JP2559418B2 - Frequency shift circuit and method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a frequency shift circuit and method, and more particularly to a frequency of a high definition signal suitable for signal processing of a high definition television compatible with a current television. A shift circuit and method.

[Conventional technology]

High-definition signals with a high frequency of image signals are frequency-converted by frequency shift into the signal band of the current television and superimposed and transmitted, and as a method of returning to the original frequency on the receiving side and realizing high-definition images, There is one disclosed in JP-A-59-171387. In this method, a frequency shift is realized by subjecting a carrier wave to a carrier suppression amplitude modulation with a high-definition signal.

[Problems to be solved by the invention]

The above frequency shift is possible with an analog signal, but recently, it is often realized in the form of a digital signal. At this time, since the signal spectrum also exists in the harmonic of the sampling frequency _s , the amplitude modulation with the carrier causes
These harmonic components are mixed in the original signal band, and depending on the setting of the carrier, the frequency band width of the high-definition signal that can be superimposed is narrowed.

An object of the present invention is to effectively remove a mixed component of a harmonic component of a sampling frequency _s into an original signal band due to amplitude modulation, and thereby a frequency shift circuit having a wide frequency bandwidth that can be superimposed as a high definition signal. And to provide a method.

[Means for solving problems]

The purpose is to separate a high-definition signal into signals in a plurality of frequency bands, perform amplitude modulation on each of the separated high-definition signals, and remove a component in which a harmonic component of _s is mixed in the original signal band. This is achieved by extracting the respective frequency-shifted high-definition signals and adding them.

[Action]

The sampling frequency _s is 4 times 4 times the color subcarrier _sc.
sc , carrier μ ₀ is μ ₀ = _{11/5 sc} , and the frequency is
The frequency shift of a high-definition signal of 1.2 _sc or more will be described as an example.

FIG. 2 is a signal spectrum diagram of frequency shift according to the conventional method. High definition signal Y _H of 1.2 _sc to 1.8 _sc is the sampling of the sampling frequency _s, exist as aliasing harmonics to 2.2 _sc to 1.8 _sc. 1.2 _sc ~ 1.8 _sc
The high-definition signal Y _{H of} is one of 0.
The signal spectrum moves to the 4 _sc to _sc band and the other to the 3.6 _sc to 4 _sc band. In addition, a signal spectrum of the folded component of 2.2 _{sc to} 2.8 _sc exists in the 0 to 0.6 _sc band due to amplitude modulation. As a result, 0.4 _sc to 0.6 candy mixing two spectra is _sc zone, the area available as a frequency shift restricted to 0.6 _sc ~ _sc band. That is, in the conventional method, the bandwidth available for frequency shift is limited to 0.4 _sc .

FIG. 1 is a spectrum diagram of an example of frequency shift according to the present invention. In the present invention, as shown in (a) and (c), a high-definition signal has a Y of 1.2 _{sc to} 1.5 _sc band.
_H1 , separated into multiple frequency band signals like Y _{H2 in} the 1.4 _{sc to} 1.8 _sc band.

The carrier μ ₀ is amplitude-modulated for each of the separated Y _H1 and Y _H2 , and frequency-shifted to 0.7 _sc to _sc band by BPF1 and BPF2 to Y _H1 ′ 0.4 _{sc to} 0.8 _sc band.
Generate the Y _H2 ′ signal. In this case, Y _H1 ′ and Y _H2 ′ do not contain aliasing from the harmonic components. Then, 0.4 _sc ~ as shown in FIG. (E) by adding the two
A high-definition signal that is frequency-shifted to the _sc band can be constructed.

As described above, according to the present invention, frequency shift with a wide bandwidth can be achieved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In each of the examples, the sampling frequency _s = 4
A case where _sc and carrier wave μ ₀ = 2.2 _sc will be described as an example.

FIG. 3 shows a first embodiment on the transmitting side. In the figure, band pass filters BPFa and BPFb denoted by ₁ and ₂ extract high-definition signals Y _H1 and Y _H2 in a frequency band as shown in FIGS. 1 (a) and 1 (c), for example. In the modulation circuit 3, the carrier wave μ ₀ generated by the generation circuit 4 is subjected to carrier wave suppression amplitude modulation with Y _H1 and Y _H2 . Specifically, the multiplication operation of μ ₀ and Y _H1 , Y _H2 and the like can be easily realized by a table-up method using ROM.

The output signal of the modulation circuit 3 is the bandpass filter 5,
6, the high-definition signal Y _H1 ′, Y obtained by frequency-shifting the regions shown in FIGS. 1 (b) and 1 (d), respectively.
Extract as _H2 '. These are added by the adder circuit 7,
A frequency-shifted high-definition signal as shown in FIG. 1 (e) is produced.

FIG. 4 shows another embodiment of the present invention, which is implemented on the transmitting side. In this embodiment, shown in FIG.
A high-definition signal of 1.2 _sc or more is modulated by the modulation circuit 3 with the carrier wave μ ₀ generated by the carrier wave generation circuit 4 to suppress the carrier wave amplitude. This amplitude-modulated signal is a bandpass filter 8,
9 (BPF1 ', BPF2') extracts the components of the respective predetermined frequency bands. The characteristics of these bandpass filters are shown in FIG. That is, the band pass filter 8 is Y _H1 ′
The component, bandpass filter 9 extracts the Y _H2 ′ component.
One of these signal components enters the switch 11 and the other level determination circuit 10. The level determination circuit 10 detects the levels of the output signals of the bandpass filters 8 and 9, and detects the level of 1 if there is a signal exceeding a specific value and 0 otherwise. Then, as shown in FIG. 6, the signal selected by the switch 11 is determined according to the level detection result. For example, when both levels are detected, it is determined that the bandpass filter 8 is a frequency-shifted signal of 1.2 _sc or more and the bandpass filter 9 is a folded signal component due to a harmonic component of the frequency _s. , Y _H1 ′ which is the original signal component is selected. In the same manner, the switch 11 selectively extracts the Y _H1 ′ and Y _H2 ′ components to form a frequency-shifted high-definition signal as in the above-described embodiment. In this embodiment, there is an advantage that the circuit scale is small because the number of modulation circuits is as small as one set and the filters before modulation can be omitted. On the other hand, there is also a problem that a malfunction occurs if the level determination or the like is incorrect.

FIG. 7 shows an embodiment of the receiving side for demodulating a frequency-shifted high-definition signal into a high-definition signal in the original frequency band. The bandpass filters shown in FIGS. 8 and 9 are separated into high-definition signals Y _H1 ′ and Y _H2 ′ with the characteristics shown in FIG. 5, for example.
These signals are synchronously detected by the synchronous detection circuit 12 based on the μ ₀ information with the carrier wave μ ₀ reproduced by the μ ₀ reproduction circuit 13, and are simultaneously detected by the simultaneous band pass filters 1 and 2 in FIG.
The Y _H1 and Y _H2 components shown in (c) are extracted, added by the adder circuit 7, and demodulated to the original high definition signal.

FIG. 8 shows a second embodiment of the receiving side, in which the bandpass filters 14 and 15 are used to detect the signals after the synchronous detection.
Extract the Y _H1 and Y _H2 components. Note that these characteristics are shown in FIG. Then, the level determination circuit 10 controls the switch 11 with the characteristics shown in FIG. 10 according to the output level of each filter, and demodulates to the original high definition signal.

〔The invention's effect〕

According to the present invention, a frequency shift circuit and method having a wide frequency band can be realized with a simple configuration.

In the example, _s = 4 _sc , μ ₀ = 2.2
_{Although sc} has been described as an example, it is clear that the present invention is effective even if these values are arbitrary numerical values.

Further, as the high-definition signal, it is clear that the effectiveness of the present invention is not impaired for general signals such as audio signals as well as image signals such as luminance signal Takashiro component and color signal Takashiro component. Is.

Further, in the present embodiment, the case of separating into two types of frequency bands is shown, but it is clear that two or more types of frequency bands can be used.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention, FIG. 2 is an explanatory view of a conventional method, and FIGS. 3, 4, 7 and 8 are one embodiment of the present invention, FIG. 5, FIG. FIG. 6, FIG. 9 and FIG. 10 are characteristic diagrams of filters used in one embodiment. 1 ... BPFa, 2 ... BPFb, 3 ... modulation circuit, 4 ... carrier generation circuit, 5,6,8,9,14,15 ... bandpass filter,
7 ...... adder circuit, 10 ...... level determination circuit, 11 ...... switch, 12 ...... synchronous detection circuit, 13 ...... mu ₀ regeneration circuit.

Claims (4)

(57) [Claims] 1. An original signal is converted into a digital signal sequence at a sampling frequency f _s , the converted digital signal sequence is separated into a plurality of frequency band sequences, and each of the separated frequency band sequences is frequency-shifted. After performing the conversion, remove the aliasing component associated with the harmonic component of the sampling frequency f _s in each frequency-converted frequency band series, and add each frequency band series from which the aliasing component has been removed. A frequency shift method characterized by outputting. 2. The frequency shift method according to claim 1, wherein the original signal is a Takashiro component of an image signal. 3. A means for converting an original signal into a digital signal sequence at a sampling frequency f _s , a means for separating the converted digital signal sequence into a plurality of frequency band sequences, and a frequency of each of the separated frequency band sequences. A means for converting each frequency by shifting, a means for removing each folding component associated with the harmonic component of the sampling frequency f _s in each frequency-converted frequency band series, and each frequency for which the folding component is removed A frequency shift circuit comprising means for adding band sequences. 4. The frequency shift circuit according to claim 3, wherein the original signal is a Takashiro component of an image signal.