Abstract:
A headset/headphone sensing jack ( 203, 208, 210 ). A two-channel sensing circuit ( 210 ) is provided which detects whether a headphone ( 101 ) or headset ( 103 ) is installed. By employing an impedance sensing circuit ( 210 ), it is possible to use a single common 2.5 mm jack ( 120 ) for both radio and telephony operation. Formerly, two separate jacks would be required for both functions. An electronic device ( 50 ) according to the present invention is further capable of switching between AM/FM radio and telephone modes depending on whether a particular headpiece ( 101, 103 ) is installed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to sensing circuits and, particularly, to circuits for sensing audio input/output plugs. 
     2. Description of the Related Art 
     Portable electronic devices, such as cellular telephones and portable radios, are well known. It is further known to provide electronic devices having combined telephone and AM/FM radio functionality. Once clipped into position onto a user&#39;s person (such as via a belt clip or armband), such devices may be used with greater freedom by way of attachable headpieces. For example, in the case of a cellular telephone, a headset may include a pair of earphones with a boom microphone extending towards the user&#39;s mouth. Such headsets usually provide a channel for the microphone and a channel for mono- or bi-naural audio output to the speakers. Similarly, stereo headphones, providing left and right stereo channels, for use with portable AM/FM radios are well known. 
     Telephone headsets and stereo headphones are typically designed mechanically to use the same 2.5 millimeter two-channel plug and jack. However, the telephone headset and the stereo headphones require different electrical signal and pin configurations. Thus, in order to provide both AM/FM radio and cellular telephone functionality, an electronic device must generally be provided with one 2.5 millimeter jack for receiving the stereo headphone plug and another for receiving the telephone headset plug. Such devices may further include circuitry for sensing the presence or absence of a single plug. However, no jacks are known for sensing two different plugs. 
     Accordingly, there is a need for a single jack which can detect the presence of either a telephone headset or stereo headphones and provide either telephone functionality or radio functionality in response to their detection. 
     SUMMARY OF THE INVENTION 
     These problems in the prior art are overcome in large part by a headset/headphone sensing jack according to an embodiment of the present invention. A two-channel sensing circuit is provided which detects whether a headphone or headset is installed. By employing an impedance sensing circuit, it is possible to use a single common 2.5 mm jack for both radio and telephony operation. Formerly, two separate jacks would be required for both functions. 
     A sensing circuit is provided which includes one or more comparators for detecting whether a headphone or headset is installed. The comparator compares impedance levels to a predetermined reference taking advantage of the two different impedances of the devices. More particularly, if a headpiece is installed a low impedance is detected; when a headpiece is not installed a high impedance is detected. Typically, a sensing circuit is provided for two channels (e.g., left and right stereo, or microphone and audio output). If both channels are at low impedance, then the stereo headphones are installed. When only one channel is at low impedance, then the other channel is the microphone input and a telephone headset is installed. If neither channel is at low impedance, then nothing is installed. An electronic device according to the present invention is further capable of switching between AM/FM radio and telephone modes depending on whether a particular headpiece is installed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention is obtained when the following detailed description is considered in conjunction with the following drawings in which: 
     FIG. 1 is a diagram illustrating a combined telephone and radio configured to receive headphones or headsets in a single jack according to an embodiment of the present invention; 
     FIG. 2 is a block diagram of the combined telephone/radio of FIG. 1; 
     FIG. 3 is a block diagram of jack sensing circuitry according to an embodiment of the present invention; and 
     FIG. 4 is a diagram illustrating a sensing circuit for use in an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings and with particular attention to FIG. 1, a diagram of an electronic device having a single receptacle and configured to sense the presence of a stereo headphone or cellular telephone headset plug is shown. The electronic device  50  includes both cellular telephone and AM/FM radio functionality as will be described in greater detail below. Externally, the electronic device  50  includes a keypad  122  for inputting telephone numbers, a view screen  124  which may be used, inter alia, for displaying a phone list and displaying the numbers which are keyed in using the keypad  122 , a housing speaker  126  and a housing microphone  128 . In addition, the electronic device  50  may include separate controls  130  for operating the integrated AM/FM radio. Finally, a jack  120  is provided which is configured to receive a plug from either a stereo headphone  101  or cellular telephone headset  103 . In particular, the stereo headphone  101  includes a headband piece  100  which couples to a pair of earphones  116 ,  118 . As is well understood in the art, the earphones provide left and right stereo channels. The stereo headphones  101  couple to the electronic device  50  via a plug  106  insertable into the jack  120 . As will be described in greater detail below, the electronic device  50  is configured to be able to detect the plug  106  and provide AM/FM stereo radio functionality to the stereo headphone  101 . When an incoming telephone call is received, the electronic device  50  is further capable of disconnecting the AM/FM radio functionality and permitting the user to answer the telephone in the conventional manner (i.e., using the housing microphone and speaker  128 ,  126  respectively). 
     FIG. 1 further illustrates a telephone headset  103  which may be a cellular telephone headset. The cellular telephone headset  103  includes a headband piece  102  which couples together a pair of earphones  112 ,  114 . In addition, a boom microphone  110  may be provided coupled to one of the earphones  112 . The cellular telephone headset  103  couples to the electronic device  50  by way of a plug  108 . The cellular telephone headset  103  may be operable to provide an AM/FM radio output, but typically only in a monophonic or binaural mode. Thus, as in the case of the stereo headphones, two-channel functionality is provided, but here a single output channel and a single input channel are provided, rather than two output channels. As will be described in greater detail below, the electronic device  50  may provide monophonic or binaural AM/FM radio functionality to the cellular telephone headset  103 ; when an incoming telephone call is received, the AM/FM radio functionality is disabled and the microphone  110  input is re-enabled. 
     The plugs  106 ,  108  are both typically 2.5 millimeter plugs, but having different signal and pin configurations. As will be discussed in greater detail below, the electronic device  50  is configured to be able to detect the insertion of the plug  108  and distinguish it from the insertion of the plug  106 . 
     Turning now to FIG. 2, a block diagram of the electronic device  50  is shown. In particular, the electronic device  50  includes a telephone unit or communication controller  200 , as well as an AM/FM radio unit or radio controller  202 . The telephone unit may be a cellular telephone unit, for example. Both the AM/FM radio unit  202  and the cellular telephone unit  200  are coupled to an antenna  256 . The antenna  256  may be a dual-use antenna such as are well known in the art. Alternatively, separate antennae may be provided for the AM/FM radio unit  202  and for the cellular telephone unit  200 . Thus, FIG. 2 is exemplary only. 
     The cellular telephone unit  200  includes a control processor  208  coupled to a transceiver  266  for providing modulation and demodulation as well as digital-to-analog and analog-to-digital conversion. The control processor  208  is configured to provide supervision over cellular telephone functions such as device identification and cell-switching. In addition, the control processor  208  is configured to supervise switching between cellular telephone and AM/FM radio functionality, as will be discussed in greater detail below. In addition, a screen  124  and a keypad  122  are coupled to the control processor  208 . A housing speaker  126  and a housing microphone  128  are further coupled to the cellular telephone unit  200 . 
     The AM/FM radio unit  202  includes an AM/FM receiver  252  which may include digital-to-analog converters as well as AM/FM demodulators. An AM/FM radio tuner control unit  254  is also provided. 
     Both the cellular telephone unit  200  and the AM/FM radio unit  202  are coupled to a plug sensing circuit  201 . The plug sensing circuit  201  includes a sensor  210  coupled to switching unit  203 . As will be described in greater detail below, the sensor  210  includes a circuit or circuits to detect the presence of one or more types of 2.5 millimeter plugs. The switching unit  203 , in turn, is configured to respond to outputs from the sensing unit  210  to switch between AM/FM radio  202  and cellular telephone  200  output and input functionality. Finally, a microphone switch  262  may be provided coupled to the plug sensing circuit  201  to switch the housing microphone  128  on or off. 
     Turning now to FIGS. 3 and 4, the plug sensing circuit  201  is illustrated in greater detail. In particular, as discussed above, the plug sensing circuit  201  includes a sensor  210  and a switching unit  203 . The switching unit  203  includes a first switch  204  and a second switch  206  coupled between the sensor  210  and the cellular telephone unit  200  and the radio unit  202 . It is noted that while the switches  204 ,  206  are illustrated as conventional switches, any type of switching circuitry, such as field effect transistors, or other logic circuitry may be employed. The switch  204  has a contact A coupled to the right stereo or mono input of the AM/FM radio unit  202 , and a second contact B coupled to the receiver output of the cellular telephone unit  200 . The switch  206  includes a contact C coupled to the left stereo output of the AM/FM radio unit  202  and a second contact D coupled to the microphone input of the telephone unit  200 . 
     As discussed above, the sensor  210  is configured to detect the presence of a plug for a cellular phone  106  or a plug for a stereo headset  108 . If a plug  106  from a stereo headphone  101  is detected, the switch  204  will be in position A and the switch  206  will be in position C. If a telephone call is received (or an outgoing call is made) while the plug  106  is being detected by the sensing circuit  210 , the control processor  208  may connect the housing microphone  128  (FIG. 2) by way of a switch  262  (FIG. 2) to cause a microphone input to be provided to the cellular telephone unit  200 . In addition, the switch  204  may be switched to the B position, so as to provide telephone output on a single channel of the stereo headphone  101 . 
     If the sensing circuit  210  detects the presence of a plug  108  from a telephone headset  103 , then the switch  204  will be maintained in the A position and the switch  206  will be maintained in the D position in the event that an outgoing or incoming telephone call is detected. However, if the radio is being used, the control processor  208  and the sensor  210  will maintain the switch  204  in the A position and the switch  206  in the C position. 
     The sensor  210  includes a sensor or channel detection circuit for each of the channels (i.e., one for right and left stereo, and microphone input and audio output. Only one such channel detection circuit is shown in FIG.  4 ). In particular, the sensing is done on both channels; if both channels are at a low impedance, then a stereo headphone is installed. If only one channel is at low impedance, then the other channel is the microphone input and a telephone headset is installed. If neither channel is at low impedance, then the system assumes that nothing is installed. 
     In particular, stereo headphones are characterized by two 8-ohm receivers. In contradistinction, the telephone headset is characterized by one 8-ohm channel (audio output) and one high impedance (&gt;10 KΩ) channel for the microphone (i.e., one for left and one for right channels. An exemplary sensing circuit for sensing one channel is shown in FIG. 4. A reference voltage is provided from a 3V source and resistors  218 ,  220  and capacitor  222  are provided to the negative input of a comparator  224 . The resistor values are chosen to provide a 0.1V reference to the negative input of the comparator  224 . A similar network is provided to the positive input of the comparator  224 . In particular, a 3V source is provided to a resistor  212  and a capacitor  216  in parallel with a resistor  214  coupled to ground. In addition, a resistor  213  is provided at the plug input. Absence of a headpiece (or presence of the microphone) will provide a first voltage at node N (i.e., comparator input) responsive to high impedance, and presence of a headpiece will provide a second voltage (responsive to low impedance). 
     The invention described in the above detailed description is not intended to be limited to the specific form set forth herein, but, on the contrary, it is intended to cover such alternatives, modifications and equivalents as can reasonably be included within the spirit and scope of the appended claims.