Patent Publication Number: US-RE48618-E

Title: Radio frequency transceiver

Description:
FIELD OF THE INVENTION 
     The present invention relates to a radio frequency transceiver; and, more particularly to a radio frequency transceiver which uses a voltage control oscillator and a phase locked loop for both of a transmitting unit and a receiving unit of the transceiver, and reduces the number of components and chip size of the transceiver. 
     DESCRIPTION OF RELATED ART 
       FIG. 1  is a diagram showing a conventional transceiver. 
     As shown, in a transmitting unit of the conventional transceiver, an in-phase signal and a quadrature-phase signal, which are converted from digital signals to analog signals in a baseband modem (not shown), are mixed with a local signal from a local oscillator (LO) in up-converters  111  and  112  to generate radio frequency signals, amplified in a power amplifier (PA)  113 , filtered in a bandpass filter (BPF)  102  and radiated through an antenna  101 . 
     In a receiving unit of the conventional transceiver, a signal received by the antenna  101  is transferred to a low noise amplifier (LNA)  105  through the BPF  102 , a balance to unblance transformer (Balun)  104 . The received signal is amplified in the LNA  105 , mixed with signals generated by the LO  109  to generate an intermediate signal in a mixer  109 . The intermediate signal is modulated in down converters  107  and  108  based on the four-divided signal of the local oscillation signal to generate an in-phase signal and a quadrature-phase signal. 
     In the conventional transceiver, a different local oscillator is used for the transmitting unit and the receiving unit, and the oscillation signal generated for the transmitting unit raises interference at the receiving unit, to thereby decrease performance of the transceiver. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a radio frequency transceiver which uses a voltage control oscillator and a phase locked loop for both of a transmitting unit and a receiving unit of the transceiver, and reduces the number of components and chip size of the transceiver. 
     In one aspect of the present invention, there is provided an apparatus for transmitting/receiving a radio frequency signal, including: a receiving unit for converting a radio frequency signal received by an antenna into an intermediate signal based on an intermediate local signal; a transmitting unit for converting an intermediate signal into a radio frequency signal based on a radio frequency local signal; and a local signal generating unit for generating the intermediate local signal and the radio frequency local signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the instant invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram showing a conventional transceiver; 
         FIG. 2  is a diagram depicting a transceiver in accordance with an embodiment of the present invention; and 
         FIG. 3  is a diagram illustrating a transceiver in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. Here, the same reference numeral is given to the same element, even though it appears in different drawings. 
       FIG. 2  is a diagram depicting a transceiver in accordance with an embodiment of the present invention. 
     As shown, the transceiver includes an antenna  201 , a bandpass filter  202 , a switch  203 , a receiving unit  210 , a transmitting unit  220 , a local signal generating unit  230 , and a baseband modem  250 . 
     The transmitting unit  220  receives a digital signal outputted from the baseband modem  250 , transmits a radio frequency (RF) signal, and includes digital-to-analog (D/A) converters  221  and  222 , an in-phase and quadrature-phase (IQ) modulator  223  and  224 , a transmitting automatic gain controller (AGC)  225 , an up-converter  224  and an amplifier  226 . 
     The digital signals from the baseband modem  250  is converted into analog signals to generate an analog in-phase signal and an analog quadrature-phase signal in the D/A converters  221  and  222 . In the IQ modulator  223  and  224 , the analog in-phase signal and the analog quadrature-phase signal are modulated based on a signal of which a center frequency is F 5  and combined to generate a modulated signal. A gain of the modulated signal is controlled in the transmitting AGC  225 , converted into an intermediate signal based on a signal of which a center frequency is F 4  in the up-converter  226  and amplified by an amplifier  227 . The amplified intermediate signal is transmitted by the antenna  201  through the bandpass filter  202 . 
     The receiving unit  210  includes a low noise amplifier  211 , a down-converter  212 , a receiving automatic gain controller (AGC)  213 , IQ demodulators  214  and  216 , bandpass filters  215  and  217 , analog-to-digital (A/D) converters  218  and  219 . 
     A signal received by the antenna  201  is transmitted to the low noise amplifier  211  to be amplified through the bandpass filter  202  and the switch  203 . In the down-converter  212 , the amplified signal is converted into an intermediate signal based on a local signal generated by the local signal generating unit  230 . The center frequency of the local signal is F 5 . The intermediate signal is demodulated to generate an in-phase (I) signal and a quadrature-phase (Q) signal in the IQ demodulators  214  and  216 , and then transferred to the baseband modem  250  through the bandpass filters  215  and  217  and the A/D converters  218  and  219 . 
     The local signal generating unit  230  generates local signals and includes a phase locked loop (PLL)  231 , a voltage controlled oscillator (VCO)  232 , a multiplier  233 , an amplifier  234 , a divider  235  and a phase shifter  236 . 
     A transmission channel is selected in the PLL  231 , and a local signal of which a center frequency is F 3  is generated for the selected channel in the VCO  232 . The local signal is multiplied by 2 to generate a signal of which the center frequency is F 4  in the multiplier  233  and divided by 2 to generate a signal of which the center frequency is F 5  in the multiplier  235 . 
     The center frequency F 5  is obtained by equations as:
 
F1(or F2)−2×F3=F5  Eq. (1)
 
F5−F3÷2   Eq. (2)
 
       FIG. 3  is a diagram illustrating a transceiver in accordance with an embodiment of the present invention. In this embodiment, the transceiver is for a 5 GHz radio local area network (LAN) which is based on IEEE802.11a standard. 
     The radio LAN transceiver sets a radio frequency 5,785 MHz, which is one of 12 transmission channels. 
     When transmitting a signal, the digital signal from the baseband modem  350  is converted into analog signal to generate an analog in-phase signal and an analog quadrature-phase signal in the D/A converters  321  and  322 . In the IQ modulators  323  and  324 , the analog in-phase signal and the analog quadrature-phase signal are modulated based on a second local signal of which a center frequency is 1,157 MHz and combined to generate a modulated signal. A gain of the modulated signal is controlled in the transmitting AGC  325 , converted into an intermediate signal based on a third local signal of which a center frequency is 4,628 MHz in the up-converter  326  and amplified by an amplifier  327 . The amplified intermediate signal is transmitted by the antenna  301  through the bandpass filter  302 . 
     In the receiving unit  310 , a receiving level is detected by a received signal strength indicator (RSSI)  318  and transmitted to the baseband modem  350 . The baseband modem  350  provides a control signal to a receiving AGC  313  to maintain the receiving level as a predetermined value. 
     If the PLL  331  of the local signal generator selects the eleventh channel, the voltage controlled oscillator  332  generates a first local signal of which center frequency is 2,314 MHz. The first local signal is multiplied and divided by two to generate the second local signal and the third local signal. The third local signal is transmitted to the up-converter  326  and the down-converter  312 . The second local signal is transmitted to the IQ modulator  323 ,  324  and the IQ demodulator  314 ,  315 . 
     In the IEEE802.11a standard, frequencies of 5 GHz RF band, a local band and an IF band in each channel are expressed in Table 1. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Channel No. 
                 RF band (MHz) 
                 Local band (MHz) 
                 IF band (MHz) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 5180 
                 2072 
                 1036 
               
               
                 2 
                 5200 
                 2080 
                 1040 
               
               
                 3 
                 5220 
                 2088 
                 1044 
               
               
                 4 
                 5240 
                 2096 
                 1048 
               
               
                 5 
                 5260 
                 2104 
                 1052 
               
               
                 6 
                 5280 
                 2112 
                 1056 
               
               
                 7 
                 5300 
                 2120 
                 1060 
               
               
                 8 
                 5320 
                 2128 
                 1064 
               
               
                 9 
                 5745 
                 2298 
                 1149 
               
               
                 10 
                 5765 
                 2306 
                 1153 
               
               
                 11 
                 5785 
                 2314 
                 1157 
               
               
                 12 
                 5805 
                 2322 
                 1161 
               
               
                   
               
            
           
         
       
     
     In the heterodyne radio frequency transceiver in accordance with the present invention, the same voltage controlled oscillator (VCO) and the phase locked loop (PLL) generate both of an RF band signal and an IF band signal, and then the transceiver has smaller number of components. Accordingly, the transceiver has a simple structure, a low manufacturing expense. If the transceiver is manufactured as a one-chip, the chip size can be considerably reduced. Further, because the intermediate frequency is different from the frequency of the VCO in the receiving unit, DC offset is reduced and the performance of the transceiver is increased. 
     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.