Abstract:
The present invention is directed to apparatus and methods for reducing sidetone feedback in a portable wireless telephone system by positioning the speaker and the microphone to reduce acoustic feedback and by controlling the amplifier gain in the transmitter section of the wireless telephone to reduce amplification of sidetone which has been acoustically coupled from the speaker to the microphone. The wireless telephone may be configured as a watch with a wrist strap for retaining it to the user, as a piece of jewelry such as a brooch or pendant, as a voice capable pager/intercom, or as an identification badge for an employee. In one embodiment, the base station includes circuitry for further reducing sidetone feedback. In additional embodiments, the wireless telephone may include a quick-release outboard battery, a retractable earpiece, and an ergonomic keypad.

Description:
This is a division of application Ser. No. 09/166,661 , filed Oct. 5. 1998, and allowed Feb. 24, 2000; U.S. Pat. No. 6,091,965, which is a divisional of application Ser. No. 08/262,735 filed Jun. 20, 1994 (issued as U.S. Pat. No. 5,819,183 on Oct. 6, 1998) which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to communications systems and in particular to a compact implementation of a wireless telephone. The present invention is also directed to a quick-release outboard battery, a retractable earpiece, and an ergonomic keypad which can be used with such a wireless telephone. 
     BACKGROUND OF THE INVENTION 
     As mobile communication has become increasingly critical to the conduct of business, a need has arisen for smaller and more compact telephones. Until now the size and shape of the telephone has been driven in large part by the size of the circuitry needed and by the need to maintain a certain separation between the telephone mouthpiece and the earpiece. Recent developments in integrated circuit technology have driven down the size of the telephone circuitry. According to Olsen, U.S. Pat. No. 4,847,818 issued Jul. 11, 1989 to Olsen and Blonder, U.S. Pat. No. 5,239,521 issued Aug. 24, 1993, however, even if the telephone unit can be sufficiently integrated to fit within a compact body, the telephone microphone and the telephone speaker must still be spaced a certain minimal distance apart in order to prevent feedback from the speaker through the microphone. 
     Feedback is inherent to telephone design. In the typical telephone, some feedback of the microphone output back through the speaker (in the form of a sidetone) is necessary to serve as an indication to the user of how loudly he or she should speak. However, this feedback can cause problems if it, in turn, is coupled back from the speaker through the microphone. The resulting feedback loop can lead to oscillations heard as an audible hum or howl. Spatial separation reduces the amount of signal coupled from the speaker to the microphone and therefore prevents oscillation. 
     In compact telephones, such as a wrist-mounted telephone, the spatial separation constraint forces the manufacturer to go through elaborate contortions to place the microphone and/or speaker as satellites attached to the telephone unit body. In Olsen, the speaker is placed at the clasp of the watch while the microphone is either located at the opposite clasp or built into the body of the telephone unit. In Blonder, a special pivoting member is used to separate the microphone from the speaker. Finally, in Yoshitake, U.S. Pat. No. 5,008,864 issued Apr. 16, 1991, a speaking tube is used to provide directionality to the telephone microphone. 
     However, none of the above solutions is very practical. Olsen and Yoshitake both require that the user remove the watch before placing or receiving a telephone call. Blonder requires the addition of a separate layer attached to the wrist strap that can pivot around the watch band. Such an approach drives up manufacturing costs and reduces reliability. 
     The feedback problem has also been addressed in the context of speaker phones. Speaker phones will howl if feedback of the sidetone from the speaker through the microphone reaches too high a level. This problem can be controlled by turning the speaker off during times when the user is speaking and by reducing the gain of the microphone amplifier during periods when the speaker is on. Another approach controls oscillation by reducing gain in the speaker amplifier during periods when the user is speaking and then reducing gain in the microphone amplifier during periods when the user is quiet. Since both approaches rely on the accurate detection of whether the user is speaking, they can cause audible discontinuities in both the received and transmitted voice transmissions at the start and end of user speech. 
     In addition to the feedback problem, portable radio telephones to date, especially those designed to be worn on the wrist, suffer from a number of deficiencies. The power sources for portable radio telephones tend to be short-lived and difficult to replace. Typically, the entire telephone unit must be placed on a recharging stand, rendering it unavailable to the user. Alternatively, the radio telephone must be shut-off to replace the battery. 
     Also, when a user cannot use the speaker phone because of the need for privacy, a separate earpiece must be located and carefully attached to the phone unit. Separate earpieces are difficult to engage with the phone and easy to misplace. 
     Additionally, key pads on portable radio telephones, similar to other miniaturized electronic devices such as calculator watches, typically are too small to be operated by hand. The user typically must utilize a pen or other pointed object to activate a particular key. 
     It is clear that there is a need in the art for a compact wireless telephone which will minimize feedback while providing an acceptable voice signal. In addition, there is a need in the art for a compact wireless telephone which includes an ergonomic keypad, a retractable earpiece attached to the wireless telephone and a power supply which is easy to replace yet long-lasting. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a low-feedback portable wireless telephone having a wireless transceiver connected to a microphone and a speaker. The wireless telephone may either be configured as a watch with a wrist strap for retaining it to the user, as a piece of jewelry such as a brooch or pendant, as a voice capable pager/intercom, or as an identification badge for an employee. 
     In the embodiment where the radio telephone is used as an identification badge, each unit preferably is given a unique code which identifies the user. The radio telephone operates as a transponder, sending an identification signal at some predetermined interval or responding to a signal from a base station. By arranging several base stations around a facility, the present identification badge/portable radio telephone can operate as a personnel locator and communicator. 
     The telephone includes a base station interface for transferring information between the telephone unit and a base station connected to the local loop of a public telecommunications network. A directional speaker for radiating speaker sound in predominately a first direction is provided. A speaker circuit connected to the base station interface and the directional speaker is provided for driving the speaker with a signal received from the base station interface. A directional microphone is positioned to be most sensitive to sound coming from a second direction at approximately 90 degrees offset from the first direction. A microphone circuit connected to the directional microphone and the base station interface is provided for driving the base station interface with a signal corresponding to sound received by the directional microphone. The microphone circuit includes an amplifier having an amplifier gain controlled to constrain the amount of speaker sound fed back to the base station. 
     According to yet another aspect of the present invention, a base station is described which works in conjunction with the above telephone to provide a cordless or cellular telephone system. 
     According to yet another aspect of the present invention, a telephone system is described in which feedback is controlled in both the base station and the telephone unit. The telephone includes a base station interface for transferring information between the telephone unit and a base station connected to the local loop of a public telecommunications network. A directional speaker is provided for radiating speaker sound in predominately a first direction. A speaker circuit connected to the base station interface and the directional speaker is provided for driving the speaker with a signal received from the base station interface. A directional microphone is positioned to be most sensitive to sound coming from a second direction at approximately 90 degrees offset from the first direction. A microphone circuit is connected to the directional microphone and the base station interface for driving the base station interface with a signal corresponding to sound received by the directional microphone. The base station includes a telephone unit interface and a telephone line interface which includes means for reducing sidetone. 
     According to yet another aspect of the present invention, a quick-release outboard battery is described for use with a compact wireless telephone. A battery clasp is attached to the compact wireless telephone. The battery clasp has a battery attachment member and electrical contacts connected to the telephone. A battery housing containing at least one battery is provided with a receiving member. The receiving member is arranged to engage with the attaching member on the battery clasp so that the at least one battery electrically engages the electrical contacts for powering the telephone. 
     In an embodiment in which the compact wireless telephone is designed to be mounted on the wrist, the battery clasp may be located on the wrist straps or attached directly to the radio telephone. 
     The attaching member on the battery clasp is designed to allow quick release of the battery housing so that a replacement battery can be easily attached to the compact wireless telephone. In the preferred embodiment, the attaching member is a T-shaped battery receiving structure. The receiving member is a T-shaped receiving slot on the battery assembly. In an alternate embodiment, the attaching member has inwardly-biased opposing hook members, which create a compression force on the battery housing to retain the battery housing to the battery clasp. 
     In the preferred embodiment, the base station can be signalled to suspend a call for a programmed period of time while a user changes the battery. 
     The present invention is also directed to a retractable earpiece assembly for a compact wireless telephone in-which an earpiece containing a transducer is attached to the radio telephone by an electrical cord. A rotatable cord spool is attached to the radio telephone for storing the cord when it is in a retracted configuration. A retraction mechanism is provided for automatically rewinding the cord onto the spool after the cord has been manually withdrawn. In one embodiment, the rotatable cord spool is retained in a housing attached to the radio telephone or to wrist straps for the wrist phone embodiment. 
     It will be understood that the compact wireless telephone may be used in combination with the quick release outboard battery and/or the retractable earpiece assembly discussed above. 
     The compact wireless telephone preferably includes an ergonomically designed keypad in which the keys are canted so that they may be operated by the user&#39;s finger rather than a pointed object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top-level block diagram of a cordless telephone system according to the present invention; 
     FIG. 2 is a front perspective view showing one embodiment of a wrist-mounted wireless telephone having a battery assembly and retractable earpiece assembly attached thereto; 
     FIG. 3 is a rear perspective view of the wrist-mounted cordless telephone of FIG. 2; 
     FIG. 4 is a side view of one embodiment of the wrist-mounted cordless telephone of FIG. 2; 
     FIG. 5A is a block diagram of a base station; 
     FIG. 5B is a more detailed block diagram of sidetone cancellation circuitry used in the base station of FIG. 5A according to the present invention;, 
     FIG. 6 is a block diagram of the internal circuitry of the wrist-mounted cordless telephone of FIG. 2; 
     FIG. 7 is a perspective view of the preferred retractable earpiece assembly; 
     FIG. 7A is schematic illustration of the earpiece of FIG. 7; 
     FIG. 8 is an exploded view of the preferred compact wireless telephone; 
     FIG. 9 is an exploded view of an alternate outboard battery assembly; 
     FIG. 10 is a perspective view of an alternate battery clasp; 
     FIG. 11 is a perspective view of alternate outboard battery assembly; 
     FIG. 12 is a rear view of the alternate outboard battery assembly of FIG. 11; 
     FIG. 13 is a bottom view of the alternate outboard battery assembly of FIG. 11; 
     FIG. 14 is a side view of the alternate outboard battery assembly attached to the alternate battery clasp; 
     FIG. 15 is a perspective view of an alternate outboard battery assembly; 
     FIG. 16 is a rear view of the alternate outboard battery assembly attached to a battery clasp; 
     FIG. 17 is a bottom view of the alternate outboard battery assembly; 
     FIG. 18 is a side view of the alternate outboard battery assembly of the present invention; 
     FIG. 19 is a perspective view of the preferred battery clasp; 
     FIG. 20 is a rear plan view of a preferred battery assembly for engagement with the battery clasp of FIG. 19; 
     FIG. 21 is a perspective view of one preferred battery assembly engaged with the preferred battery clasp as attached to the base plate of the phone; 
     FIG. 22 is a perspective view of the preferred battery clasp attached to the base plate of the phone; 
     FIG. 23 is a perspective view of one embodiment of the preferred battery assembly; 
     FIG. 24 is a bottom view of the battery assembly of FIG. 23; 
     FIG. 25 is a perspective view of an alternate embodiment of the preferred battery assembly; and 
     FIG. 26 is a bottom view of the battery assembly of FIG.  25 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the spirit and scope of the present inventions. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present inventions is defined by the appended claims. 
     A top-level block diagram of a wireless telephone system  10  is shown in FIG.  1 . In the system of FIG. 1, wireless telephone unit  12  is connected through a base station  14  to the local loop  16  of a public telecommunications network  18 . Base station  14  includes an RF interface for communicating with wireless telephone unit  12  and telephone line interface circuitry which can be connected to local loop  16  in order to communicate over public telecommunications network  18  (see FIG.  5 A). The telephone line interface circuitry may be a simple telephone line connection such as is used in the typical cordless telephone. 
     Alternatively, in systems  10  which support cellular communications, base station  14  includes circuitry which communicates through a Mobile Telecommunications Switching Office (MTSO)(not shown) to public telecommunications network  18 . In such systems, each base station  14  is assigned to a cell and the MTSO determines which cell is to communicate with telephone unit  12 . Base stations for use in cellular or cordless telephone applications are well known in the art and will not, therefore, be described in detail. 
     Wireless telephone unit  12  is designed to be easily carried by a user. In one embodiment, such as is shown in FIG. 2, unit  12  is configured as a wrist-mounted radio telephone  100  which can be attached to a user with a wrist band  132 . In another embodiment, unit  12  may be worn as a pin or brooch. In another embodiment, unit  12  may be suspended from a chain worn around the neck of a user, attached to clothing in a manner similar to an employee badge, or placed in a pocket. 
     FIG. 2 is a perspective view of the preferred embodiment of wireless telephone unit  12 . In FIG. 2, compact wireless telephone  100  has a keypad  102 , an LCD  104 , and a speaker  106 . The LCD  104  preferably displays the phone number dialed for an outgoing call or the source number for an incoming call, the date and time, indicates a low battery condition, and whether the intercom or mute functions are activated (see FIG.  6 ). A microphone  108  is provided on the front edge of the telephone  100 . The microphone  108  preferably is directionally offset from the speaker  106  by 90 degrees. 
     Program keys  110  are provided on the side of the telephone  100  for programming the memory of the telephone (as will be discussed below). Volume keys  107  are provided on the opposite side of the radio telephone  100  for adjusting the volume of the speaker  106  (see FIG.  4 ). The keypad  102  includes the primary twelve keys on a standard telephone and three additional keys for a Talk function  112 , a Hold function  116 , and an Intercom function  114 . 
     As discussed above, prior key pads on portable electronic devices are typically so small that the user needs a pointed object such as a pen to activate an individual key. The individual keys on the keypad  102  preferably are canted or tilted so as to present a high point  103  which facilitates operation by a user&#39;s finger. 
     A retractable earpiece assembly  120  preferably is attached to the front edge of the telephone  100  by a hinge mechanism  124 . An outboard battery assembly  130  is attached to the rear edge of the telephone  100  by a similar hinge mechanism  126  (see FIG.  3 ). The wrist strap  132  is provided for attaching the compact wireless telephone  100  to the wrist of a user. However, it will be understood that the present compact wireless telephone  100 , battery assembly  130 , or earpiece  120  may be configured in any shape that is convenient for the user. 
     FIG. 3 is a rear perspective view of the compact wireless telephone  100  showing an alternate outboard battery assembly  130 . As will be discussed in detail below, a pair of rear hook members  134  engage with corresponding slots (not shown) to releasably retain a battery housing  136  to the phone  100 . 
     The feedback loop formed by transmission of sidetone back from the receiver to the transmitter is a critical problem in the design of a compact telephone or speaker phone. Sidetone is generated by the 2-wire to 4-wire hybrid circuit required by the telephone company and, to a lesser extent, by reflections occurring within network  18  itself. In addition, many standard telephone integrated circuits have sidetone generation built in. All sources of sidetone are summed, amplified and routed through the user&#39;s speaker. This output must be loud enough to hear and, consequently, may be loud enough to be picked up and amplified by the telephone unit transmitter. 
     As noted above, spatial separation can be helpful in minimizing the amount of sidetone fed back through the transmitter. As components get smaller, however, it is more and more difficult to achieve meaningful separation in a useful design. Therefore steps must be taken not only to isolate the transmitted and received sounds but also to reduce the amplification of sidetone reflected through the transmitter of telephone unit  12 . 
     One embodiment which reduces transmission of sidetone back through the transmitter of telephone unit  12  is shown in FIGS. 2 and 4. FIG. 4 is a side view of a wireless telephone unit  100  which can be used in a cellular or cordless telephone system  10 . In the embodiments shown in FIGS. 2 and 4, spatial separation of the received and transmitted sound is enhanced by placing speaker  106  so that sound is radiated in a direction “d” which is a minimum of 90 degrees away from the direction in which microphone  108  is pointed. 
     In one such an embodiment, spatial separation is enhanced by using a directional speaker and a directional microphone as speaker  106  and microphone  108 . One such directional speaker is a Model No. KR2083 speaker available from Keyrin of Taiwan. One such directional microphone is a Model No. WM62-A microphone available from Matsushita of Tokyo, Japan. Further acoustic separation can be achieved by canting speaker  106  such that the direction is greater than 90 degrees. In addition, if speaker  106  and microphone  108  are directional enough, angles of less than 90 degrees are possible. 
     Finally, as can be seen in FIG. 2, speaker  106  and microphone  108  are placed as far away from each other as possible while still remaining in the same package. By placing speaker  106  and microphone  108  so that their mounting axes are offset approximately 90 degrees or greater and by placing speaker  106  and microphone  108  on the diagonal at opposite corners of telephone unit  100 , acoustic coupling of speaker  106  to microphone  108  is minimized. The combination of directionality with positioning results in an embodiment in which speaker  106  can be located 2.5 cm (0.984 inches) from microphone  108 . In the preferred embodiment, as is shown in FIGS. 2 and 4, the speaker  106  is located 3.5 cm (1.38 inches) from the microphone  108 . 
     The placement of speaker  106  and microphone  108  in a compact device such as wireless telephone unit  12  can lead to some problems due to magnetic coupling of speaker magnets to oscillator inductors. Communications devices such-as telephone unit  12  typically include high Q tank circuits which are very sensitive to outside disturbances. The magnetic field and flux generated by the speaker magnet of speaker  106  can cause a disturbance in the oscillators which can feedback through speaker  106  to form another oscillatory loop. In one embodiment, oscillator inductors are shielded and placed as far physically from speaker  106  as possible. For example, in the telephone unit  12  of FIG. 2 shielded oscillator inductors are clustered in the vicinity of microphone  108  to reduce magnetic coupling between the inductors and speaker  106 . 
     The interaction of the oscillator inductors with the speaker magnet can also result in a microphonic effect seen when the speaker  106  magnetic field is moved suddenly with respect to the oscillator inductors. Such an effect can be minimized by providing a secure, mechanically stable environment such that when telephone unit  12  is disturbed, both the speaker magnet and the inductors move together. In one embodiment, a soft rubber bonnet or boot is placed around speaker  106  in order to provide additional mechanical stability. In another embodiment, an annular ring is placed around speaker  106 . In another embodiment, a soft rubber cushion is built into the rubber keypad to provide the required mechanical support. It will be understood that a variety of techniques and elastomeric materials are available for achieving mechanical stability. 
     In addition to physical separation of speaker  106  and microphone  108  to reduce feedback of sidetone, steps have been taken to reduce sidetone. For instance, the frequency of oscillation of sidetone feedback tends to be centered about a particular frequency. Therefore, the effects of sidetone on telephone unit  12  can be minimized by either providing a notch filter at that frequency in the circuit driving speaker  106  or by reducing feedback of the sidetone at that frequency in the 2-wire to 4-wire hybrid circuit. One method of reducing feedback of the sidetone within the 2-wire to 4-wire hybrid circuit is shown in FIGS. 5A and 5B. 
     In FIG. 5A, base station  14  includes a polarity and overvoltage protection circuit  80 , a loop holding circuit  82 , a 2-wire to 4-wire hybrid circuit  84 , a wireless telephone interface  86 , a ring detect circuit  88  and a controller  90 . Polarity and overvoltage protection circuit  80  is of the type typically used in electronic telephones. Loop holding circuit  82  draws the off-hook current required to tell local loop  16  that base station  14  wishes to be connected to public telecommunications network  18 . 2-wire to 4-wire hybrid circuit  84  provides the signal separation and rejoining required by the telephone company. Wireless telephone interface  86  communicates with telephone unit  12  through any known means of wireless communication (radio, infrared, ultrasonic, etc.). Controller  90  controls the interface with local loop  16  and communication over wireless telephone interface  86  Ring detect circuit  88  detects the ring signal received from local loop  16  and generates an interrupt to controller  90  regarding the detection of the ring signal. 
     One embodiment of a 2-wire to 4-wire hybrid circuit  84  is shown in FIG.  5 B. In circuit  84  of FIG. 5B, a transformer  91  isolates base station  14  from local loop  16 . Transformer  91  includes windings  92  and  93 . Winding  92  is connected to the local loop side of hybrid circuit  84  while winding  93  is connected to the telephone side of circuit  84 . Winding  93  has three taps 94.1-3. Taps 94.1 and 94.2 are electrically connected to a receiver amplifier circuit  95  in a manner known in the art while tap 93.3 is electrically connected to transmitter amplifier circuit  97 . Audio received at transformer  91  from local loop  16  is out of phase and is therefore differentially summed by amplifier  96  of receiver amplifier circuit  95 . Meanwhile, an audio signal obtained from transmitter amplifier circuit  97  is in phase and therefore cancelled. In one embodiment, cancellation is frequency dependent. That is, a notch filter is used to attenuate frequencies centered around those frequencies associated with sidetone oscillations. In practice the frequency of sidetone oscillation varies according to the construction of hand unit  10  and the placement of speaker  106  and microphone  108 . Therefore, the circuit must be tuned to compensate. In one such embodiment, amplifiers  96  and  98  are Model No. LM324 operational amplifiers such as are available from Motorola. In such an embodiment, an advantageous choice of impedances Z 1 -Z 12  is as follows: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Z1 
                 0.1 
                 μF 
               
               
                   
                 Z2 
                 0.1 
                 μF in series with 100 kΩ 
               
               
                   
                 Z3 
                 2 
                 MΩ 
               
               
                   
                 Z4 
                 100 
                 kΩ 
               
               
                   
                 Z5 
                 100 
                 kΩ 
               
               
                   
                 ZG 
                 10 
                 kΩ 
               
               
                   
                 Z7 
                 100 
                 kΩ 
               
               
                   
                 Z8 
                 680 
                 Ω 
               
               
                   
                 Z9 
                 0.1 
                 μF 
               
               
                   
                 Z10 
                 330 
                 Ω 
               
               
                   
                 Z11 
                 6.8 
                 kΩ 
               
               
                   
                 Z12 
                 100 
                 kΩ 
               
               
                   
                   
               
             
          
         
       
     
     Feedback of sidetone can also be controlled by judicious selection of transmitter amplifier gains. Transmitter amplifier gains may be set so that sidetones received by microphone  108  are not amplified above a threshold level. One embodiment of a low feedback wireless telephone unit  12  is shown in FIG.  6 . In telephone unit  12  of FIG. 6, telephone unit  12  includes a controller  38 , a base station interface circuit  40  for transferring information between base station  14  and telephone unit  12 , a speaker circuit  42 , a directional speaker  44 , a microphone circuit  46  and a directional microphone  48 . Speaker circuit  42  is connected to base station interface circuit  40  and directional speaker  44  and is used for driving directional speaker  44  with a speaker signal received from base station  14 . Microphone circuit  46  is connected to directional microphone  48  and base station interface circuit  40  and is used for driving base station interface circuit  40  with a microphone signal corresponding to sound, including speaker sound, received by directional microphone  48 . 
     In the embodiment shown in FIG. 6, speaker circuit  42  includes an AF amplifier  52 , a high pass filter  54 , an expander  56 , deemphasis  58 , optional descrambler  59 , band pass filter  60 , optional mute gate  62  and output amplifier  64 . In one such embodiment, speaker circuit  42  is designed to provide approximately 29.6 dB of gain at 1 kHz. 
     Microphone circuit  46  is designed to have an amplifier gain controlled to limit the amount of speaker sound fed back to the base station. In the embodiment of FIG. 6, microphone circuit  46  includes a preamplifier  66 , a bandpass filter  68 , optional scrambler/bandpass filter  70 , preemphasis  72 , compressor  74 , mute gate  76  and summing amplifier  78 . In one such embodiment, preamplifier  66  has a gain of 20 dB, scrambler/bandpass filter  70  has unity gain, preemphasis  72  adds 6 dB/octave of preemphasis and summing amplifier  78  has unity gain. In addition, the transmitter amplifier of base station interface  40  is part of the Motorola MC2833 transmitter integrated circuit, which adds 9.5 dB of gain. 
     In one embodiment, antenna  79  of base station interface  40  is a dipole antenna embedded in the wrist strap of wireless telephone unit  12 . In an alternate embodiment, antenna  79  is a loop antenna embedded in or as an integral part of cover plate  150  of wireless telephone unit  100  (such as is shown in FIG.  8 ). 
     FIGS. 7 is a perspective view of the preferred retractable earpiece assembly  120 . FIG. 7A is a schematic illustration of the retractable earpiece assembly  120  having an earpiece  140  containing a transducer  141  attached to the earpiece housing  122  by a cord  144 . The cord  144  preferably is braided to provide increase strength and greater reliability. The cord  144  is engaged with a rotatable cord spool  146 . A retraction mechanism  148 , such as a coiled leaf spring, automatically rewinds the cord  144  onto the spool  146  after the cord has been manually withdrawn. A switch  142  is provided to activate the transducer  141  when the earpiece  140  is withdrawn a predetermined distance from the earpiece housing  122  and deactivate the transducer  141  when the earpiece  140  is retracted. A hinge mechanism  147  is provided for attaching the wrist strap  132  to the earpiece assembly  120 . A retraction mechanism known to be suitable for this purpose is disclosed in U.S. Pat. No. 3,984,645 issued to Kresch on Oct. 5, 1976, which is hereby incorporated by reference. 
     FIG. 8 is an exploded view of the preferred compact wireless telephone  100 . Cover plate  150  has keypad openings  152  for the keypad  102 . A speaker opening  154  is provided in the uppermost corner of the cover plate  150  so as to be as far from the microphone opening  158  as possible. A midplane  156  is provided to support the keypad  102 . A cutout  158  is provided in the midplane  156  for the speaker  106 . An LCD  104  is interposed between the midplane  156  and the printed circuit board  160  so that the LCD  104  is visible through the openings  162 ,  164  in the midplane  156  and cover plate  150 , respectively. A back plate  166  is provided with numerous removable supports  168  to support the PC board  160  and other components. The removable supports  168  may be snapped off during assembly to make room for electrical components as required. Finally, the back plate  166  has portions of a hinge mechanism  124 ,  126  for attaching the radio telephone  100  to a user. 
     The back plate  166  may also include a non-audible tactile annunciator  184  to alert the user that a page or call is being received. Although the annunciator  184  is preferably a micro-motor with an eccentric cam, it will be understood that a variety of vibro-tactile mechanisms are suitable for this purpose, such as a piezo-electric device, and that the present invention is not limited by the particular mechanism disclosed. 
     When assembled, the present compact wireless telephone  100  is only 0.275 inches (7.0 mm) thick. The preferred phone  100  is 1.57 inches (39.9 mm) in the direction “W” and 2.17 inches (55.1 mm) in the direction “L” so that it does not extend out orthogonally from the user&#39;s wrist. The preferred wrist mounted compact wireless phone embodiment can therefore easily be worn even by individuals with small wrists. 
     FIG. 19 is a perspective view of a preferred battery clasp  300  having a “hot shoe” battery receiving structure  302 . The battery receiving structure  302  is generally “T” shaped, with a top portion  304  which is wider than a bottom portion  306 . The top portion  304  has a pair of detents  308  on each edge for retaining a battery assembly (see FIG. 21) to the clasp  300 . In the preferred embodiment, the detents  308  also operate as electrical contact points. 
     The edges  310  of the top portion  304  form rails for engaging with a corresponding “T” shaped opening  312  in a battery assembly  314  (see FIG.  20 ). The battery assembly  314  preferably has spring-loaded electrical contacts  316  for releasably engaging with the detents  308 . The spring-loaded contacts  316  allow the battery assembly  314  to be slid on and off of the battery receiving structure  302 . The electrical contacts  316  preferably have a flexing portions (not shown) similar to those disclosed in FIG. 9 which extend past the hinge  320  to the phone  100  (see also FIGS.  2  and  3 ). However, it will be understood that a variety of techniques may be used to electrically connect the battery assembly  314  with the phone  100 , such as, for example, a shielded wire. 
     The process of exchanging a battery, known as lock-and-load, allows the user to quickly substitute a fresh battery as needed without terminating a call in progress. The user presses the Hold key  116  to signal to the base station  14  to suspend the call. The RF interface is terminated and the base station  14  holds the call for a programmed period of time. During this Hold period, the user may change batteries. With the battery replaced, the user reestablishes communication with the base station  14  by again pressing the Hold key  116 . The RF link is reestablished and the call reconnected to the line. The PC board  160  preferably contains a series of capacitors which provide power to the control circuit to maintain the time of day while the user changes the battery assembly  130 . 
     The clasp  300  has a hinge  320  for engagement with a corresponding hinge on  124  on the back plate  166  (see FIGS.  21  and  22 ). Additionally, a hinge  322  is provided on the opposite side of the clasp  300  for engagement with a wrist strap (not shown). Although the clasp  300  is generally configured for use with a wrist mounted phone, it will be understood that the present quick-release clasp  300  may be used with other configurations of the phone  100 . 
     FIG. 22 illustrates the clasp  300  attached to the back plate  166 . FIG. 21 illustrates one embodiment of the battery assembly  314  engaged with the clasp  300  of FIG.  22 . 
     FIG. 23 is a perspective view of one embodiment of the preferred battery assembly  314  having a primary portion  326  and a secondary portion  328 . The secondary portion  328  is preferably shaped to follow the contour of a users wrist (see FIG.  21 ). FIG. 24 is a bottom view of the battery assembly  314  showing the “T” shaped opening  312  for engagement with the battery receiving structure  302 . The opening  312  is preferably wider at the entrance  324  to facilitate engagement with the battery receiving structure  312 . The battery assembly  314  preferably has three battery compartments  330 . 
     FIG. 25 is a perspective view of an alternate preferred battery assembly  314 ′ for engagement with the clasp  300 . FIG. 26 is a bottom view of the battery assembly  314 ′ showing the “T” shaped opening  312  for engagement with the battery receiving structure  302 . The battery assembly  314 ′ is designed to hold up to four batteries in the compartments  330 ′. 
     FIG. 9 is an exploded view of an alternate outboard battery assembly  130 . Battery clasp  170  has a hinge  126 ′ for connecting with the hinge  126  on the base plate  166 . A second hinge  172  is provided for connecting to the wrist strap  132  (see FIG.  2 ). A pair of electrical contacts  174 ,  176  are attached to the battery clasp  170  by an electrical contact retaining member  178 . The electrical contacts  174 ,  176  have a flex portions  180  which connects to a flex circuit (not shown) in the radio telephone  100 . The flex portions  180  allows the battery assembly  130  to rotate on the hinge mechanism  126 ,  126 ′ while maintaining a connection with the phone  100 . 
     FIG. 9 illustrates an outboard battery assembly  130  with three batteries  182  contained in the housing  136 . The batteries  182  preferably are common nickel metal hydride batteries which are low cost and readily available. However, it will be understood that a variety of batteries and battery configurations are possible and that the present invention is not limited in any way by the specific number or type of batteries  182  contained in the outboard battery assembly  130 . 
     FIG. 10 is a perspective view of the battery clasp  170  with a battery receiving surface  193 . A pair of rear hook members  190  having body portions  192  and rear hook portions  194  are provided proximate the hinge  126 ′. Opposing front hook member  196  with a front hook portion  198  is provided proximate the hinge  172 . 
     FIG. 11 is a perspective view of the outboard battery assembly  130  illustrating a front receiving slot  200  in the battery housing  136 . FIG. 12 is a rear view of the outboard battery assembly  130  showing rear receiving slots  202  in the housing  136 . FIG. 13 is a bottom view of the battery housing  136  showing battery compartments  204  for retaining the batteries  182 . A pair of dividers  206 ,  208  preferably are provided inside the battery housing  136  to maintain a separation between the batteries  182  and to orient the batteries  182  with respect to the electrical contacts  174 ,  176 . 
     FIG. 14 is a side view of the alternate outboard battery assembly  130  engaged with the battery clasp  170 . The front hook portion  198  and rear hook portions  190  preferably are biased inward towards the battery housing  136  so that they engage with the front receiving slot  200  and the rear receiving slots  202  (see FIG.  13 ). The battery clasp  170  preferably is constructed of a lightweight constructed material such as metal or plastic, which allows the front hook member  196  and rear hook members  190  to create a compressive retaining force on the battery housing  136 . 
     To remove the outboard battery assembly  130  from the battery clasp  170 , the user merely slides the battery housing  136  along the battery receiving surface  193  toward the front hook portion  198  of the front hook member  196 . This movement releases the battery housing  136  from the rear hook portions  190 , allowing the outboard battery assembly  130  to be tipped and removed from the battery clasp  170 . Installation of a fresh battery assembly  130  is performed by reversing the above procedure. A call may be retained by the base station  14  as discussed above. 
     FIG. 15 is a perspective view of an alternate outboard battery assembly  210  in which the battery housing  212  has a primary portion  214  and a secondary portion  216 . The secondary portion  216  provides additional space for holding battery elements (not shown). FIG. 16 is a rear view of the alternate outboard battery assembly  210  having a pair of rear receiving slots  230  for engaging with the rear hook members  224  on the battery clasp  220 . FIG. 17 is a bottom view of the battery housing  212  showing a front hook engaging member  232  for engaging with the front hook  222  (see FIG.  18 ). The front hook engaging means  232  may also-operate as a divider between the battery compartments  204 ′ for separating and orienting the batteries (not shown). 
     FIG. 18 is a side view of the alternate outboard battery assembly  210  engaged with a battery clasp  220 . The battery clasp  220  has a front hinge  126 ″ for engaging with the compact wireless telephone  100  and a rear hinge  172  double prime for engaging with a wrist strap (not shown). The secondary portion  216  of the battery housing  212  is designed to generally follow the contour of the human wrist along the wrist strap (not shown). The battery clasp  220  has a front hook  222  and a pair of rear hooks  224  which are biased to create a compression force on the housing  212  so as to retain the alternate outboard battery assembly  210  to the clasp  220 . The alternate battery assembly  210  is installed and removed in a similar manner to the battery assembly  130 . 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. Although the above inventions have been described in connection with a cordless telephone system, it should be apparent that the concepts extend to any cordless or cellular telephone application requiring a compact, portable telephone or speaker phone unit. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.