Abstract:
A radio frequency receiver using an auto gain controller, and a radio frequency receiving method. The radio frequency receiving method includes receiving and attenuating a radio frequency signal including one or more inband signals of at least one channel and an inter-band signal between the inband signals according to a predetermined attenuation degree, amplifying an output signal, and measuring a signal-to-noise ratio of the inband signal of a desired channel of the output signal where the inter-band signal adjacent to the desired channel is a representative of an inband noise and controlling the attenuation degree so that the measured signal-to-noise ratio is maintained higher than a previous signal-to-noise ratio.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 2004-58406, filed Jul. 26, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present general inventive concept relates to a radio frequency (RF) receiver and an RF receiving method, and more particularly, to an RF receiver using an auto gain controller (AGC) to increase a signal-to-noise ratio (SNR) of a received signal to optimize a reception of an RF signal, and an RF receiving method thereof.  
         [0004]     2. Description of the Related Art  
         [0005]     8 vestigial side band (VSB) modulated digital broadcasting signals or other broadcasting signals are signals received according to a modulation method of transmitting a signal to a single carrier. Here, several signals of the 8 VSB modulated digital broadcasting signals or the other signals include a multichannel through which a frequency bandwidth varies. Multichannel signals are adjacent to one another in channels. Thus, noise caused due to intermodulation or the like can be a serious problem.  
         [0006]     The ‘intermodulation’ refers to a phenomenon in which a frequency component including a combination of a sum of and a difference between harmonic frequencies of two or more different input frequency signals is output in a process of processing an RF signal including a non-linear device. An intermodulation signal is noise interrupting an original signal and is generally called intermodulation distortion (IMD).  
         [0007]      FIG. 1  is a waveform illustrating a frequency spectrum of a digital broadcasting signal using an 8 VSB transmission method.  
         [0008]     For example, the digital broadcasting signal shown in  FIG. 1  includes only three channels a, b, and c. As shown in  FIG. 1 , the three channels a, b, and c to be selected are referred to as inbands, and two intervals d and e respectively between two channels a and b and between two channels b and c are referred to as inter-bands.  
         [0009]     Intermodulation signals are generated in received neighboring RF signals due to a non-linearity of each device of a receiving system. In the interval e, a dotted line indicates a magnitude of a desired inter-band signal, and a solid line indicates that the magnitude of an inter-band signal is increased by intermodulation. An intermodulation signal does not exist only in an inter-band. Thus, an inband includes noise by the intermodulation signal.  
         [0010]     If a power of the signals of neighboring channels is greater than a power of a signal of a desired channel, this problem gets more serious. Therefore, a precise gain control method is required to improve an SNR so as to accurately select only signals of substantially desired channels.  
       SUMMARY OF THE INVENTION  
       [0011]     In order to solve the foregoing and/or other problems, the present general inventive concept provides an RF receiver using an AGC to attenuate an RF signal depending on a result of measuring an SNR of a received RF signal to improve an SNR, and an RF receiving method thereof.  
         [0012]     Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.  
         [0013]     The foregoing and/or other aspects and advantages of the present general inventive concept may be achieved by providing a radio frequency receiver including an attenuator to receive and attenuate a radio frequency signal including one or more inband signals of at least one channel and an inter-band signal between the inband signals so as to be proportional to a predetermined attenuation degree, an amplifier to amplify a signal output from the attenuator, and a signal-to-noise ratio adjuster measure a signal-to-noise ratio of the inband signal of a desired channel of the signal output from the amplifier and to control the attenuation degree of the attenuator so that the measured signal-to-noise ratio is maintained higher than a previous signal-to-noise ratio.  
         [0014]     If the measured signal-to-noise ratio is higher than the previous signal-to-noise ratio, the signal-to-noise ratio adjuster may increase or decrease the attenuation degree of the attenuator in an identical direction to a previous increase or decrease direction.  
         [0015]     If the measured signal-to-noise ratio is lower than the previous signal-to-noise ratio, the signal-to-noise ratio adjuster may increase or decrease the attenuation degree of the attenuator in an opposite direction to the previous increase or decrease direction.  
         [0016]     If the measured signal-to-noise ratio is higher than the previous signal-to-noise ratio, and the attenuation degree of the attenuator is equal to one of maximum or minimum values, the signal-to-noise ratio adjuster may increase or decrease the attenuation degree of the attenuator in the opposite direction to the previous increase or decrease direction.  
         [0017]     The signal-to-noise ratio adjuster may include a first band pass filter to filter an output signal of the amplifier to separate the inband signal of the desired channel of the received signal, a second band pass filter to filter the output signal of the amplifier to separate the inter-band signal of the received signal adjacent to the inband signal of the desired channel, a first auto gain control detector measure a power of the inband signal separated by the first band pass filter, a second auto gain control detector to measure a power of the inter-band signal separated by the second band pass filter, and a solver measure a signal-to-noise ratio of the inband signal using the power measured by the first auto gain control detector as a power of a signal and the power measured by the second auto gain control detector as a power of noise and to control the attenuation degree of the attenuator according to the measured signal-to-noise ratio.  
         [0018]     The first and second band pass filters may be surface acoustic wave (SAW) filters.  
         [0019]     The radio frequency signal may be a digital television broadcasting signal using an 8 vestigial side band (VSB) method.  
         [0020]     The radio frequency receiver may further include a mixer installed between the amplifier and the signal-to-noise ratio adjuster to receive a signal of a predetermined local oscillator so as to transform a frequency of the received digital broadcasting signal into a frequency bandwidth of a channel to be selected, and a radio frequency filter to filter an output signal of the mixer to separate the broadcasting signal having the frequency bandwidth, and to transmit the separated signal to the signal-to-noise ratio adjuster.  
         [0021]     The foregoing and/or other aspects and advantages of the present general inventive concept may also be achieved by providing a tuner including a radio frequency receiver to control an attenuation degree of a signal according to a signal-to-noise ratio of an inband signal obtained from a power of the inband signal as a power of a signal and a power of an inter-band signal as a power of noise so as to select a desired broadcasting signal of a digital television broadcasting signal using an  8  vestigial side band method.  
         [0022]     The foregoing and/or other aspects and advantages of the present general inventive concept may also be achieved by providing a radio frequency receiving method including receiving and attenuating a radio frequency signal including inband signals of at least one channel and an inter-band signal between the inband signals so as to be proportional to a predetermined attenuation degree amplifying an output signal and measuring a signal-to-noise ratio of an inband signal of a desired channel of the output signal and controlling the attenuation degree so that the measured signal-to-noise ratio is maintained higher than a previous signal-to-noise ratio.  
         [0023]     If the measured signal-to-noise ratio is higher than the previous signal-to-noise ratio, the attenuation degree may be increased or decreased in an identical direction to a previous increase or decrease direction.  
         [0024]     If the measured signal-to-noise ratio is lower than the previous signal-to-noise ratio, the attenuation degree may be increased or decreased in an opposite direction to the previous increase or decrease direction.  
         [0025]     If the measured signal-to-noise ratio is higher than the previous signal-to-noise ratio, and the attenuation degree is equal to one of maximum or minimum values, the attenuation degree may be increased or decreased in the opposite direction to the previous increase or decrease direction.  
         [0026]     The controlling of the attenuation degree may include filtering the amplified signal to separate the inband signal of a desired channel of the received signal and measuring a power of the separated inband signal, filtering the amplified signal to separate an inter-band signal of the received signal adjacent to the inband signal of the desired channel, measuring a power of the separated inter-band signal and measuring a signal-to-noise ratio of the inband signal using the power of the inband signal as a power of a signal and the power of the inter-band signal as a power of noise, and controlling the attenuation degree according to the measured signal-to-noise ratio.  
         [0027]     The powers of the inband and inter-band signals may be separated using surface acoustic wave filters.  
         [0028]     The radio frequency signal may be a digital television broadcasting signal using an 8 vestigial side band method.  
         [0029]     The radio frequency receiving method may further include receiving a signal of a predetermined local oscillator so as to transform a frequency of the received digital broadcasting signal into a frequency bandwidth of a channel to be selected, and filtering an output signal except the broadcasting signal and transmitting the filtered signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0031]      FIG. 1  is a waveform illustrating a frequency spectrum of a conventions digital broadcasting signal using an 8 VSB transmission method;  
         [0032]      FIG. 2  is a block diagram of an RF receiver using an AGC according to an embodiment of the present general inventive concept;  
         [0033]      FIG. 3  is a flowchart illustrating an operation of a solver shown in  FIG. 2 ;  
         [0034]      FIG. 4  is a block diagram of an RF receiver using an AGC according to another embodiment of the present general inventive concept; and  
         [0035]      FIG. 5  is a flowchart illustrating an operation of an RF receiver using an AGC according to an embodiment of the present general inventive concept. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept while referring to the figures.  
         [0037]      FIG. 2  is a block diagram of an RF receiver  200  using an AGC according to an embodiment of the present general inventive concept.  
         [0038]     The RF receiver  200  shown in  FIG. 2  may be installed in a digital broadcasting receiving system using an  8 VSB transmission method. Alternatively, the RF receiver  200  may be installed in a system of receiving a multichannel RF signal transmitted via a single carrier. The RF receiver  200  may be installed in a tuner of an RF receiving system or other devices measuring and improving a signal-to-noise ratio (SNR) of a received signal (input signal).  
         [0039]     Referring to  FIG. 2 , the RF receiver  200  includes an AGC amplifier  210  and an SNR adjuster  230 .  
         [0040]     The AGC amplifier  210  includes an attenuator  211  and an amplifier  213 .  
         [0041]     The attenuator  211  is controlled by the SNR adjuster  230  to attenuate a magnitude of the received signal. The received signal includes a desired signal component combined with a number of undesired signals. However, both the desired signal component and undesired signals are attenuated by the attenuator  211 .  
         [0042]     The amplifier  213  amplifies an output of the attenuator  211  to a desired magnitude.  
         [0043]     In an intermodulation signal that is a noise of a signal, a 3 rd  intermodulation distortion (IMD) is the greatest problem. The intermodulation signal is generated when a signal passes through a non-linear circuit of the amplifier  213  and/or between the amplifier  213  and the SNR adjuster  230 .  
         [0044]     However, if the input signal passes through the non-linear circuit after the attenuation of the attenuator  211 , an output having the 3 rd  IMD is three times more decreased than a desired output signal. Thus, a total SNR is improved.  
         [0045]     The SNR adjuster  230  includes a first band pass filter (BPF)  231 , a second BPF  233 , a first AGC detector  235 , a second AGC detector  237 , and a solver  239 .  
         [0046]     The SNR adjuster  230  measures an SNR of a received channel and controls the attenuator  211  to attenuate a magnitude of input signals and obtain a desired SNR. The SNR adjuster  230  measures a power of an inband instead of accurate noise of the inband to measure a magnitude of noise including the 3rd IMD inserted into the inband.  
         [0047]     The first BPF  231  separates only a signal of a desired inband from a received multichannel signal. The first BPF  231  may be a surface acoustic wave (SAW) filter. The channels a, b, and c shown in  FIG. 1  correspond to inbands from which an inband signal of a desired channel is separated.  
         [0048]     The second BPF  233  separates only an inter-band signal corresponding to noise from the received multichannel signal. The second BPF  233  may be the SAW filter. The intervals d and e shown in  FIG. 1  correspond to inter-bands. If the first BPF  231  filters the inband b, the second BPF  233  filters the inter-band e.  
         [0049]     The first AGC detector  235  measures a power of a signal of the inband separated by the first BPF  231 .  
         [0050]     The second AGC detector  237  measures a power of noise from the inter-band signal separated by the second BPF  233 .  
         [0051]     The solver  239  obtains a ratio of the power of the noise of the inter-band measured by the second AGC detector  237  to the power of the inband signal measured by the first AGC detector  235  to obtain an SNR of the inband so as to control an attenuation degree of the attenuator  211 .  
         [0052]      FIG. 3  is a flowchart illustrating an operation of the solver  239  of  FIG. 2 .  
         [0053]     In operation S 301 , the solver  239  measures an SNR. In operation S 303 , the solver  239  compares the measured SNR with a previous SNR.  
         [0054]     If the solver  239  determines in operation S 303  that the measured SNR is higher than the previous SNR, in operation  305 , the solver  239  determines whether a current attenuation degree of the attenuator  211  is different from a maximum or minimum attenuation degree of the attenuator  211 .  
         [0055]     If the solver  239  determines in operation S 305  that the current attenuation degree is different from the maximum or minimum attenuation degree, in operation S 307 , the solver  239  controls the attenuator  211  to increase the current attenuation degree by one step. That is, if the current attenuation degree is between the maximum value and the minimum value, the attenuation degree is increased by a certain value (one step).  
         [0056]     If the solver  239  determines in operation S 303  that the measured SNR is lower than the previous SNR or determines in operation S 305  that the current attenuation degree reaches the maximum or minimum attenuation degree, in operation S 309 , the solver  239  controls the attenuator  211  to increase the current attenuation degree by one step in an opposite direction to a current attenuation direction of the attenuator  211 . That is, if the current attenuation degree is the same as or not the maximum value and the minimum value, the attenuation degree is changed by a certain value (one step) in the opposite direction. In other words, if the attenuator  211  increases the attenuation degree by the unit of one step, the solver  239  controls the attenuator  211  to lower the attenuation degree by the unit of one step. If the attenuator  211  lowers the attenuation degree by the unit of one step, the solver  239  controls the attenuator  211  to increase the attenuation degree by the unit of one step.  
         [0057]      FIG. 4  is a block diagram of an RF receiver  400  using an AGC according to another embodiment of the present general inventive concept.  
         [0058]     The RF receiver  400  may be used in a tuner or the like to select a signal of a desired channel from a multichannel RF signal. The RF receiver  400  will be described with reference to a digital TV broadcasting receiving system using an  8 VSB modulation method according to the Advanced Television System Committee (ATSC) standards.  
         [0059]     The ATSC standards were adopted by U.S. Federal Communication Commission (FCC) in Dec. 24, 1996 and mainly relate to compression and transmission of video and audio streams. According to the ATSC standards, image signals are compressed with MPEG2, acoustic and voice signals are compressed with AC- 3 , and such signals are transmitted using a VSB transmission technique. In a VSB modulation method, a broadcasting signal is transmitted with a single carrier. A frequency spectrum of a digital broadcasting signal using an 8 VSB transmission method is represented by a waveform shown in  FIG. 1 .  
         [0060]     The RF receiver  400  includes an antenna  401 , an attenuator  211 , an amplifier  213 , a mixer  403 , an RF filter  405 , and an SNR adjuster  230 . The SNR adjuster  230  includes a first BPF  231 , a second BPF  233 , a first AGC detector  235 , a second AGC detector  237 , and a solver  239 .  
         [0061]     The mixer  403  that is a non-linear device and the RF filter  405  are connected between the AGC amplifier  210  and the SNR adjuster  230 . The same reference numerals of the RF receiver  400  as those of the RF receiver  200  denote like elements and thus will not be described herein.  
         [0062]     If a digital TV broadcasting signal is received via the antenna  401 , the attenuator  211  and the amplifier  213  attenuates and amplifies the digital TV broadcasting signal through a feedback of the solver  239 . A frequency of the digital TV broadcasting signal of which gain has been adjusted, is changed by the mixer  403  which has received a frequency of a local oscillator (LO), and then the digital TV broadcasting signal is filtered by the RF filter  405  to be a signal in an intermediate frequency bandwidth.  
         [0063]     The digital TV broadcasting signal having passed through the amplifier  213  passes through the mixer  403  and the RF filter  405  so as to produce an intermodulation signal due to a signal of adjacent channels and nonlinearity of the amplifier  213  and the mixer  403 . A portion of the band intermodulation signal may be removed by the RF filter  405  and first BPF  231 . However, the 3 rd  IMD in the inband is not removed. As a result, an SNR of the received signal may be deteriorated.  
         [0064]     However, the solver  239  measures an SNR via the first and second BPFs  231  and  233  and the first and second AGC detectors  235  and  237  and controls the attenuator  211  to attenuate the received signal based on the measured SNR. That is, all portions of the received signal including the inband signal and the inter-band signal can be attenuated according to the measured SNR. As a result, the magnitude of the noise caused by intermodulation in the inband by the amplifier  213 , the mixer  403 , and the like are considerably reduced, and the SNR improves.  
         [0065]      FIG. 5  is a flowchart illustrating an operation of an RF receiver using an AGC according to an embodiment of the present invention. The operation of the RF receiver  200  has been described with reference to  FIGS. 1 through 4 . However, the RF receiver  400  shown in  FIG. 4  will be exemplarily explained with reference to  FIG. 5 .  
         [0066]     The solver  239  controls the attenuator  211  to attenuate a digital broadcasting signal received via the antenna  401  to a current attenuation degree. The amplifier  213  amplifies the digital broadcasting signal to have the same magnitude as a desired inband signal. In operation S 501 , the mixer  403  and the RF filter  405  changes the amplified digital broadcasting signal into a broadcasting signal in an intermediate frequency bandwidth.  
         [0067]     In operation S 503 , the first BPF  231  filters the digital broadcasting signal to obtain an inband signal of a desired channel.  
         [0068]     In operation S 505 , the second BPF  233  filters the digital broadcasting signal to obtain noise that is representative of an inter-band signal adjacent to the desired channel.  
         [0069]     In operation S 507 , the first and second AGC detectors  235  and  237  measure a power of the inband signal obtained by the first BPF  231  and a power of the noise obtained by the second BPF  233 , respectively.  
         [0070]     In operation S 509 , the solver  239  measures an SNR using the powers measured by the first and second AGC detectors  235  and  237 . In operation S 511 , the solver  239  compares the measured SNR with a previous SNR to control an attenuation degree of the attenuator  211  so as to attenuate the received digital broadcasting signal.  
         [0071]     The operation of an RF receiver using an AGC can be performed according to the above-described process.  
         [0072]     As described above, in an RF receiver using an AGC, and an RF receiving method according to an embodiment of the present general inventive concept, the influence of noise of an intermodulation signal produced by a non-linear device that may be installed in the RF receiver on an RF signal including a multichannel, can be reduced. Also, an SNR of a received signal can be improved.  
         [0073]     Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.