Abstract:
A terrestrial-digital multimedia broadcasting (T-DMB) and digital audio broadcasting (DAB) low intermediate frequency (IF) receiver comprises a low noise amplifier (LNA), an image rejection down-conversion mixer, a low pass filter, an amplifier, a local oscillator, a phase-locked loop, and an automatic gain controller (AGC). Particularly, the LNA, the image rejection down-conversion mixer, the low pass filter, the amplifier, the AGC, the local oscillator, and the phase-locked loop are integrated in monolithic semiconductor integrated circuit substrate. The AGC supplies a gain control signal to the LNA and the amplifier according to the magnitude of the RF signal, and the gain control signal is controlled by a null control signal based on a null signal comprised in a received radio frequency (RF) signal.

Description:
[0001]     This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 10-2005-0076765 filed in Korea on Aug. 22, 2005, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a terrestrial-digital multimedia broadcasting (T-DMB) and digital audio broadcasting (DAB) receiver.  
         [0004]     2. Description of the Background Art  
         [0005]     A conventional receiver uses a super-heterodyne mode that converts a received signal into a signal at an intermediate frequency (IF) band and then into a signal at a baseband.  
         [0006]     The IF is used to improve the performance of the receiver using a filter that effectively filters a specific frequency band. A surface acoustic wave (SAW) filter is generally used as the aforementioned filter.  
         [0007]     A conventional DAB receiver uses an L-band of the radio frequency (RF) spectrum ranging from 1,450 MHz to 1,492 MHz. On the other hand, a conventional T-DMB receiver uses a Band-III band of the RF spectrum ranging from 174 MHz to 245 MHz. Also, the conventional DAB and T-DMB receivers use an IF of 38.912 MHz and have a channel bandwidth of 1.536 MHz.  
         [0008]      FIG. 1  illustrates a simplified block diagram of a conventional receiver.  
         [0009]     A RF signal that is received by an antenna  101  is supplied to a low noise amplifier (LNA)  102 . An output signal of the LNA  102  is transmitted to a mixer  103 , which subsequently moves the transmitted signal to the IF band.  
         [0010]     An output signal of the mixer  103  passes through a band-pass filter  104  and is transmitted to an amplifier  105 . A demodulator  107  receives an output signal of the amplifier  105 . A local oscillator  108  generates a frequency to make the received RF signal move to the IF band and, supplies the generated frequency to the mixer  103 .  
         [0011]     The band-pass filter  104  is a SAW filter that is generally used in the typical super-heterodyne mode.  
         [0012]     The LNA  102 , the mixer  103 , the amplifier  105 , and the local oscillator  108  are integrated into a single receiver chip  106 , and the band-pass filter  104  (i.e., the SAW filter) is disposed outside the receiver chip  106 .  
         [0013]     The SAW filter is a filter for telecommunications using mechanical vibrations from a piezoelectric substrate. On the piezoelectric substrate, two slit patterned metal plates are arranged to face in opposite direction on both sides of the piezoelectric substrate. When an electric signal is inputted from one direction, a surface acoustic wave is generated on the piezoelectric substrate.  
         [0014]     The surface acoustic wave, which is also called “mechanical vibration,” is converted into an electric signal in the opposite direction to the input direction. If the surface acoustic wave of the piezoelectric substrate has a different frequency from the inputted electric signal, the signal transmission does not take place. As a result, the SAW filter functions as a band-pass filter that passes only a frequency identical to a mechanical-physical frequency of the SAW filter.  
         [0015]     As compared with a filter using the LC resonance principle, the SAW filter generally passes a very narrow bandwidth, and thus, can be effective to select a desired signal frequency with a narrow bandwidth since the SAW filter can almost completely filter out unnecessary signal frequencies.  
         [0016]     However, the SAW filter is a mechanical filter, and thus, often has a limitation in reducing the volume. As illustrated in  FIG. 1 , in the case that the receiver using the band-pass filter  104  (i.e., the SAW filter) is constructed in a single integration chip, the SAW filter usually cannot be integrated therein, thereby being placed outside the receiver chip  106 .  
         [0017]     Since the SAW filter is expensive, the total manufacturing cost for the receiver often increases.  
         [0018]     Therefore, when such a receiver using the SAW filter is implemented to a mobile telecommunications terminal, the SAW filter may become a main factor that increases the price of the receiver. Also, it may be difficult to integrate the receiver into a single chip.  
         [0019]     A receiver that receives a single RF signal by a single antenna can receive a single corresponding frequency band. Therefore, when at least two frequency bands need to be received, a number of receiver chips are necessary to receive the frequency bands individually. As a result, the overall volume of the telecommunications devices may increase, and the manufacturing costs may also increase.  
         [0020]     A signal that is received by the antenna of the receiver usually includes a noise signal. An attenuation level of the signal varies differently depending on the transmission path through the channels. Hence, an automatic gain controller (AGC) is employed to control the received signal to have the consistent magnitude.  
         [0021]     However, for a signal at a certain frequency band, an information contained signal section is often not consecutive, and an information contained section and a null section that does not contain information coexist. Since the signal at the null section has the smaller magnitude than that at the information contained section, an amplification gain of the amplifier increases when the AGC operates at the null section. After the null section, the increased amplification gain is maintained at the information contained section. As a result, it may difficult to maintain the consistent magnitude of the signal received at the information contained section.  
       SUMMARY OF THE INVENTION  
       [0022]     Accordingly, one embodiment of the present invention is directed to provide a T-DMB and DAB low IF receiver that can be easily integrated into a single chip and manufactured at low costs.  
         [0023]     Another embodiment of the present invention is directed to provide a dual band T-DMB and DAB low IF receiver that can be easily integrated into a single chip and manufactured at low costs.  
         [0024]     Still another embodiment of the present invention is directed to provide a T-DMB and DAB low IF receiver and a dual band T-DMB and DAB low IF receiver that can maintain the consistent magnitude of a received RF signal.  
         [0025]     A T-DMB and DAB low IF receiver according to an embodiment of the present invention comprises a low noise amplifier (LNA) suppressing a noise signal of a received radio frequency (RF) signal and amplifying the received RF signal, wherein the received RF signal includes a T-DMB signal or a DAB signal, an image rejection down-conversion mixer converting a frequency band of the RF signal outputted from the LNA into a low IF band and rejection an image frequency band, a low pass filter filtering a low frequency band of a signal outputted from the image rejection down-conversion mixer, an amplifier amplifying a signal outputted from the low pass filter, a local oscillator generating a frequency for the down-conversion and supplying the frequency to the image rejection down-conversion mixer, a phase-locked loop moving the frequency of the local oscillator to a certain frequency and locking the certain frequency, and an automatic gain controller (AGC) controlling amplification gains of the LNA and the amplifier, wherein the LNA, the image rejection down-conversion mixer, the low pass filter, the amplifier, the AGC, the local oscillator, and the phase-locked loop are integrated in a monolithic semiconductor integrated circuit substrate; the AGC supplies a gain control signal to the LNA and the amplifier according to the magnitude of the RF signal; and the gain control signal is controlled by a null control signal based on a null signal comprised in the RF signal.  
         [0026]     In the embodiment of the present invention, the null control signal may control the gain control signal at a section of the null signal.  
         [0027]     In the embodiment of the present invention, the null control signal may control the gain control signal to have a consistent signal level at the section of the null signal.  
         [0028]     In the embodiment of the present invention, the signal level may be a signal level of the gain control signal prior to receiving the null signal.  
         [0029]     In one embodiment of the present invention, the RF signal of the LNA may comprise a signal at one frequency band of a Band-III ranging between about 174 MHz and about 245 MHz or an L-band ranging between about 1,450 MHz and about 1,492 MHz.  
         [0030]     The configuration according to the embodiment of the present invention allows the removal of the SAW filter without degrading the performance of the receiver, and thus, the manufacturing cost can be reduced and the easier single-chip implementation can be achieved.  
         [0031]     A dual band terrestrial-digital multimedia broadcasting (T-DMB) and digital audio broadcasting (DAB) low intermediate frequency (IF) receiver according to another embodiment of the present invention comprises: a first low noise amplifier (LNA) suppressing a noise signal of a received first radio frequency (RF) signal and amplifying the received first RF signal, wherein the received first RF signal includes a T-DMB signal, a second low noise amplifier (LNA) suppressing a noise signal of a received second radio frequency (RF) signal and amplifying the received second RF signal, wherein the received second RF signal includes a DAB signal, an image rejection down-conversion mixer converting frequency bands of the first and second RF signals respectively outputted from the first and second LNAs into a low IF band and rejection an image frequency band, a low pass filter filtering a low frequency band of a signal outputted from the image rejection down-conversion mixer, an amplifier amplifying a signal outputted from the low pass filter, a local oscillator generating a frequency for the down-conversion and supplying the frequency to the image rejection down-conversion mixer, a phase-locked loop moving the frequency of the local oscillator to a certain frequency and locking the certain frequency, and an automatic gain controller (AGC) controlling amplification gains of the first and second LNAs and the amplifier, wherein the first and second LNAs, the image rejection down-conversion mixer, the low pass filter, the amplifier, the AGC, the local oscillator, and the phase-locked loop are integrated in a monolithic semiconductor integrated circuit substrate; the AGC supplies a gain control signal to the first and second LNAs and the amplifier according to the magnitude of the first and second RF signals; and the gain control signal is controlled by a null control signal based on a null signal comprised in each of the first and second RF signals.  
         [0032]     In the other embodiment of the present invention, the null control signal may control the gain control signal at a section of the null signal.  
         [0033]     In the other embodiment of the present invention, the null control signal may control the gain control signal to have a consistent signal level at the section of the null signal.  
         [0034]     In the other embodiment of the present invention, the signal level may be a signal level of the gain control signal prior to receiving the null signal.  
         [0035]     In the other embodiment of the present invention, the first RF signal of the first LNA may comprise a signal at a Band-III frequency band ranging between about 174 MHz and about 245 MHz, and the second RF signal of the second LNA may comprise a signal at an L-band frequency band ranging between about 1,450 MHz and about 1,492 MHz.  
         [0036]     The configuration according to the other embodiment of the present invention allows the removal of the SAW filter without degrading the performance of the receiver and simultaneously the receipt of the signals at the two frequency bands. Thus, the manufacturing cost can be reduced and the easier single-chip implementation can be achieved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]     The invention will be described in detail with reference to the following drawings in which like numerals refer to like elements.  
         [0038]      FIG. 1  illustrates a simplified block diagram of a conventional receiver using a SAW filter.  
         [0039]      FIG. 2  illustrates a simplified block diagram of a T-DMB and DAB low IF receiver according to an embodiment of the present invention;  
         [0040]      FIG. 3  illustrates a simplified block diagram of a dual band T-DMB and DAB low IF receiver according to an embodiment of the present invention; and  
         [0041]      FIG. 4  illustrates a control signal and a received signal including a null section in the case of using a T-DMB and DAB low IF receiver or a dual band T-DMB and DAB low IF receiver according to an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0042]     Exemplary embodiments of the present invention will be described in a more detailed manner with reference to the drawings.  
         [0043]      FIG. 2  illustrates a simplified block diagram of a T-DMB and DAB low IF receiver according to an embodiment of the present invention.  
         [0044]     The receiver comprises an LNA  202 , an image rejection down-conversion mixer  203 , a low pass filter  204 , an amplifier  205 , a local oscillator  208 , a phase-locked loop  209 , and an AGC  211 . The receiver is particularly a T-DMB and DAB low IF receiver in which the LNA  202 , the image rejection down-conversion mixer  203 , the low pass filter  204 , the amplifier  205 , the local oscillator  208 , the phase-locked loop  209 , and the AGC  211  are integrated into a single chip, i.e., a receiver chip  206 .  
         [0045]     An antenna  201  receives a RF signal and transmits the RF signal to the LNA  202  to suppress a noise signal and amplify the RF signal. An output signal of the LNA  202  is transmitted to the image rejection down-conversion mixer  203  that removes an image frequency component and performs a down-conversion of a frequency band of the RF signal into a low IF band.  
         [0046]     The low pass filter  204  that filters a signal at the low frequency band receives an output signal of the image rejection down-conversion mixer  203 . An output signal of the low pass filter  204  is transmitted to the amplifier  205 , and the demodulator  207  receives an output signal of the amplifier  205 .  
         [0047]     The local oscillator  208  generates a frequency that allows the down-conversion of the RF signal into the low IF signal by the image rejection down-conversion mixer  203 . The generated frequency is provided to the image rejection down-conversion mixer  203 . The phase-locked loop  209  supplies a signal to the local oscillator  208  to move and lock the frequency generated by the local oscillator  208 .  
         [0048]     The AGC  211  controls amplification gains of the LNA  202  and the amplifier  205 .  
         [0049]     The receiver receives a signal that is attenuated as passing through channels. Particularly, the attenuation level varies depending on the receipt conditions.  
         [0050]     The AGC  211  maintains a certain intensity level of the signal by controlling the amplification gains of the LNA  202  and the amplifier  205 .  
         [0051]     For a signal at a certain frequency band, an information contained signal section is not often consecutive, and an information contained section and a null section that does not contain information coexist. The magnitude of the signal at the null section is usually smaller than that at the information contained section. If the AGC  211  operates at the null section as same as at the information contained section, the amplification gain of the LNA  202  or the amplifier  205  at the null section increases, and the increasing amplification gain is maintained even at the information contained section after the null section. As a result, it is often difficult to obtain an appropriate level of the amplification.  
         [0052]     The AGC  211  supplies the LNA  202  or the amplifier  205  with a gain control signal that can maintain a consistent level of the amplification gain of the LNA  202  or the amplifier  205  according to the magnitude of the RF signal inputted to the receiver.  
         [0053]     A null control signal CTL controls the gain control signal according to the null section of the RF signal inputted to the receiver.  
         [0054]     More specifically, the null control signal CTL controls the gain control signal based on the null section, and the amplification gain of the LNA  202  or the amplifier  205  according to the magnitude of the signal.  
         [0055]     Although  FIG. 2  illustrates the case that the null control signal CTL is supplied from outside of the receiver chip  206 , the null control signal CTL may be generated inside of the receiver chip  206 .  
         [0056]     Due to the gain control signal and the null control signal CTL, the gain of the LNA  202   b  or the amplifier  205   b  can be maintained at a consistent level.  
         [0057]     Therefore, the null control signal CTL stops the AGC  211  from controlling the amplification gain of the LNA  202  or the amplifier  205  during the receipt of the null signal, or maintains a consistent level of a certain gain control signal or a gain control signal prior to receiving a null symbol. That is, the null control signal CTL controls the amplification gain not to increase abnormally at the null section.  
         [0058]     Detailed description of the null signal will be provided in  FIG. 4  later.  
         [0059]     Although not illustrated, a portion  210  marked with a dotted line in  FIG. 2  comprises a high pass filter, and thus, the SAW filter can be removed without degrading the performance of the receiver.  
         [0060]     Hence, the high pass filter may be provided in multiple numbers (e.g., more than one) at any regions within the dotted portion  210 . At least one high pass filter may be placed at a terminal next to the image rejection down-conversion mixer  203  or the low pass filter  204 .  
         [0061]     The high pass filter (not shown) removes the low frequency components of the image rejection down-conversion mixer  203 , the low pass filter  204  and the amplifier  205 .  
         [0062]     The cut-off frequency of the high pass filter is about 0.192 MHz or less.  
         [0063]     A guard band is set between the frequency bands to separate usage bands of the individual signals. Although a range of the frequency at the guard band varies form country to country using a frequency resource, the guard band generally has a minimum frequency of about 0.192 MHz or 0.176 MHz.  
         [0064]     In the present embodiment, the cut-off frequency of the high pass filter is set at about 0.192 MHz or less. Thus, the high pass filter can filter a signal of a desired channel from signals provided from adjacent channels while rejection a DC signal.  
         [0065]     On the basis of the above-described configuration, the SAW filter can be removed without degrading the performance of the receiver. Thus, the receiver can be manufactured at low costs and easily integrated into a single chip.  
         [0066]     The high pass filter is to remove a DC component that is usually generated during several processes including the amplification of the RF signal received at the antenna  201  and the mixing.  
         [0067]     The high pass filter may also function as a DC offset calibrator that calibrates a DC offset because the DC offset calibrator has a function as the high pass filter.  
         [0068]     Generally, the DC offset calibrator detects the DC offset at an output terminal of a receiver; generates a DC offset calibration signal based on the DC offset detection; and supplies the DC offset calibration signal to a DC offset compensated amplifier of the DC offset calibrator to thereby remove the DC offset.  
         [0069]     The removal of the DC offset by the DC offset calibrator provides substantially the same effect as the removal of a frequency component at the low frequency band by the high pass filter.  
         [0070]     The DC offset calibrator can generate a loop within the receiver, and the loop type DC offset calibrator can remove the frequency component at the low frequency band as similar to the high pass filter.  
         [0071]     The DC offset calibrator as described above is one exemplary type, and can be configured in various types within the receiver.  
         [0072]     The cut-off frequency of the DC offset calibration loop within the DC offset calibrator is about 0.192 MHz or less.  
         [0073]     The LNA  202  and the amplifier  205  may comprise a programmable gain amplifier or a variable gain amplifier.  
         [0074]     According to the embodiment of the present invention, the T-DMB and DAB low IF receiver receives a range of frequencies at the Band-III of the frequency spectrum between about 174 MHz and about 245 MHz or at the L-band of the frequency spectrum between about 1,450 MHz and about 1,492 MHz and supplies a range of frequencies between about 0.768 MHz and about 0.960 MHz as a center frequency to the output terminal of the receiver.  
         [0075]     A band width of the frequency at the output terminal of the receiver in the present embodiment is about 1.536 MHz. The frequency at the output terminal of the receiver according to the embodiment of the present invention is limited to about 768 kHz or more because a part of the frequency component at the output terminal of the receiver is likely to enter into a negative frequency region when the center frequency is about 768 kHz or less in the case that the band width of the frequency at the output terminal of the receiver is about 1.536 MHz.  
         [0076]     Also, according to the embodiment of the present invention, the center frequency at the output terminal of the receiver is limited to about 0.960 MHz (i.e., the upper limit). The reason for setting this upper limit is because when the center frequency is about 0.960 MHz or more, adjacent signals may be pertained to the intended signal since the guard band has a frequency of about 0.192 MHz or 0.176 MHz.  
         [0077]     Particularly, the output terminal of the receiver chip  206  may have a center frequency of about 850 kHz.  
         [0078]     The demodulator  207  receives a signal of the output terminal of the receiver.  
         [0079]      FIG. 3  illustrates a simplified block diagram of a dual band T-DMB and DAB low IF receiver according to another embodiment of the present invention.  
         [0080]     The receiver comprises a first LNA  302 , a second LNA  312 , an image rejection down-conversion mixer  303 , a low pass filter  304 , an amplifier  305 , a local oscillator  308 , a phase-locked loop  309 , and an AGC  313 . The receiver is particularly a dual band T-DMB and DAB low IF receiver in which the first and second LNAs  302  and  312 , the image rejection down-conversion mixer  303 , the low pass filter  304 , the amplifier  305 , the local oscillator  308 , the phase-locked loop  309 , and the AGC  313  are integrated into a single chip, i.e., a receiver chip  306 .  
         [0081]     A first antenna  301  receives a first RF signal and transmits the first RF signal to the first LNA  302  to suppress a noise signal and amplify the first RF signal. A second antenna  31  receives a second RF signal and transmits the second RF signal to the second LNA  312  to suppress a noise signal and amplify the second RF signal.  
         [0082]     An output signal of the first LNA  302  and an output signal of the second LNA  312  are transmitted to the image rejection down-conversion mixer  303  that removes an image frequency component and performs the down-conversion of a frequency band pertained to each of the first and second RF signals into a low IF band.  
         [0083]     The low pass filter  304  that filters a signal at the low frequency band receives an output signal of the image rejection down-conversion mixer  303 . An output signal of the low pass filter  304  is transmitted to the amplifier  305 , and the demodulator  307  receives an output signal of the amplifier  305 .  
         [0084]     The local oscillator  308  generates a frequency that allows the down-conversion of the first and second RF signals into the low IF signal by the image rejection down-conversion mixer  303 . The generated frequency is provided to the image rejection down-conversion mixer  303 . The phase-locked loop  309  supplies a signal to the local oscillator  308  to move and lock the frequency generated by the local oscillator  308 .  
         [0085]     The AGC  313  controls amplification gains of the first and second LNAs  302  and  312  and the amplifier  305 .  
         [0086]     The receiver receives a signal that is attenuated as passing through channels. Particularly, the attenuation level varies depending on the receipt conditions.  
         [0087]     The AGC  313  maintains a certain intensity level of the signal by controlling the amplification gains of the first and second LNAs  302  and  312  and the amplifier  305 .  
         [0088]     For a signal at a certain frequency band, an information contained signal section is not often consecutive, and an information contained section and a null section that does not contain information coexist. The magnitude of the signal at the null section is usually smaller than that at the information contained section. If the AGC  313  operates at the null section as same as at the information contained section, the amplification gain of the first and second LNAs  302  and  312  or the amplifier  305  at the null section increases, and the increasing amplification gain is maintained even at the information contained section after the null section. As a result, it is often difficult to obtain an appropriate level of the amplification.  
         [0089]     The AGC  313  supplies the first and second LNAs  302  and  312  or the amplifier  305  with a gain control signal that can maintain a consistent level of the amplification gain of the first and second LNAs  302  and  312  or the amplifier  305  according to the magnitude of each of the first and second RF signals inputted to the receiver.  
         [0090]     A null control signal CTL controls the gain control signal according to the null section of each of the first and second RF signals inputted to the receiver.  
         [0091]     More specifically, the null control signal CTL controls the gain control signal based on the null section, and the amplification gain of the first and second LNAs  302  and  312  or the amplifier  305  according to the magnitude of the signal.  
         [0092]     Although  FIG. 3  illustrates the case that the null control signal CTL is supplied from outside of the receiver chip  306 , the null control signal CTL may be generated inside of the receiver chip  306 .  
         [0093]     Due to the gain control signal and the null control signal CTL, the gain of the first and second LNAs  302  and  312  or the amplifier  305  can be maintained at a consistent level.  
         [0094]     Therefore, the null control signal CTL stops the AGC  313  from controlling the amplification gain of the first and second LNAs  302  and  312  or the amplifier  305  during the receipt of the null signal, or maintains a consistent level of a certain gain control signal or a gain control signal prior to receiving a null symbol. That is, the null control signal CTL controls the amplification gain not to increase abnormally at the null section.  
         [0095]     Detailed description of the null signal will be provided in  FIG. 4  later.  
         [0096]     Although not illustrated, a portion  310  marked with a dotted line in  FIG. 3  comprises a high pass filter, and thus, the SAW filter can be removed without degrading the performance of the receiver.  
         [0097]     Hence, the high pass filter may be provided in multiple numbers (e.g., more than one) at any regions within the dotted portion  310 . At least one high pass filter may be placed at a terminal next to the image rejection down-conversion mixer  303  or the low pass filter  304 .  
         [0098]     The high pass filter (not shown) confined within the dotted portion  310  removes the low frequency components of the image rejection down-conversion mixer  303 , the low pass filter  304  and the amplifier  305 . On the basis of the above-described configuration, the SAW filter can be removed without degrading the performance of the receiver. Thus, the receiver can be manufactured at low costs and can be easily integrated into a single chip.  
         [0099]     The high pass filter is to remove a DC component that is usually generated during several processes including the amplification of the first and second RF signals received respectively at the first and second antennas  301  and  311  and the mixing.  
         [0100]     The above-described configuration allows the removal of the SAW filter without degrading the performance of the receiver, and thus, the manufacturing cost can be reduced and the receiver can be easily integrated into a single chip.  
         [0101]     The cut-off frequency of the high pass filter is about 0.192 MHz or less.  
         [0102]     A guard band is set between the frequency bands to separate usage bands of the individual signals. Although a range of the frequency at the guard band varies form country to country using a frequency resource, a minimum frequency value of the guard band is generally about 0.192 MHz or 0.176 MHz.  
         [0103]     In the present embodiment, the cut-off frequency of the high pass filter is set at about 0.192 MHz or less. Thus, the high pass filter can filter a signal of a desired channel from signals provided from adjacent channels while rejection a DC signal.  
         [0104]     The aforementioned high pass filter may also function as a DC offset calibrator because the DC offset calibrator has a function as the high pass filter.  
         [0105]     Generally, the DC offset calibrator detects the DC offset at an output terminal of a receiver; generates a DC offset calibration signal based on the DC offset detection; and supplies the DC offset calibration signal to a DC offset compensated amplifier of the DC offset calibrator to thereby remove the DC offset.  
         [0106]     The removal of the DC offset by the DC offset calibrator provides substantially the same effect as the removal of a frequency component at the low frequency band by the high pass filter.  
         [0107]     The DC offset calibrator can generate a loop within the receiver, and the loop type DC offset calibrator can remove the frequency component at the low frequency band as similar to the high pass filter.  
         [0108]     The DC offset calibrator as described above is one exemplary type, and can be configured in various types within the receiver.  
         [0109]     The cut-off frequency of the DC offset calibration loop within the DC offset calibrator is about 0.192 MHz or less.  
         [0110]     The first and second LNAs  302  and  312  and the amplifier  305  may comprise a programmable gain amplifier or a variable gain amplifier.  
         [0111]     According to the present invention, the first antenna  301  of the dual band T-DMB and DAB low IF receiver particularly receives a range of frequencies at the Band-III of the frequency spectrum, and the second antenna  311  thereof receives a range of frequencies at the L-band of the frequency spectrum. The first and second antennas  301  and  311  performs the down-conversion of the received signal frequencies into a center frequency ranging from about 0.768 MHz to about 0.960 MHz, and this center frequency is supplied to an output terminal of the receiver.  
         [0112]     A band width of the frequency at the output terminal of the receiver in the present embodiment is about 1.536 MHz. The frequency at the output terminal of the receiver according to the other embodiment of the present invention is limited to about 768 kHz or more because a part of the frequency component at the output terminal of the receiver is likely to enter into a negative frequency region when the center frequency is about 768 kHz or less in the case that the band width of the frequency at the output terminal of the receiver is about 1.536 MHz.  
         [0113]     Also, according to the other embodiment of the present invention, the center frequency at the output terminal of the receiver is limited to about 0.960 MHz (i.e., the upper limit). The reason for setting this upper limit is because when the center frequency is about 0.960 MHz or more, adjacent signals may also be comprised since the guard band has the minimum frequency of about 0.192 MHz or 0.176 MHz according to the specification set differently from country to country using a frequency resource.  
         [0114]     The phase-locked loop  309  transmits the signal to allow the down-conversion of the received signal frequency at the Band-III or at the L-band into the center frequency ranging from about 0.768 MHz to about 0.960 MHz and then the transmission of the converted signal to the output terminal of the receiver.  
         [0115]     Therefore, the dual band T-DMB and DAB low IF receiver according to the other embodiment of the present invention receives the signals at the two frequency bands (i.e., the Band-III band and the L-band).  
         [0116]     In the case of receiving the signal at the Band-III of the frequency spectrum, the signal goes sequentially through the first antenna  301 , the first LNA  302 , the image rejection down-conversion mixer  303 , the low pass filter  304 , and the amplifier  305 . In the case of receiving the signal at the L-band of the frequency spectrum, the signal goes through the second antenna  311 , the second LNA  312 , the image rejection down-conversion mixer  303 , the low pass filter  304 , and the amplifier  305 .  
         [0117]     Particularly, the output terminal of the receiver chip  306  may have a center frequency of about 850 kHz.  
         [0118]     The demodulator  307  receives a signal of the output terminal of the receiver.  
         [0119]      FIG. 4  illustrates a null control signal and a received RF signal including a null section in the case of using a dual band T-DMB and DAB low IF receiver according to an embodiment of the present invention.  
         [0120]      FIG. 4  illustrates the null control signal and the received RF signal including the null section to describe the embodiments illustrated in  FIGS. 2 and 3 , and thus, can be applied commonly to  FIGS. 2 and 3 . Particularly, the null control signal is labeled as “Control signal” in  FIG. 4 .  
         [0121]     The description provided herein below is based on the embodiment described in  FIG. 3 .  
         [0122]     In  FIG. 4 , the received RF signal (i.e., the first RF signal or the second RF signal) comprises information contained sections  401   a  and  401   b  and the null section  402 . The received RF signal is labeled as “Received signal.” 
         [0123]     Depending on the intensity of the received RF signal Received signal, the gain control signal that controls the amplification gains of the first and second LNAs  302  and  312  and the amplifier  305  is supplied to the first and second LNAs,  302  and  312  and the amplifier  305 .  
         [0124]     Based on the null section comprised in the received RF signal Received signal, the null control signal Control signal controls the gain control signal, which is supplied to the first and second LNAs  302  and  312  and the amplifier  305 .  
         [0125]     The null control signal Control signal may be supplied from inside or outside of the receiver  306 .  
         [0126]     The null control signal Control signal according to the present embodiment turns on at a section defined before and after the start of the null section  402  and turns off at a section defined before and after the end of the null section  402 .  
         [0127]     It will be apparent for those skilled in the art that the null control signal Control signal that controls the gain control signal can also be controlled by other methods in addition to the above-described turn-on/off method.  
         [0128]     If the null control signal Control signal turns on right before the end of the information contained section  401   a  or  401   b,  the null control signal Control signal controls the gain control signal to be a certain gain control signal.  
         [0129]     Particularly, the null control signal Control signal controls the gain control signal to maintain a predetermined consistent signal level.  
         [0130]     The predetermined consistent signal level may be a signal level of the gain control signal that makes the signal level or the amplification gain value become ‘1’ right before the end of the information contained section  401   a  or  401   b.  The value ‘1’ means a disallowed state of the amplification of the received RF signal.  
         [0131]     The above control of the gain control signal by the null control signal Control signal can reduce an abnormal increase in the amplification gain at the null section  402 .  
         [0132]     According to various embodiments of the present invention, the T-DMB and DAB low IF receiver can reduce the manufacturing costs and allow an easier implementation of the single chip integration process by being able to remove the conventional SAW filter.  
         [0133]     According to various embodiments of the present invention, the dual band T-DMB and DAB low IF receiver can receive the signals at the two frequency bands and remove the conventional SAW filter. Thus, the manufacturing costs can be reduced, and the receiver can be easily integrated into a single chip.  
         [0134]     According to various embodiments of the present invention, the T-DMB and DAB low IF receiver can maintain the magnitude of the received signal at a consistent level.  
         [0135]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.