Abstract:
A wide-band multimode frequency synthesizer using a Phase Locked Loop (PLL) is provided. The multiband frequency synthesizer includes a multimode prescaler, a phase detector/a charge pump, a swallow type frequency divider, and a switching bank LC tuning voltage-controlled oscillator having wide-band and low phase noise characteristics. The multimode prescaler operates in five modes and divides a signal up to 12 GHz. The wide-band frequency synthesizer can be used in various fields such as WLAN/HYPERLAN/DSRC/UWB systems that operate in the frequency range from 2 GHz to 9 GHz. The wide-band multimode frequency synthesizer includes a frequency/phase detector for comparing a frequency and phase of a reference high-frequency signal with a frequency and phase of a feedback high-frequency signal; a charge pump for producing an output current corresponding to the result of the comparison performed by the frequency/phase detector; a loop filter for producing an output voltage corresponding to an accumulated value of the output current of the charge pump; a voltage-controlled oscillator for generating an oscillation signal having a frequency corresponding to the output voltage of the loop filter; and a variable frequency divider for dividing an output signal of the voltage-controlled oscillator by a designated integer value, and outputting the result as a feedback signal, wherein at lease two of an amount of unit pumping charges of the charge pump, an RLC value of the loop filter, an RLC value of the voltage-controlled oscillator, and a divisor value of the variable frequency divider are controlled according to a band.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to and the benefit of Korean Patent Application Nos. 2005-119530, filed Dec. 8, 2005, and 2006-74089, filed Aug. 7, 2006, the disclosures of which are incorporated herein by reference in their entirety. 
   BACKGROUND 
   1. Field of the Invention 
   The present invention relates to a multimode frequency synthesizer using a phase-locked loop (PLL) that can be installed in 802.11 b/g HYPERLAN (HIgh PErformance Radio LAN), Dedicated Short Range Communications (DSRC), 802.11 a, and Ultra Wide Band (UWB) systems having applications in a 2˜9 GHz frequency band. 
   2. Discussion of Related Art 
   Recently, as mobile communication services are becoming increasingly widespread, available frequency bands are becoming saturated, and several terminals are required to enjoy various mobile communication services. As a result, developers all over the world are working on a reconfigurable mobile communication system capable of reconfiguring mobile communication services in software and enabling access to various mobile communication services using one terminal regardless of encoding and decoding method. To access necessary services using one terminal regardless of time and place, a wide-band Radio Frequency (RF) transceiver of a mobile communication system is required. 
   To manufacture the multiband multimode RF transceiver, a wide-band Local Oscillator (LO) are required.  FIG. 8  illustrates a conventional wide-band frequency synthesizer including a phase frequency detector  20 , a charge pump  30 , a low pass filter  40 , a voltage-controlled oscillator  50 , and a variable frequency divider  70 . 
   To satisfy requirements that vary depending on field of application when the frequency synthesizer for multiband multimode is manufactured, there should be a certain amount of flexibility in selecting components of the frequency synthesizer. However, use of a voltage-controlled oscillator, a high speed prescaler, a charge pump, and a loop filter diminishes flexibility in the construction of the frequency synthesizer. Therefore, a plurality of voltage-controlled oscillators and phase-locked loop (PLL) loops are used to manufacture the multiband frequency synthesizer. However, using a plurality of voltage-controlled oscillators and PLL loops results in increased chip size and power consumption. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a multiband multimode frequency synthesizer generating a wide-band (e.g., from 2 GHz to 9 GHz) frequency. 
   The present invention is also directed to a multiband wide-band frequency synthesizer capable of reducing an occupied area and electric power consumption by using a multimode prescaler. 
   The present invention is also directed to a wide-band frequency synthesizer with low noise using an inductor-switching voltage-controlled oscillator. 
   One aspect of the present invention provides a variable frequency divider for dividing an externally applied oscillation signal by a designated integer value and outputting the divided signal as a feedback signal, the variable frequency divider comprising: a prescaler for selecting one of a plurality of dual divisor value sets according to an external frequency selection signal; a main counter for counting the number of output pulses of the prescaler; and a swallow counter for designating an interval divided by a specific divisor value of the dual divisor value sets. 
   Another aspect of the present invention provides a frequency synthesizer including: a frequency/phase detector for comparing a frequency and phase of a reference high-frequency signal with a frequency and phase of a feedback high-frequency signal; a charge pump for producing an output current corresponding to the result of the comparison performed by the frequency/phase detector; a loop filter for producing an output voltage corresponding to an accumulated value of the output current of the charge pump; a voltage-controlled oscillator for generating an oscillation signal having a frequency corresponding to the output voltage of the loop filter; and a variable frequency divider for dividing an output signal of the voltage-controlled oscillator by a designated integer value, and outputting the result as a feedback signal, wherein at lease two of an amount of unit pumping charges of the charge pump, an RLC value of the loop filter, an RLC value of the voltage-controlled oscillator, and a divisor value of the variable frequency divider are controlled according to a band. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  illustrates frequency band allocation for 802.11b/g, HYPERLAN (HIgh PErformance Radio LAN), Dedicated Short Range Communications (DSRC), 802.11a, and Ultra Wide Band (UWB); 
       FIG. 2  is a block diagram of a wide-band multimode frequency synthesizer according to an exemplary embodiment of the present invention; 
       FIG. 3  is a circuit diagram of a multimode prescaler illustrated in  FIG. 2  according to an exemplary embodiment of the present invention; 
       FIG. 4  is a circuit diagram of a mode controller illustrated in  FIG. 3  according to an exemplary embodiment of the present invention; 
       FIG. 5  is a circuit diagram of a charge pump illustrated in  FIG. 1  according to an exemplary embodiment of the present invention; 
       FIG. 6  is a circuit diagram of an adaptive loop filter illustrated in  FIG. 1  according to an exemplary embodiment of the present invention; 
       FIG. 7  is a circuit diagram of a wide-band LC tuning voltage-controlled oscillator having a switching function illustrated in  FIG. 1  according to an exemplary embodiment of the present invention; and 
       FIG. 8  is a block diagram of a conventional frequency synthesizer. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Hereinafter, exemplary embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms. Therefore, the following embodiments are described in order for this disclosure to be complete and fully enabling of practice of the present invention by those of ordinary skill in the art. 
   A frequency synthesizer illustrated in  FIG. 2  includes a frequency/phase detector for comparing the frequency and phase of a reference high-frequency signal with the frequency and phase of a feedback high-frequency signal; a charge pump  400  for producing a current corresponding to the result of the comparison by the frequency/phase detector; a loop filter  500  for producing a voltage corresponding to an accumulated value of the output current of the charge pump; a voltage-controlled oscillator  200  for generating an oscillation signal having a frequency corresponding to the output voltage of the loop filter  500 ; and a variable frequency divider  300  for dividing the output signal of the voltage-controlled oscillator  200  by a designated integer value to output the divided signal as a feedback signal. 
   Here, the variable frequency divider  300  includes a prescaler  301  for selecting one of a plurality of dual divisor value sets, a main counter  307  for counting the number of output pulses of the prescaler  301 , and a swallow counter  308  for designating an interval divided by a specific divisor value of the dual divisor value sets. 
   Meanwhile, when a system including the frequency synthesizer requires a divide-by-2 tuning clock in addition to a main tuning clock corresponding to a channel to be tuned, a 2-frequency divider  204  may be further included as illustrated. 
   As illustrated in  FIG. 1 , a 802.11b/g system uses a frequency range of 2.7 GHz to 2.8 GHz, a HYPERLAN system uses a frequency range of 5.1 GHz to 5.3 GHz, a DSRC system uses a frequency range of 5.4 GHz to 5.5 GHz, a 802.11a system uses a frequency range of 5.5 GHz to 5.7 GHz, and a UWB system uses a frequency range of 3.2 GHz to 8.9 GHz. 
   A wide-band multimode frequency synthesizer on which a multimode prescaler is mounted as illustrated in  FIG. 2  may be used for 802.11 b/g, HYPERLAN, DSRC, 802.11 a, and UWB systems according to a mode selection bit. A terminal having the wide-band frequency synthesizer of the present embodiment may select a desired frequency band for reception and transmission by adjusting the mode selection bit. Generally, the selection of the frequency band corresponds to selection of a communication method type, for example, selecting one of wireless LAN or Digital Multimedia Broadcasting (DMB). 
   The wide-band frequency synthesizer of  FIG. 2  includes a phase frequency detector/switching charge pump  400 , an adaptive loop filter  500 , a wide-band LC tuning voltage-controlled oscillator  200  that can be switched, and a multimode variable frequency divider  300  in which a multimode prescaler is included. Also, it may further include an input buffer  202  for buffering a reference clock having a different frequency for each frequency band and/or an output buffer for buffering a clock output from the voltage-controlled oscillator  200 . 
   The multimode variable frequency divider  300  that divides an externally applied oscillation signal by the designated integer value to output the result as a feedback signal includes a prescaler  301  for selecting one of a plurality of dual divisor value sets corresponding to a band selected according to an external frequency band selection signal, a main counter for counting the number of output pulses of the prescaler  307 , and a swallow counter  308  for designating an interval divided by a specific divisor value of the dual divisor value sets. 
   The multimode prescaler  301  divides an output signal of the voltage-controlled oscillator  200  into a frequency corresponding to f pre  of  FIG. 2 . The multimode prescaler  301  divides the output signal of the voltage-controlled oscillator  200  by ⅔, ⅘, 8/9 and 16/17 according to the mode selection bit, which is an externally applied control signal. According to the mode selection bit, the oscillation frequency of the voltage-controlled oscillator  200 , a value of the loop filter  500  of  FIG. 2 , the amount of current of the charge pump  400  may be appropriately selected based on an application frequency band (802.11b/g, HYPERLAN, DSRC, 802.11a, and UWB) of  FIG. 1 . 
   The swallow counter  308  and the main counter  307  control the count according to setting bits C 1  to C 5 . The oscillation frequency may be roughly or finely controlled according to the setting bits C 1  to C 5  and the mode selection bit. 
   That is, one of the illustrated four dual divisor value sets is selected by the mode selection bit, for example, when a second dual divisor value set (Prsc 2 ) is selected. The main counter  307  counts the output signal f pre  of the prescaler  301  tip to the number set by the setting bits C 1  to C 5 , and the swallow counter  308  is set to count to a smaller number than the main counter  307  by the setting bits C 1  to C 5 . 
   In the beginning, a signal output from the voltage-controlled oscillator  200  and divided-by-5 according to the second dual divisor value set Prsc 2  is output from the prescaler  301 . When the swallow counter finishes counting while the swallow counter and the main counter count the signal divided-by-5, a signal MC is input to the prescaler  301 . The prescaler that receives the signal MC changes the divisor value into 4 and the main counter continues counting the remaining signals divided-by-4. Accordingly, the output signals f div  of the main counter  307  may be result values divided by various divisor values according to a fixed output of the voltage-controlled oscillator. 
     FIG. 3  illustrates a high-speed multimode prescaler  301  used for the wide-band frequency synthesizer of  FIG. 2  according to the exemplary embodiment of the present invention. The illustrated multimode prescaler  301  includes two current-mode mode logic (CML) D flip-flops  320  and  330 , three D flip-flops  340 ,  350  and  360 , a mode controller  310 , a selector  380 , and a differential-to-single ended signal converter  370 . 
   A multi-stage cascade-connected flip-flop comprises the three D flip-flops  340 ,  350  and  360  and a CML D flip-flop  330  among the components so that an initial stage receives the oscillation signal and counts to a multiple of 2. In addition, an additional flip-flop comprises another CML D flip-flop  320  so that the additional flip-flop receives the oscillation signal and supports a dual counting mode. The selector  380  selects one of output signals of the flip-flop output stages of the multi-stage cascade-connected flip-flop and outputs the selected signal, and the mode controller  310  controls operation of the additional flip-flop according to the output signal of the swallow counter. 
   The CML D flip-flops  320  and  330 , which are high-speed frequency dividers for diving high output signals of the voltage-controlled oscillator  200 , include AND logic or OR logic. The three D flip-flops  340 ,  350  and  360 , which are frequency dividers for dividing a frequency divided by the CML D flip-flops  320  and  330  into a lower frequency, may be implemented as static logic or CML. The signal converter  370  is a circuit for converting a differential signal into a single signal. The selector  380  is implemented as a four-to-one multiplexer that selects one of signals f d1 , f d2 , f d3  and f d4  divided according to the mode selection bits S 1  and S 2  and outputs the selected signal as f pre . The mode controller  310  of  FIG. 3  receives an output signal f d2  of the D flip-flop  1   340 , an output signal f d3  of the D flip-flop  2   350  and an output signal f d4  of the D flip-flop  3   360 , and generates an output signal MO according to a mode control input signal MC and mode control bits S 1  and S 0  of  FIG. 3 . According to the output signal MO, one of the operation modes of the multimode prescaler  301 —divide-by-⅔, ⅘, 8/9 and 16/17—is selected. 
   The mode control input signal MC is a setting signal generated by the swallow counter  308  of  FIG. 2 , and the output signal MO of the mode controller  310  is input to the CML D flip-flop  320  of  FIG. 3 . When the mode control bits are S 1 /S 2 =0/0, the prescaler  301  of  FIG. 3  performs a divide-by-⅔ operation, when the mode control bits are S 1 /S 2 =0/1, the prescaler performs a divide-by-⅘ operation, when the mode control bits are S 1 /S 2 =1/0, the prescaler performs a divide-by- 8/9 operation, and when the mode control bits are S 1 /S 2 =1/1, the prescaler performs a divide-by- 16/17 operation. 
     FIG. 4  illustrates the mode controller  310  of  FIG. 3  according to an exemplary embodiment of the present invention. Referring to  FIG. 4 , the mode controller  310  includes three two-to-one multiplexers  312 ,  314  and  316 , and four OR gates  311 ,  313 ,  315  and  317 . The mode controller  310  applies a result value obtained by performing OR and MUX operations on a plurality of signals generated by the multi-stage cascade-connected flip-flop  330 ,  340 ,  350  and  360  and the output signal MC of the swallow counter  308 , to the flip-flop  320  as a control signal. 
   In  FIG. 4 , an output signal of the D flip-flop  1   340  of  FIG. 3  is input to an input port C 0  of  FIG. 4 , an output signal of the D flip-flop  2   350  of  FIG. 3  is input to an input port C 1 , and an output signal of the D flip-flop  3   360  of  FIG. 3  is input to an input port C 2 . The mode control signals S 1  and S 0  are input to selection terminals s 1  of illustrated multiplexers  312 ,  314  and  316 . 
   In the multiplexers  312 ,  314  and  316 , when the selection terminals s 1  are high, input terminals I 1  of the multiplexers  312 ,  314  and  316  are selected, and when the selection terminals s 1  are low, input terminals I 0  of the multiplexers  312 ,  314  and  316  are selected. Describing operations of the mode controller  310  in more detail, when the mode control signal is S 1 /S 0 =0/0, the multiplexer  1   312  selects the input terminal I 0 . Therefore, after the setting signal of the swallow counter  308  of  FIG. 2  is output at the output terminal MO through the input terminal MC, the setting signal is input to an input terminal B of the CML D flip-flop  1   320  of  FIG. 3 . As a result, the prescaler  301  finally performs the divide-by-⅔ operation. 
   Based on the above description, when the mode control signals are S 1 /S 0 =0/1, the multiplexer  312  selects the input terminal I 1  and the multiplexer  2   314  selects the input terminal I 0 . Therefore, a signal formed by combining the setting signal of the swallow counter  308  of  FIG. 2  and the signal f d2  input through the input terminal C 0  of  FIG. 4  at OR 1   313  of  FIG. 4  is output at the output terminal MO and input to the input terminal B of the CML_D flip-flop  1   320  of  FIG. 3  so that the prescaler  301  performs a divide-by-⅘ operation. 
   In addition, when the mode control signal is S 1 /S 0 =1/0, the multiplexer  1   312  of  FIG. 4  selects the input terminal I 1 , the multiplexer  2   314  selects the input terminal I 1 , and the multiplexer  3   316  selects the input terminal I 0 . Therefore, after a signal formed by combining, at OR 2   315  of  FIG. 4  through OR 1   313  of  FIG. 4 , the setting signal of the swallow counter  308  of  FIG. 2 , the signal f d2  input through the input terminal C 0  of  FIG. 4 , and the signal f d3  input through the input terminal C 1  of  FIG. 4 , is output at the output terminal MO of  FIG. 4  and input to the input terminal B of the CML_D flip-flop  1   320  of  FIG. 3  so that the prescaler  301  performs a divide-by- 8/9 operation. 
   Further, when the mode control signal is S 1 /S 0 =1/1, the multiplexer  1   312  of  FIG. 4  selects the input terminal I 1 , the multiplexer  2   314  selects the input terminal I 1 , and the multiplexer  3   316  selects the input terminal I 1 . Therefore, after a signal formed by combining, at OR 1   313  of  FIG. 4  through OR 2   315  of  FIG. 4 , the setting signal of the swallow counter  308  of  FIG. 2 , the signal f d2  input through the input terminal C 0  of  FIG. 4 , the signal f d3  input through the input terminal C 1  of  FIG. 4 , and the signal f d4  input through the input terminal C 2  of  FIG. 4 , is output at the output terminal MO of  FIG. 4  and input to the input terminal B of the CML_D flip-flop  1   320  of  FIG. 3  so that the prescaler  301  performs a divide-by- 16/17 operation. According to the present invention, the division ratio of the multimode prescaler  301  of  FIG. 3  may be extended to 32/33, 64/65, 128/129, etc. 
   The phase frequency detector/switching charge pump  400  of  FIG. 2  consist of a phase frequency detector and a charge pump, and  FIG. 5  illustrates an embodiment of the charge pump. The illustrated charge pump  420  has a structure that can switch current according to a corresponding mode in  FIG. 2 . In the charge pump  420  of  FIG. 5 , V 0 , V 1 , V 2  and V 3  are switches that are turned on or off according to the mode control signals S 1  and S 0  and control current of the charge pump  420 . In the charge pump  420 , four current sources I 0 , I 1 , I 2  and I 3  that constitute a plus current source block  423  have different sizes from four current sources I 0 , I 1 , I 2  and I 3  that constitute a minus current source block  424 , and current from both sets of current sources is output or intercepted according to the on/off status of the switches V 0  to V 3 . Up and Dn signals of  FIG. 5  are generated at the phase frequency detector (not shown). 
     FIG. 6  illustrates a loop filter  500  of  FIG. 2 . The loop filter  500  is a second order low-pass filter having a loop filter value set appropriately for a desired application band based on the on/off status of the switches V 0  to V 3  of  FIG. 2  according to the mode control signals S 1  and S 0 . In  FIG. 2 , capacitors C 0  to C 3  for storing electricity, resistors R 0  to R 3  for filtering, and capacitors C 02 , C 12 , C 22  and C 32  for filtering have different values from one another, their values being determined according to the application band of  FIG. 1 . The above method is applied to a third or fourth order loop filter. 
     FIG. 7  illustrates the wide-band LC tuning voltage-controlled oscillator  200  of  FIG. 2  according to an exemplary embodiment of the present invention. The voltage-controlled oscillator  200  of  FIG. 7  includes an LC tuner comprising two inductors L and four switching inductors, two MOS varactors VR, and eight switching capacitors. The voltage-controlled oscillator  200  turns switches V 0  to V 3  on/off according to a combination of the mode control signals S 1 /S 0  and the setting bits C 1  to C 5  of the program counter  307  of  FIG. 2  to thereby generate a desired oscillation frequency and amplitude. 
   As described above, according to the mode control bit, which is an externally applied control signal, the divisor value of a variable divisor  300  is determined, a pumping charge of the charge pump  40  is determined, an RC integer value among circuit integer values of the loop filter  500  is determined, and an integer value of the oscillation circuit of the voltage-controlled oscillator and/or a current value of a tail current source are determined. Accordingly, even when a width of frequency fluctuation according to change in a frequency band is large, the frequency synthesizer can operate smoothly. 
   A multiband multimode frequency synthesizer of the present invention generates a multiband frequency that has a bandwidth range from several to several tens of GHz. Also, since a multimode prescaler is embedded in the frequency synthesizer of the present invention, occupied area and power consumption can be reduced. 
   In addition, the frequency synthesizer of the present invention uses an inductor-switching voltage-controlled oscillator to generate a wide-band oscillation frequency having a low noise characteristic. 
   Further, the frequency synthesizer of the present invention in which the multimode prescaler is embedded can generate a radio frequency within a band appropriate for a desired application according to a mode control signal. 
   While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.