Abstract:
An active antenna, the electrical length of which can be varied with the use of an inductor coil and which has an amplification circuit, is provided. The active antenna comprises a passive antenna module, which receives a signal within a predetermined frequency band and adjusts an electrical length thereof; and an amplification circuit, which amplifies a signal output from the passive antenna module at an antenna port and transmits the amplified signal to a digital broadcast receiver. The active antenna obtains a high signal-to-noise ratio by amplifying the signal at the antenna port in a digital broadcast receiver, which receives data-in-national television system committee (dNTSC).

Description:
[0001]     This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2003-0082230 filed on Nov. 19, 2003 in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an antenna for receiving wireless signals, and more particularly, to an active antenna with an inherent amplifier, the electrical length of which can be adjusted by using inductor coils.  
         [0004]     2. Description of the Related Art  
         [0005]     Currently in North America, the National Television System Committee (NTSC) broadcast system has been adopted for analog TV broadcasting, and the Advanced Television System Committee (ATSC) broadcast system has been adopted for digital TV broadcasting. A data-in-NTSC (dNTSC) video broadcast, in which digital signals are interleaved into an NTSC band and broadcasted, is carried out in VHF-H bands. Outdoor antenna or indoor antenna models have been used for VHF-H band antennas for receiving dNTSC video broadcasts. Indoor antennas may be more convenient than outdoor antennas because it is easier to connect an indoor antenna to a digital set-top box (STB), which is necessary for receiving digital broadcasts, than to connect an outdoor antenna to a digital STB.  
         [0006]      FIG. 1  illustrates a frequency spectrum based on the dNTSC system in a VHF-H band. An analog broadcast signal  100  and a digital broadcast signal  200  are carried on a carrier after being modulated using a double side band (DSB) modulation method. In the NTSC broadcast system, the analog broadcast signal  100 , the frequency of which ranges between f cl  and f ch , is carried on a carrier and then broadcast. In the dNTSC broadcast system, the digital broadcast signal  200 , i.e., a dNTSC data signal, which is beyond the frequency band of the analog broadcast signal  100 , is additionally carried on the carrier and then broadcast together with the analog broadcast signal  100 .  
         [0007]      FIG. 2  is a table showing frequencies of various signals shown in  FIG. 1 , which are indicated in different VHF channels 7 through 13. Referring to  FIG. 2 , a carrier wave has a frequency range from about 170 MHz to 220 MHz. Analog broadcast signals in VHF channels 7 through 13 all have a frequency bandwidth of about 0.1 MHz. dNTSC data in VHF channels 7 through 13 all have a frequency bandwidth of about 0.76 MHz.  
         [0008]     An indoor antenna is not suitable for receiving VHF-H band signals which include digital broadcast signals because of many spatial restrictions. In addition, due to these spatial restrictions, it is very difficult to set the size of an antenna according to the desired frequency band and to design the antenna as a dipole antenna, in particular. The length of a dipole antenna amounts to half of the frequency of the dipole antenna. For example, a dipole antenna should have a length of 0.88 m to cover a frequency of 170 MHz (300/170/2=0.88 m). However, an antenna of such size is unsuitable and inconvenient to use indoors. Thus, it is necessary to design an antenna which has the desired electrical length but also occupies a smaller space.  
         [0009]     Signals within a VHF-H band are more likely to be corrupted by noise than signals in a higher frequency band. Thus, it is necessary to amplify the signals in the VHF-H band in order to obtain a higher signal-to-noise ratio (SNR). Since signals amplified at the antenna port of a digital broadcast receiver are more likely to have a higher signal-to-noise ratio than the signals amplified in other parts of the digital broadcast receiver, it is necessary to develop a digital broadcast receiver which actively amplifies signals using an antenna to obtain a higher SNR.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention provides a VHF-H band antenna of which the electrical length can be increased with the use of serial inductors.  
         [0011]     The present invention also provides a digital receiving apparatus, which can overcome the limitations of a conventional passive antenna and can obtain a high signal-to-noise ratio (SNR) by amplifying signals at an end of an antenna.  
         [0012]     In accordance with an exemplary embodiment of the present invention, there is provided an active antenna comprising a passive antenna module, which receives a signal within a predetermined frequency band that is input spatially by adjusting an electrical length thereof, and an amplification circuit, which amplifies a signal output from the passive antenna module at an antenna port and transmits the amplified signal to a digital broadcast receiver.  
         [0013]     The active antenna further comprises a bias-stabilizing module, which stabilizes a bias voltage applied from the digital broadcast receiver by removing components other than the bias component from the bias voltage.  
         [0014]     The active antenna can also comprise a bias-blocking module, which blocks the bias current generated by the bias voltage applied from the digital broadcast receiver and allows the signal output from the signal-amplifying module pass through the same, and a signal-blocking module, which prevents the signal from being transmitted along a path of the bias current passing through the bias-stabilizing module.  
         [0015]     The active antenna further comprises an electrostatic discharge (ESD) protecting module, which protects the bias voltage applied from the digital broadcast receiver against deleterious electrostatic discharges so that the bias voltage can be maintained at a predetermined level or lower.  
         [0016]     The digital broadcast receiver preferably receives data-in-national television system committee (dNTSC) data transmitted in a VHF-H band.  
         [0017]     The passive antenna module can comprise an inductor coil, which varies the electrical length of the passive antenna module to receive a predetermined signal, a first capacitor, which matches impedance thereof with that of the inductor coil for a predetermined frequency band, and a second capacitor, which serves as a tuning point for the predetermined frequency band.  
         [0018]     The predetermined frequency band is preferably a VHF-H band.  
         [0019]     The signal-amplifying module can comprise a transistor, which amplifies a signal input to a base thereof from the passive antennal module by a predetermined gain and outputs the amplified signal to a collector thereof, and at least one resistor, which controls the bias voltage of the transistor.  
         [0020]     Also, the active antenna can further comprise a capacitor, which matches impedances of the signal output from the passive antenna module and input to the signal amplifying module.  
         [0021]     The bias-stabilizing module can comprise a voltage regulator, which attenuates the noise component included in the bias voltage applied from the digital broadcast receiver, and at least one capacitor, which stabilizes the bias voltage applied thereto.  
         [0022]     The bias-blocking module may serve as a capacitor, which couples signals output from the signal-amplifying module.  
         [0023]     The signal-blocking module preferably includes two inductors.  
         [0024]     The electrostatic discharge (ESD) protecting module is preferably a Zener diode. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The above features, as well as other features and advantages of the present invention, will become more apparent through a detailed description of the exemplary embodiments thereof, with reference to the attached drawings in which:  
         [0026]      FIG. 1  illustrates the frequency spectrum based on the dNTSC broadcast system in a VHF-H band;  
         [0027]      FIG. 2  is a table showing frequencies of various signals shown in  FIG. 1 ;  
         [0028]      FIG. 3  is a block diagram of an active antenna according to an exemplary embodiment of the present invention; and  
         [0029]      FIG. 4  is a schematic circuit diagram of an active antenna according to an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     The present invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. In the drawings, the same reference numerals represent the same elements.  
         [0031]      FIG. 3  is a block diagram of an active antenna according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , a bias current supplied from a receiver (Rx) signal output unit, i.e., a digital broadcast receiver (such as a set-top box), is input to the active antenna  1000  and passes through an electrostatic discharge (ESD) protecting module  900 . The ESD protecting module  900  protects the input voltage against electrostatic discharges so that the input voltage can be maintained at a predetermined level or lower. After passing through the ESD protecting module  900 , the bias current passes through a signal-blocking module  500 . The signal-blocking module  500  prevents the signal output from the signal amplifying module  400  from being transmitted along a bias line, i.e., a path of the bias current passing through a bias-stabilizing module  600 , by impedance mismatching. A bias-blocking module  800  blocks the bias current while allowing AC current pass through the same. Therefore, the bias current output from the ESD protecting module  900  cannot flow in a direction from a portion of a path indicated by “a” to a portion of a path indicated by “d”. Instead, the bias current output from the ESD protecting module  900  flows to the signal-blocking module  500  in a direction from “a” to “b,” as shown in  FIG. 3 .  
         [0032]     A bias current passing through the signal-blocking module  500  is input to the bias-stabilizing module  600 . The bias-stabilizing module  600  stabilizes the bias current input thereto by removing undesired components, such as ripples or noise, from the corresponding bias current. A bias current output from the bias-stabilizing module  600  is input to the signal-amplifying module  400  via the signal-blocking module  500  to then be grounded.  
         [0033]     An input signal path will now be described with reference to  FIG. 3 . A signal is input to the active antenna  1000  via a passive antenna module  300 , which is a conventional passive antenna. The signal passing through the passive antenna module  300  is input to the signal-amplifying module  400 . The signal-amplifying module  400  amplifies the signal input thereto so that the amplified signal becomes compatible with the set-top box. The amplified signal passes through the bias-blocking module  800 . Since the amplified signal is AC current, it can pass through the bias-blocking module  800 , which blocks the bias current and allows the AC current to pass through. The amplified signal passing through the bias-blocking module  800  is not transmitted along a path from “d” to “c”, but is transmitted only to the bias-blocking module  800  because the signal-blocking module  500  prevents the signal from being transmitted along the bias line by impedance mismatching. The signal passing through the bias-blocking module  800  cannot be transmitted in a direction from “b” to “a”, due to the signal-blocking module  500 . Instead, the signal passing through the bias-blocking module  800  is input to the ESD protecting module  900 . A signal passing through the ESD protecting module  900  is finally input to the set-top box as the Rx signal output.  
         [0034]      FIG. 4  is a schematic circuit diagram of the active antenna  1000  according to an exemplary embodiment of the present invention.  
         [0035]     Referring to  FIG. 4 , the passive antenna module  300  is of a passive type, that is, the passive antenna module  300  is composed of substantially passive devices, and comprises a variable inductor coil L 3 , which can vary the electrical length of the passive antenna module  300  in a range between 12 cm and 22 cm. Therefore, the passive antenna module  300  can cover a frequency band from 170 MHz to 220 MHz, i.e., a VHF-H band. In order to increase the SNR in the VHF-H frequency band by impedance matching, a coupling capacitor C 7  is coupled to the variable inductor coil L 3 . The passive antenna module  300  further includes a capacitor C 8 , which serves as a tuning point, and a Zener diode D 1 , which maintains the magnitude of an AC signal input to the active antenna  100  at a predetermined level or lower. A commercially available diode model RLS4148 is preferably used as the Zener diode D 1 .  
         [0036]     A signal is spatially input to the passive antenna module  300  and then transmitted to the signal-amplifying module  400  via the coupling capacitor C 7 . The signal-amplifying module  400  includes a transistor Q 1 , which amplifies the signal input thereto. A voltage of 8 V is applied from the set-top box to the collector in the transistor Q 1 . A resistor R 3  in parallel with a capacitor C 5 , and a resistor R 2  are connected in series between the collector and the base of the transistor Q 1 . The resistors R 2  and R 3  control the bias voltage of the transistor Q 1 . A base voltage is determined by the resistor R 2 , the resistor R 3 , the capacitor C 5 , and properties of the transistor Q 1 . In the illustrative embodiment, a voltage of 0.7 V is applied to the base of the transistor Q 1  and serves as a threshold voltage. A capacitor C 9  matches impedances of the signal output from the passive antenna module  300  to then be input to the signal amplifying module  400 .  
         [0037]     A transistor BFP196LAN, manufactured by SimensAG, can be used as the transistor Q 1 . It is preferable to amplify the signal in the signal amplifying-module  400  located closer to the passive antenna module  300  rather than in the set-top box, because the closer the signal is to the input port of the active antenna  1000 , the less the signal is distorted. Also, a signal with less distortion is more likely to have a high SNR after being amplified. The transistor Q 1  is designed such that its gain becomes 12 dB in the VHF-H band. In this case, the current at the collector of the transistor Q 1  is 50 mA.  
         [0038]     With reference to  FIG. 4 , the signal input to the base of the transistor Q 1  is amplified by a predetermined gain and then output from the collector of the transistor Q 1 . Since the signal output from the collector of the transistor Q 1  is an AC signal, it can pass through the capacitor C 6 . The capacitor C 6  serves as a coupling capacitor, with regard to output signals from the transistor Q 1 . The signal output from the collector of the transistor Q 1  is controlled using an inductor L 1  to perform inductance mismatching so that it cannot be transmitted in a direction from “d” to “c”. A signal passing through the capacitor C 6  is controlled by an inductor L 2  to perform inductance mismatching so that it cannot be transmitted in a direction “a” to “b”. Therefore, the signal passing through the capacitor C 6  is input to the set-top box as the Rx signal output.  
         [0039]     Referring to  FIG. 4 , a bias voltage of 12 V is applied to the Rx signal output port from the set-top box. The bias voltage applied to the Rx signal output port protects the input voltage against sudden electrostatic discharges caused by the Zener diode D 2  so that the input voltage can be maintained at the predetermined level or lower. Like in the Zener diode D 1 , diode model No. RLS4148 can be used as the Zener diode D 2 . Since the bias current passing through the Zener diode D 2  is DC current, it cannot pass through the capacitor C 6  and flow toward the inductor L 2 . A bias current passing through the inductor L 2  is input to a voltage regulator U 1 . The voltage regulator U 1  can be realized as voltage regulator model No. 78L09. The voltage regulator U 1  attenuates the noise component included in the power supply voltage applied from the Rx signal output port, i.e., the set-top box. More specifically, the voltage regulator U 1  stabilizes the bias voltage by removing components other than the bias component from the bias voltage. A bias voltage of 12 V is applied to an input port  1  of the voltage regulator U 1 , and a bias voltage of 9 V is applied to an output port  3  of the voltage regulator U 1 . The bias voltage applied to the output port  3  of the voltage regulator U 1  is dropped to 8 V while passing through the resistor R 1 , so that a bias voltage of 8 V is supplied to the collector of the transistor q 1 . The bias-stabilizing module  600  comprises the voltage regulator U 1  and four capacitors C 1 , C 2 , C 3  and C 4 . Each of the four capacitors C 1  through C 4  stabilizes a bias voltage input thereto.  
         [0040]     Thus, a bias voltage of 8 V is applied to the collector of the transistor Q 1 , and a voltage of 0.7 V is applied to the base of the transistor Q 1 .  
         [0041]     Therefore, the active antenna according to the present invention is better able than a conventional passive antenna to reduce the influence of the length of an antenna on the frequency band that the antenna can cover. Numerous test results show that the present invention can attenuate the variation of frequency with respect to the length of an antenna by variably setting the electrical length of the passive antenna module  300 . Therefore, the active antenna according to the present invention, can serve as a broadband antenna.  
         [0042]     According to the present invention, an indoor antenna responsible for the VHF-H band can be used in a very small space.  
         [0043]     In addition, it is possible to obtain a high signal-to-noise ratio by amplifying dNTSC data at the antenna port in a digital receiver.  
         [0044]     Moreover, the active antenna according to the present invention can reduce the influence of the length of the antenna on the frequency band that the antenna can cover more than a conventional passive antenna. Therefore, the active antenna according to the present invention can serve as a broadband antenna.  
         [0045]     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims. Therefore, the described embodiments are to be considered in all respects only as illustrative and not restrictive to the scope of the invention.