Abstract:
One embodiment includes a system configured to identify a preferred channel for radio communication from a plurality of consecutive integer frequencies including preferred channels and non-preferred channels, the system further to generate a plurality of radio channels corresponding to a plurality of consecutive integer frequencies based on a generation of reference frequencies, identifies preferred channels and non-preferred channels from the plurality of radio channels, where frequency synthesizer settling times of the preferred channels are faster than frequency synthesizer settling times of the non-preferred channels, scan the preferred channels for radio activity, select one of preferred channels responsive to the scanned radio activity; and utilize one of the reference frequencies to generate a radio frequency corresponding to the selected one of the preferred channels.

Description:
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/583,248, filed Jun. 25, 2004, the contents of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     In conventional radio systems or ICs, a frequency synthesizer may be used to generate the transmit carriers and/or the receiver Intermediate Frequency (IF). The synthesizer typically includes a Phase Locked Loop (PLL) frequency multiplier that generates the desired high frequency from a lower oscillator frequency. The lower oscillator frequency is typically generated using a quartz crystal. Typical crystal frequencies used are 12, 16, or 20 MHz. 
     The synthesizer must be able to generate a range of carrier and IF frequencies across the frequency range of operation of the radio. A conventional radio designed to operate in the worldwide 2.4 GHz ISM band is one example. A typical such device may support eighty four, 1 MHz radio channels, with the lowest channel being 2400 MHz and the highest being 2483 MHz. 
     Such radio devices or systems are often used to transmit relatively small packets of data, and are bi-directional. One example is a wireless mouse or keyboard. Such devices typically transmit only a few bytes at a time. In order to provide a robust data link, such systems may use a bi-directional radio system, with all data transfers being acknowledged using a handshake packet transmitted by the receiver after correct reception of a data packet. When not actively sending data (or receiving a handshake), such radio systems typically operate in a low power mode, as they are battery powered and power conservation is extremely desirable. 
     Typically, a conventional radio device of the type described above will transmit a pre-amble (conventionally a 1010101 . . . pattern) at the beginning of a transmission in order to allow the receiver to lock on to the transmitted signal. The receiver may, for example, use the pre-amble pattern to set the thresholds on its data slicer. The current drawn by the synthesizer is typically a significant proportion of the current drawn by the radio in its transmit and receive modes. The pre-amble is typically about 32 μs in duration. 
     Frequency synthesizers used in conventional applications typically take 100-200 μs to settle at the desired frequency. When switching between transmit and receive modes, it is necessary for the synthesizer to change frequency because the frequency required in the receive mode is offset from the transmit carrier frequency by the IF frequency. The timing of a packet transfer between a transmitter and a receiver may therefore be as shown in  FIG. 1 . 
     As can be seen from the timing diagram of  FIG. 1 , the synthesizer settling period may dominate the time that the radio is in its high current modes. For short data packets, the settling periods drive the power consumed by the radio in transmitting a packet. Any reduction in synthesizer settling current will therefore directly reduce the power consumed in sending a data packet, and so increase the battery life of the radio device. 
       FIG. 2  is a somewhat schematic block diagram of a conventional synthesizer  200 . In the conventional synthesizer implementation  200  shown in  FIG. 2 , the typical time required for the synthesizer to settle may be significantly less than the worst case. In this case, it is possible for the “transmitter” to begin sending data as soon as the synthesizer is detected as having settled, rather than always waiting for a fixed worst-case lock period. Unfortunately, however, this is not possible when the synthesizer re-settles after the “receiver” sends the handshake and switches between reception and transmission. This is because of the danger that the synthesizer in the “receiver” will settle before that of the “transmitter” and so send the handshake before the “transmitter” is ready to receive the handshake. Therefore, in that case, the fixed, worst case synthesizer settling time must be used. 
     As shown in  FIG. 2 , the conventional synthesizer includes a phase divider  210 , a loop filter  220 , a voltage controlled oscillator (VCO)  230 , and a divide by N counter  240 . In the conventional method, the phase divider  210  divides the incoming 20 MHz XTAL frequency down to 1 MHz in order to obtain N*1 MHz channel resolution. The VCO frequency is equal to the N counter integer value multiplied by the reference frequency (REF). For example, where:
         N0=2400   N1=2401   N2=2402   . . .   N80=2480
 
then:
   VCO Freq=N*Ref   2400 Mhz=2400*1 Mhz   2401 Mhz=2401*1 Mhz   2402 Mhz=2402*1 Mhz   . . .   2480 Mhz=2480*1 Mhz
 
The settling time is inversely proportional to the REF frequency, in this case 1 MHz.
       

     In order to minimize the power consumption in a conventional radio system as shown in  FIG. 3 , it is necessary to minimize both the typical and worst case synthesizer settling times. In many radio systems of this type, the choice of channel is arbitrary. The large number of channels (for example eighty-four channels) available may be vital in supporting applications where there may be many similar radio systems operating within range of each other, or when operating in the presence of other (non-compatible) radio systems that use that same frequency band, and so block some of the channels from being useable by the radio system in question. However, even in radio system that must support such a large number of channels, in the great majority of applications or installations, it will be rare for every channel to be used. 
     Referring to  FIG. 3 , a conventional radio system includes a phase lock loop (PLL) circuit  200  receiving a reference frequency signal (such as from a crystal) and outputting a radio channel frequency. PLL logic  310  provides divide control and PLL loop compensation. In the conventional method, the VCO frequency is equal to the N counter integer value multiplied by the reference frequency divided by an M counter integer value. Assuming a 20 MHz reference frequency, for instance, and an M counter value of 20, the resulting VCO frequencies would be the same as above given the same N counter values. 
     Unfortunately, this conventional technology has several disadvantages. For instance, existing radio systems with frequency synthesizers used for both TX carrier generation and RX IF generation have the disadvantage that the power consumed when transmitting data is the same on all channels. The channels with the slowest settling time therefore determine the power consumed by the system. Moreover, the higher reference frequency is more immune to filter leakage (PLL drift) and the higher reference frequency is easier to simulate. It would be desirable, therefore, to have a system that enabled faster settling time and lower power use in radio communication. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of the present invention, an improved radio device having a synthesizer architecture provides an average settling time that is significantly reduced on a subset of the channels supported and thereby provides improved power consumption characteristics. A radio system preferably incorporates a radio having a subset of channels with faster settling times designated as being “preferred” channels. A method of reducing power consumption in a radio system by scanning and selecting preferred channels before non-preferred channels is also disclosed. Preferred channels preferably are those with lower power consumption requirements due, for instance, to faster settling times. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments thereof, made with reference to the accompanying figures, in which: 
         FIG. 1  is a timing diagram showing settling time operation of a conventional radio; 
         FIG. 2  is a somewhat schematic block diagram showing an architecture of a conventional PLL solution; 
         FIG. 3  is a somewhat schematic block diagram of a conventional system comprising the conventional PLL solution of  FIG. 2 ; 
         FIG. 4  is a flowchart showing operation of a novel method of finding the preferred channels according to one aspect of the present invention; 
         FIG. 5  is a somewhat schematic block diagram illustrating an architecture of an improved PLL solution according to a preferred embodiment of the present invention; and 
         FIG. 6  is a somewhat schematic block diagram showing an improved radio system including the improved PLL solution of  FIG. 5  according to another aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An improved radio device with a synthesizer architecture is described in which the average settling time is significantly reduced on a subset of the channels supported, and power consumption is thereby improved. A radio system is also described which incorporates such a radio having a subset of channels designated as being “preferred” channels. Various sample embodiments of the present inventive principles will now be described below with reference to  FIGS. 5 and 6 . 
       FIG. 5  illustrates an architecture of an improved PLL solution according to a preferred embodiment of the present invention. In  FIG. 6 , an improved radio system is illustrated which preferably includes the improved phase lock loop (PLL) synthesizer architecture shown in  FIG. 5 . Referring to  FIG. 5 , an improved PLL solution  500  preferably includes a frequency divider  510 , a filter  520 , a VCO  530 , and a divide by N counter  540 . In this embodiment, the XTAL frequency is divided down into a range of various reference frequencies (e.g., REF=1, 2, 4, 5, 10, 20 MHz) using the frequency divider  510 . The lowest integer multiple from an M counter is preferably used by the frequency divider  510  to obtain the desired frequency. Again, the VCO frequency is equal to the N integer counter value multiplied by the reference frequency. In this case, where:
         M0=1   M1=20   M2=10   . . .   M80=1
 
and
   N0=120   N1=2401   N2=1201   . . .   N80=184
 
then
   VCO Freq=N*Ref   2400 MHz=120*20 MHz   2401 MHz=2401*1 MHz   2402 MHz=1201*2 MHz   . . .   2480 MHz=124*20 MHz       

     Again, the settling time is inversely proportional to the reference frequency (REF). Using this approach, 1 MHz resolution is available, but the average PLL settling time is improved. For instance, the average settling time using the reference frequencies REF=1, 2, 4, 5, 10, 20 MHz is much faster than the average settling time for a 1 MHz reference frequency. 
     Referring to  FIG. 6 , an improved radio system  600  preferably includes a PLL  500  and PLL Logic  610 . In this system  600 , the PLL  500  receives a reference frequency from a reference source (such as a crystal) and control input from the PLL Logic  610 . The radio system outputs on a selected radio channel. Preferably, M and N counters are used to generate the VCO frequency of the PLL. The following chart illustrates various M and N counter values used to generate various VCO frequencies in this embodiment. Again, this chart assumes a 20 MHz reference frequency input into the PLL  500 . 
                                         M0 counter = 1   N counter = 120   VCO Freq = 2400       M1 counter = 20   N counter = 2401   VCO Freq = 2401       M2 counter = 10   N counter = 1201   VCO Freq = 2402       M3 counter = 20   N counter = 2403   VCO Freq = 2403       M4 counter = 5   N counter = 601   VCO Freq = 2404       M5 counter = 20   N counter = 2405   VCO Freq = 2405       M6 counter = 10   N counter = 1203   VCO Freq = 2406       M7 counter = 20   N counter = 2407   VCO Freq = 2407       M5 counter = 5   N counter = 602   VCO Freq = 2408       M6 counter = 20   N counter = 2409   VCO Freq = 2409       M6 counter = 2   N counter = 241   VCO Freq = 2410                    
According to this embodiment, faster reference frequencies are enabled, allowing faster settling times and reduced power consumption by the radio system.
 
     A method of using the features of the improved architectures described above to reduce power consumption during transmission of a given packet of data will now be described with additional reference to  FIG. 4 . Referring now to  FIGS. 4-6 , an improved synthesizer is preferably designed such that a portion of the channels have a faster settling time. The channels having the faster settling times are preferably designated as “preferred” channels. 
     Under most practical operating conditions, the radio system  600  may use one of the preferred channels. The resulting reduction of synthesizer settling time when using these channels may lead to a significant reduction in power consumption. Only in rare cases where it is necessary to use a non-preferred channel would the synthesizer settling time be longer, and power consumption consequently higher. 
     In an improved radio device  600  constructed according to principles of the present invention, the “fast” channels available in the preferred architecture may be used to reduce the power required to transmit a given packet of data. For instance, power consumption can be improved when the radio system  600  incorporates a channel selection protocol that selects a “fast” channel for use if one is available, and only uses a “slow” channel if no “fast” channel is available. 
     An implementation of such a channel selection method is described for instance with reference specifically to  FIG. 4 . Referring to  FIG. 4 , when a receiver is initialized (for example when power is applied), the receiver preferably selects a channel for use. To do this, the receiver preferably scans the available channels to find a channel that is not already in use by another compatible radio system. The receiver also preferably listens for evidence of radio activity from incompatible systems on each channel that it scans. 
     In a most preferred embodiment, the receiver first scans the preferred “fast” channels. If it finds a fast channel that is free of both other compatible radio traffic and interference, the receiver selects that channel. In this embodiment, only if the receiver is unable to find a “fast” channel that is free of compatible radio traffic and free of interference does the receiver scan the non-preferred, “slow” channels. 
     In another step, an event occurs that causes the transmitter to need to transmit data. If the transmitter has already established a communications link with the receiver on a given channel during a previous transmission, that channel is considered used. If no previously established link exists, the transmitter searches for the receiver channel. The transmitter may search for a receiver channel by sending a “connect request” packet. The connect request packet preferably contains the unique ID number of the transmitter (which is transmitted to, and stored by the receiver during system configuration). The transmitter preferably transmits a “connect request” packet on each channel in a desired sequence. 
     In one implementation, for instance, the transmitter may transmit this packet on the “fast” channels first. In another implementation, however, it may transmit on each channel in turn without regard to which channels are fast and which are slow. When the receiver receives a “connect request” packet containing the unique ID of a transmitter with which it has been configured to communicate, the receiver sends a response packet. 
     In a further step, the transmitter is “connected” to the receiver (i.e., a data link is established), and the transmitter transmits data packets on the channel on which it received a connect response. In another step, the transmitter and receiver preferably continue to use this channel until such time as either the receiver is reset or the channel is found to suffer from interference. The phase lock loop (PLL) may include a programmable M counter and N counter (e.g., integer counters) providing bandwidth adjustment. The wireless communication scheme may also be capable of channel hopping. 
     In a first alternative embodiment, specific integer M counter and N counter values that are presented can be replaced with other generic integer values. In a second alternative embodiment, the user may elect to use half of the preferred channels, a third of the preferred channels, or any other reasonable combination as desired by the user. In a third alternative embodiment, bandwidth compensation can be provided. This can be done in several ways. For example, bandwidth compensation can be achieved by adjusting the VCO gain (Mhz/V) or by controlling the internal components of the filter. 
     An improved radio device according to a preferred embodiment of the present invention has been described above having two different categories of settling times. More specifically, in the earlier-described embodiment, the radio device was described as including “fast” and “slow” channels, designated as “preferred” and “non-preferred” channels, respectively. In another alternative implementation, however, three or more different categories of synthesizer settling times may be implemented. In this alternative embodiment, respective speeds of the channels can be identified so that rather than simply having “preferred” and “non-preferred” channels, the channels can be ranked in order of preference based on their speed. In this manner, the method can be modified so that the receiver tries the fastest channels first, then the next fastest, and so on, trying the slower channels only if no faster channel is available. 
     Various preferred methods of finding a channel have also been described previously in terms of a one-way data stream. In a further alternative embodiment, a method of finding a channel may be implemented in a system in which data may be passed in either direction (bi-directional data exchange). In a bi-directional system, the “receiver” preferably selects the channel to use, and the “transmitter” preferably tries to find the receiver. 
     In a still further implementation, when no connection (or link) exists, the transmitter may perform the steps described in the earlier embodiment as being performed by the receiver, and vice-versa. Once a connection has been established, the receiver can preferably begin listening on the selected channel for data, and the transmitter preferably only transmits when it has data to send. 
     In one embodiment, data exchange is asynchronous. The method may also be applied, however, to synchronous systems. In such systems, the “reconnection” process is preferably unchanged. The receiver may poll the transmitter for data periodically, or the receiver and transmitter may each maintain accurate clocks that allow them to exchange data periodically, with a pre-determined interval between transmissions. 
     As can be seen from the foregoing description of various embodiments, a primary advantage of an improved radio and system constructed according to principles of the present invention is the significant reduction in the amount of power consumed in transmitting data between radios in typical applications and installations. 
     For purposes of clarity, many of the details of the invention and the methods of designing and manufacturing the same that are widely known have been omitted from the following description. It should also be appreciated that reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. And the particular features, structures, or characteristics of the various embodiments may be combined as suitable in one or more embodiments of the invention. 
     Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, the inventive aspects may lie in less than the combination of all features of any single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention. 
     Having described and illustrated the principles of the invention in various embodiments thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variation coming within the spirit and scope of the following claims.