Patent Publication Number: US-2005143020-A1

Title: Transceiver module

Description:
BACKGROUND  
      The present invention relates to a transceiver module, and more particularly, to a transceiver module that is used in a wireless communication system for processing RF signals.  
      Wireless communication has been a field undergoing rapid development in recent years. A mobile phone (or cellular phone) system is an example of wireless communication system. With the technology advancing from the second generation (2G) to the third generation (3G), an increasing number of functions are built inside the mobile phone handsets. Aside from providing the normal functions of a phone, some mobile phone handsets in the market also have built-in data transmission functions, multimedia applications, and even global positioning systems (GPS).  
      There are some key components that are always used in a wireless communication system. Taking cellular phone as an example, the basic components are base band (BB) modules, transceiver modules, and antennas. A base band module always includes a base band IC, and the primary task of which is to process the base band signals. For instance, voice or data signals are encoded/decoded by the base band IC. Normally, a transceiver module is connected to an antenna to transmit (or receive) RF signals through the antenna. A transceiver module always includes a RF transceiver IC (abbreviated as RF IC), a power amplifier module (abbreviated as PAM), a T/R switch, and several filters.  FIG. 1  shows a schematic diagram of a conventional transceiver module. The transceiver module  100  receives a base band signal BB_OUT from a base band module (not shown), generates a radio frequency signal RF_OUT 2  according to the base band signal BB_OUT, and transmits the signal RF_OUT 2  through an antenna  10 . The transceiver module  100  also receives a radio frequency signal RF_IN 1  from the antenna  10 , and then generates a base band signal BB_IN according to the radio frequency signal RF_IN 1 . The signal BB_IN will be further processed by the above mentioned base band module. For clarity, only one receive path and one transmit path are shown in  FIG. 1 , even though a transceiver module usually contains several receive paths and several transmit paths to process signals on different frequency bands (such as the frequency bands used in GSM-900, DCS-1800, or PCS-1900 systems).  
      The transceiver module  100  shown in  FIG. 1  contains a T/R switch  110 , a power amplifier module (PAM)  120 , a filter  130 , and a transceiver IC  140 . The transceiver IC  140  receives a base band signal BB_OUT from a base band module (not shown in  FIG. 1 ) and up-converts its frequency to generate a radio frequency signal RF_OUT 1 . The transceiver IC  140  also receives a radio frequency signal RF_IN 2  from the filter  130  and down-converts its frequency to generate a base band signal BB_IN. The power amplifier module  120  is electrically connected between the transceiver IC  140  and the T/R switch  110 . It receives the signal RF_OUT 1  from the transceiver IC  140 , amplifies the signal RF_OUT 1  to generate a radio frequency signal RF_OUT 2 , and sends the signal RF_OUT 2  to the T/R switch  110 . The filter  130  is electrically connected between the T/R switch  110  and the transceiver IC  140 . It receives a radio frequency signal RF_IN 1  from the T/R switch  110 , filters the signal RF_IN 1  to generate a radio frequency signal RF_IN 2 , and sends the signal RF_IN 2  to the transceiver IC  140  for further processing. Generally speaking, the filter  130  could be a surface acoustic wave filter (abbreviated as SAW filter).  
      Taking the widely used GSM-900, DCS-1800, PCS-1900 systems as an example, the power level of the radio frequency signal RF_OUT 1  is roughly at a 1 mW level. However, after amplification by the power amplifier module  120 , it is sometimes required that the power level of the radio frequency signal RF_OUT 2  is at a 2W level. The amplification ratio is so high that power amplifier module must contain a plurality of GaAs heterojunction bipolar transistors (abbreviated as HBT) connected in series to complete the amplification task as described in the related art. In the example shown in  FIG. 1 , there are three power amplifiers connected in series. In addition, the power amplifier module  120  further comprises a power detector  124  and a comparator  125 . The power detector  124  detects a power level of the radio frequency signal RF_OUT 2 . The comparator  125  compares the detected power level of the signal RF_OUT 2  with a control level, and adjusts the amplification ratios of the power amplifiers  121 ,  122 ,  123  according to the comparing result. In some instances, the power detector  124  and the comparator  125  are circuit components formed by CMOS or BiCMOS.  
      Because the power amplifier module  120  contains more than one power amplifiers connected in series, and more than one manufacturing processes are used to produce the power amplifier module  120  (a HBT manufacturing process uses GaAs as the substrate to produce the power amplifiers  121 ,  122 ,  123 , and a CMOS or BiCMOS manufacturing process uses silicon as the substrate to produce the power detector  124  and the comparator  125 ), the cost of each power amplifier module  120  is high. Further, every power amplifier module  120  is quite large. The result of this is that it is difficult to encapsulate the transceiver module  100  as a whole and reduce its IC size simultaneously. Theses problems are considered drawbacks of the related art.  
      Another drawback of the power amplifier module of the related art is that it has inferior power efficiency.  FIG. 2  shows an example of a power efficiency curve of the power amplifier module  120  shown in  FIG. 1 . In GSM systems, the power amplifier module  120  is always designed such that it is capable of outputting RF signals with power levels up to 2W to endure an inferior environment. However, at most of the time, it is operated to output RF signals with power levels ranging from 10 mW to 100 mW. When the power level of the RF signals outputted by the power amplifier module  120  ranges from 10 mW to 100 mW, the power efficiency of the power amplifier module is quite poor. The lower the outputted power level is, the worse the power efficiency becomes. This situation not only increases the rate of power consumption which shortening handset standby time, but also causes the battery lifetime to decrease. This is also considered a drawback of the related art.  
     SUMMARY  
      It is therefore an objective of the present invention to provide a transceiver module used in a wireless communication system to solve the above-mentioned problems.  
      According to an embodiment of the present invention, a transceiver module used in a wireless communication system is disclosed. The disclosed transceiver module comprises a transceiver IC, a T/R switch, and an amplification path electrically connected between the transceiver IC and the T/R switch. The transceiver IC comprises a pre-amplifier unit electrically connected to the amplification path. The pre-amplifier unit receives a first RF signal and amplifies the first RF signal to generate a second RF signal. The amplification path receives the second RF signal from the pre-amplifier unit, amplifies the second RF signal to generate a third RF signal, and sends the third RF signal to the T/R switch. The disclosed transceiver module uses only one discrete power amplifier transistor in the amplification path to amplify the second RF signal.  
      It is an advantage of the present invention that the disclosed transceiver module is smaller than that of the related art and the associated cost is also lower. Besides, it is easier to encapsulate the transceiver module as a whole. Another advantage of the present invention is that by operating it appropriately, the disclosed transceiver module has better power efficiency over a wider operating range than that of the related art.  
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a schematic diagram of a transceiver module of the related art.  
       FIG. 2  is a plot of a power efficiency curve of the power amplifier module of the transceiver module of  FIG. 1 .  
       FIG. 3  is a schematic diagram of a transceiver module according to the present invention.  
       FIG. 4  is a plot of three power efficiency curves of the transceiver module of  FIG. 3 .  
       FIG. 5  is a plot of a power efficiency curve from the combination of three power efficiency curves of  FIG. 4 . 
    
    
     DETAILED DESCRIPTION  
       FIG. 3  shows a transceiver module according to an embodiment of the present invention. The transceiver module  300  receives a base band signal BB_OUT from a base band module (not shown), and generates a radio frequency signal RF_OUT 3  according to the base band signal BB_OUT. It also receives a radio frequency signal RF_OUT 3  from an antenna  30 , and generates a base band signal BB_IN according to the radio frequency signal RF_OUT 3 . Please note that in  FIG. 3 , only a transmit path and a receive path of the transceiver module  300  for signal processing on a single frequency band are shown. However, it&#39;s also possible that the transceiver module of the present invention contains more than one transmit/receive paths for signal processing on a plurality of frequency bands.  
      In this embodiment, the transceiver module  300  includes a T/R switch  310 , a transceiver IC  340 , an amplification path  320 , and a filter  330 . The T/R switch  310  is used to switch the antenna  30  between a transmit state and a receive state. A transmitter part  350  of the transceiver IC  340  receives the base band signal BB_OUT, up-converts the frequency of the signal BB_OUT to generate a radio frequency signal RF_OUT 1 , and pre-amplifies the signal RF_OUT 1  to generate a radio frequency signal RF_OUT 2 . A receiver part  370  of the transceiver IC  340  receives a radio frequency signal RF_IN 2  from the filter  330 , down-converts its frequency and then demodulates it to generate the base band signal BB_IN. The amplification path  320  is electrically connected between the transceiver IC  340  and the T/R switch  310 . It receives the signal RF_OUT 2  that is already pre-amplified by the transceiver IC  340 , amplifies the signal RF_OUT 2  to generate a radio frequency signal RF_OUT 3 , and sends the amplified signal RF_OUT 3  to the T/R switch  310 . The filter  330  is electrically connected between the T/R switch  310  and the transceiver IC  340 . It receives the radio frequency signal RF_IN 1  from the T/R switch  310 , filters the signal RF_IN 1  to generate a radio frequency signal RF_IN 2 , and sends the filtered signal RF_IN 2  to the transceiver IC  340 . As in the related art mentioned above, the filter  330  could be a SAW filter.  
      In the transceiver module  100  of the related art, a plurality of series-connected power amplifiers are set inside the integrated circuit of the power amplifier module  120  to amplify RF signals. However, in the present invention, only one discrete power amplifier transistor  325  is used in the amplification path  320  to amplifier RF signals. Wherein in the given examples, the power amplifier transistor  325  could be a circuit component with GaAs substrate, such as GaAs heterojunction bipolar transistor. Furthermore, since all the extra control circuits are set inside the transceiver IC  340 , the size of the amplification path  320  in this embodiment will be much smaller than the power amplifier module  120  of the related art.  
      In this embodiment, the transceiver IC  340  contains a transmitter part  350  and a receiver part  370 . Aside from components used to up-convert the frequency of the base band signal BB_OUT to generate the radio frequency signal FR_OUT 1 , the transmitter part  350  also contains a pre-amplifier unit  355  and an amplifier control unit  360 . This point further makes the transceiver module  300  of this embodiment different from the related arts. The pre-amplifier unit  355  pre-amplifies the signal RF_OUT 1  to generate the signal RF_OUT 2 . The amplifier control unit  360  controls the amplification ratios of the pre-amplifier unit  355  and the discrete power amplifier transistor  325 . In some instances, both the pre-amplifier unit  355  and the amplifier control unit  360  could be circuit elements produced through manufacturing process using silicon substrate, such as CMOS manufacturing process or BiCMOS manufacturing process. Although the pre-amplifier unit  355  and the amplifier control unit  360  are set inside the transceiver IC  340 , the cost and size of the transceiver IC  340  will increase only slightly since only manufacturing process using silicon substrate is used. Hence, by using only a discrete power amplifier transistor in the amplification path  320  and a Si-based transceiver IC  340 , the total cost of the whole transceiver module will be lower than that of the related arts, and the total size will also be smaller.  
      In the embodiment shown in  FIG. 3 , there are two parallel-connected power amplifiers  357 ,  359  set inside the pre-amplifier unit  355 . However, a design engineer can also connect the power amplifiers in series rather than in parallel. The number of power amplifiers set inside the pre-amplifier unit  355  depends on the need of amplifying RF signals. The amplifier control unit  360  in  FIG. 3  contains a power detector  362  and a comparator  364 . The power detector  362  is electrically connected to the amplification path  320  to detect a power level of the signal RF_OUT 3  and it sends the detected power level to a comparator  364 . The comparator  364  compares the detected power level of the signal RF_OUT 3  from power detector  362  with a control level, and controls the amplification ratios of the power amplifiers  357 ,  358 , and the discrete power amplifier transistor  325  according to the comparing result.  
      Furthermore, with the transceiver module  300  disclosed in this embodiment, the system can dynamically determine how to use the pre-amplifier unit  355  and the discrete power amplifier transistor  325  to amplify RF signals according to the amplification requirement.  FIG. 4  shows three power efficiency curves the transceiver module  300  of  FIG. 3  could have. The curve in the left hand side is the power efficiency curve when only the power amplifier  357  is used to amplify RF signals. The curve in the middle is the power efficiency curve when both the power amplifiers  357 ,  359  are used to amplify RF signals. And the curve in the right hand side is the power efficiency curve when the power amplifiers  357 ,  359  and the discrete power amplifier transistor  325  are all used to amplify RF signals. Apparently, by using different combination in different output power level range, the system will have a better power efficiency curve. Taking the curves shown in  FIG. 4  as an example, the curve in the left hand side has a maximum power efficiency when output power is near 10 mW, the curve in the middle has a maximum one when output power is near 100 mW, and the curve in the right hand side has a maximum one when output power is near 1W. When the required power level of the signal RF_OUT 3  is at a 10 mW level, the system can use only the power amplifier  357  to amplify RF signals, and turning off the power amplifier  359  and bypassing the discrete power amplifier transistor  325 . When the required power level of the signal RF_OUT 3  at a 100 mW level, the system can use both the power amplifiers  357  and  359  to amplify RF signals, and bypassing the discrete power amplifier transistor  325 . When the required power level of the signal RF_OUT 3  is at a 1W level, the system can use the power amplifiers  357 ,  359  and the discrete power amplifier transistor  325  as a whole to amplify RF signals.  FIG. 5  shows a power efficiency curve of the transceiver module  300  when the above-mentioned switching method is applied. It is apparent that even when the required power level of the signal RF_OUT 3  is not high (i.e. between 10 mW and 100 mW), the system still has good power efficiency, which is much better than that of the related art.  
      Although a transceiver module capable of transmitting and receiving RF signals is used as an example to illustrate the present invention, the present invention can also be applied in transmitters that cannot receive RF signals. By removing the receiver part  370  and the filter  330  shown in  FIG. 3 , the transceiver module  300  can become a transmitter module and still keep the characteristics of the present invention.  
      These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.