Abstract:
A system and method are provided for communicating a radio frequency (RF) signal. In use, a baseband signal is mixed with a plurality of oscillator signals with different phases in an interleaving manner. The mixed baseband signal is then communicated as an RF signal.

Description:
RELATED APPLICATION(S) 
   This application claims the benefit of U.S. Provision Application No. 60/458,621, filed Mar. 31, 2003, entitled DIRECT CONVERSION TRANSMITTER WITH QUADRATURE BALANCING AND LOW LO FEEDTHROUGH. 

   FIELD OF THE INVENTION 
   The present invention relates to circuitry, and more particularly to direct-conversion circuitry. 
   BACKGROUND OF THE INVENTION 
   Direct-conversion is an alternative wireless transmitter architecture to the well-established superheterodyne, particularly for highly integrated, low-power terminals. Its fundamental advantage is that the transmitted signal is mixed directly to radio frequency (RF) without the use of an intermediate frequency. This means less hardware complexity, lower component count and a simpler frequency plan. 
   In direct-conversion transmitters the most serious problem is that of local oscillator (“LO”) feed-through due to a variety of on-chip coupling mechanisms. While the LO is necessary to convert the baseband signal to RF for transmission, if significant LO leakage occurs in the middle of the up-converted signal spectrum, the signal will be corrupted and rendered unreceivable. 
   Furthermore, in modern communication systems, the transmitter must be able to control the power that it is transmitting. The LO feed-through amplitude cannot be controlled as it is an unwanted byproduct of circuit non-idealities. This forces the transmitting signal to always be much larger than the LO feed-through. 
   Traditionally, LO feed-through can be reduced through the use of on-chip or external calibration schemes at the cost of additional hardware size and complexity. 
   Another problem in direct-conversion transmitters is in-phase and quadrature (“IQ”) imbalance of the LO and signal path. Traditionally, direct conversion transmitters and receivers need a local oscillator with quadrature outputs for vector modulation and demodulation. However, when the quadrature signal components are not equal in amplitude and not exactly 90 degrees out of phase, the signal degrades in quality. 
   Quadrature phases are typically derived by passing a reference local oscillator through a CR-RC phase shift network. Ideally, this creates two signals with equal amplitude and 90 degrees of phase difference. However, this depends on the accuracy of resistors and capacitors which make up the phase shift network. The resistors and capacitors can vary by up to 15 percent in a typical integrated circuit causing the in-phase and quadrature components to have different amplitudes and a phase difference not equal to 90 degrees. 
   In addition, layout differences between the in-phase and quadrature paths can cause additional amplitude/phase imbalance. Contributing to further in-phase/quadrature imbalance, the circuits in the in-phase and quadrature paths (i.e. amplifiers and mixers) have physical properties that differ. Many feedback calibration schemes have been proposed and implemented to mitigate quadrature imbalance at the cost of hardware and/or system complexity. 
   A conventional direct conversion transmitter is illustrated in  FIG. 1 . As illustrated in  FIG. 1 , a direct conversion transmitter takes the modulated in-phase and quadrature baseband signals  100 ,  101  and translates the signal to an RF frequency by multiplying them by a quadrature LO. Specifically, the transmitter multiplies the baseband signals  100 ,  101  with two different phases  102 ,  103  of a local oscillator  107  using a first mixer  110  and a second mixer  111 . The in-phase and quadrature baseband signals can be denoted BB I  and BB Q . The two phases  102 ,  103  of the local oscillator are 90 degrees apart and thus, are known as the in-phase (“I”)  102  and quadrature (“Q”)  103  components and can be denoted LO I  and LO Q  respectively. The mixer outputs  104 ,  105  are summed together to produce the RF signal  106 . The RF signal  106  can be represented by Equation 1.
 
 RF=BB   I   ×LO   I   +BB   Q   ×LO   Q   Equation 1
 
   Another conventional direct conversion architecture is shown in  FIG. 2 . This differential direct conversion architecture is more resilient to self generated noise than the one illustrated in  FIG. 1 . In  FIG. 2 , the I and Q baseband signals are differential signals composed of positive and negative components. The equivalent single-ended baseband in-phase signal to the differential baseband in-phase signal is described by Equation 2. In Equation 2, BB I  denotes the single-ended in-phase signal, BB I,pos  denotes the positive component of the differential signal, and BB I,neg  denotes the negative component of the differential signal. A differential signal has a positive and negative component which subtract to form the signal. Equation 3 describes the quadrature relationship in similar terms.
 
 BB   I =( BB   I,pos   −BB   I,neg )  Equation 2
 
 BB   Q =( BB   Q,pos   −BB   Q,neg )  Equation 3
 
In Equation 2 and Equation 3, BB I,pos,  BB I,neg , BB Q,pos , BB Q,neg  correspond to  200 ,  201 ,  202 ,  203 , respectively, in  FIG. 2 .
 
   The differential direct conversion architecture shown in  FIG. 2  uses differential LO signals to mix the baseband signal to RF. The polyphase network  205  is a circuit which converts the local oscillator voltage waveform  204  into four voltage waveforms  206 ,  207 ,  208 ,  209  at the same frequency as LO but at 0, 180, 90, 270 degrees offset compared to the local oscillator signal  204  respectively. 
   Collectively, these four signals  206 ,  207 ,  208 ,  209  are referred to as polyphase local oscillator signals. To facilitate the present description, the following signals  206 ,  207 ,  208 ,  209  are denoted as LO 0 , LO 180 , LO 90 , LO 270  corresponding to their phase shift compared to the local oscillator  204 . Shifting a sinusoidal signal 180 degrees in phase is the same as inverting the signal. Therefore, the equivalent single-ended in-phase and quadrature LO signals, denoted LO I  and LO Q , are described mathematically in Equations 4 and 5.
 
 LO   I   =LO   0   −LO   180   Equation 4
 
 LO   Q   =LO   90   −LO   270   Equation 5
 
The differential quadrature baseband signals are routed to the differential mixers  210 ,  211  where they are multiplied by the differential local oscillator signals.
 
   At the first mixer  210 , the differential in-phase baseband signal (BB I ) is multiplied by the in-phase LO (LO I ). Likewise, at the second mixer  211 , the differential quadrature baseband signal (BB Q ) is multiplied by the quadrature LO (LO Q ). Equation 6 describes the mixing process and summing process  212  of the differential signals to generate the RF signal  213 . Likewise, Equation 7 is a simplified version of Equation 6 where all the differential signals are represented as single-ended signals.
 
 RF =( BB   I,pos   −BB   I,neg )×( LO   0   −LO   180 )+( BB   Q,pos   −BB   Q,neg )×( LO   90   −LO   270 )  Equation 6
 
 RF=BB   I   ×LO   I   +BB   Q   ×LO   Q   Equation 7
 
   Now, to elucidate the problems with direct conversion transmitters, LO feed-through and imbalance distortions will be added to Equations 6 and 7. LO feed-through is added to the output of the mixers. LO C1  represents the differential LO feed-through from the polyphase LO signal to the output of mixer  210 , and LO C2  represents the differential LO feed-through at the at output of mixer  211 . Likewise the amplitude and phase imbalance of the mixers and the polyphase LO signals can be accounted for at the output of each mixer. A complex multiplicative term, A 1 e jP1 , represents a random amplitude variation (“A 1 ”) and a random phase variation (“P 1 ”) introduced by the first mixer  210 , the signal path  200 ,  201  and LO path  206 ,  207  connected to the mixer. Likewise, A 2 e P2  represents a random amplitude and phase variation introduced by the second mixer  211  and the signal  202 ,  203  and LO paths  208 ,  209  connected to it. Thus, with these distortions added, Equations 6 and 7 become Equations 8 and 9.
 
 RF =( BB   I,pos   −BB   I,neg )×( LO   0   −LO   180 ) ×A 1e jP1   =LO   C1 +( BB   Q,pos   −BB   Q,neg )×( LO   90   −LO   270 ) ×A 2e jP2   =LO   C2   8
 
 RF=BB   I   ×LO   I   ×A 1e jP1   =LO   C1   =BB   Q   ×LO   Q   ×A 2e jP2   =LO   C2   Equation 9
 
   As seen in Equations 8 and 9, the RF distortion grows as A 1  and A 2  differ and as P 1  and P 2  differ. As the distortion increase, it is harder for the signal to be received and decoded. Likewise as LO C1  and LO C2  increase, they become the dominant component of the RF signal in Equation 8 and 9. 
   There is thus a need for a transmitter for overcoming these problems and/or providing general improvements over prior art transmitters. 
   SUMMARY OF THE INVENTION 
   A system and method are provided for communicating a radio frequency (RF) signal. In use, a baseband signal is mixed with a plurality of oscillator signals with different phases in an interleaving manner. The mixed baseband signal is then communicated as an RF signal. 
   In one embodiment, the oscillator signals may include an oscillator signal frequency substantially equal to an RF signal frequency of the RF signal. Further, the RF signal may be modulated over a finite bandwidth. 
   In another embodiment, the oscillator signals may have phase differences of 0, 90, 180, and 270 degrees. Further, the mixing may be carried out by a plurality of mixers. 
   In use, the oscillator signals may be input to the mixers in the interleaving manner. Moreover, this may be accomplished by switching which oscillator signals are input to which mixers. Still yet, the switching may occur at a rate that is faster than a bandwidth of the RF signal. Optionally, the switching may occur in a substantially random manner, or even in a random manner. 
   In still another embodiment, the baseband signal may be inverted using an interleaving operation. Also, the baseband signal may be routed to at least one mixer using an interleaving operation. A plurality of the baseband signals may be provided including an in-phase baseband signal and a quadrature baseband signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a conventional single-ended direct-conversion transmitter; 
       FIG. 2  is a block diagram of the conventional differential direct-conversion transmitter; 
       FIG. 3  is a block diagram of a differential direct-conversion transmitter with local-oscillator phase interleaving and baseband signal interleaving; 
       FIGS. 4   a–d  show the four configurations of the baseband signal interleaver; 
       FIGS. 5   a–d  show the four configurations of the local-oscillator phase interleaver; 
       FIG. 6  is an illustration of a wireless communication system in which one embodiment may be used; and 
       FIG. 7  illustrates the functional components of a wireless communication device, shown in block diagram format. 
   

   DETAILED DESCRIPTION 
   Turning to one embodiment in  FIG. 3 , the differential direct conversion architecture described in  FIG. 2  is enhanced with two switching matrices: 1) the local oscillator phase interleaver (“LOPI”)  326  circuit, and 2) the baseband interleaver (“BBI”)  304 . Each has four combinations of connections. 
   The BBI  304  routes the in-phase baseband signals  300 ,  301  and quadrature baseband signals  302 ,  303  to a first up-conversion mixer  309  and the second up-conversion mixer  310 . Continuing the terminology established in the example of  FIG. 2 , the differential in-phase baseband signals are denoted BB I,pos , BB I,neg  while the differential quadrature signals are denoted BB Q,pos , BB Q,neg . By periodically switching the BBI configuration, the in-phase and quadrature baseband signals are routed alternately to each mixer. Thus, any imbalances in the baseband path affect the in-phase and quadrature signals similarly mitigating the adverse effect. 
   The baseband interleaver  304  circuit switches between one of four combinations of connections illustrated in  FIG. 4 . In addition, in two of the states it inverts the incoming baseband signals. In state  1  illustrated in  FIG. 4   a,  the baseband interleaver passes BB I,pos    400  and BB I,neg    401  to the first mixer and BB Q,pos    402  and BB Q,neg    403  to the second mixer. 
   In the second state illustrated in  FIG. 4   b,  the baseband interleaver inverts the incoming signals, BB I,pos    410  and BB I,neg    411 , prior to routing them to the first mixer. Likewise, the baseband interleaver inverts BB Q,pos    412  and BB Q,neg    413  before routing them to the second mixer. In state  3  illustrated in  FIG. 4   c,  BB I,pos    420  and BB I,neg    421  are routed to the second mixer while BB Q,pos    422  and BB Q,neg    403  are routed to the first mixer. 
   Finally in state 4 illustrated in  FIG. 4   d,  the baseband interleaver inverts the incoming signals and routes the inverted BB I,pos    430  BB I,neg    431  to the second mixer and the inverted BB Q,pos    432  and BB Q,neg    433  to the first mixer. Returning to  FIG. 3 , the baseband signals  305 ,  306  arriving at the first mixer  309  are described by Equations 21, 22, 23,and 24.
 
State 1 : BB   I,pos   −BB   I,neg   Equation 21
 
State 2: (−1)* BB   I,pos −(−1)* BB   I,neg   Equation 22
 
State 3 : BB   Q,pos   −BB   Q,neg   Equation 23
 
State 4: (−1)* BB   Q,pos −(−1)* BB   Q,neg   Equation 24
 
To facilitate the description of this embodiment, Equations 21, 22, 23 and 24 can be represented by the notations +BB I , −BB I , +BB Q , and −BB Q  respectively. +BB I  represents the differential in-phase baseband signal with positive polarity. −BB I  represents the differential in-phase baseband signal with negative polarity. +BB Q  represents the differential baseband signal with negative polarity. −BB Q  represents the differential quadrature baseband signal with negative polarity.
 
   Likewise, the baseband signals  307 ,  308  arriving at the second mixer  310  are described by Equations 25, 26, 27, and 28.
 
State 1 : BB   Q,pos   −BB   Q,neg   Equation 25
 
State 2: (−1)* BB   Q,pos −(−1)* BB   Q,neg   Equation 26
 
State 3 : BB   I,pos   −BB   I,neg   Equation 27
 
State 4: (−1)* BB   I,pos −(−1)* BB   I,neg   Equation 28
 
   As in the case with Equations 21–24, the Equations 25, 26, 27 and 28 can be represented by the notations +BB Q , −BB Q , +BB I , and −BB I , respectively. 
   Returning to  FIG. 3 , the local oscillator  320  waveform is transformed by a polyphase circuit  321  into four waveforms  322 ,  323 ,  324 , and  325  each at the same frequency as the LO but with a phase shift referenced to the local oscillator phase. To continue the terminology established in the example associated with  FIG. 2 , these four polyphase local oscillator signals  322 ,  323 ,  324 ,  325  will be denoted LO 0 , LO 90 , LO 180 , LO 270  respectively. 
   The LO phase interleaver circuit  326  periodically switches configuration so that the LO 0  and LO 180  periodically are routed to the first mixer  309  and are periodically routed to the second mixer  310 . Likewise, the LO phase interleaver  326  periodically routes LO 90  and LO 270  to the second mixer  310  and then to the first mixer  309 . By switching the polyphase local oscillator signals to different mixers, it modulates the LO feed-though signal causing the LO feed-through peak energy to be reduced. 
   In the context of the present description, “interleaving” may refer to the plain and ordinary meaning thereof, as well as any sort of switching, exchanging, toggling, swapping, interchanging, etc. 
   Four LOPI combinations are illustrated in  FIGS. 5   a,    5   b,    5   c  and  5   d.  In state 1, as illustrated in  FIG. 5   a,  LO 0    500  and LO 180    501  are routed to the first mixer and LO 90   502  and LO 270    503  are routed to the second mixer. In the second state, as illustrated in  FIG. 5   b,  the LO 0    510  and LO 180    511  are routed to the first mixer; however, they have been interchanged compared to the routing in state 1 represented in  FIG. 5   a.  The effect of this interchange is to reverse the polarity of the signal. Returning to  FIG. 5   b,  LO 90    512  and LO 270    513  are routed to the second mixer; however, they too have been interchanged compared to state  1 . 
   In state  3 , as illustrated in  FIG. 5   c,  LO 0    530  and LO 180    531  are routed to the second mixer and LO 90    532  and LO 270    533  are routed to the first mixer. In the fourth state, as illustrated in  FIG. 5   d,  the LO 0    540  and 0 LO 180    541  are routed to the second mixer; however, they have been interchanged compared to the routing in state 3 represented in  FIG. 5   c.  The effect of this interchange is to reverse the polarity of the signal. Returning to  FIG. 5   d,  LO 90    542  and LO 270    543  are routed to the first mixer; however, they too have been interchanged compared to state  3 . 
   Returning to  FIG. 3 , through the processes of local oscillator phase interleaving, each mixer input sees each polyphase LO signal LO 0,  LO 90,  LO 180,  LO 210.  Thus, if a phase or amplitude imbalance of one mixer distorts one LO component then it distorts all components. The LO signals  327 ,  328  arriving at the first mixer  309  are described by Equations 29, 30, 31 and 32. Likewise the LO signals  329 ,  330  arriving at the second mixer  310  are described by Equations 33, 34, 35 and 36.
 
State 1 : LO   0   −LO   180   Equation 29
 
State 2 : LO   180   −LO   0   Equation 30
 
State 3 : LO   90   −LO   270   Equation 31
 
State 4 : LO   270   −LO   90   Equation 32
 
State 1 : LO   90   −LO   270   Equation 33
 
State 2 : LO   270   −LO   90   Equation 34
 
State 3 : LO   0   −LO   180   Equation 34
 
State 4 : LO   180   −LO   0   Equation 36
 
   To facilitate the present description, Equations 29, 30, 31 and 32 can be represented by the notations +LO I , −LO I , +LO Q , and +LO Q  respectively. +LO I  represents the differential in-phase local oscillator signal with positive polarity. −LO I  represents the differential in-phase local oscillator signal with negative polarity. +LO Q  represents the differential local-oscillator signal with positive polarity. −LO Q  represents the differential quadrature local-oscillator signal with negative polarity. As in the case with Equations 29–32, the Equations 33,34,35 and 36 can be represented by the notations +LO Q , −LO Q , +LO I , and −LO I  respectively. 
   The LO feed-through at the output of the first mixer  309  and the second mixer  310  is dependent on the LO signal applied to the mixer and the individual characteristics of the mixer itself. Therefore, the LO feed-through at the output of first mixer  309  can be defined by Equations 37, 38, 39, and 40 and the LO feed-through at the output of the second mixer  310  can be define by Equations 41, 42, 43, and 44. The LO feed-through is defined by three subscripts and a precedent sign in these equations. As it is a function of the mixer, the first subscript indicates which mixer the feed-through is associated with. The switch matrix determines the LO feed-through relative polarity represented by a +/− precedent sign and its second subscript represents the in-phase or quadrature LO component. The third subscript, F, distinguishes it from the LO signal.
 
State 1 : +LO   1,I,F   Equation 37
 
State 2 : −LO   1,I,F   Equation 38
 
State 3 : +LO   1,Q,F   Equation 39
 
State 4 : −LO   1,Q,F   Equation 40
 
State 1 : +LO   2,Q,F   Equation 41
 
State 2 : −LO   2,Q,F   Equation 42
 
State 3 : +LO   2,I,F   Equation 43
 
State 4 : −LO   2,I,F   Equation 44
 
   A complex multiplicative term, A 1 e jp1 , represents a random amplitude variation (“A 1 ”) and a random phase variation (“P 1 ”) introduced by the first mixer  309 , the signal path  305 ,  306  and LO path  327 ,  328  connected to the mixer. Likewise, A 2 e P2  represents a random amplitude and phase variation introduced by second mixer  310  and the signal  307 , 308  and LO paths  329 , 330  connected to it. Combining  315  the differential mixer outputs  311 ,  312 ,  313 ,  314  forms the RF output signal  316 . The RF output corresponding to the four interleaving states is described by Equations 45, 46, 47 and 48. 
   
     
       
         
           
             
               
                 State 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
                 ⁢ 
                 
                   : 
                 
               
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     ( 
                     
                       + 
                       
                         BB 
                         I 
                       
                     
                     ) 
                   
                   × 
                   
                     ( 
                     
                       + 
                       
                         LO 
                         I 
                       
                     
                     ) 
                   
                   × 
                   A1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P1 
                     
                   
                 
                 + 
                 
                   LO 
                   
                     1 
                     , 
                     I 
                     , 
                     F 
                   
                 
                 + 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 45 
               
             
           
           
             
               
                 
                   
                     ( 
                     
                       + 
                       
                         BB 
                         Q 
                       
                     
                     ) 
                   
                   × 
                   
                     ( 
                     
                       + 
                       
                         LO 
                         Q 
                       
                     
                     ) 
                   
                   × 
                   A2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P2 
                     
                   
                 
                 + 
                 
                   LO 
                   
                     2 
                     , 
                     Q 
                     , 
                     F 
                   
                 
               
             
             
               
                   
               
             
           
           
             
               
                 State 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 2 
                 ⁢ 
                 
                   : 
                 
               
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     ( 
                     
                       - 
                       
                         BB 
                         I 
                       
                     
                     ) 
                   
                   × 
                   
                     ( 
                     
                       - 
                       
                         LO 
                         I 
                       
                     
                     ) 
                   
                   × 
                   A1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P1 
                     
                   
                 
                 - 
                 
                   LO 
                   
                     1 
                     , 
                     I 
                     , 
                     F 
                   
                 
                 + 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 46 
               
             
           
           
             
               
                 
                   
                     ( 
                     
                       - 
                       
                         BB 
                         Q 
                       
                     
                     ) 
                   
                   × 
                   
                     ( 
                     
                       - 
                       
                         LO 
                         Q 
                       
                     
                     ) 
                   
                   × 
                   A2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P2 
                     
                   
                 
                 - 
                 
                   LO 
                   
                     2 
                     , 
                     Q 
                     , 
                     F 
                   
                 
               
             
             
               
                   
               
             
           
           
             
               
                 State 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 3 
                 ⁢ 
                 
                   : 
                 
               
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     ( 
                     
                       + 
                       
                         BB 
                         Q 
                       
                     
                     ) 
                   
                   × 
                   
                     ( 
                     
                       + 
                       
                         LO 
                         Q 
                       
                     
                     ) 
                   
                   × 
                   A1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P1 
                     
                   
                 
                 + 
                 
                   LO 
                   
                     1 
                     , 
                     Q 
                     , 
                     F 
                   
                 
                 + 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 47 
               
             
           
           
             
               
                 
                   
                     ( 
                     
                       + 
                       
                         BB 
                         I 
                       
                     
                     ) 
                   
                   × 
                   
                     ( 
                     
                       + 
                       
                         LO 
                         I 
                       
                     
                     ) 
                   
                   × 
                   A2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P2 
                     
                   
                 
                 + 
                 
                   LO 
                   
                     2 
                     , 
                     I 
                     , 
                     F 
                   
                 
               
             
             
               
                   
               
             
           
           
             
               
                 State 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 4 
                 ⁢ 
                 
                   : 
                 
               
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     ( 
                     
                       - 
                       
                         BB 
                         Q 
                       
                     
                     ) 
                   
                   × 
                   
                     ( 
                     
                       - 
                       
                         LO 
                         Q 
                       
                     
                     ) 
                   
                   × 
                   A1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P1 
                     
                   
                 
                 - 
                 
                   LO 
                   
                     1 
                     , 
                     Q 
                     , 
                     F 
                   
                 
                 + 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 48 
               
             
           
           
             
               
                 
                   
                     ( 
                     
                       - 
                       
                         BB 
                         I 
                       
                     
                     ) 
                   
                   × 
                   
                     ( 
                     
                       - 
                       
                         LO 
                         I 
                       
                     
                     ) 
                   
                   × 
                   A2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P2 
                     
                   
                 
                 - 
                 
                   LO 
                   
                     2 
                     , 
                     I 
                     , 
                     F 
                   
                 
               
             
             
               
                   
               
             
           
         
       
     
   
   Equations 45, 46, 47, and 48 can be reduced to Equations 49, 50, 51, and 52 by combining signs. 
   
     
       
         
           
             
               
                 State 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
                 ⁢ 
                 
                   : 
                 
               
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     BB 
                     I 
                   
                   × 
                   
                     LO 
                     I 
                   
                   × 
                   A1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P1 
                     
                   
                 
                 + 
                 
                   LO 
                   
                     1 
                     , 
                     I 
                     , 
                     F 
                   
                 
                 + 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 49 
               
             
           
           
             
               
                 
                   
                     BB 
                     Q 
                   
                   × 
                   
                     LO 
                     Q 
                   
                   × 
                   A2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P2 
                     
                   
                 
                 + 
                 
                   LO 
                   
                     2 
                     , 
                     Q 
                     , 
                     F 
                   
                 
               
             
             
               
                   
               
             
           
           
             
               
                 State 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 2 
                 ⁢ 
                 
                   : 
                 
               
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     BB 
                     I 
                   
                   × 
                   
                     LO 
                     I 
                   
                   × 
                   A1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P1 
                     
                   
                 
                 - 
                 
                   LO 
                   
                     1 
                     , 
                     I 
                     , 
                     F 
                   
                 
                 + 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 50 
               
             
           
           
             
               
                 
                   
                     BB 
                     Q 
                   
                   × 
                   
                     LO 
                     Q 
                   
                   × 
                   A2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P2 
                     
                   
                 
                 - 
                 
                   LO 
                   
                     2 
                     , 
                     Q 
                     , 
                     F 
                   
                 
               
             
             
               
                   
               
             
           
           
             
               
                 State 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 3 
                 ⁢ 
                 
                   : 
                 
               
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     BB 
                     Q 
                   
                   × 
                   
                     LO 
                     Q 
                   
                   × 
                   A1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P1 
                     
                   
                 
                 + 
                 
                   LO 
                   
                     1 
                     , 
                     Q 
                     , 
                     F 
                   
                 
                 + 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 51 
               
             
           
           
             
               
                 
                   
                     BB 
                     I 
                   
                   × 
                   
                     LO 
                     I 
                   
                   × 
                   A2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P2 
                     
                   
                 
                 + 
                 
                   LO 
                   
                     2 
                     , 
                     I 
                     , 
                     F 
                   
                 
               
             
             
               
                   
               
             
           
           
             
               
                 State 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 4 
                 ⁢ 
                 
                   : 
                 
               
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     BB 
                     Q 
                   
                   × 
                   
                     LO 
                     Q 
                   
                   × 
                   A1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P1 
                     
                   
                 
                 - 
                 
                   LO 
                   
                     1 
                     , 
                     Q 
                     , 
                     F 
                   
                 
                 + 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 52 
               
             
           
           
             
               
                 
                   
                     BB 
                     I 
                   
                   × 
                   
                     LO 
                     I 
                   
                   × 
                   A2 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ⅇ 
                     
                       j 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P2 
                     
                   
                 
                 - 
                 
                   LO 
                   
                     2 
                     , 
                     I 
                     , 
                     F 
                   
                 
               
             
             
               
                   
               
             
           
         
       
     
   
   In Equations 49 through 52, it can be seen that the RF signal LO feed-through components, LO 1,I,F , LO 1,Q,F , LO 2,I,F , and LO 2,Q,F , oscillate between positive and negative values. This results in the LO feed-through energy being spectrally spread away from the desired signal spectrum. 
   Since the LO feed-through term is being modulated at a frequency of the interleaving clock  340 , the LO feed-through is being spread with over a bandwidth equivalent to the frequency of the interleaving clock. As the interleaving clock frequency increases, the in-band distortion caused by the LO feed-through is reduced. Furthermore, by using a delta signal modulator  341  the switching behavior of the BBI and LOPI can be modified as to shape the spectral characteristics of the LO feed-through. 
   In Equations 49 through 52, it can be seen that the RF signal quadrature imbalance components  A1ejP1  and A 2 e jP2  are each multiplied to both the in-band and quadrature baseband signal components. The RF in-phase component BB 1 *LO I  has is modified by two values: A 1 e jP1  for states 1 and2 and A 2 e jP2  for states  3  and  4 . The quadrature baseband signal follows the opposite pattern for amplitude and phase imbalance. When the in-phase and quadrature signal components are modified by the amplitude and phase distortions at a much higher frequency than their own modulation bandwidths, the two distortion products are averaged together in effect. This is shown in Equation 53.
 
 RF =( BB   I   *LO   I )*(( A 1 e   jP1   +A 2)+( BB   Q   *LO   Q )*(( A 1 e   jP1   +A 2 e   jP2 )/2)  Equation 53
 
   So while the amplitude and phase distortion are still present in the RF signal, each signal component is distorted in the same fashion. Furthermore, the rapid switching of amplitude and phase distortion causes this distortion to be spread over a wide frequency and thus lowering its effects on in-band signal components. 
   The present embodiment may thus provide a solution for important drawbacks of direct conversion transmitters: LO feed-through and quadrature imbalance. 
     FIG. 6  is an illustration of a multi-mode wireless communication system in which one embodiment may be used. It should be understood that the components shown in  FIG. 6  are merely representative of one mode of wireless communication system and that other communication systems may use different components in order to achieve similar, or even different results. For example, a wired transceiver communication system may also be employed. The claims, therefore, are not intended to be limited to the system shown in  FIG. 6 . For example, the present technology may be implemented in a single-mode system. 
   In the wireless communication system of  FIG. 6 , multi-mode, wireless communication devices, otherwise referred to herein simply as wireless communication devices, are shown as wireless communication devices  100   a ,  100   b , and  100   n,  one or more wireless communication devices being assigned to each user in the system. The designations a, b, and n on the wireless communication device identifiers correspond respectively to a first user, a second user, and an nth user, representing “n” number of users in the communication system. Although only three wireless communication devices  100  are shown in  FIG. 6 , it should be understood that a wireless communication system typically comprises many thousands of users. 
   Referring again to  FIG. 6 , control station  120  typically includes interface and processing circuitry for providing system control to base stations  110   a  through  110   n,  representing one through “n” base stations comprising the wireless communication system. Base stations are provided for transmitting and receiving communication signals to and from wireless communication devices. Each base station  110  provides a coverage area ranging up to several miles in radius from the base station location. As wireless communication devices travel within the coverage area of each base station, communication signals to be transferred to and from the wireless communication device are routed generally through the particular base station to which the wireless communication device is most closely located. 
   Control station  120  provides circuitry for routing communications between wireless communication devices operating in various base station coverage areas, as well as between remote stations and land-line telephone users through a Public Switch Telephone Network, shown in  FIG. 6  as the PSTN  130 . Control station  120  may, alternatively, or in addition to, be connected to computer network  160  to provide communications between wireless communication devices in the communication system and various known computing devices connected to computer network  160 , such as personal computers, mainframe computers, digital cameras, email systems, remotely controlled devices, and so on. 
   Control station  120  typically comprises a telecommunications switch (not shown) and a Base Station Controller (BSC) (also not shown). The telecommunication switch provides a switching interface to PSTN  130  while the BSC provides the necessary hardware and software for communications to take place between base stations. Control station  120  provides other functions in the communication system as well, such as billing services and data services. 
   Control station  120  may be coupled to the base stations by various means such as dedicated telephone lines, optical fiber links, or microwave communication links. When a call is initiated by a wireless communication device, a paging message is transmitted to one or more base stations proximate to the wireless communication device initiating the call, generally over a paging channel. The paging message is routed to control station  120 , where it is processed and routed either to PSTN  130  or to one or more base stations proximate to a wireless communication device for which the call is intended. When a call is initiated from PSTN  130 , a paging message is received by control station  120  where it is then converted into a format suitable for the particular wireless communication system. 
   In the exemplary embodiment, the wireless communication device  100  is able to communicate in at least two modes, or types, of communications, data communications and voice communications. Data communication mode is used when it is desirous to send or receive information generally suitable for digital computational devices, such as laptop computers. Data is generally transmitted in discreet segments called packets. Each data packet generally contains overhead information used for a variety of purposes. For example, many data packets contain a data field used to store an error detection code. The error detection code may be used to check a received data packet to ensure that it was received intact; that is, the data was not corrupted during the transmission process. 
   Voice communication mode is used when it is desirous to transmit acoustic information, including human speech, facsimile tones, music, or other audible forms of communication. In voice communication mode, audio information is transmitted using one or more well-known wireless communication modulation techniques, such as CDMA, TDMA, AMPS, and others. 
   During typical voice communications, an over the air channel is established between one or more base stations and a wireless telephone. The channel is maintained throughout the duration of the voice call, no matter how much or little voice activity is occurring between the wireless telephone and the base station. In many instances, voice data is digitized and formatted into packets prior to transmission. Voice packets differ from data packets in that no information as to a destination address is contained within the voice packets. That is, a connection is first established between two locations, then voice data is transmitted between the two locations. No address information need be contained within the voice packets as the source and destination of the voice packets are predetermined by the connection. 
   Data mode may further include a capability of transmitting voice in certain applications. In this scenario, voice is digitized. The digitized voice signals may be encrypted to provide for secure voice transmissions over the air. The digitized voice signals are then formatted into data packets, which are then transmitted over the air using well-known data transmission protocols. As explained above, each data packet contains information as to the address, or destination, of where the data packet is to arrive. 
     FIG. 7  illustrates the functional components of a wireless communication device, or wireless communication device,  100 , shown in block diagram format. It should be understood that the components shown in  FIG. 7  are merely representative of one mode of wireless communication device and that other communication devices may use different components in order to achieve similar, or even different results. The claims, therefore, are not intended to be limited to the system shown in  FIG. 7 . 
   Wireless communication device  100  is capable of multi-mode communications, meaning that it can operate in several modes of communications, such as voice communications or data communications. It should be understood that voice communications comprise any audio information including speech, music, or audible tones used for call processing, modems, and facsimile machines. Data communications comprise synchronous or asynchronous data transmission. In addition to these modes, wireless communication device is also capable of other modes of communications as well. 
   A user of wireless communication device  100  initiates communications generally by using input device  200 . Input device  200  comprises a keypad in the exemplary embodiment, however, input device  200  could be any device which accepts user commands, such as a voice response device which converts voice commands into electrical signals suitable for processing by controller  202 . During voice communications, the user speaks into microphone  204 , which transforms acoustic energy into electrical energy and sends the electrical signals to controller  202  for processing. 
   Microphone  204  may be substituted for input device  200  in an application where a second audio input device is undesirable. In many instances, a voice encoder/decoder, generally known as a Codec, is used between microphone  204  and controller  202 , or is incorporated within controller  202 , to convert the electrical signals from microphone  204  into a format more suitable for transmission over a limited bandwidth air interface. 
   Speaker  206  is used to convert received electrical signals into acoustic signals. Speaker  206  may comprise a speaker suitable for low volume acoustic outputs, typically for use in a traditional telephone application, or speaker  206  may comprise a loudspeaker, suitable for high volume acoustic outputs, typically for use in a dispatch applications. In another embodiment, speaker  206  may comprise a combination of the high volume and low volume acoustic speakers. 
   Wireless communication device  100  further comprises display  208  for allowing a user to view operational characteristics of the wireless communication device. Such displays are common in many of today&#39;s wireless devices including telephones and remote data terminals. 
   Data port  210  serves as an interface between controller  202  and external hardware devices. Data port  210  generally allows a variety of bi-directional data communications to take place between wireless communication device  100  and the external device. Such external devices include laptop computers, facsimile machines, and remote data terminals, among others. 
   When a user initiates voice or data communications, an identification code corresponding to a second communication device, generally a telephone number, is entered using input device  200 . In the exemplary embodiment, input device  200  comprises keys corresponding to digits 0 through 9, as well as additional function keys, such as SEND, END, and so forth. Input device  200  may also comprise one or more keys used to classify an outgoing communication as being a data communication or a voice communication. 
   For example, a user wishing to initiate a data communication might press a key designated for data communications, then dial a telephone number corresponding to a data device that the user wishes to communicate with. In one embodiment, all calls from wireless communication device  100  are assumed to be voice calls, unless classified as some other mode of communication, as described by one of the methods above. 
   Controller  202  serves as the main computational unit of wireless communication device  100 . Although controller  202  is shown as a single element in  FIG. 7 , it should be understood that controller  202  may comprise one or more individual components such as one or more Application Specific Integrated Circuits (ASICs) in combination with memory devices, bus controllers, and other support devices well known to those skilled in the art. 
   To facilitate the transmission and receipt of wireless RF signals in the foregoing context, an RF transceiver  212  and an antenna  214  are coupled to controller  202  for sending and receiving such signals. Similar to the controller  202 , one or more ASICs in combination with memory devices, bus controllers, etc. may be used to provide the RF transceiver  212 . Moreover, the aforementioned direct-conversion receiver may be incorporated into the RF transceiver  212  and/or controller  202  in any desired capacity for providing an improved system. 
   Working in conjunction with the controller  202  is memory  216 . The memory  216  is a device used to store information represented in digital format. Examples of memory  216  include random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), non-volatile memory, and other known storage devices. 
   While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.