GB2361595A

GB2361595A - Switching circuit of a radio frequency module in a set-top box for preventing interference between a two-way communication path and a modulated signal

Info

Publication number: GB2361595A
Application number: GB0105576A
Authority: GB
Inventors: Jong Jin Lee
Original assignee: Samsung Electro Mechanics Co Ltd
Current assignee: Samsung Electro Mechanics Co Ltd
Priority date: 2000-03-30
Filing date: 2001-03-07
Publication date: 2001-10-24
Anticipated expiration: 2021-03-07
Also published as: GB2361595B; DE10111441A1; GB0105576D0; DE10111441B4

Abstract

A switching circuit of a radio frequency module (figure 5) for a cable set-top box (STB) including a radio frequency modulator 42 for modulating audio/video signals into a television signal. The switching circuit comprises a radio frequency input connector RF-in for connecting the switching circuit to a radio frequency cable, a cable connector CA-out1 for connecting the switching circuit to a cable modem tuner, a first signal distributor 41-1 having its input terminal connected to the radio frequency input connector and its first output terminal connected to the cable connector and at its second output terminal , a high pass filter 41-2 having its input terminal connected to the second output terminal of the first signal distributor, a tuner connector int-out for connecting the switching circuit to an internal tuner of the radio frequency module for the cable set-top box, a second signal distributor 41-4 for distributing an output signal from the high pass filter to its first output terminal connected to the tuner connector and at its second output terminal a mixer 41-6 having its first input terminal connected to the second output terminal of the second signal distributor and its second input terminal connected to an output terminal of the radio frequency modulator, and a radio frequency output connector connected to a television for transmitting an output signal from the mixer to the television. The apparatus is for preventing interference between a two-way communication path and a modulated signal, i.e. allowing communication between a STB and a cable network without interfering with a television signal received from the cable network.

Description

2361595 SWITCHING CIRCUIT OF RADIO FREQUENCY MODULE IN CABLE SET-TOP BOX

BACKGROUND OF THE INVENTION 5 Field of the Invention

The present invention relates in general to switching circuits of radio frequency modules in cable set-top boxes, and more particularly to a switching circuit of a radio frequency modulator in a cable set-top box, which is capable of being readily connected to a cable modem tuner for two-way communication and preventing an interference between signals transmitted and received and an interference between a communicated signal and a modulated signal.

Description of the Prior Art

In USA and other countries,, a cable or Internet set-top box is generally employed which allows a television to receive a ground-wave broadcast, satellite broadcast,, Internet broadcast., etc. via a single cable. This cable set-top box generally comprises a tuner for tuning the set-top box to a desired channel to receive a broadcasting signal of the desired channel through a cable, a channel demodulator for demodulating an output signal from the tuner into audio and video (AN) signals, and a radio frequency (RF) modulator for mixing the AN signals from the channel demodulator with an output signal from a VTR, DVD or etc. and transmitting the resulting signal to a television.

With reference to Fig. 1, there is shown in block form an internal 30 construction of a conventional set-top box. As shown in this drawing, the I conventional set-top box comprises a tuner 14, channel demodulator 15 and RF modulator 16 as mentioned above) which are made in individual chassis independently of one another. The tuner 14, channel demodulator 15 and RF modulator 16 made in individual chassis are then assembled in 5 a'main board of the set-top box.

Fig. 2 shows transmission and reception frequency bands of the conventional set-top box of Fig. 1, based on, for example, a cable. As shown in this drawing, the reception frequency band (RFB) is 47MHz860MHz, covering a ground-wave broadcasting signal, satellite broadcasting signal and Internet broadcasting signal. The transmission frequency band (TFB) is 5MHz-42MHz, covering a signal provided from a cable modem tuner.

Among the above signals, high-power transmission signals (5MHz42MHz) are blocked by first and second high pass filters 12 and 13 in Fig. 1. As a result'. the high-power transmission signals have no effect on the tuner 14 and RF modulator 16.

Fig. 3 is a detailed diagram of a switching circuit in Fig. 1, and Fig. 4 is a view showing the outer appearance of the switching circuit of Fig. 3. As shown in these drawings, the switching circuit includes a first amplifier 16a for amplifying a signal received through a cable, and a distributor 16b for distributing an output signal from the first amplifier 16a. One distributed signal from the distributor 16b is supplied to the tuner, and the other distributed signal from the distributor l6b is amplified by a second amplifier 16c, mixed with an output signal from a modulator l6e by a mixer 16d and then supplied to a television via an RF output connector RF-out.

2 However,, the above-mentioned conventional switching circuit of the RF modulator in the set-top box can-not be readily connected to the cable modem tuner because it has no connector for connection to the cable modem tuner. In this regard, for two-way communication based on the cable modem tuner contained in the set-top box, the conventional switching circuit must be electrically connected to the cable modem tuner via separate wiring, resulting in an inconvenience of use.

As a result, there is a need for a switching circuit to enable two-way 10 communication with no interference between signals transmitted and received and with no interference between a communicated signal and a modulated signal.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem.

In accordance with the present invention, the above and other objects can be accomplished by the provision of a switching circuit of a radio frequency module for a cable set-top box including a radio frequency modulator for modulating audio/video signals into a television signal, comprising a radio frequency input connector for connecting the switching circuit to a radio frequency cable; a cable connector for connecting the switching circuit to a cable modem tuner; a first signal distributor having its input terminal connected to the radio frequency input connector and its first output terminal connected to the cable connector and its second output terminal, the first signal distributor distributing a signal received via the input terminal to the first and second output terminals; a high pass filter having its input terminal connected to the second output terminal of the first signal distributor, the high pass filter passing a signal received 3 through its input terminal at a predetermined frequency band; a tuner connector for connecting the switching circuit to an internal tuner of the radio frequency module for the cable set-top box; a second signal distributor for distributing an output signal from the high pass filter to its first output terminal connected to the tuner connector and its second output terminal; a mixer having its first input terminal connected to the second output terminal of the second signal distributor and its second input terminal connected to an output terminal of the radio frequency modulator, the mixer mixing signals received through its first and second input terminals; and a radio frequency output connector connected to a television for transmitting an output signal from the mixer to the television.

It is an advantage of the present invention to provide a switching circuit of a radio frequency modulator in a cable set-top box, which is capable of being readily connected to a cable modem tuner for two-way communication and preventing an interference between signals transmitted and received and an interference between a communicated signal and a modulated signal, so that the radio frequency modulator can be simply and conveniently connected to the cable modem tuner for two-way communication and have an improved, undesired signal interference exclusion characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will be more clearly understood from the following detailed, non-limiting description taken in conjunction with the accompanying drawings, in which:

Fig. I is a block diagram showing an internal construction of a conventional set-top box; Fig. 2 is a view showing transmission and reception frequency bands of the conventional set-top box of Fig. 1; Fig. 3 is a detailed diagram of a switching circuit in Fig. 1; Fig. 4 is a view showing the outer appearance of the switching circuit of Fig. 3; Fig. 5 is a perspective view showing the outer appearance of a radio frequency module for a cable set-top box to which the present invention is applied; Fig. 6 is a block diagram showing an internal construction of the radio frequency module of Fig. 5; Fig. 7 is a detailed diagram of an embodiment of a switching circuit in Fig. 6; Fig. 8 is a detailed diagram of an alternative embodiment of the switching circuit in Fig. 6; and Fig. 9 is a detailed diagram of another embodiment of the switching circuit in Fig. 6.

DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS In brief, the present invention provides a switching circuit of a radio frequency (RF) module in an NTSC or PAL cable set-top box,. which is capable of being readily connected to a cable modem tuner for two-way communication and preventing an interference between signals transmitted and received and an interference between a communicated signal and a modulated signal.

Fig. 5 is a perspective view showing the outer appearance of an R-F module for a cable set-top box to which the present invention is applied.

As shown in this drawing, installed in the outer part of the RY module for the cable set-top box are an RT input connector RF-in which is provided for connection to a cable to receive a signal via the cable, a cable connector CA-out which transmits the signal received by the RF input connector RF-in to a cable modem tuner of the set-top box, and an RF output connector RF-out which transmits the signal received by the RF input connector RF-in to a television. Input/output pins (IOPs) are arranged on a predetermined portion of the outer part of the RF module for connections to external blocks.

In particular, the RF module for the cable set-top box is connected to the cable modem tuner via the cable connector CA-out such that the signal received via the cable is distributed and transferred to the cable modem tuner via the cable connector CA-out and a signal transmitted from the cable modem tuner is transferred to the RF input connector RF-in via the cable connector CA-out.

With reference to Fig. 6, there is shown in block form an internal construction of the RF module of Fig. 5. As shown in this drawing, the RF module for the cable set-top box comprises a switching circuit 21 for distributing a signal received via the RF input connector RF-in to the cable connector CA-out and a tuner connection terminal int-out, mixing the received signal with an RF-modulated signal and outputting the resulting signal via the RF output connector R.F-out, a tuner 23 for tuning to an output signal from the switching circuit 21, a channel demodulator 24 for demodulating an output signal from the tuner 23 into audio and video signals, and an RF modulator 22 for modulating the audio and video signals from the channel demodulator 24 into a television signal.

The RF modulator 22 is enabled in response to a modulation voltage MB+ 6 to receive audio and video signals AUDIO and VIDEO, a clock signal SCL and a data signal SDA and output a modulated television signal.

In the above manner, the switching circuit is designed to enable two-way communication of the RF module for the cable set-top box and prevent an interference between signals transmitted and received and an interference between a communicated signal and a modulated signal.

Fig. 7 is a detailed diagram of an embodiment of the switching circuit in Fig. 6, Fig. 8 is a detailed diagram of an alternative embodiment of the switching circuit in Fig. 6; and Fig. 9 is a detailed diagram of another embodiment of the switching circuit in Fig. 6.

With reference to Figs. 7 to 9, the switching circuits 21, 31 and 41 commonly include an R-F input connector R-F-in for connecting each switching circuit to an R-F cable, a cable connector CA-out for connecting each switching circuit to a cable modem tuner, and a first signal distributor 21-1 31-1 or 41-1 having its input terminal connected to the RF input connector RF-in and its first output terminal connected to the cable connector CA-out and its second output terminal. The first signal distributor 21-1, 31-1 or 41-1 is adapted to distribute a signal received via its input terminal to its first and second output terminals. A high pass filter 21-2, 31-2 or 41-2 has its input terminal connected to the second output terminal of the first signal distributor 21-1, 3 1 -1 or 41 - 1. The high pass filter 21-2, 31-2 or 41-2 is adapted to pass a signal received through its input terminal at a predetermined frequency band. A tuner connector int-out is provided to connect each switching circuit to an internal tuner of the RF module for the cable set-top box. A second signal distributor 21-4, 31-4 or 41-4 is adapted to distribute an output signal from the high pass filter 21-2, 31-2 or 41-2 to its first output terminal connected to the tuner 7 connector int-out and its second output terminal. A mixer 21-6, 31-6 or 41-6 has its first input terminal connected to the second output terminal of the second signal distributor 21-4, 31-4 or 41-4 and its second input terminal connected to an output terminal of the RF modulator 22, 32 or 42.

The mixer 21-6,, 31-6 or 41-6 is adapted to mix signals received through its first and second input terminals. An RF output connector RF-out is connected to a television to transmit an output signal from the mixer 21-6, 31-6 or 41-6 to the television.

A first control voltage and a second control voltage are supplied from a power supply, not shown, under control of a controller (not shown) of the set-top box. The power supply is adapted to supply a booster voltage and a modulation voltage. In the present embodiment, the booster voltage BB+ may be applied as both the first control voltage and second control voltage. Alternatively, the booster voltage BB+ may be applied as the first control voltage, and the modulation voltage MB+ or a separate control voltage CB+ may be applied as the second control voltage. In this case, the booster voltage BB+ is always supplied and the modulation voltage MB+ or control voltage CB+ is supplied only when the operation of the RF modulator 32 is required.

The above-stated components are provided commonly in the embodiments of Figs. 7 to 9, as shown in those drawings. Next, a description will be given of different components in the embodiments of Figs. 7 to 9.

With reference to Fig. 7, the switching circuit 21 further includes a first amplifier 21-3 having its input terminal connected to an output terminal of the high pass filter 21-2 and its output terminal connected to an input terminal of the second signal distributor 21-4. The first amplifier 21-3 is enabled in response to the first control voltage to amplify an output signal 8 from the high pass filter 21-2. A second amplifier 21-5 has its input terminal connected to the second output terminal of the second signal distributor 21-4 and its output terminal connected to the first input terminal of the mixer 21-6. The second amplifier 21-5 is enabled in response to the second control voltage to amplify an output signal from the second output terminal of the second signal distributor 21-4.

With reference to Fig. 8, the switching circuit 31 further includes an amplifier 31-3 having its input terminal connected to an output terminal of the high pass filter 31-2 and its output terminal connected to an input terminal of the second signal distributor 31-4. The amplifier 31-3 is enabled in response to the first control voltage to amplify an output signal from the high pass filter 31-2. A switch 31-5 is connected between the second output terminal of the second signal distributor 31-4 and the first input terminal of the mixer 31-6 to perform a switching operation in response to the second control voltage.

The switch 31-5 is turned on/off in response to the control voltage CB+ which is supplied synchronously with the modulation voltage MB+.

Namely, the switch 31-5 is turned off if the control voltage CB+ is supplied and on if the control voltage CB+ is not supplied.

With reference to Fig. 9, the switching circuit 41 further includes an amplifier 41-3 having its input terminal connected to an output terminal of the high pass filter 41-2 and its output terminal connected to an input terminal of the second signal distributor 41-4. The amplifier 41-3 is enabled in response to the first control voltage to amplify an output signal from the high pass filter 41-2. A first switch 41-5 is connected between the second output terminal of the second signal distributor 41-4 and the first input terminal of the mixer 41-6 to perform a switching operation in 9 response to the second control voltage. A second switch 41-7 is connected between the output terminal of the RF modulator 42 and the second input terminal of the mixer 41-6 to perform a switching operation in response to the second control voltage.

The first and second switches 41-5 and 41-7 are turned on/off in response to the control voltage CB+ which is supplied synchronously with the modulation voltage MB+. Namely, the first switch 41-5 is turned off if the control voltage CB+ is supplied and on if the control voltage CB+ is not supplied, and the second switch 41-7 is turned on if the control voltage CB+ is supplied and off if the control voltage CB+ is not supplied.

Now, a detailed description will be given of the operation of the switching circuit of the R-F module for the cable set-top box with the above-stated construction in accordance with the present invention with reference to Figs. 5 to 9.

In the present invention, the switching circuit is provided in the RF module for the cable set-top box, as shown in Fig. 6, to enable two-way communication between the set-top box and a cable broadcasting system connected to the set-top box via a cable. For the two-way communication, the switching circuit performs a switching operation between a communicated signal and a modulated signal to prevent an interference therebetween, which will hereinafter be described in detail.

First, with reference to Fig. 7, the booster voltage BB+ is applied as the first and second control voltages. This booster voltage BB+ is always supplied to the first and second amplifiers 21-3 and 21-5. The modulation voltage MB+ is supplied only when the operation of the RF modulator 22 is required.

According to the first embodiment of the present invention, in the switching circuit 21, the first signal distributor 21-1 distributes a signal received via the RF input connector RF-in to its first and second output terminals. The output signal from the first output terminal of the first signal distributor 21-1 is supplied to the cable modem tuner via the cable connector CA-out. Further, the first signal distributor 21-1 receives a signal transmitted from the cable modem tuner via the cable connector CA-out and transfers the received signal to the RF input connector RF-in.

10.

If the modulation voltage MB+ is not supplied, the RF modulator 22 is not enabled. The output signal from the second output terminal of the first signal distributor 21-1 is supplied to the first amplifier 21-3 through the high pass filter 21-2. At this time, an output signal from the cable modem tuner,- transmitted via the cable connector CA-out, is transferred to the RF input connector RF-in by the first signal distributor 21-1, but it is blocked by the high pass filter 21-2 such that it is not transferred to the first amplifier 21-3. This has the effect of preventing an interference between signals transmitted and received.

Tbe. first amplifier 21-3 amplifies the output signal from the high pass filter 21-2 and transfers the amplified signal to the second signal distributor 21-4, which then. distributes the transferred signal to its first and second output terminals. The output signal from the first output terminal of the second signal distributor 21-4 is transferred to the internal tuner 23 via the tuner connection terminal int-out, and the output signal from the second output terminal of the second signal distributor 21-4 is amplified by the second amplifier 21-5 and then transmitted to the television via the mixer 21-6 and RT output connector RF-out.

11 On the other hand) in the case where the modulation voltage MB+ is supplied, the RF modulator 22 is enabled to modulate input audio/video signals and feed the resulting signal to the mixer 21-6, which then transmits the modulated signal to the television via the RF output. 5 connector RF-out.

With reference to Fig. 8, the booster voltage BB+ is applied as the first control voltage, and the control voltage CB+ is applied as the second control voltage. The booster voltage BB+ is always supplied to the amplifier 31-3. The control voltage CB+ is supplied to the switch 31-5 synchronously with the modulation voltage MB+.

The switching circuit 31 of the second embodiffient is partially the same in operation as the switching circuit 21 of the first embodiment, stated above.

That is,, the process from the first signal distributor 21-1 to the second signal distributor 21-4 in Fig. 7 is the same as that from the first signal distributor 3 1 -1 to the second signal distributor 31-4 in Fig. 8. Therefore, a description of the same process will be omitted. Also, the operation of the R-F modulator is performed in the same manner in the first and second embodiments and a description thereof will thus be omitted.

According to the second embodiment of the present invention, in the switching circuit 31, the second signal distributor. 31-4 distributes the output signal from the amplifier 31-3 to its fist and second output terminals. The output signal from the first output terminal of the second signal distributor 31-4 is transferred to the internal tuner via the tuner connection terminal int-out.

In the case where the modulation voltage MB+ is not supplied, namely, the control voltage CB+ is not supplied, the switch 31-5 is turned on to 12 transfer the output signal from the second output terminal of the second signal. distributor 31-4 to the mixer 31-6, which then transmits the transferred signal to the television via the RF output connector RF-out.

Alternatively, if the modulation voltage MB+ is supplied, namely, the control voltage CB+ is supplied, the switch 31-5 is turned off, thereby causing the connection between the second signal distributor 31-4 and the mixer 31-6 to be cut off. At this time, the RF modulator 32 is enabled to modulate input audio/video signals and feed the resulting signal to the television through the mixer 31-6 and RF output connector RF-out.

In this manner, the switch 31-5 is turned on/off according to whether the control voltage CB+ is supplied. This switching operation has the effect of preventing an interference between the output signal from the second output terminal of the second signal distributor 31-4 and the output signal from the RF modulator 32, thereby improving the quality of the output signal from the R-F modulator 32.

Similarly to the second embodiment of Fig. 8, in the third embodiment of Fig. 9,,' the booster voltage BB+ is applied as the first control voltage, and the control voltage CB+ is applied as the second control voltage. The booster voltage BB+ is always supplied to the amplifier 41-3. The control voltage CB+ is supplied to the first and second switches 41-5 and 41-7 synchronously with the modulation voltage MB+.

According to the third embodiment of the present invention, in the switching circuit 41, the second signal distributor 41-4 distributes the output signal from the amplifier 41-3 to its first and second output terminals. The output signal from the first output terminal of the second signal distributor 41-4 is transferred to the internal tuner via the tuner 13 connection terminal int-out.

In the case where the control voltage CB+ is not supplied, the first switch 41-5 is turned on. and the second switch 41-7 is turned off. As a result, the output signal from the second output terminal of the second signal distributor 41-4 is transferred through the first switch 41-5 to the mixer 41-6, which then transmits the transferred signal to the television via the RF output connector RF-out. Also, the output signal from the RF modulator 42 is blocked by the second switch 41-7.

Alternatively, if the control voltage CB+ is supplied, the first switch 41-5 is turned off and the second switch 41-7 is turned on, thereby causing the connection between the second signal distributor 41-4 and the mixer 41-6 to be cut off. At this time, the RF modulator 42 is.enabled to modulate input audio/video signals and feed the resulting signal to the television through the second switch 41-7, mixer 41-6 and RF output connector RFout.

In this manner, the first and second switches 41-5 and 41-7 are alternately 20 turned on/off according to whether the modulation voltage MB+ or control voltage CB+ is supplied. These alternating switching operations have the effect of more certainly preventing an interference between the output signal from the second output terminal of the second signal distributor 41 4 and the output signal from the RF modulator 42, thereby improving the quality of the output signal from the RF modulator 42.

The above-described switching circuit of the RF module for the set-top box is applicable to NITSC, PAL and SECOM systems.

As apparent from the above description, a radio frequency module for a

14 cable set-top box having a switching circuit of the present invention can be simply and conveniently connected to a cable modem tuner for two-way communication. Further,, the present switching circuit prevents an interference between signals transmitted.and received and an interference between a communicated signal and a modulated signal. Therefore, this switching circuit has the effect of improving an undesired signal interference exclusion characteristic.

Although the preferred embodiments of the present invention have been 10 disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope of the invention.

Claims

1. A switching circuit of a radio frequency module for a cable set-top box including a radio frequency modulator for modulating audio/video signals into a television signal, comprising: a radio frequency input connector for connecting said switching circuit to a radio frequency cable; a cable connector for connecting said switching circuit to a cable modem tuner; a first signal distributor having its input terminal connected to said radio frequency input connector and its first output terminal connected to said cable connector and its second output terminal, said first signal distributor distributing a signal received v4a said input terminal to said first and second output terminals; a high pass filter having its input terminal connected to said second output terminal of said first signal distributor, said high pass filter passing a signal received through its input terminal at a predetermined frequency band; a tuner connector for connecting said switching circuit to an internal tuner of the radio frequency module for the cable set-top box; a second signal distributor for distributing an output signal from said high pass filter to its first output terminal connected to said tuner connector and its second output terminal; a mixer having its first input terminal connected to said second output terminal of said second signal distributor and its second input terminal connected to an output terminal of said radio frequency modulator, said mixer mixing signals received through its first and second input terminals; and a radio frequency output connector connected to a television for transmitting an output signal from said mixer to the television.

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2. The switching circuit as set forth in Claim 1, further comprising: a first amplifier having its input terminal connected to an output terminal of said high pass filter and its output terminal connected to an input terminal of said second signal distributor, said first amplifier being enabled in response to a first control voltage to amplify the output signal from said high pass filter; and a second amplifier having its input terminal connected to said second output terminal of said second signal distributor and its output terminal connected to said first input terminal of said mixer, said second amplifier being enabled in response to a second control voltage to amplify an output signal from said second output terminal of said second signal distributor.

3. The switching circuit as set forth in Claim 1, further comprising:

an amplifier having its input terminal connected to an output terminal of said high pass filter and its output terminal connected to an input terminal of said second signal distributor, said amplifier being enabled in response to a first control voltage to amplify the output signal from said high pass filter; and a switch connected between said second output terminal of said second signal distributor and said first input terminal of said mixer for performing a switching operation in response to a second control voltage.

4. The switching circuit as set forth in Claim 1, further comprising:

an amplifier having its input terminal connected to an output terminal of said high pass filter and its output terminal connected to an input terminal of said second signal distributor, said amplifier being enabled in response to a first control voltage to amplify the output signal from said high pass filter; 17 a first switch connected between said second output terminal of said second signal distributor and said first input terminal of said mixer for performing a switching operation in response to a second control voltage; and a second switch connected between said output terminal of said radio frequency modulator and said second input terminal of said mixer for performing a switching operation in response to said second control voltage.

5. A switching circuit generally. as herein described, with reference to and/or as illustrated in Figures 5 to 9 of the accompanying drawings.

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