in device  12 ) and the amplifier U 1 C. Resistor R 4  may provide electrostatic discharge (ESD) protection to device  12 . Resistor R 4  may have any suitable resistance and, as one example, may have a resistance of 4.7 kilohms. 
     Amplifier U 1 D may be configured as a differential amplifier that uses the difference between the voltage on the left audio path (L) and the (attenuated) voltage from the left audio output  244  to generate the input  240  for codec  226  (e.g., to receive the incoming analog signals from accessory  14  conveyed on the bidirectional path L). The differential amplifier U 1 D may have associated resistors R 8 , R 9 , and R 10 . The resistors R 8 , R 9 , and R 10  may have any suitable resistances and, as one example, these resistors may have resistances of 44.2 kilohms, 22.1 kilohms, and 44.2 kilohms, respectively. 
     Circuits  280  and  282  may handle signals carried on the right channel audio path (R) in path  16 . For example, circuits  280  and  282  may handle signals output from the right channel output (R_OUT)  232  and may generate the right channel input (R_IN) for input  238 . With one suitable arrangement (as illustrated in the  FIG. 6  example), circuits  280  and  282  may handle signals for the right channel in a manner equivalent to how circuits  276  and  278  handle signals for the left channel. If desired, the capacitance of capacitor C 2  may be equivalent to capacitor C 1 . The resistances of resistors R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , and R 20  may be approximately equivalent to the corresponding resistors in circuits  276  and  278 . The amplifiers U 2 A, U 2 B, U 2 C, and U 2 D may be configured in a manner equivalent to amplifiers U 1 A, U 2 B, U 2 C, and U 2 D, respectively. If desired, transistor Q 2  may be similar to (or identical to) transistor Q 1 . 
     If desired, device  12  may include power supply circuitry such as circuitry  284 . With one suitable arrangement, circuitry  284  may convert an internal power supply voltage V to the power supply voltage VDD 1  used in the circuitry of  FIG. 6  and a power supply voltage VDD 2  that is fed to accessory  14  over a power supply line (PWR) in path  16 . With one suitable arrangement, the output of circuitry  284  may be coupled to the female power supply connector  45  (e.g., the sleeve connector in device  12 ). As shown schematically by resistor R 30  in  FIG. 6 , there may be a non-zero resistance between the connector  45  in device  12  and circuitry  284 . As one example, the resistance between circuitry  284  and connector  45  may be approximately 1.0 ohms. 
     Circuitry  284  may include capacitors C 10  and C 11 , resistors R 38  and R 39 , and amplifiers U 6  and U 7 . As examples, the capacitor C 10  may have a capacitance of approximately 10.0 microfarads, the capacitor C 11  may have a capacitance of approximately 1.0 microfarads, and the resistors R 38  and R 39  may each have a resistance of approximately 14.0 kilohms. Resistor R 60  is a schematic representation of the resistance between circuitry  284  and the circuits in  FIG. 6  which circuitry  284  powers (e.g., resistance R 60  may have a relatively small resistance). 
     The illustrative circuit configuration of  FIG. 6  may also include a ground noise detection circuit such as circuit  286 . Circuit  286  may be used to sense variations in the voltage of ground lines in path  16  (from parasitic resistances in path  16 ) and to generate signals associated with the variations for codec  226 . With one arrangement, ground noise sensing circuit  286  may provide ground noise signals to the ground detect (GND_DET) input  288  of codec  226 . Codec  226  may use the ground noise signals to reduce noise (e.g., to reduce noise in speakers SL and SR) by adjusting the outputs of the left and right channel audio outputs  355  and  232  as appropriate. 
     Circuit  286  may include an amplifier U 3 B with a positive input connected directly to the ground contact (GND) in the female connector  45  of device  12  that couples with the male ground connector  47  of accessory  14 . Schematically, circuit  286  may also include resistors R 26  and R 27 . Resistors R 26  and R 27  may represent the resistance between the negative input of amplifier U 3 B and the output of the amplifier and the ground in device  12 , respectively. With one suitable arrangement, resistor R 27  may have a resistance of approximately 1.0 ohms and resistor  26  may have a resistance of approximately 30 milliohms. With another suitable arrangement, resistor R 27  may have any suitable resistance and resistor R 26  may have a resistance that is approximately three-hundredths the resistance of resistor R 27 . In general, resistors R 27  and R 26  may have any suitable resistances. 
     Resistors R 29  and R 30  may schematically represent the resistance between the female connectors  45  of device  12  and the circuitry in device  12  connected to those connectors. As one example, resistors R 29  and R 30  may each have a resistance of approximately 1.0 ohms due to parasitic resistances, printed circuit board resistances, and other sources of resistance. Resistors R 29  and R 30  are generally not actual resistors and are shown in  FIG. 6  merely to illustrate parasitic resistances that may exist in the arrangement of  FIG. 6 . 
       FIG. 7  shows an illustrative circuit configuration in external equipment  14  in which a pair of hybrid circuits can be coupled to the left and right audio lines in path  16  to provide two bidirectional paths between device  12  and external equipment  14 . As shown in  FIG. 7 , hybrid circuit  264  of  FIG. 4  may be formed from circuit  302 , circuit  304 , and from shared circuit  300  (e.g., a circuit that produces a shared reference voltage such as reference voltage VB 2  and that produces a microphone bias signal such as V_MIC). Hybrid circuit  266  of  FIG. 4  may be formed from circuit  306 , circuit  308 , and from shared circuit  300 . 
     Shared circuit  300  may generate one or more reference voltages such as reference voltage VB 2  for circuits  302  and  306  (as examples). Circuit  300  may receive a power supply voltage PWR from device  12  over path  16  and may generate the reference voltage VB 2 . With one suitable arrangement, amplifier U 10 A may produce a signal at its output that is approximately equal to the voltage of the power line PWR−0.75 volts (as one example). 
     Circuit  300  may include capacitors such as capacitors C 28 , C 16 , C 17 , and C 18 . With one arrangement, capacitor C 28  may help to reduce noise in circuit  300 . In general, capacitors C 28 , C 16 , C 17 , and C 18  may have any suitable capacitances. The capacitances of these capacitors need not be equal. As one example, capacitors C 28 , C 16 , C 17 , and C 18  may each have a capacitance of 1.0 microfarads. 
     Zener diodes U 11  and U 12  may provide reference voltage differences in circuit  300 . With one suitable arrangement, zener diodes U 11  and U 12  may be configured to have a breakdown voltage of approximately 1.225 volts. 
     Circuit  300  may include resistors R 61 , R 62 , R 63 , R 64 , R 65 , R 66 , R 67 , and R 68 . In general, the resistors in circuit  300  may have any suitable resistances and each of the resistors may have a different resistance. As one example, the resistors R 61 , R 62 , R 63 , R 64 , R 65 , R 66 , R 67 , and R 68  may have resistances of approximately 118.0 kilohms, 75.0 kilohms, 6.2 kilohms, 44.2 kilohms, 44.2 kilohms, 44.2 kilohms, 13.3 kilohms, and 59.0 kilohms, respectively. 
     Circuit  300  may also include amplifiers U 10 A and U 10 B. Amplifier U 10 A may be configured as a voltage follower (e.g., the output of amplifier U 10 A may be connected to its negative input) that produces a voltage approximately equal to the voltage of PWR−0.75 volts. In addition, circuit  300  may include multiple ground points. With one suitable arrangement, circuit  300  may include connections to a signal ground SGND 1  in accessory  14  and connections to a power ground PGND in accessory  14 . The signal ground SGND 1  and the power ground PGND may be connected to signal and power ground lines in path  16  that converge into a single ground line (see, e.g., the  FIG. 5  example). This type of arrangement may help to reduce noise of components in accessory  14  that handle signals that can potentially be sensitive to noise on power supply signals. If desired, a second signal ground such as SGND 2  may be used in circuit  300  in addition to or instead of the signal ground SGND 1 . 
     Circuit  302  may be a part of hybrid circuit  264 . In operation, circuit  302  may function as a current source (such as current source  204  of  FIG. 3 ) that produces a current on the left channel (L) audio line in path  16 . The current produced by circuit  302  may be proportional to the left channel audio signals (L_IN) generated by the left microphone amplifier in circuit  310 . Capacitor C 14  may help to reduce noise in circuit  302  and may have any suitable capacitance. As one example, capacitor C 14  may have a capacitance of 1.0 microfarads. Circuit  302  may have an amplifier U 8 A with a positive input connected to the power supply voltage PWR through a resistor such as resistor R 42 . As one example, resistor R 42  may have a resistance of 7.5 kilohms. The amplifier U 8 A may be configured as a voltage follower with the negative input coupled to the output of the amplifier. With one suitable arrangement, the output and negative input of amplifier U 8 A may be coupled to the left microphone amplifier in circuit  310  through resistors R 43  and R 44 . Resistors R 43  and R 44  may have any suitable resistances As one example, resistors R 43  and R 44  may have resistances of approximately 44.2 kilohms. The amplifier U 8 A may help to prevent current from power supply line PWR from passing into and through resistor R 44  while providing the voltage of its positive input to resistor R 44 . 
     Amplifier U 8 B may be configured as a differential amplifier with a positive input that receives the reference voltage VB 2  from circuit  300  and a negative input connected to a node between resistors R 43  and R 44 . With this type of arrangement, when the voltage L_IN from circuit  310  is zero, the output of amplifier U 8 B may be at (PWR−0.075−VBE(Q 3 )) volts and the output current of transistor Q 3  may be determined by dividing 0.75 volts by the resistance of resistor R 42 . When the voltage on L_IN from circuit  310  is nonzero, the output of amplifier U 8 B may be reduced by a given factor equal to the voltage of L_IN multiplied by the resistance of R 44  divided by the resistance of R 43 . The output current of transistor Q 3  in this arrangement may be reduced by subtracting the given factor divided by the resistance of resistor R 42 . The output of circuit  302  (i.e., the current added to left channel audio line L in path  16 ) may therefore be proportional to the voltage of L_IN with an additional constant (DC) bias current. 
     Circuit  304  may be another part of hybrid circuit  264 . In operation, circuit  304  may receive signals from the left channel audio line L in path  16  and from the output (L_IN) of circuit  310  and may generate left audio channel signals (L_OUT) for the left channel speaker  312 . If desired, the left and right channel speakers  312  and  314  may include amplifier circuitry. Resistors R 45  and R 46  may form an attenuator circuit similar in operation to the attenuator circuit  178  of  FIG. 3 . In particular, resistors R 45  and R 46  may reduce the voltage of signals L_IN from circuit  300  to one-fourth its initial voltage and provide the reduced voltage to the positive input of amplifier U 8 D. In general, resistors R 45  and R 46  may have any suitable resistances. As one example, resistors R 45  and R 46  may have resistances of approximately 22.1 kilohms and 44.2 kilohms, respectively. 
     Circuit  304  may include amplifier U 8 C coupled to the left audio path (L) in path  16 . Amplifier U 8 C may be configured as a voltage follower (e.g., may have its negative input connected to its output). If desired, there may be a resistor such as resistor R 47  located between the left audio path (L) (e.g., the tip connector  45  in accessory  14 ) and the amplifier U 8 C. Resistor R 47  may provide electrostatic discharge (ESD) protection to device  12 . Resistor R 47  may have any suitable resistance and, as one example, may have a resistance of 4.7 kilohms. 
     Amplifier U 8 D may be configured as a differential amplifier that uses the difference between the voltage on the left audio path (L) and the (attenuated) voltage from the left microphone amplifier in circuit  300  to generate the left audio channel signals L_OUT for the left speaker  312  (e.g., to receive the incoming analog signals from device  12  conveyed on the bidirectional path L). The differential amplifier U 8 D may have associated resistors R 48  and R 49 . The resistors R 48  and R 49  may have any suitable resistances and, as one example, resistors R 48  and R 49  may have resistances of 22.1 kilohms and 44.2 kilohms, respectively. 
     Circuits  306  and  308  may handle signals carried on the right channel audio path (R) in path  16 . For example, circuits  306  and  306  may handle signals (R_IN) output from the right channel microphone amplifier in circuit  310  and may generate the right channel speaker signals (R_OUT) for the right channel speaker  314 . With one suitable arrangement (as illustrated in the  FIG. 7  example), circuits  306  and  308  may handle signals for the right channel in a manner equivalent to how circuits  302  and  304  handle signals for the left channel. If desired, the capacitance of capacitor C 15  may be equivalent to capacitor C 14 . The resistances of resistors R 51 , R 52 , R 53 , R 54 , R 55 , R 56 , R 57 , and R 58  may be approximately equivalent to the corresponding resistors in circuits  302  and  304 . The amplifiers U 9 A, U 9 B, U 9 C, and U 9 D may be configured in a manner equivalent to amplifiers U 8 A, U 8 B, U 8 C, and U 8 D, respectively. If desired, transistor Q 4  may be similar to (or identical to) transistor Q 3 . 
     If desired, accessory  14  may include microphone amplifier circuitry  310 . Microphone amplifier circuitry  310  may generate microphone signals that are sent to device  12  using hybrid circuits. Microphone circuitry  310  can include a first microphone M 1  and a second microphone M 2 . With one suitable arrangement, microphone M 1  can be located near the left speaker SL and microphone M 2  can be located near the right speaker SR to detect ambient noise near the speakers as part of a noise cancellation operation. With another suitable arrangement, microphone M 1  can be used to detect a user&#39;s voice and microphone M 2  can be used to detect ambient noise around microphone M 2  as part of a microphone noise cancellation operation. 
     Circuitry  310  may include circuitry for generating a left microphone signal such as amplifier U 10 C, resistors R 69  and R 70 , capacitor C 19 , and transistors D 1  coupled to microphone M 1 . Microphone M 1  may be coupled between a first signal ground SGND 1  and resistor R 70 . Resistor R 70  may be coupled to the microphone bias line from circuit  300 . As an example, resistors R 69  and R 70  may have resistances of approximately 68.0 kilohms and 2.2 kilohms, respectively. Capacitor C 19  may have a capacitance of approximately 1.0 microfarad. 
     Circuitry  310  may also include circuitry for generating a left microphone signal such as amplifier U 10 D, resistors R 68  and R 72 , capacitor C 20 , and transistors D 2  coupled to microphone M 2 . Microphone M 2  may be coupled between a second signal ground SGND 2  and resistor R 72 . Resistor R 72  may be coupled to the microphone bias line from circuit  300 . As an example, resistors R 68  and R 72  may have resistances of approximately 68.0 kilohms and 2.2 kilohms, respectively. Capacitor C 20  may have a capacitance of approximately 1.0 microfarad. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20090714
Publication Date: 20100803
Grant Date: 20100803
Priority Date: 20090714
Inventors: FARRAR DOUGLAS M.
SANDER WENDELL B.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/1083", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R1/1083", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R5/033", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/033", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/1041", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/1041", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/07", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2420/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2420/03", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2460/07", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 42358877