JP3954426B2 - Remodulator and digital receiver incorporating the remodulator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a BS signal that is being broadcast in a digital format in a BS digital broadcast or a terrestrial digital broadcast that is scheduled to be carried out, various data signals, and a signal (digital) added with various messages generated inside a receiver. The present invention relates to a remodulator that remodulates a carrier wave with a signal and generates an amplitude-modulated wave of a residual sideband similar to an analog terrestrial broadcast wave, and a digital tuner or a digital receiver incorporating the remodulator.
[0002]
[Prior art]
Conventionally, there is no remodulator that remodulates the received radio wave of BS digital broadcasting as a digital signal (without converting it to an analog signal) and generates an amplitude-modulated wave of a residual sideband similar to an analog terrestrial broadcast wave. It was.
[0003]
In addition, if there is a digital tuner or digital receiver in which such a remodulator is incorporated, the amplitude modulation wave of the residual sideband obtained from the digital modulator is used in an analog television receiver currently used in ordinary homes. Although digital broadcasting contents can be distributed and enjoyed, such a digital tuner or digital receiver has not yet existed.
[0004]
[Problems to be solved by the invention]
In a digital tuner or a digital receiver, since the video signal demodulated inside the apparatus is a digital signal, when a residual sideband amplitude modulated wave similar to the NTSC broadcast wave is generated from the demodulated digital signal, It is necessary to convert a digital signal to an analog signal once by a D / A converter. As a result, the remodulator must be configured by an analog circuit, and the frequency of the modulated high frequency signal becomes unstable. there were.
[0005]
In addition, a general remodulator has a problem that a channel for outputting a modulated wave is limited to a specific channel. The reason is that modulation of high-frequency signals involves generation of unnecessary signals in addition to the desired signal, but the conventional method requires a number of filters for removing each channel or the number corresponding to it. Because.
[0006]
An object of the present invention is to provide a remodulator that solves the conventional problems such as the frequency of a high-frequency signal after modulation becomes unstable or the channel that outputs a modulated wave is limited to a specific channel, and the remodulation thereof. It is to provide a digital receiver incorporating the vessel.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present inventor has incorporated into a digital tuner or a digital receiver, and as a result of earnestly studying what a remodulator should be used for the above-described purpose, It is most desirable to directly modulate (remodulate) the carrier wave with a digital signal demodulated inside the receiver or a digital signal with some other signal added thereto, in order to solve the above-mentioned problems in the prior art. paying attention to, the present invention re-modulator, and is obtained by constituting the digital receiver incorporating the re-modulator.
[0008]
In other words, re-modulator according to the present invention receives a video output signal of the MPEG decoder, an NTSC encoder that generates an NTSC signal in the form of digital signals, they receive the output signal and the digital carrier signal of the NTSC encoder A digital amplitude modulation circuit that multiplies both signals and generates an amplitude modulated wave in the form of a digital signal, and a digital that receives the output signal of the digital amplitude modulation circuit and forms the band of the signal into a residual sideband of the NTSC signal VSB filter, first D / A converter that converts the output signal of the digital VSB filter into an analog signal, first analog BPF that limits the band of the output signal of the first D / A converter, audio of the MPEG decoder audio decoder for generating a digital audio signal by receiving the output signal, the output signal of voice decoder and digital Digital frequency modulation circuit that receives a digital carrier signal and frequency modulates the digital carrier signal with the output signal of the audio decoder to generate a frequency modulated wave in the form of a digital signal, and the output signal of the digital frequency modulation circuit is analog A second D / A converter for converting into a signal, a second analog BPF for band-limiting the output signal of the second D / A converter, and an output signal of the first analog BPF and the second analog BPF It is characterized by comprising a mixing circuit for receiving and mixing the output signals.
[0009]
Further, by the present invention Lud digital receiver is characterized in that incorporating a re-modulator according to the present invention.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on an embodiment of the invention with reference to the accompanying drawings.
An embodiment of a remodulator according to the present invention described below forms part of a BS digital tuner and generates a TV signal being broadcast in BS digital broadcasting, various data signals, and an internal receiver. It is assumed that the remodulator generates a VHF or UHF television broadcast wave (residual sideband amplitude modulated wave) by modulating (remodulating) a carrier wave with a signal (digital signal) to which a message is added.
In the above, the BS digital tuner may be a BS digital receiver.
Furthermore, the BS digital tuner and the BS digital receiver may be a terrestrial digital tuner or a terrestrial digital receiver when terrestrial digital broadcasting is performed.
[0011]
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 modulation unit, and 8 is NTSC encoder, 9 is an amplitude modulation circuit, 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 LPF, 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 divider, 23 is a mixer, 24 is an oscillator, 25 is an analog BPF, and 26 is a mixer , 27 is an oscillator, and 28 is a CPU.
IN represents an input terminal, and OUT-1 to OUT-5 represent output terminals.
[0012]
The operation will be described.
The BS-IF signal is applied to the input terminal IN of the BS digital tuner 1 and supplied to the front end 2. In the front end 2, a 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.
[0013]
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 the decoded video signal to the video processing / graphics 5. Video processing / graphics 5 is a component signal obtained by combining video signals such as video signals and data broadcast signals among signals decoded by the MPEG decoder 4 and various messages generated in the receiver in a specific format. Is output in the form of
[0014]
The video signal synthesized by the video processing / graphics 5 is converted from a digital signal to an analog signal by the D / A converter / LPF 6 and is connected to the terminal from the output terminal OUT-1 called a so-called D terminal. Is output to the machine.
Up to this point, this is the circuit part inherent in the existing BS digital tuner.
[0015]
Except for the NTSC encoder, the part described below is a part newly added to the BS digital tuner according to the present invention.
On the other hand, the output signal (component signal) of the video processing / graphics 5 is also supplied to the video modulation unit 7 constituting the remodulator of the present invention.
The video modulation unit 7 includes an NTSC encoder 8, an amplitude modulation circuit 9, and a digital VSB filter 10.
[0016]
In the video modulation unit 7, the digital video component signal supplied to the NTSC encoder 8 is encoded in the same circuit, but 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, and is 6.0 MHz in this embodiment.
[0017]
Since the amplitude-modulated wave generated by the amplitude modulation circuit 9 is an amplitude-modulated wave in both sidebands, it is passed through the digital VSB filter 10 and spectrally shaped into an amplitude-modulated wave in the residual sideband. The digital VSB filter 10 is configured by a normally used transversal filter, and its tap coefficient is controlled by the CPU 28.
[0018]
In the present embodiment, since the video carrier frequency at the output of the amplitude modulation circuit 9 is 6 MHz, the maximum frequency of the signal that passes is 10.2 MHz. Therefore, the digital VSB filter 10 needs to have a performance of passing a signal having a frequency up to 10.2 MHz.
[0019]
The output signal of the digital VSB filter 10 is applied to the changeover contacts h1 and h2 of the changeover switch SW1, and the changeover operation of the changeover switch SW1 is interlocked with that of the changeover switch SW2. That is, when the amplitude-modulated video signal is output from the BS digital tuner 1, the movable piece of the changeover switch SW1 is brought down to the contact point h2, and the movable piece of the changeover switch SW2 is brought down to the contact point i1 side. When a baseband NTSC signal is output from the BS digital tuner 1, the movable piece of the changeover switch SW1 is brought down to the contact point h1, and the movable piece of the changeover switch SW2 is brought down to the contact point i2.
[0020]
First, a case where an 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. It is converted into a sideband amplitude modulated wave. The converted analog residual sideband amplitude-modulated wave is supplied to the analog BPF 12 when the movable piece of the changeover switch SW2 is tilted toward the contact i1, and an unintended signal is removed there.
[0021]
Next, a case where a baseband NTSC signal is output from the BS 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 it is converted into an NTSC signal in the form of an analog signal. Converted. The converted NTSC signal in the form of an analog signal is supplied to the analog LPF 13 when the movable piece of the changeover switch SW2 is tilted to the contact i2 side, where an unintended signal is removed and output from the output terminal OUT-3. Is done.
[0022]
Here, processing of the audio signal will be described.
The audio signal decoded by the MPEG decoder 4 is supplied to the audio modulation unit 14.
Here, the audio modulation unit 14 includes an audio decoder 15 and a frequency modulation circuit 17.
[0023]
The audio signal decoded by the MPEG decoder 4 is supplied to the audio decoder 15 in the audio modulation unit 14 to obtain a decoded digital audio signal. The audio signal is converted from a digital signal to an analog signal by the D / A converter / LPF 16 and output from the output terminal OUT-2.
[0024]
On the other hand, the digital audio signal decoded by the audio decoder 15 is supplied to the frequency modulation circuit 17, and a frequency-modulated sine wave having a frequency of 10.5 MHz generated by the CPU 28 is frequency-modulated by the supplied signal. Generate a frequency-modulated wave.
[0025]
The frequency modulation 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 cascaded analog BPF 19.
[0026]
The frequency modulation wave (audio signal) that has been converted to an analog signal and from which unnecessary signals have been removed and the amplitude modulation wave (video signal) that is the output signal of the analog BPF 12 are supplied to the mixing circuit 20 and synthesized. The output signal of the mixing circuit 20 has a video carrier frequency of 6.0 MHz and an audio carrier frequency of 10.5 MHz. The signal bandwidth is a residual sideband of 4.75 to 10.75 MHz.
[0027]
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 output signal of the distributor 22) is combined with a local oscillation signal having a frequency of 2,306 MHz oscillated by the oscillator 24, and the frequency of the video carrier is converted to a signal of 2,300 MHz. It is supplied to the analog BPF 25.
Note that the analog BPF 25 is for removing unnecessary signals generated during signal synthesis in the mixer 23.
[0028]
The output signal of the analog BPF 25 is supplied to the mixer 26. In the mixer 26, the supplied signal (output signal of the BPF 25) is combined with a local oscillation signal having a frequency of 391.9 MHz oscillated by the oscillator 27, and a signal having a video carrier frequency of 91.25 MHz (one channel). TV signal) and output from the output terminal OUT-4.
[0029]
In the above, in order to set the frequency of the video carrier wave of the signal output from the output terminal OUT-4 to 91.25 MHz, the frequency oscillated by the oscillator 27 is set to 2,391.25 MHz. By setting a frequency higher than the oscillation frequency of the oscillator 24 (this oscillation frequency is fixed to 2,306 MHz) by the frequency of the video carrier as the oscillation frequency of the oscillator 27, a television signal having a desired video carrier frequency can be obtained. can get.
[0030]
In the present embodiment, the frequency conversion from the signal having the intermediate frequency of 6.0 MHz, which is the output signal of the mixer 20, by the two heterodynes is performed for each channel with respect to the signal output from the output terminal OUT-4. This is to eliminate the need to equip the filter with a filter.
[0031]
The output terminal OUT-5 is a terminal for taking out the output signal of the distributor 22 as it is. The above-mentioned video carrier frequency is 6.0 MHz, the audio carrier frequency is 10.5 MHz, and the bandwidth is 4.75 to 10.5. A 75 MHz residual sideband television signal is extracted. The extracted signal can be converted to a VHF / UHF television broadcast wave band by another frequency converter installed outside the BS digital tuner 1.
[0032]
Finally, the present invention is, in addition to the re-modulator described above, digital receiver incorporating the re-modulator is intended to cover (respectively for BS and terrestrial broadcast).
[0033]
【The invention's effect】
At present, commercially available BS digital tuners already process NTSC encoding as digital signals, and digital terrestrial broadcasting digital tuners that are scheduled to be implemented will have the same configuration. The remodulator of the present invention is highly compatible with a digital tuner or a digital receiver having such a circuit configuration, and is convenient for achieving no adjustment.
[0034]
Also, digital receiver incorporating the present invention re-modulator, it is conceivable to use as AM retransmission apparatus of a BS digital broadcasting and terrestrial digital broadcasting, the digital modulation unit, a high frequency stability In addition, it is advantageous in that it is easy to adjust the VA ratio (video / audio level ratio) when transmitting to the common reception facility through the adjacent channel.
[0035]
Further, according to the remodulator of the present invention, since the conventional remodulator is a double sideband amplitude modulation, it is a residual bandband amplitude modulation, so that the obtained signal is received by a home analog television receiver. There is no problem when receiving with the machine.
[0036]
Further, according to the remodulator of the present invention, the target signal frequency was obtained by directly modulating a high-frequency sine wave without using an intermediate frequency in the conventional method. Since the signal is an intermediate frequency signal having a constant frequency, output at an arbitrary frequency is facilitated.
[Brief description of the drawings]
FIG. 1 shows a remodulator according to the invention in a block diagram.
[Explanation of symbols]
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 Unit 8 NTSC Encoder 9 Amplitude Modulation Circuit 10 Digital VSB Filter 11 D / A Converter 12 Analog BPF
13 Analog LPF
14 Audio Modulation Unit 15 Audio Decoder 16 D / A Converter / LPF
17 Frequency modulation circuit 18 D / A converter 19 Analog BPF
20 Mixing Circuit 21 Amplifier 22 Divider 23 Mixer 24 Oscillator 25 Analog BPF
26 Mixer 27 Oscillator 28 CPU
IN input terminal SW-1, SW-2 selector switch OUT-1, OUT-2, OUT-3, OUT-4, OUT-5 Output terminal

Claims (2)

Receives the video output signal of the MPEG decoder, NTSC encoder that generates an NTSC signal in the form of digital signals,
A digital amplitude modulation circuit that receives an output signal of the NTSC encoder and a digital carrier signal, multiplies both signals, and generates an amplitude modulated wave in the form of a digital signal;
A digital VSB filter that receives an output signal of the digital amplitude modulation circuit and forms a band of the signal into a residual sideband of the NTSC signal;
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;
Audio decoder for generating a digital audio signal by receiving the audio output signal of the MPEG decoder,
A digital frequency modulation circuit that receives an output signal of the audio decoder and a digital carrier signal, frequency-modulates the digital carrier signal with the output signal of the audio decoder, and generates a frequency-modulated wave in the form of a digital signal;
A second D / A converter for converting an 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 a mixing circuit for receiving and mixing the output signal of the first analog BPF and the output signal of the second analog BPF Remodulator characterized by comprising .   A digital receiver comprising the remodulator according to claim 1.

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