Abstract:
A quadrature voltage-controlled oscillator includes an oscillation module that provides a first signal and a second signal having predetermined frequencies, and a coupling module that couples the first signal and the second signal in a manner such that the second signal has a quadrature phase difference with respect to the first signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on and claims priority from Korean Patent Application No. 10-2005-0085768 filed on Sep. 14, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Apparatuses consistent with the present invention relate to a quadrature voltage-controlled oscillator and a transceiver including the same, and more particularly, to a quadrature voltage-controlled oscillator and a transceiver including the same that can reduce a phase noise or a phase error by separating an oscillating area from a coupling area.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, voltage-controlled oscillators modulate a frequency by changing the capacitance of a variable capacitor through a voltage control. The voltage controlled oscillator, which is necessary for all electronic communication systems, is used to up-convert or down-convert a frequency corresponding to a predetermined signal.  
         [0006]     According to the signal environment, which includes a single intermediate frequency (IF), a double IF or direct conversion, a wireless transceiver may include a predetermined number of voltage controlled oscillator circuits.  
         [0007]     Modulation methods require a quadrature signal. In the case of direct conversion (or zero IF), a quadrature part oscillating frequency is necessary for recovering an original signal. A quadrature voltage controlled oscillator generates the frequency.  
         [0008]      FIG. 1  is a circuit diagram showing a structure of a related art quadrature voltage-controlled oscillator.  
         [0009]     Referring to  FIG. 1 , a quadrature voltage-controlled oscillator includes in-phase blocks  104 ,  106 ,  118 ,  120 ,  142  and  144 , quad-phase blocks  122 ,  124 ,  136 ,  138 ,  146  and  148 , coupling blocks  108 ,  110 ,  126  and  128  and inductor-capacitor (LC) tank blocks  112 ,  114 ,  116 ,  130 ,  132  and  134 .  
         [0010]     Here, NMOS transistors  118  and  120 , and PMOS transistors  104  and  106  are used for in-phase oscillation. NMOS transistors  136  and  138 , and PMOS transistors  122  and  124  are used for quad-phase oscillation.  
         [0011]     In addition, PMOS transistors  126 , and  128  are used for coupling to generate a quadrature signal.  
         [0012]     Resonance is generated in the LC tank that consists of inductors  112  and  130  and diodes  114 ,  116 ,  132 , and  134 . In this case, the diodes refer to varactor diodes. The oscillation frequency is determined by changing a capacitance value according to the voltage supplied via a terminal  150 .  
         [0013]     In addition, each of terminals  142 ,  144 ,  146 , and  148  refers to an in-phase positive signal output terminal, an in-phase negative signal output terminal, a quad-phase positive signal output terminal, and a quad-phase negative signal output terminal, respectively. A terminal  140  is connected to a DC ground.  
         [0014]     In  FIG. 1 , circuits of the in-phase and quad-phase are identical to each other, and each generates a differential signal having a phase difference of 180 degrees. The differential signals are denoted by I+, I−, Q+, and Q−.  
         [0015]     The quadrature voltage-controlled oscillator illustrated in  FIG. 1  is resonated by negative resistance generated by an upper PMOS transistor and a lower NMOS transistor. The resonance frequency is determined by the LC tank block as above.  
         [0016]     The resonance frequency determined by the LC tank block can be calculated from Equation (1).  
               f   =     1     2   ⁢   π   ⁢     LC           ,           (   1   )             
        where L denotes the inductance of the inductors  112  and  130 , and C denotes the capacitance of the varactor diodes  114 ,  116 ,  132  and  134 .        
 
         [0018]     In  FIG. 1 , in addition to generating a desired frequency by using an NMOS transistor, and a coupling circuit configured for generating a quadrature frequency by using a PMOS transistor, a desired frequency may also be generated by using a PMOS transistor and a coupling circuit configured for generating a quadrature frequency by using an NMOS transistor, which is illustrated in  FIG. 2 .  
         [0019]     The quadrature voltage-controlled oscillator illustrated in  FIG. 2  and the quadrature voltage-controlled. oscillator illustrated in  FIG. 1  have different transistors used for oscillation or coupling. However, functions of each device are identical.  
         [0020]     According to the structure of the related art quadrature voltage-controlled oscillator illustrated in  FIGS. 1 and 2 , a phase noise and a phase error of the whole circuit are increased because noise components caused by the couplings are added to the circuit.  
         [0021]     Due to the complexity of the circuit, a phase noise and a phase error may be increased because of conflict of differential quadrature signal lines when a layout is performed.  
       SUMMARY OF THE INVENTION  
       [0022]     The present invention provides a quadrature voltage-controlled oscillator that generates a quadrature signal which has a reduced phase noise and phase error while maintaining its power consumption and frequency tuning range, and a wireless transceiver including the same.  
         [0023]     The present invention also provides a quadrature voltage-controlled oscillator which minimizes noise effects caused by coupling by separating an oscillating unit from a coupling unit.  
         [0024]     According to an aspect of the present invention, there is provided a quadrature voltage-controlled oscillator including an oscillation module that oscillates a first signal and a second signal having predetermined frequencies, and a coupling module that couples the first signal and the second signal so that the second signal has a quadrature phase difference with respect to the first signal.  
         [0025]     According to another aspect of the present invention, there is provided a wireless transceiver including a low-noise amplifier that amplifies radio frequency (RF) signals, a quadrature voltage-controlled oscillator that provides oscillation signals by separating an oscillating area from a coupling area, a mixer that outputs baseband signals by mixing the amplified RF signal with the oscillation signal, and a baseband processor that processes the output baseband signals. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The above and other aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:  
         [0027]      FIG. 1  is a circuit diagram showing a structure of a related art quadrature voltage controlled oscillator;  
         [0028]      FIG. 2  is a circuit diagram showing a structure of another related art quadrature voltage controlled oscillator;  
         [0029]      FIG. 3  is a block diagram showing a structure of a wireless transceiver according to an exemplary embodiment of the present invention;  
         [0030]      FIG. 4  is a block diagram showing a structure of a quadrature voltage-controlled oscillator according to an exemplary embodiment of the present invention;  
         [0031]      FIG. 5  is an exemplary circuit diagram of the quadrature voltage-controlled oscillator illustrated in  FIG. 4 ;  
         [0032]      FIG. 6  is a circuit diagram showing a structure of a quadrature voltage-controlled oscillator according to another exemplary embodiment of the present invention;  
         [0033]      FIG. 7  is an exemplary circuit diagram of the quadrature voltage-controlled oscillator illustrated in  FIG. 6 ;  
         [0034]      FIGS. 8A and 8B  are graphs showing a result of a simulation according to the related art and the present invention. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0035]     Aspects of the present invention and methods of accomplishing the same may be understood more readily by reference to the following detailed description of the preferred embodiments and the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art, and the present invention will only be defined by the appended claims. Like reference numerals refer to like elements throughout the specification.  
         [0036]     The present invention is described hereinafter with reference to flowchart illustrations of user interfaces, methods, and computer program products according to exemplary embodiments of the invention. It should be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which are executed via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer usable or computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded into a computer or other programmable data processing apparatus to cause a series of operational steps to be performed in the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute in the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.  
         [0037]     And each block of the flowchart illustrations may represent a module, segment, or portion of code, which includes one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.  
         [0038]     A quadrature voltage controlled oscillator and a transceiver including the same according to an exemplary embodiment of this invention will now be described more fully with reference to the accompanying drawings.  
         [0039]      FIG. 3  is a block diagram showing a structure of a wireless transceiver according to an exemplary embodiment of the present invention. For convenience, a transmitting process and a receiving process of a wireless transceiver  300  will be separately described.  
         [0040]     The operation of a transceiver  300  in a transmitting process according to an exemplary embodiment of the present invention will be described in the following.  
         [0041]     A baseband signal output by a baseband processor  390  is amplified in a baseband amplifier  340 . In this case, the baseband signal includes an in-phase signal and a quadrature-phase signal. The amplified baseband signal is combined with an oscillation signal generated in a quadrature voltage-controlled oscillator  380  according to an exemplary embodiment of the present invention in an up-mixer  330 , and becomes a radio frequency (RF) signal. In this case, the quadrature voltage-controlled oscillator  380  provides in-phase and quadrature-phase oscillation frequencies at the same time, and an oscillation circuit and a coupling circuit composing the quadrature voltage-controlled oscillator are separated from each other. The RF signal is amplified in a power amplifier  320 , and output to a wireless channel via an antenna  310 .  
         [0042]     The power amplifier  320  used in the transmitting process may include several stages of amplifiers used to reduce distortion and to obtain high benefits.  
         [0043]     The operation of a wireless transceiver  300  in the receiving process will now be described in the following.  
         [0044]     The RF signal input by the wireless channel via the antenna  310  is amplified by a low noise amplifier  350 .  
         [0045]     The amplified RF signal becomes a baseband signal via a down-mixer  360 , and then is amplified in a baseband amplifier  370 .  
         [0046]     In this case, a quadrature voltage-controlled oscillator  380  provides in-phase and quadrature-phase oscillation frequencies to the down-mixer  360  at the same time. In addition, the signal amplified in the baseband amplifier  370  includes an in-phase signal and a quadrature-phase signal. Each differential signal has a phase difference of 180 degrees, and may be provided to the baseband processor  390 .  
         [0047]     A switch  315  stops an RF signal output from the power amplifier  320  from being input to the low noise amplifier  350 , and an RF signal input via the antenna  310  from being transmitted to the power amplifier  320 . In a full duplex method, a duplexer is used instead of the switch  315 .  
         [0048]     The antenna  310 , the switch  315 , the power amplifier  320 , and the low noise amplifier  350  may be collectively referred to as an “RF module”.  
         [0049]     A quadrature voltage-controlled oscillator according to an exemplary embodiment of the present invention may be applied to any wireless transceiver if a circuit needs a quadrature signal.  
         [0050]      FIG. 4  is a block diagram showing a structure of a quadrature voltage-controlled oscillator-according to an exemplary embodiment of the present invention.  
         [0051]     Referring to  FIG. 4 , the quadrature voltage-controlled oscillator according to an exemplary embodiment of the present invention includes an oscillation module and a coupling module  420  for generating a quadrature frequency, which is located at the bottom of the oscillation module  410 .  
         [0052]     The term “module”, as used herein, means, but is not limited to, a software or hardware component, such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC), which performs certain tasks. A module may advantageously be configured to reside on the addressable storage medium and configured to be executed on one or more processors. Thus, a module may include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functionality provided for in the components and modules may be combined into fewer components and modules, or further separated into additional components and modules.  
         [0053]     The coupling module  420  generates a quadrature frequency using output signals of the quadrature voltage-controlled oscillator I+, I−, Q+, and Q− signals  430 . Accordingly, the oscillation module  410  and the coupling module  420  are separated from each other, and a noise caused by coupling does not influence the phase noise of the oscillation module  410 .  
         [0054]      FIG. 5  is an exemplary circuit diagram of the quadrature voltage-controlled oscillator illustrated in  FIG. 4 , which specifically illustrates the oscillation module  410  and the coupling module  420 .  
         [0055]     Referring to  FIG. 5 , the quadrature voltage-controlled oscillator includes in-phase blocks  502  and  503 , quad-phase blocks  509  and  510 , coupling blocks  507 ,  508 ,  513 , and  514  and LC tank blocks  504 ,  505 ,  506 ,  511 ,  512 , and  513 .  
         [0056]     In this case, PMOS transistors  502  and  503  are used for in-phase oscillation, and PMOS transistors  509  and  510  are used for quad-phase oscillation.  
         [0057]     NMOS transistors  507 ,  508 ,  513 , and  514  are used for coupling to generate a quadrature signal.  
         [0058]     Resonance is generated in the LC tank that consists of inductors  506  and  513  and diodes  504 ,  505 ,  511 , and  512 . In this case, the diodes are varactor diodes. The oscillation frequency is determined by changing a capacitance value according to the voltage provided via a terminal  517 .  
         [0059]     The output stage of the quadrature voltage controlled oscillator is denoted by I+, I−, Q+, and Q− in  FIG. 5 , each of which is connected to a gate terminal of the NMOS transistor composing the coupling module  420 .  
         [0060]     That is, I+ is connected to a gate terminal of the NMOS transistor  514 , I− is connected to a gate terminal of the NMOS transistor  513 , Q+ is connected to a gate terminal of the NMOS transistor  507 , and Q− is connected to a gate terminal of the NMOS transistor  508 .  
         [0061]     The circuit of the in-phase unit and the circuit of a quad-phase are identical, each of which generates a differential signal having a phase difference of 180 degrees. The differential signals are denoted by I+, I−, Q+, and Q−.  
         [0062]     The quadrature voltage-controlled oscillator illustrated in  FIG. 5  is resonated by negative resistance generated by the PMOS transistors  502 ,  503 ,  509 , and  510  composing the oscillation module  410 . The resonance frequency can be calculated from Equation 1.  
         [0063]     Referring to  FIG. 5 , when the coupling module  420  is connected to the bottom of the oscillation module  410 , which may include PMOS transistors, and the coupling module  420  may include NMOS transistors.  
         [0064]     An output signal of the quadrature voltage-controlled oscillator is connected to a drain of the NMOS transistor composing the coupling module  420 .  
         [0065]      FIGS. 4 and 5  illustrate that the coupling module  420  is connected to the bottom of the oscillation module  410 . However,  410  and  420  may be located to the top of the module.  
         [0066]     That is to say, as illustrated in  FIG. 6 , a quadrature voltage-controlled oscillator according to another exemplary embodiment of the present invention includes an oscillation module  610  and a coupling module  620 , which may be connected to the bottom of the coupling module  620 .  
         [0067]     An exemplary circuit diagram of the oscillation module  610  and the coupling module  620  is illustrated in  FIG. 7 , and its basic structure is identical to the circuit diagram illustrated in  FIG. 5 .  
         [0068]     The only difference is that the oscillation module  610  consists of NMOS transistors, while the coupling module  620  consists of PMOS transistors.  
         [0069]     A simulation of the exemplary embodiment of the present invention was performed in a range of 4.8 to 6.1 GHz according to the IEEE802.11a standard. Here, it is assumed that the whole circuit is operated in 1.2 volts.  
         [0070]      FIG. 8A  is a graph showing the result of a simulation according of the related art, and  FIG. 8B  is a graph showing the result of a simulation according to the exemplary embodiment of the present invention. The results are as shown in Tables 1 and 2.  
                                                           TABLE 1                                       Phase Noise (dBc/Hz)                    @4.8 GHz   @6.1 GHz                            Prior Art   −113.8   −109.0           Exemplary Embodiment of   −116.8   −112.2           Present Invention                        
         [0071]     Table 1 shows phase noises at different frequencies. The phase noise is for the case where offset frequency is 1 MHz. Referring to Table 1, a phase noise according to the exemplary embodiment of the present invention increases by about 3 dB in a range of 4.8 to 6.1 GHz than the phase noise according to the related art.  
                                                           TABLE 2                                       Phase Error (Deg.)                    @4.8 GHz   @6.1 GHz                            Prior Art   0.008   0.02           Exemplary Embodiment of   0.004   0.006           Present Invention                      
 
         [0072]     Table 2 shows phase errors at different frequencies. Each of signals I+, I−, Q+, and Q− has to maintain a certain phase difference. When the signals cannot maintain the phase difference, the phase error indicates the phase difference. As shown in Table 2, the phase error can be reduced, and especially, is effective when the frequency is higher.  
         [0073]     As shown in  FIGS. 8A and 8B , the implementation of the exemplary embodiment of the present invention makes high-frequency elements smaller.  
         [0074]     According to the exemplary embodiments of the present invention as described above, a phase noise or a phase error can be reduced by separating an oscillation unit from a coupling unit in a quadrature voltage-controlled oscillator, and a circuit can be simplified.  
         [0075]     Although a quadrature voltage-controlled oscillator and a transceiver including the same have been described in connection with the exemplary embodiments of the present invention, it will be apparent to those skilled in the art that various modifications and changes may be made thereto without departing from the scope and spirit of the invention. Therefore, it should be understood that the above exemplary embodiments are not limitative, but illustrative in all aspects.