Background Art [2] Generally, a digital TV system includes a digital set top box for receiving a digital signal and a digital TV for outputting a digital image.

[3] The digital set top box includes an amplifying unit for amplifying an RF signal inputted through an antenna, a digital tuner for outputting an image base band signal and a sound base band signal by modulating the amplified RF signal, a microcomputer for outputting a control signal, a power supplying unit for supplying power, an RF modulating unit for converting the image and sound base band signals into image and sound signals using the control signal outputted from the microcomputer, and an RF outputting unit for outputting the modulated image and sound signals to the digital TV.

[4] The digital TV is designed to display a channel signal of a channel by selecting the image and sound signal inputted as an RF input.

[5] In the prior digital set top box, the sound base signal outputted from the digital tuner is however inputted as a monophonic signal into the RF modulating unit and the frequency of the inputted sound signal is modulated to 15 KHz. Therefore, the prior set top box has a problem in that it cannot modulate a high frequency sound stereo signal such as a sound sap signal and a stereophonic signal.

Disclosure of Invention Technical Problem [6] The present invention has been made in an effort to solve the above-described problem. It is an object of the present invention to provide a digital set top box that can perfectly modulate even a sound stereo signal having a high frequency.

[7] It is another object of the present invention to provide a digital set top box that can enable a TV audience to heat a stereo sound by modulating a sound stereo signal such as a monophonic signal (L+R), a sound sap signal, and stereophonic signal (L-R), and a telemetry signal using an RF modulating unit and outputting the modulated signal to the digital TV.

Technical Solution [8] According to an aspect of the present invention, there is provided a digital set top box comprising a digital tuner outputting an image base band signal and a sound base band signal; a controller providing a control signal; a power supplying unit supplying power; a sound stereo encoder receiving the sound and image base band signals from the digital tuner and outputting a reference frequency signal and a sound stereo signal; an RF modulator receiving the reference frequency signal, the sound stereo signal, the image base signal, and the control signal, modulating the signals into image and sound signals and outputting the image and sound signals; and an RF outputting unit outputting the image and sound signals from the RF modulator to a digital TV.

[9] According to another aspect of the present invention, there is provided a digital set top box comprising a power supplying unit supplying power; a digital tuner outputting sound and image base band signals; a sound stereo encoder receiving the sound and image base band signals from the digital tuner and outputting a reference frequency signal and a sound stereo signal; an RF modulator receiving the reference frequency signal, the sound stereo signal, the image base signal, and the control signal and outputting image and sound signals.

[10] According to still another aspect of the present invention, there is provided a digital set top box comprising a digital tuner; a sound stereo encoder encoding sound and image base band signals outputted from the digital tuner to output a reference frequency signal and a sound stereo signal; and an RF modulator modulating the sound stereo signal according to the reference frequency signal into sound and image signals and outputting the sound and image signals to a digital TV.

Advantageous Effects [11] According to a digital set top box of the present invention, it can be possible that all of sound stereo signals are modulated by an RF modulator and outputted to a digital TV.

[12] As a result, the audience can hear all of the sound signals regardless of the format limitation of the sound signal.

Brief Description of the Drawings [13] FIG. 1 is a block diagram of a digital set top box according to the present invention; [14] FIG. 2 is a view illustrating a connection relation between a power line, sound stereo encoder and RF modulator of a digital set top box according to the present invention; and [15] FIG. 3 is a view illustrating a connection relation between a sound stereo encoder and an RF modulator of a digital set top box according to the present invention.

Best Mode for Carrying Out the Invention [16] A digital set top box according to the present invention will be described in more detail in conjunction with the accompanying drawings.

[17] FIG. 1 shows a block diagram of a digital set top box according to the present invention.

[18] Referring to FIG. 1, the inventive digital set top box includes a booster amplifying unit 110, a digital tuner 120, a microcomputer 130, a power supplying unit 140, a sound stereo encoder 150, an RF modulator 160, an RF outputting unit 170.

[19] The booster amplifying unit 110 is designed to amplify an RF signal inputted through an antenna ANT. Although the booster amplifying unit 110 is not the essential element, it can provide an advantage of improving the performance of the set top box by amplifying the signal from the antenna ANT.

[20] The digital tuner 120 is designed to modulate an RF signal inputted through the booster amplifying unit 110 and the RF outputting unit 170 and transmit the modulated RF signal as an image base band signal and a sound base band signal. Here, it should be noted that a wire connecting the RF outputting unit 170 to the digital tuner 120 is omitted in the drawing to avoid the complication of the drawing.

[21] The microcomputer 130 is designed to output a serial data address/serial clock (SDA/SCL) signal that is a control signal. The power supplying unit 140 is designed to supply the power.

[22] The sound stereo encoder 150 is operated by the power supplied from the power supplying unit 140 to output a reference frequency signal and a sound stereo signal by receiving a left/right sound base band signal and a image base band signal that are outputted from the digital tuner 120.

[23] The RF modulator 160 is operated by the power supplied from the power supplying unit 140 to modulate the image base band signal from the digital tuner 120 and a SDA/ SCL signal from the microcomputer 130 and output the signals as the image signal and the sound stereo signal. At this point, the RF is designed to modulate the encoded sound stereo signal using the reference frequency signal. In addition, the RF modulator 160 can be applied to both of UHF and VHF signals. The internal structuree of the RF modulator 160 can be varied according to the signal format. However, it should be noted that the RF modulator 160 is designed functioning to modulate any signals regardless of the signal format.

[24] The RF outputting unit 170 is designed to output the image and sound stereo signals from the RF modulator 160 to the digital TV 200 or output the RF signal from the antenna ANT to the digital tuner 120.

[25] FIG. 2 is a view illustrating a connection relation between the power line and the sound stereo encoder and the RF modulator of the digital set top box according to the present invention.

[26] Referring to FIG. 2, provided on the power line extending from the power supplying unit 140 are a regulator 180 and high capacitors C1, C2 and C3 that can remove a sound hum and stabilize the power by removing noise and ripple.

[27] Disposed between the power line extending from the power supplying unit 140 and the sound stereo encoder 150 are an inductor LI and a capacitor C4 that can remove a sound buzz generated by a horizontal frequency of the image base band signal.

[28] FIG. 3 shows a connection relation between the sound stereo encoder and the RF modulator of a digital set top box according to the present invention.

[29] Referring to FIG. 3, provided between the sound stereo encoder 150 and the RF modulator 160 is a band pass filter 190 that can remove the harmonics of the reference frequency, which are generated in the sound stereo encoder 150.

[30] The operation of the digital set top box according to the present invention will be described hereinafter in more detail.

[31] When the left/right sound base band signal and the image base band signal that are outputted from the digital tuner 120 are inputted to the sound stereo encoder 150, the signals are combined in the sound stereo encoder 150 and outputted as a sound stereo signal. Here, the sound stereo signal includes a mono (monophonic=L+R) signal, a sound sap signal, a stereo sound (stereophonic=L-R) signal, and a telemetry signal.

[32] The sound stereo signal and the reference frequency (4MHz) are inputted from the sound stereo encoder 150 to the RF modulator 160. The image base band signal is inputted from the digital tuner 120 to the RF modulator 160. The RF modulator 160 modulates the inputted signals and outputs the modulated signals to the digital TV through the RF outputting unit 170.

[33] As a result, it becomes possible to hear the stereo sound from the digital TV 200.

[34] Meanwhile, the sound hum is generated from the sound signal of the RF modulator 160 by the noise and ripple contained in the power supplied from the power supplying unit 140 and the sound buzz is generated by the horizontal frequency component (15.734KHz) of the image base band signal outputted from the digital tuner 120.

[35] In order to remove such a variety of noise, by providing the regulator 160 and the high capacitors C1, C2 and C3 on the power line extending from the output of the power supplying unit 140, the generation of the sound hum can be prevented. In addition, by connecting the inductor LI and the capacitor C4 to the power line inputted to the sound stereo encoder 150, the generation of the sound buzz can be prevented.

[36] In addition, when the sound stereo signal is inputted from the sound stereo encoder 150 to the RF modulator 160, since the harmonics are generated in the reference frequency and inputted into the RF modulator 160, the band pass filter 190 is connected between the sound stereo encoder 150 and the RF modulator 160 to prevent the generation of the harmonics.

[37] According to the present invention, since the sound stereo encoder is installed in the digital set top box, all of the sound stereo signals (the mono (monophonic=L+R), sound sap, stereo sound (stereophonic=L+R), and telemetry signals) outputted from the digital tuner are modulated by the RF modulator and outputted to the digital TV, the audience can hear the stereo sound.

[38] In addition, even when the sound stereo encoder is installed in the digital set top box, since the harmonics of the reference frequency can be removed by inserting the band pass filter into the output of the sound stereo encoder and the noise and ripple contained in the power can be removed by the regulator, capacitors and inductor, the audience can hear the more fine sound.

Mode for the Invention [39] The digital set top box is characterized in that the sound stereo encoder for encoding the sound signal is further provided. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Industrial Applicability [40] According to the present invention, by providing the sound stereo encoder in the digital set top box, all of the sound stereo signals outputted from the digital tuner are modulated by the RF modulator and outputted to the digital TV, thereby making it possible for the audience to hear the stereo sound regardless of the sound signal format. <BR> <BR> <P>[41]<BR> [42]