Abstract:
An adaptive wireless receiver and method thereof is disclosed in the present invention. The receiver includes an antenna, a bandpass filter, a front-end unit and a demodulator. Elements inside the front-end unit can be reused when the receiver operates in a zero intermediate frequency (ZIF) mode and in a low intermediate frequency (LIF) mode. The front-end unit includes a first and second down-conversion mixer, an analog filter, a first and second analog-to-digital converter (ADC), and a digital filter.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application, titled Adaptive Wireless Receiver, Ser. No. 60/811,902, filed on Jun. 8, 2006, the specification of which is incorporated herein in its entirety by this reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to wireless communication systems and in particular to an adaptive wireless receiver that supports multiple standards and/or multiple frequency bands. 
         [0004]    2. Description of the Related Art 
         [0005]    Currently, the increase demand for wireless communication systems has resulted in continuing development of wireless receivers. The receivers are commonly employed in radio frequency (RF) signal transmission. In the wireless communication field, the receivers usually are capable of receiving RF signals through an antenna. The receivers convert these RF signals to desirable intermediate frequency (IF) signals before they are converted to a baseband frequency. These IF signals are then transferred to their destinations where the IF signals will be used. 
         [0006]      FIG. 1  illustrates a block diagram of a prior art receiver  100 . The receiver  100  usually is composed of an antenna  110 , a bandpass filter (BPF)  120 , a RF front-end unit  130 , a demodulator  140  and a processor  150 . After being received by the antenna  110 , RF signals are filtered by the BPF  120 . The RF front-end unit  130  performs the tasks of down-translating the RF signals from high frequency to a specific IF, i.e., a low frequency. The demodulator  140  will demodulate the IF signals from the RF front-end unit  130  and the processor  150  will further process the IF signals based upon the requirements of the applications. Many topological configurations have been developed for the receivers  100  to satisfy different requirements of various applications, for example, zero IF (ZIF) receiver and low IF (LIF) receiver. The ZIF receiver and the LIF receiver are both suitable for high integration. 
         [0007]      FIG. 2  illustrates a prior art ZIF wireless receiver  200 . A RF frond-end  230  is included in the ZIF wireless receiver  200 . The RF front-end unit  230  can be composed of a low noise amplifier (LNA)  231 , down-conversion mixers  232  and  233 , lowpass filters (LPFs)  234  and  235 , analog-to-digital converters (ADCs)  236  and  237 . The ZIF wireless receiver  200  can translate the received RF signal to baseband frequency centered around the DC&#39;s frequency directly with an I/Q down-conversion. The cutoff frequency of the LPFs  234  and  235  is half of that of the bandwidth of the desired channel. The ZIF wireless receiver  200  has many advantages, for example, high integration. Additionally, the output of the ZIF wireless receivers  200  is an I (in-phase) and Q (qradrature-phase) signal without any carrier signal. However, using the two LPFs  234  and  235  for channel selection in both I/Q paths requires a great silicon area, especially for low band-width and low noise applications. As a result, the complexity and cost of the integrated circuit where the ZIF wireless receiver  200  is embedded will be greatly increased. In addition, the mismatch between the I path and the Q path and a DC offset caused by the mix between the RF signal and the LO signal can adversely affect the performance of the ZIF wireless receiver  200 . 
         [0008]      FIG. 3  depicts a prior art LIF wireless receiver  300 . The LIF wireless receiver  300  includes a RF front-end unit  330  that consists of a LNA  331 , down-conversion mixers  332  and  333 , a filter  334 , a combiner  335  and an ADC  336 . The LIF wireless receiver  300  translates the received RF signal to a specific lower intermediate frequency signal that is somewhat away from the baseband frequency. The filter  334  can filter out an image (i.e., reject an image) included in the IF signal. Two components of the filtered IF signal in the I and Q paths are combined (i.e., added or subtracted) by the combiner  335  and then the filtered IF signal will be converted from analog to digital by the ADC  336  and demodulated by the demodulator  140 . The output of the LIF wireless receiver  300  includes a carrier signal. The combiner  335  can be included in the filter  334 . In one embodiment, the filter  334  can be an image rejection filter. The main drawback for the LIF wireless receiver  300  is the low IRR (image rejection rate) caused by the mismatch between the I and Q paths, which greatly limits the performance of the receiver system. 
         [0009]    In various applications, for example, a mobile digital TV, there are different operating standards with different natures, for example, DVB-H, T-DMB and ISDB-T. To support all these different standards, the ZIF and LIF topologies should be integrated into one single silicon circuit. However, because of the incompatibility between the ZIF and LIF topologies, more tuners are required to support these different standards in traditional solutions. Furthermore, the reuse of hardware is very limited in the traditional solutions. Hence, the performance of the receiver system is limited and the silicon area of the integrated circuit will be significantly expanded when both topologies are included. 
         [0010]    It is thus desirous to have an apparatus and method that provide an adaptive wireless receiver supporting multiple standards and/or multiple frequency bands with reduced silicon area, simple configuration and high integration. It is to such apparatus and method the present invention is primarily directed. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    In one embodiment, there is disclosed an adaptive receiver for processing a radio frequency (RF) signal to support multiple standards. The receiver includes an antenna, a bandpass filter (BPF), a front-end unit, and a demodulator. The antenna receives the RF signal. The BPF filters the RF signal. The front-end unit processes the filtered signal from the BPF and generates digitalized signals. The demodulator demodulates the digitalized signals. The front-end unit executes channel selection when the adaptive wireless receiver operates in a zero intermediate frequency (ZIF) mode and executes image rejection when the adaptive wireless receiver operates in a low intermediate frequency (LIF) mode. 
         [0012]    In one embodiment, there is disclosed an apparatus for converting a bandpassed (BP) radio frequency (RF) signal to a desired intermediate frequency (IF) signal. The apparatus includes a low noise amplifier (LNA), a first and second mixer, an analog filter, a first and second analog-to-digital converter (ADC), and a digital filter. The LNA amplifies the BP RF signal and generates an amplified RF signal. The first mixer converts the amplified RF signal from RF to IF and generates an in-phase (I) signal. The second mixer converts the amplified RF signal from RF to IF and generates a quadrature-phase (Q) signal. The analog filter filters the I and Q signals. The first and second ADCs convert the filtered I and Q signals from analog to digital. The digital filter filters the digitalized I and Q signals. 
         [0013]    In another embodiment, there is disclosed a method for converting a radio frequency (RF) signal to an intermediate frequency (IF) signal by a receiver. The method includes the steps of (a) filtering the RF signal with a frequency band, (b) amplifying the filtered RF signal, (c) down-converting the amplified RF signal to an IF signal including an in-phase (I) signal and a quadrature-phase (Q) signal when the receiver operates in a zero intermediate frequency (ZIF) mode and in a low intermediate frequency (LIF) mode, (d) filtering the IF signal, (e) converting the filtered IF signal to a digital signal including a digitalized I signal and a digitalized Q signal, and (f) filtering the digital signal. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Advantages of the present invention will be apparent from the following detailed description of exemplary embodiments thereof, which description should be considered in conjunction with the accompanying drawings, in which: 
           [0015]      FIG. 1  is a block diagram of a prior art receiver; 
           [0016]      FIG. 2  is a block diagram of a prior art zero intermediate frequency (ZIF) wireless receiver; 
           [0017]      FIG. 3  is a block diagram of a prior art low intermediate frequency (LIF) wireless receiver; 
           [0018]      FIG. 4  is a simplified block diagram of an adaptive wireless receiver consistent with the invention; and 
           [0019]      FIG. 5  is a simplified schematic diagram of a straightforward implementation of a digital image rejection function of the wireless receiver in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 4  illustrates a simplified block diagram of an adaptive wireless receiver  400  according to the present invention. Because the adaptive wireless receiver  400  is similar to the ZIF (zero intermediate frequency) wireless receiver  200  and the LIF (low intermediate frequency) wireless receiver  300 , the similar components thereof are indicated by similar symbols for clarity. The adaptive wireless receiver  400  described in details below can operate in both ZIF mode and LIF mode. The adaptive wireless receiver  400  is configured to support multiple standards and different frequency bands. The adaptive wireless receiver  400  includes the antenna  110 , the bandpass filter (BPF)  120 , a RF front-end unit  430  and the modulator  140 . The RF front-end unit  430  includes a LNA (low noise amplifier)  431 , down-conversion mixers  432  and  433 , an analog filter  434 , ADCs (analog-to-digital converters)  435  and  436 , and a digital filter  437 . 
         [0021]    The antenna  110  is used to receive the RF signal from a remote location. The number of the antenna  110  is not fixed, so any number of antennas can be used based upon the requirements of different applications. Connected to the antenna  100  is the BPF  120  with a bandwidth having desired cutoff frequencies. The BPF  120  is employed for the purpose of band selection. The BPF  120  can filter the RF signal to eliminate undesired interfering signals (i.e., spurious external signals) from the RF signal with a specific frequency band. The filtered signal has a narrower band (i.e., a spectrum) where many channels are included therein. The adaptive wireless receiver  400  is capable of selecting a channel in the signal band in response to a command as will be described in detail below. The number of the BPF  120  is also not fixed, so any number of BPFs can be used according to the desired frequency band requirement for the RF signal. 
         [0022]    The filtered signal is then delivered to the LNA  431  that can amplify the filtered signal. The amplified signal is sent to the down-conversion mixers  432  and  433 . The adaptive wireless receiver  400  further includes a local oscillator (LO) (not shown) that generates a local oscillator signal. The LO signal can be adjusted accordingly by the LO. The LO signal is then mixed with the amplified signal from the LNA  431  at the down-conversion mixer  432  in an in-phase (I) path of the adaptive wireless receiver  400 . In other words, the amplified signal for the LNA  431  is translated to much lower frequencies by the down-conversion mixer  432  by mixing with the LO signal from the LO. Hence, the down-conversion mixer  432  generates an IF signal in the I path that is called a down-converted I signal (i.e., an I signal) herein for abbreviation. 
         [0023]    The phase of the LO signal from the LO is shifted ninety degrees by a unit, for example, a phase shifter. The amplified signal from the LNA  431  is also processed through a quadrature-phase (Q) path of the adaptive wireless receiver  400 . Specifically, the output of the LNA  431  is inputted into the down-conversion mixer  433  that mixes the amplified signal with the phase shifted LO signal to generate a down-converted Q signal (i.e., a Q signal). The down-converted I and Q signals are separately sent from the down-conversion mixers  432  and  433  to the analog filter  434 . In this embodiment, the down-converted I and Q signals form an IF signal. 
         [0024]    If the adaptive wireless receiver  400  operates in the ZIF mode, the received RF signal is down-converted to the baseband frequency, i.e., a center frequency of  0  Hz around DC by the down-converted mixers  432  and  433 . The analog filter  434  may be configured as a lowpass filter (LPF) to select a desired channel in the IF band. The signals from the analog filter  434  are converted from analog to digital by the ADCs  435  and  436 . The digitalized signals from the ADCs  435  and  436  are further fed to the digital filter  437 . The digital filter  437  can also be configured as a LPF to provide additional channel selection for the IF signal. The use of the digital filter  437  can greatly relax the rigorous requirement for design of the analog filter  434  and consequently the silicon area of the adaptive wireless receiver  400  may be reduced. 
         [0025]    If the adaptive wireless receiver  400  operates in the LIF mode, the received RF signal is down-converted to a specific IF signal. The LO enables the desired channel in the band of the RF signal to be translated to a specific IF that is close to the DC. The channel adjacent to the desired channel is the image interfering the IF signal. Similar to the ZIF mode, the analog filter  434  may also be configured as a LPF for the purpose of selecting a desired channel in the band of the IF signal. The cutoff frequencies of the analog filter  434  can be selected as large as the bandwidth of the desired channel such that the silicon area of the receiver system is reduced. The channel selection can also eliminate interfering signals including the image. In other words, the analog filter  434  is configured as an image rejection filter for being capable of removing an image from a desired signal. The filtered I and Q signals are fed to the ADCs  435  and  436  for conversion from analog to digital. The digitalized I and Q signals are further fed to the digital filter  437 . The image is further prevented from interfering with the desired IF signal by the digital filter  437 . The digital filter  437  can be implemented as a polyphase filter. 
         [0026]    As described before, only an analog filter is configured in a receiver for image rejection in traditional solutions. To achieve good image rejection, the circuitry design of the analog filter was very complex and therefore the cost for the receiver was significantly increased. In this embodiment, the insertion of the digital filter  437  will improve the image rejection function only implemented by an analog filter in traditional solutions. Additionally, the insertion of the digital filter  437  will relax the serious requirement for the analog filter and reduce the complexity of the receiver. 
         [0027]    In this embodiment, the analog filter  434  can be configured as a complex filter. The digital filter  437  can also be configured as a complex filter. Whether in the ZIF mode or in the LIF mode, the filtered signal from the digital filter  437  is then delivered to the demodulator  140  where the demodulation is done. The demodulated signal can be sent to the processor  150  (not show in  FIG. 4 ) for further signal processing to satisfy the requirements of different applications. 
         [0028]    In order to ensure optimal signal processing, the two path, i.e., the I path and the Q path should be as identical as possible to remain path match. Accordingly, identical down-conversion mixer  432  and  433  and ADCs  435  and  436  should be used to obtain good match between the I and Q paths. This will ensure that any adverse effect caused by the elements in the I path and the Q path can be minimized. 
         [0029]      FIG. 5  illustrates a schematic diagram  500  of an implementation of the digital image rejection function. The digital image rejection function is implemented by the digital filter  437  that mainly consists of multipliers  510 ,  520 ,  530  and  540  and adders  550  and  560 . The digitalized I signal (i.e., the digitalized signal at the I path) is sent to the multiplier  510  to be multiplied by a cosine signal and the product of the multiplier  510  is then fed to the adder  550 . The digitalized I signal is also sent to the multiplier  520  to be multiplied by a sine signal and the product of the multiplier  520  is then fed to the adder  560 . Similarly, the digitalized Q signal (i.e., the digitalized signal at the Q path) is delivered to the multiplier  530  to be multiplied by the sine signal described previously and the product of the multiplier  530  is then sent to the adder  550 . The digitalized Q signal also is fed to the multiplier  540  to be multiplied by the cosine signal described previously and the product of the multiplier  540  is then delivered to the adder  560 . The product from the multiplier  510  is added to the product from the multiplier  520  and then a sum is generated by the adder  550 . The product from the multiplier  520  is subtracted from the product from the multiplier  540  and then a differential value (the differential value can be called a sum) is generated by the adder  560 . The sums from both adders  550  and  560  are further delivered to the demodulator  140 . 
         [0030]    In the LIF mode, the image included in the digitalized I and Q signals can be rejected through the aforementioned method, i.e., the digital filter  437  further select a desired channel from the IF band. In the ZIF mode, the digital filter  437  in  FIG. 4  can further select a desired channel from the IF band through the above-mentioned method after the desired channel selection done by the analog filter  434 . 
         [0031]    In operation, the adaptive wireless receiver  400  can translate a RF signal to an IF signal in the ZIF mode and the LIF mode. The adaptive wireless receiver  400  is characterized by high integration, simple configuration and reduced cost. The antenna  110  receives the RF signal and delivers the RF signal to the BPF  120  for band selection. The BPF  120  can eliminate spurious external signals from the RF signal to prevent the spurious external signal from interfering with the RF signal. The filtered signal from the BPF  120  is then sent to the RF front-end unit  430  for further signal processing. 
         [0032]    In the RF front-end unit  430 , the LNA  431  amplifies the filtered signal from the BPF  120  and the amplified signal is then sent to the down-conversion mixer  432  and  433 . The LO (not shown) included in the adaptive wireless receiver  400  generates the LO signal that can be phase shifted ninety degrees by a phase shifter. The amplified signal from the LNA  431  is mixed with the LO signal at the down-conversion mixer  432  to generate the I (in-phase) signal at the I path. The amplified signal from the LNA  431  is also mixed with the phase shifted LO signal at the down-conversion mixer  433  to generate the Q (quadrature-phase) signal at the Q path. The I and Q signals are both fed to the analog filter  434 . 
         [0033]    In the ZIF mode, the analog filter  434  is used to select the desired channel from the IF band. The ADCs  435  and  436  convert the analog signals from the analog filter  434  to the corresponding digital signals in the I and Q paths respectively. After receiving the digital signals from the ADCs  435  and  436 , the digital filter  437  selects a desired channel from the IF band. 
         [0034]    In the LIF mode, the analog filter  434  eliminates spurious signals at image frequencies (i.e., the image) to prevent them from interfering with the desired IF signal. The filtered signals from the analog filter  434  are converted from analog to digital by the ADCs  435  and  436 . The digitalized signals in the I and Q paths are sent to the digital filter  437 . Because of the insufficient image rejection of the analog filter  434 , the digital filter  437  is employed to further eliminate the spurious signals at the image frequencies (i.e., the image). Hence, the image is prevented to interfere with the desired signal. 
         [0035]    The use of the digital filter  437  can overcome the signal filtering insufficiency caused by the analog filter  434  and hence relax the serious requirements to the analog filter  434 . As a result, the complexity of the adaptive wireless receiver  400  is reduced and the cost thereof is greatly decreased. 
         [0036]    Compared with the traditional solutions, the adaptive wireless receiver  400  has a high integration feature. The reuse of the hardware, for example, the analog filter  434  for channel selection in the ZIF mode and for image rejection in the LIF mode and the digital filter  437  for further channel selection in the ZIF mode and for further image rejection in the LIF mode, greatly reduces the cost of the adaptive wireless receiver  400  and enhances the integration of the circuitry system. 
         [0037]    The embodiments that have been described herein, however, are but some of the several which utilize this invention and are set forth here by way of illustration but not of limitation. It is obvious that many other embodiments, which will be readily apparent to those skilled in the art, may be made without departing materially from the spirit and scope of the invention as defined in the appended claims. Furthermore, although elements of the invention may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.