JP2003304461A - Remodulator, and digital tuner or digital receiver incorporating it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid the problem that in a conventional remodulator for remodulating a broadcast wave in a BS digital broadcast into a current analog television wave, the frequency of a high frequency signal after modulation becomes unstable, and/or a channel for outputting a modulated wave is limited to a specific channel, etc. <P>SOLUTION: This remodulator comprises an NTSC encoder 8 for generating an NTSC signal in the form of a digital signal, a digital amplitude modulator circuit 9 for generating an amplitude modulated wave in the form of a digital signal by multiplying the output signal of the NTSC encoder and a digital carrier signal together, a digital VSB filter 10 for forming a residual sideband wave from the output of the digital amplitude modulator circuit, a D/A converter 11, an analog BPF 12, an audio decoder 15 for generating a digital audio signal, a digital frequency modulator circuit 17 for generating a frequency modulated wave in the form of a digital signal from the output signal of the audio decoder and the digital carrier signal, a D/A converter 18, an analog BPF 19, and a mixer circuit 20 for receiving and mixing the output signal of the analog BPF 12 and the output signal of the analog BPF 19. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital television broadcasting signal, various data signals, and various messages generated inside a receiver in BS digital broadcasting and terrestrial digital broadcasting to be implemented. A re-modulator that re-modulates a carrier wave with a signal (digital signal) to which is added to generate an amplitude-modulated wave of a vestigial sideband similar to an analog terrestrial broadcast wave, and a digital tuner or digital device incorporating the re-modulator. Regarding the receiver.

[0002]

2. Description of the Related Art Conventionally, re-modulation is performed by re-modulating a received radio wave of a BS digital broadcast as a digital signal (without converting it into an analog signal) to generate an amplitude-modulated wave of a residual sideband wave similar to an analog terrestrial broadcast wave. There was no vessel.

Further, if there is a digital tuner or digital receiver incorporating such a re-modulator, the amplitude-modulated wave of the residual sideband obtained from the digital tuner or digital receiver is used in an analog television currently used in ordinary households. Although digital broadcast contents can be enjoyed by distributing to receivers, such a digital tuner or digital receiver has not existed yet.

[0004]

In a digital tuner or digital receiver, since the video signal demodulated inside the device is a digital signal, the residual sideband amplitude similar to that of the NTSC broadcast wave is generated from the demodulated digital signal. To generate a modulated wave, it is necessary to convert the digital signal into an analog signal with a D / A converter, and as a result,
There is a problem that the re-modulator has to be configured by an analog circuit and the frequency of the high frequency signal after modulation becomes unstable.

Further, in the general re-modulator, there is a problem that the channel for outputting the modulated wave is limited to a specific channel. The reason for this is that modulation of high-frequency signals involves the generation of unnecessary signals in addition to the desired signal, but in the conventional method, filters to remove them are required for each channel, or a number corresponding thereto. Because.

An object of the present invention is to provide a re-modulator which solves the conventional problems such as the frequency of a modulated high frequency signal becoming unstable and the channel for outputting a modulated wave being limited to a specific channel, and It is to provide a digital tuner or a digital receiver incorporating the remodulator.

[0007]

To achieve the above objectives, the inventor has wondered what a remodulator incorporated into a digital tuner or receiver should be and used for that purpose. As a result of diligent study, the direct carrier wave is modulated (re-modulated) by the digital signal demodulated in the digital tuner or the digital receiver or the digital signal added with some other signal. Focusing on what is most desirable to solve the problems, the present invention provides a remodulator of the present invention and a digital tuner or digital receiver incorporating the remodulator.

That is, the remodulator according to the present invention is
An NTSC encoder that receives a video output signal of an EG decoder or a digital signal obtained by adding another video signal to the output signal to generate an NTSC signal in the form of a digital signal, and receives an output signal of the NTSC encoder and a digital carrier signal Then, the two signals are multiplied to generate an amplitude modulation wave in the form of a digital signal, and the output signal of the digital amplitude modulation circuit is received to change the band of the signal to the residual sideband of the NTSC signal. A digital VSB filter to be formed, a first D / A converter for converting an output signal of the digital VSB filter into an analog signal,
A first analog BPF for band-limiting the output signal of the first D / A converter, a voice output signal of the MPEG decoder or a digital signal obtained by adding another voice signal to the output signal to receive a digital voice signal. An audio decoder for generating, a digital frequency modulation for receiving an output signal of the audio decoder and a digital carrier signal, frequency-modulating the digital carrier signal by the output signal of the audio decoder, and generating a frequency modulated wave in the form of a digital signal. Circuit, a second D / A converter for converting the output signal of the digital frequency modulation circuit into an analog signal, a second analog BPF for band limiting the output signal of the second D / A converter, and the first A mixing circuit for receiving and mixing the output signal of the analog BPF and the output signal of the second analog BPF. It is an feature.

A digital tuner or digital receiver according to the present invention is characterized by incorporating the remodulator according to the present invention.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments of the invention with reference to the accompanying drawings. An embodiment of a re-modulator according to the present invention described below constitutes a part of a BS digital tuner and is generated in a BS digital broadcast television signal, various data signals and a receiver internal signal. It is assumed that the carrier is a remodulator that modulates (remodulates) a carrier wave with a signal (digital signal) to which a message or the like is added to generate a VHF or UHF television broadcast wave (residual sideband amplitude modulation wave). Further, in the above, the BS digital tuner may be a BS digital receiver. Furthermore, BS digital tuner and B
The S digital receiver may be a terrestrial digital tuner or a terrestrial digital receiver when terrestrial digital broadcasting is performed.

FIG. 1 shows a remodulator according to the invention in a block diagram. In FIG. 1, 1 is a BS digital tuner, 2 is a front end, 3 is a TS processor, 4
Is an MPEG decoder, 5 is video processing / graphics,
6 is a D / A converter / LPF, 7 is a video modulator, 8 is an NTSC encoder, 9 is an amplitude modulator, 10 is a digital VSB filter, 11 is a D / A converter, 12 is an analog BPF, 13 is an analog LPF, 14 Is an audio modulator, 15 is an audio decoder, 16 is a D / A converter / L
PF, 17 is a frequency modulation circuit, 18 is a D / A converter, 19 is an analog BPF, 20 is a mixing circuit, 21 is an amplifier, 22 is a distributor, 23 is a mixer, 24 is an oscillator, 2
5 is an analog BPF, 26 is a mixer, 27 is an oscillator, and 28 is a CPU. IN is the input terminal,
Further, OUT-1 to OUT-5 indicate output terminals, respectively.

The operation will be described. BS-IF signal is B
It is applied to the input terminal IN of the S digital tuner 1 and supplied to the front end 2. In the front end 2, the channel selected from the received satellite channels is demodulated. The demodulated signal is supplied to the TS processor 3, from which a TS (transport stream) signal is extracted. The extracted TS signal is supplied to the MPEG decoder 4.

The MPEG decoder 4 decodes the MPEG-encoded video signal, audio signal, data broadcast signal, and various control information from the supplied TS signal and supplies it to the video processing / graphics 5. The video processing / graphics 5 is a component signal obtained by synthesizing a video signal, a data broadcasting signal, and other video-related signals among the signals decoded by the MPEG decoder 4 and various messages generated inside the receiver in a specific format. Output in the form of.

A video signal synthesized by the video processing / graphics 5 is converted from a digital signal to an analog signal by a D / A converter / LPF 6, and is connected to the so-called D terminal from an output terminal OUT-1. Is output to the receiver. Up to this point, the circuit part is originally included in the existing BS digital tuner.

Except for the NTSC encoder, the parts described below are parts newly added to the BS digital tuner according to the present invention. On the other hand, the output signal (component signal) of the image processing / graphics 5 is also supplied to the image modulator 7 constituting the re-modulator of the present invention.
The video modulation section 7 is composed of an NTSC encoder 8, an amplitude modulation circuit 9, and a digital VSB filter 10.

In the video modulator 7, the digital video component signal supplied to the NTSC encoder 8 is
Encoded in the same circuit, the encoded output is an NTSC signal in the form of a digital signal.
The encoded digital NTSC signal is supplied to the amplitude modulation circuit 9, where it is multiplied by a sine wave in the form of a digital signal generated by the CPU 28 to generate an amplitude modulation wave. The frequency of the sine wave signal generated by the CPU 28 is the video carrier frequency of the modulated signal, which is 6.0 MHz in this embodiment.

The amplitude modulation wave generated by the amplitude modulation circuit 9 is a double sideband amplitude modulation wave.
The spectrum is shaped into an amplitude modulation wave of the residual sideband through the B filter 10. The digital VSB filter 10 is composed of a normally used transversal filter, and its tap coefficient is controlled by the CPU 28.

In this embodiment, since the video carrier frequency at the output of the amplitude modulation circuit 9 is 6 MHz, the maximum frequency of the passing signal is 10.2 MHz. Therefore, the digital VSB filter 10 has a frequency of 1
It must have the ability to pass signals up to 0.2 MHz.

The output signal of the digital VSB filter 10 is applied to the switching contacts h1 and h2 of the changeover switch SW1. The changeover operation of the changeover switch SW1 is interlocked with that of the changeover switch SW2. That is, when outputting the amplitude-modulated video signal from the BS digital tuner 1, the movable piece of the changeover switch SW1 is connected to the contact h2.
The movable piece of the changeover switch SW2 is tilted to the contact i1 side. On the other hand, when outputting a so-called baseband NTSC signal from the BS digital tuner 1, the movable piece of the changeover switch SW1 is changed to the contact point h1 and then to the changeover switch. The movable pieces of SW2 are tilted to the contact i2 side.

First, the case where the amplitude-modulated video signal is output from the BS digital tuner 1 will be described. The residual sideband amplitude-modulated wave of the video signal spectrum-shaped by the digital VSB filter 10 is supplied to the D / A converter 11 when the movable piece of the changeover switch SW1 is tilted to the contact h2 side, and the residual analog signal is left there. Converted to sideband amplitude modulated waves. In the converted analog residual sideband amplitude-modulated wave, the movable piece of the changeover switch SW2 contacts the contact i1.
When the signal is tilted to the side, the signal is supplied to the analog BPF 12, where an unintended signal is removed.

Next, the baseband NTSC signal is converted to BS.
The case of outputting from the digital tuner 1 will be described. The NTSC signal in the form of a digital signal encoded by the NTSC encoder 8 is supplied to the D / A converter 11 when the movable piece of the changeover switch SW1 is tilted to the contact h1 side, where the NT in the form of an analog signal is provided.
Converted to SC signal. The converted NTSC signal in the form of an analog signal is supplied to the analog LPF 13 by moving the movable piece of the changeover switch SW2 to the contact i2 side, where an unintended signal is removed, and the output terminal OU is removed.
It is output from T-3.

Now, the processing of the audio signal will be described. The audio signal decoded by the MPEG decoder 4 is supplied to the audio modulator 14. Here, the voice modulator 1
Reference numeral 4 is composed of an audio decoder 15 and a frequency modulation circuit 17.

The audio signal decoded by the MPEG decoder 4 is supplied to the audio decoder 15 in the audio modulator 14 to obtain a decoded digital audio signal. This audio signal is converted from a digital signal to an analog signal by the D / A converter / LPF 16 and output terminal O
It is output from UT-2.

On the other hand, the digital audio signal decoded by the audio decoder 15 is supplied to the frequency modulation circuit 17, and the supplied signal frequency-modulates a digital sine wave having a frequency of 10.5 MHz generated in the CPU 28. Then, a frequency modulated wave is generated.

The frequency-modulated wave generated by the frequency modulation circuit 17 is converted into an analog signal by the D / A converter 18, and unnecessary signals are removed by the analog BPF 19 connected in cascade.

A frequency-modulated wave (audio signal) converted into an analog signal from which unnecessary signals are removed, and an amplitude-modulated wave (video signal) which is an output signal of the analog BPF 12 described above.
And are supplied to the mixing circuit 20 to be combined. As the output signal of the mixing circuit 20, the frequency of the video carrier is 6.0 MH.
z, the frequency of the sound carrier is 10.5 MHz. Moreover, the bandwidth of the signal is 4.75 to 10.75 MHz.
Is the residual sideband.

The output signal of the mixing circuit 20 is amplified by the amplifier 21, passed through the distributor 22, and then supplied to the mixer 23. In the mixer 23, the supplied signal (the distributor 2
2 output signal) is the frequency 2, 3 oscillated by the oscillator 24
It is combined with the local oscillation signal of 06MHz, the frequency of the video carrier is converted into the signal of 2,300MHz, and the analog B
It is supplied to the PF 25. The analog BPF 25 is
This is for removing unnecessary signals generated when signals are combined in the mixer 23.

The output signal of the analog BPF 25 is supplied to the mixer 26. In the mixer 26, the supplied signal (the output signal of the BPF 25) is combined with the local oscillation signal of the frequency 2,391.25 MHz oscillated by the oscillator 27, and the signal of the video carrier frequency of 91.25 MHz (one channel TV signal) and output terminal O
It is output from UT-4.

In the above, the frequency of the video carrier of the signal output from the output terminal OUT-4 is 91.25 MH.
In order to set z, the frequency to be oscillated by the oscillator 27 is 2,
The frequency is 391.25 MHz, but this is set by setting the frequency higher than the oscillation frequency of the oscillator 24 (this oscillation frequency is fixed to 2,306 MHz) by the frequency of the desired output video carrier as the oscillation frequency of the oscillator 27. , A television signal having the frequency of any desired video carrier is obtained.

Further, in the present embodiment, the frequency conversion from the signal of the intermediate frequency of 6.0 MHz which is the output signal of the mixer 20 by the two heterodynes is applied to the signal output from the output terminal OUT-4. , To eliminate the need to equip a filter for each channel.

The output terminal OUT-5 is a terminal for taking out the output signal of the distributor 22 as it is, and the frequency of the video carrier is 6.0 MHz, the frequency of the audio carrier is 10.5 MHz, and the bandwidth is 4.75. ~ 10.75MHz
The television signal in the vestigial sideband of is extracted. The extracted signal can be frequency-converted into VHF and UHF television broadcast wave bands by another frequency converter installed outside the BS digital tuner 1.

Finally, the present invention includes, in addition to the remodulator described above, a digital tuner or digital receiver (for BS and terrestrial broadcasting, respectively) incorporating the remodulator.

[0033]

The BS digital tuner currently on the market has already processed the NTSC encoding up to the digital signal as it is, and the digital tuner for terrestrial digital broadcasting which is scheduled to be implemented will have the same configuration. Since it can be considered, the remodulator of the present invention has a high affinity with a digital tuner or a digital receiver having such a circuit configuration, and is convenient for achieving no adjustment.

A digital tuner or digital receiver incorporating the re-modulator of the present invention may be used as an AM re-transmission device for BS digital broadcasting or terrestrial digital broadcasting. High frequency stability can be ensured and VA ratio (level ratio of video and audio) even when transmitting to the joint reception equipment on adjacent channels.
It has the advantage that it is easy to adjust.

Further, according to the re-modulator of the present invention, the conventional re-modulator is the double sideband amplitude modulation, whereas the remodulator is the residual band-zone amplitude modulation. There is no problem when receiving with an analog TV receiver.

Further, according to the remodulator of the present invention, the frequency of the target signal is obtained by directly modulating the high frequency sine wave without using the intermediate frequency in the conventional method. Since the modulated signal is an intermediate frequency signal having a constant frequency, it is easy to output at an arbitrary frequency.

[Brief description of drawings]

FIG. 1 shows a remodulator according to the invention in a block diagram.

[Description of Codes] 1 BS Digital Tuner 2 Front End 3 TS Processor 4 MPEG Decoder 5 Video Processing / Graphics 6 D / A Converter / LPF 7 Video Modulation Section 8 NTSC Encoder 9 Amplitude Modulation Circuit 10 Digital VSB Filter 11 D / A Converter 12 Analog BPF 13 Analog LPF 14 Voice modulator 15 Voice decoder 16 D / A converter / LPF 17 Frequency modulator 18 D / A converter 19 Analog BPF 20 Mixer 21 Amplifier 22 Distributor 23 Mixer 24 Oscillator 25 Analog BPF 26 Mixer 27 oscillator 28 CPU IN input terminal SW-1, SW-2 changeover switch OUT-1, OUT-2, OUT-3, OUT-4, O
UT-5 output terminal

Claims (2)

[Claims] 1. An NTSC encoder for receiving a video output signal of an MPEG decoder or a digital signal obtained by adding another video signal to the output signal to generate an NTSC signal in the form of a digital signal, and an output signal of the NTSC encoder. A digital amplitude modulation circuit that receives a digital carrier signal and multiplies both of these signals to generate an amplitude modulation wave in the form of a digital signal, receives an output signal of the digital amplitude modulation circuit, and sets the band of the signal to an NTSC signal V formed on the residual sideband of the
SB filter, first D / A converter for converting the output signal of the digital VSB filter into an analog signal, first analog BPF for band limiting the output signal of the first D / A converter, audio of the MPEG decoder An audio decoder that receives an output signal or a digital signal obtained by adding another audio signal to the output signal to generate a digital audio signal, receives an output signal of the audio decoder and a digital carrier signal, and outputs the digital carrier signal A digital frequency modulation circuit that frequency-modulates the output signal of the audio decoder to generate a frequency-modulated wave in the form of a digital signal; a second D / A converter that converts the output signal of the digital frequency modulation circuit into an analog signal; Second analog BPF for band limiting the output signal of the second D / A converter, and the first analog BPF. Log BPF
Of the second analog BPF and a mixing circuit for receiving and mixing the output signal of the second analog BPF. 2. A digital tuner or a digital receiver incorporating the remodulator according to claim 1.