Abstract:
A voice-operated communications interface permits communications between two or more groups using incompatible communications devices such as two-way radios.

Description:
RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application No. 60/201,304, filed May 2, 2000 and entitled “VOICE-OPERATED RADIO INTERFACE.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to communications. More specifically, this invention relates to a communications interface between two or more disparate systems. 
     2. Description of Related Art 
     Public crisis events (such as natural disasters or terrorist actions) may demand responses by several public safety agencies, including police, firefighters, and medical and rescue services. In order for these agencies to deploy their services more effectively and remediate the situation more quickly, it is critical to establish command and control communications with as little delay as possible. Therefore, it is desirable at least for the commanders of first response agencies to be able to communicate with one another in order to coordinate their operations at the scene. Unfortunately, a lack of interoperability (i.e. useable connectivity) between the communications apparatus of many such organizations often impedes such cooperation in practice. A similar deficiency may arise when military units require real-time transfer of information but utilize dissimilar radio-frequency bands and/or modulation schemes. 
     A proposed solution to this problem is a central device to receive all of the various RF signals and rebroadcast them over the appropriate RF bands. Such a device, however, is large and bulky, must be transported rather than carried, requires the on-site availability of significant power resources, requires highly trained personnel to set up and operate, and is expensive both to purchase and to maintain. A portable and rapidly deployable device that provides such interoperability has not yet existed, much less a device that has such features combined with ease of operation and low cost. 
     SUMMARY OF THE INVENTION 
     An interface according to an embodiment of the invention includes a number of input/output (I/O) ports, a corresponding number of voice-operated-transmit (VOX) circuits, and a switching matrix. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of an interface  100  according to an embodiment of the invention; 
     FIG. 2 illustrates an exemplary application of an interface  100 ; 
     FIG. 3 shows a block diagram of a VOX circuit  20  according to an embodiment of the invention; 
     FIG. 4 shows a schematic diagram of a priority circuit  150  according to an embodiment of the invention; 
     FIG. 5 shows a block diagram of an alternate implementation  22  of a VOX circuit according to an embodiment of the invention; 
     FIG. 6 shows a block diagram of a switching matrix  30 ; 
     FIG. 7 shows an alternate implementation  32  of a switching matrix according to an embodiment of the invention; 
     FIG. 8 illustrates an exemplary application of an alternate implementation  102  of an interface according to an embodiment of the invention; 
     FIG. 9 shows a block diagram of the alternate implementation  102  of an interface according to an embodiment of the invention; 
     FIG. 10 shows a block diagram of an input port  12 ; 
     FIG. 11 shows a schematic diagram of an input select circuit  360 ; 
     FIG. 12 shows a block diagram of a supply voltage monitor circuit  300 ; and 
     FIG. 13 shows a block diagram of an alternate implementation  302  of a supply voltage monitor circuit. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a block diagram of an interface  100  according to an embodiment of the invention. Interface  100  connects to a number of communications devices via input/output ports  10 . Specifically, interface  10  receives an input signal S 10  from, and transmits an output signal S 16  and a PTT (push-to-transmit) command S 60  to, the communications device connected to each input/output port  10 . 
     Interface  100  includes a number of VOX circuits  20 , each receiving a input signal S 10  via the respective I/O port  110 . Each VOX circuit is also coupled to a common control bus that carries a priority signal S 50  to the VOX circuits  20 . In accordance with these inputs, each VOX circuit  20  outputs a channel activation signal S 30  to a switching matrix  30  and a PTT command S 60  through the respective I/O port  10 . As described below, the VOX circuits  20  may be identical to one another, or one or more of the VOX circuits  20  may be adjusted or constructed differently from another according to the characteristics of a particular communications device. 
     Interface  100  also includes a switching matrix  30  that receives the input signals S 10  and channel activation signals S 30  and produces the output signals S 16  accordingly. In the signal paths between I/O port  10  and switching matrix  30 , it may be desirable to provide circuits (active and/or passive) that perform signal conditioning operations such as RF suppression, DC blocking, lowpass filtering, and/or signal level adjustment (not shown). 
     FIG. 2 shows a block diagram of an application of interface  100 . In this example, communications devices  1 A- 1 D include portable two-way radios (e.g. ‘walkie-talkies’, transceivers) that may communicate on different bands (such as HF, VHF, UHF, sideband, etc.) and/or using different modulation schemes, and one communications device  1  is provided for each communications path to be supported. Because the communications devices  1 A- 1 D used to support the various paths are stand-alone off-the-shelf units, they can be replaced easily and individually in case of failure. Moreover, adding a communications path to a new service group may be performed easily on-site, e.g. by simply connecting a communications device drawn from one of the members of that group to interface  100  as described below. Further implementations of interface  100  extend such interoperability to other communications devices such as cellular and wireline telephones, 3-wire or 4-wire intercoms, tape recorders, and one-way radios. 
     Each communications device  1  is connected to a corresponding I/O port  10  through a signal and control cable  220  that carries input signal S 10 , output signal S 16 , and PTT command S 60 . Cable  220  may terminate at either end with one or more standard connectors (such as 2.5- or 3.5-mm miniature audio plugs), and/or specialized connectors may be used, depending upon the particular physical characteristics of the associated communications device. It is also possible for the audio and PTT command signals to be carried between port  10  and a communications device  1  over two or more separate cables rather than through a single signal and control cable  220 . Upon connection with communications devices  1 A- 1 D as described above, interface  100  operates as described herein to enable users of communications devices  2 A- 2 D (each matching a respective one of the devices  1 A- 1 D) to communicate with each other. 
     FIG. 3 shows a block diagram of a VOX circuit  20  according to an embodiment of the invention. Conditioning circuit  110  receives input signal S 10  and outputs a conditioned audio signal to rectifying circuit  120 . Conditioning circuit  110  may perform signal processing operations on input signal S 10  such as gain, equalization, and filtering. In an exemplary implementation, conditioning circuit  110  provides variable gain by including an operational amplifier (op amp) configured to have variable resistive feedback. The several VOX circuits  20  may be implemented on separate circuit boards within interface  100 , or one or more of the VOX circuits  20  may be implemented on the same board. 
     Conditioning circuit  110  may be constructed to perform equalization operations as desired according to the output characteristics of a particular communications device. For example, a cellular or wireline telephone may provide an audio signal having a different spectral distribution than a two-way radio. 
     Existing VOX designs are often disfavored because of a susceptibility to false keying in response to interference such as ambient noise. It may be desirable for conditioning circuit  110  to narrow the frequency content of the signal it outputs to rectifying circuit  120  in order to enhance rejection of ambient noise by VOX circuit  20 . For example, conditioning circuit  110  may include a bandpass filter centered at approximately 125 Hz, which corresponds to a fundamental frequency (F 0 ) of the voice of a typical adult male speaker (alternatively, the frequency may be limited to a band near or including 210 Hz, the fundamental frequency of the voice of a typical adult female speaker). Depending upon the intended application, the energy content of one or more different frequency bands may be used to establish a keying event. In a case where gain and bandpass equalization or filtering is provided, it may also be desirable to divide the bandpass operation into a lowpass and a highpass operation such that the gain operation may be performed between the filtering operations. 
     Another feature that may help to reduce the probability of false keying is the provision of RF shielding within and around VOX circuit  20 . This shielding may comprise filtering on the input and output signal paths, on the paths to the power supply rails, and on paths between stages. Additional RF shielding may be provided in the construction of the enclosure which houses the apparatus. In this way, the sensitivity of VOX circuit  20  to a RF burst from a nearby transmitter may be significantly reduced. 
     Rectifying circuit  120  receives the conditioned audio signal and outputs a peak signal S 20 . In one implementation, rectifying circuit  120  includes a nonlinear device such as a PN junction device. For example, the nonlinear device may be a diode or the base-emitter or base-collector junction of a bipolar junction transistor (BJT). 
     Comparator  140  receives peak signal S 20  and compares it to a reference voltage Vc. In one example, the reference voltage Vc has an approximate value of Vcc/3. When the voltage of peak signal S 20  exceeds the reference voltage Vc, comparator  140  outputs a channel activation signal S 30 . It is possible but not necessary to choose a different reference voltage Vc for each VOX circuit  20 . 
     It may be desirable to continue channel activation signal S 30  for some period of time after the voltage of peak signal S 20  falls below the reference voltage Vc. Timing circuit  130  provides a tail delay to continue a level of peak signal S 20 . In one example, timing circuit  130  includes a capacitance to ground in parallel with a resistance. When peak signal S 20  is active, the capacitance is charged. When the conditioned audio signal becomes less active or inactive, the charged capacitance maintains a voltage level of peak signal S 20  until the resistance discharges it to ground. In a further example, the resistance is variable to provide a time constant of from less than one second to several seconds. 
     Priority circuit  150  receives peak signal S 20  and channel activation signal S 30  and outputs PTT command signal S 60  to the associated communications device. Priority circuit  150  is also coupled to a bidirectional priority signal S 50 . In an exemplary implementation, priority signal S 50  is common to all of the VOX circuits  20 . 
     Priority circuit  150  responds to an activation of either channel activation signal S 30  (by comparator  140 ) or priority signal S 50  (by another instance of priority circuit  150 ). In a case where channel activation signal S 30  becomes active, priority circuit  150  asserts priority signal S 50  and does not assert PTT command signal S 60 . As a result, other channels are prevented from being activated, and the associated channel is maintained in receive mode. 
     In a case where another circuit asserts priority signal S 50 , priority circuit  150  asserts PTT command signal S 60  and prevents assertion of channel activation signal S 30 . As a result, the channel is prevented from being activated and is switched into transmit mode. 
     FIG. 4 shows an exemplary implementation of priority circuit  150  that includes a peak suppression element  210 , a mode select element  220 , a PTT closure element  230  (all implemented in this example using FETs), and a diode  240 . This implementation also includes two resistances  250  and  260  (each resistance having a value of 100 kilohms) that may slow a response of mode select element  220  and reduce an incidence of false responses. 
     In a case where priority circuit  150  receives channel activation signal S 30 , mode select element  220  is turned on. The resulting path to ground in mode select element  220  prevents peak suppression element  210  from being turned on, thus preventing peak suppression element  210  from pulling peak signal S 20  to ground. The same path to ground also prevents PTT closure element  230  from being turned on, thus maintaining the associated communications device in a receive mode. Channel activation signal S 30  also causes priority signal S 50  to be asserted through diode  240 . 
     In a case where priority circuit  150  receives priority signal S 50 , peak suppression element  210  is turned on. The resulting path to ground in peak suppression element  210  pulls peak signal S 20  to ground, thus preventing channel activation signal S 30  from being asserted (by keeping peak signal S 20  from exceeding the reference voltage Vc and by preventing charging of the capacitance in timing circuit  130 ). Priority signal S 50  also causes PTT closure element  230  to turn on, thus pulling PTT command S 60  to ground and sending a PTT closure command to the associated communications device. 
     FIG. 5 shows a VOX circuit  22  according to an alternate implementation of VOX circuit  20 . VOX circuit  22  includes an initialization circuit  170  that prevents the assertion of channel activation signal S 30  during power-up of the interface  100 . For example, initialization circuit may pull peak signal S 20  below the reference voltage Vc (e.g. to ground) during power-up. In an exemplary implementation, initialization circuit  170  includes a BJT having its collector coupled to peak signal S 20 , its emitter coupled to ground, and its base coupled to a supply voltage of interface  100  through a capacitance. A transient occurring on the supply voltage during power-up causes the capacitance to conduct a voltage to the base of this BJT, creating a conductive path between the collector and emitter until the supply voltage reaches a steady state. 
     FIG. 6 shows a block diagram of a switching matrix  30 . Each input signal S 10  is inputted to a corresponding analog switch Sw 1 . Switch Sw 1  is closed upon assertion of channel activation (CA) signal S 30 , at which time input signal S 10  passes through resistance R 1  onto a common bus. A corresponding multiplexer M 1  also receives CA signal S 30 , and assertion of CA signal S 30  causes that multiplexer M 1  to select a null input for output signal S 16 . The other multiplexers M 1  (i.e. those receiving an unasserted CA signal S 30 ) select the input signal S 10  on the common bus for the corresponding output signals S 16 . In an exemplary implementation, switches Sw 1  and multiplexers M 1  are implemented using analog multiplexers of the 74HCT family. 
     FIG. 7 shows an alternate implementation  32  of a switching matrix according to an embodiment of the invention. In this implementation, a circuit Ckt 1  conditions the signal on the common bus before it passes into multiplexers M 1 . Rather than a null input as shown in FIG. 6, a nonnull input based on a reference voltage Vr is selected by the multiplexer M 1  corresponding to the asserted CA signal S 30 . The nonnull input may be produced by a circuit Ckt 2  as shown in FIG.  7 . Reference voltage Vr may be chosen to be at least one-quarter of Vcc; in one embodiment, reference voltage Vr is approximately one-half of Vcc. Use of a nonnull voltage rather than a null voltage may improve audio quality by reducing popping noise at keying events. 
     FIG. 8 illustrates an exemplary application of an alternate implementation  102  of an interface according to an embodiment of the invention that includes an U/O port  12  that communicates with a telephone, which may be wired (e.g. having a landline connection to the PSTN) and/or wireless (e.g. having a connection to a cellular telephone network), over a cable  220   t . In one embodiment of the invention, cable  220   t  includes an acoustic coupler. FIG. 9 shows a block diagram of interface  102 . In order to compensate for a difference in audio quality (e.g. spectral content) in the signal provided by the telephone and/or the acoustic coupler, I/O port  12  may include gain and/or equalization operations in conditioning circuits 310-340 as shown in FIG.  10 . In an exemplary implementation, conditioning circuit  340  outputs an active differential (e.g. balanced) output on acoustic coupler output signal S 96  to compensate for inefficiencies in the transfer of acoustic energy to the telephone. 
     FIG. 11 shows a schematic diagram of an input select circuit  360 . By providing a short or an open circuit across input select terminals T 98 , cable  220   t  causes circuit  360  to select input signal S 10   t  from among signals S 90   c  and S 92   c  (corresponding to acoustic coupler input signal S 90  and wired input signal S 92 , respectively). 
     In a similar manner, an interface according to an embodiment of the invention may also be adapted to support communications paths to other keyed and nonkeyed devices such as 3-wire or 4-wire intercoms, tape recorders, or one-way radios. In an alternative embodiment, two or more interfaces  100  may be connected for increased capacity. 
     FIG. 12 shows a block diagram of a supply voltage monitor circuit  300  including two voltage level sensors  310  and  320 . Each of these sensors  310  and  320  monitors the supply voltage by indicating a relation between the supply voltage and a predetermined threshold voltage. FIG. 13 shows a block diagram of an alternate implementation  302  of a supply voltage monitor circuit, in which each sensor  310 / 320  includes a voltage divider  312 / 322  and a threshold detector  314 / 324 . In this implementation, sensor  320  is configured to have a higher threshold voltage than sensor  310 . When sensor  320  indicates the predetermined relation between the supply voltage and its higher threshold voltage, the indication signal is also inputted to suppression circuit  330 , which suppresses an indication by sensor  310  of a relation between the supply voltage and the lower threshold voltage. 
     An interface  100  according to an embodiment of the invention is designed to work reliably and at low power. Because the current demand of apparatus  100  is kept at a minimum, and because the communications devices  1 A- 1 D are self-powered, apparatus  100  may operate reliably on common, primary-type, DC battery cells, a vehicle cigarette-lighter jack, or another low-power source such as may be readily available on the scene (e.g. a +28 VDC aircraft power bus), with no need for an inverter, generator or landline AC supply. 
     In addition to the benefits mentioned above, an interface according to an embodiment of the invention may be extremely portable and inexpensive, especially in comparison to existing alternatives. Moreover, such an interface allows a user with only minimal training to deploy a system for interoperated support of multiple communication paths and leave it to operate unattended. 
     In a further embodiment of the invention, switching matrix  30  is configurable so that an organizational structure among the communications devices  1 A- 1 D may be incorporated. For example, communications received from members of one service group may generally be transmitted only to radios within that group, while communications received from any commander may be transmitted by all other communications devices. In a further embodiment of the invention, at least one of the cables  220  supports an additional control path so that the configuration of switching matrix  30  may be controlled at least in part by a control signal from the corresponding communications device. 
     In an interface according to a further embodiment of the invention, at least one of the cables  220  is replaced by a low-power RF link. For example, such a link may conform to a version of the Bluetooth specification (e.g. as approved for Part 15 radio devices operating in the 2.4 GHz ISM band or similar devices operating in another band). In a further implementation, a cable  220  carries an input signal S 10  and a corresponding output signal S 16 , while a low-power RF link as described above carries the corresponding PET command S 60 .