JPS6320981A - Receiver for television signal - Google Patents

Abstract

PURPOSE:To raise the stability of action, to improve an S/N and to reproduce the base band video signal of a high quality by providing a compensation filter for changing the amplitudefrequency characteristic of a digitized video signal. CONSTITUTION:An IF filter 41 wide band-processes the signal component of the objective channel in an IF signal which a tuner 3 outputs, and an adjacent and unobjective signal is removed. A characteristic compensation filter 61 which consists of symmetric transversal filters and the like can satisfactorily compensate a residual side wave band signal for the amplitude-frequency characteristic without the occurrence of a phase distortion. A local control circuit 21 for controlling a local oscillation frequency controls the characteristic compensation filter 61 through a conductor 22. With such a constitution, the total amplitude- frequency characteristic does not change with respect to a change in the local oscillation frequency, namely the change in the carrier frequency of an IF signal. That is, with setting the frequency of the characteristic compensation filter 61 to follow the change in the IF frequency, an almost constant characteristic can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television signal receiving device, and more particularly to a television signal receiving device that is amplitude modulated and transmitted in a vestigial sideband.

Prior Art The prior art related to the present invention will be explained below with reference to FIG. Figure 2 shows the radio frequency (RF) received by antenna 1.
) The television signal is converted into a predetermined intermediate frequency (1, F 2 ) signal by a tuner 3 controlled by a local oscillator control circuit 2 and then supplied to an IF filter 4 . This IF
The RF television signal which is the input signal arriving at the filter 4 has a carrier frequency of flQ and f as shown in FIG. 3(A).
The upper sideband component up to sQ and the lower sideband component up to f20 are asymmetrical, so-called vestigial sideband signals. Therefore, if the tuner 2 is a lower heterodyne, as shown in (B). By setting the gain at the IF carrier frequency f+1 as a bar and making the gain of the double-side band transmission part change almost linearly, an amplification and detection circuit that compensates for the overall frequency characteristic and processes the IF multiplied signal is created. This is arranged for the purpose of flattening the amplitude-frequency characteristic of the baseband video signal outputted by 5' as shown in FIG. The baseband video signal sent to the conductor 51 is currently A/D.
After being digitized by a converter 6 and subjected to predetermined signal processing in a luminance Y channel processing circuit 7 and a chromaticity C channel processing circuit 8, it is transmitted to R, (lr
, B are sent to the signal output terminal 10. Furthermore, the amplification/detection circuit 6 and the tuner 3 are each configured to be able to control the gain of the amplifier, and are also controlled in the form of a known delay time GC, so that the conductor 51 can be controlled in response to a wide range of received signal level changes of the incoming input signal. Maintain the video signal level at a constant value.

“Problems to be Solved by the Invention In the conventional device described above, the IF filter 4 compensates for the total amplitude-frequency characteristic of the television signal in the vestigial sideband, and for this purpose, the IF multiplied signal carrier frequency component In principle, it is necessary to attenuate edB with respect to the center of the IF band.Therefore, the total maximum gain of the tuner 3 and the amplification/detection circuit 5 compensates for the sdB attenuation for the carrier frequency component described above. This is a factor that deteriorates the operational stability of oscillations and the like of amplifiers that handle high frequency signals such as RF-IF multiplied signals.

Furthermore, when the level of the incoming input signal is high, that is, under the condition that the gain of the tuner 3 is reduced by controlling the delay tom GO described above, the power loss of the F filter 4 reduces the S/F of the video signal sent to the conductor 51. In this case, as described above, in the configuration of the conventional device which requires adB attenuation for the IF carrier wave, the S/N deteriorates undesirably.

Furthermore, among the characteristics of the IF filter 4, it is practically difficult to adjust or maintain a predetermined characteristic, especially in the vicinity of the IF carrier wave, and this results in deterioration of image quality.

Means for Solving the Problems According to the present invention, a television signal receiving apparatus includes a tuner that converts an incoming input signal into a signal multiplied by a predetermined IF, and a signal component of a desired channel from the IF multiplied signal outputted by the tuner. an IF filter that attenuates undesired interference signal components without effectively changing amplitude-frequency characteristics;
an xy signal processing circuit that receives the output signal of F as input and sends out a baseband video signal; an A/D conversion circuit coupled to the output of this circuit; and an A/D conversion circuit that changes the amplitude-frequency characteristics of the digitized video signal. At least a second compensation filter is arranged.

Operation In the device according to the present invention described above, the IF filter selects only the signal component of the desired channel by substantially wideband processing, and in particular, the amplitude-frequency characteristic near the IF multiplied signal carrier is made approximately flat, and the adjacent unbalanced signal component is made substantially flat. Predetermined filter characteristics are given to remove only signal components of desired channels. This IF filter therefore does not generate any extra power losses for the processing of the residual sideband television signal in conjunction with the tuner and the IF signal processing circuit.

Characteristic compensation filters compensate for the amplitude-frequency characteristics of digitized baseband video signals through asymmetric sideband transmission and broadband IF filter processing in the receiving device without causing phase distortion. It has an effect.

Embodiments An embodiment of the present invention will be described below in detail with reference to the drawings, but components that operate in the same way as conventional devices and have no difference in characteristics will be given the same reference numerals and detailed explanations will be omitted. FIG. 1 is a block diagram showing an embodiment of the present invention.
In the figure, the IF multiplied signal output by the tuner 3 is subjected to wideband processing on the signal component of the desired channel by the IF filter 41, and adjacent undesired signals are removed.

This IF filter 41 is configured as shown in FIG. 4(A).
Assuming that the tuner 3 is a lower heterodyne for an incoming input signal with a carrier frequency of The characteristics are set to remove undesired adjacent channel components.

Practically speaking, the IP filter 41 operates at frequencies f20 to f, for example, at which lower sideband components are completely transmitted. , 17 frequency, it is desirable to have a cutoff characteristic as shown by the solid line a in Figure 4) in the range of f21o to '110, but it is also possible to have the cutoff characteristic as shown by the broken line in the same figure. Various other characteristics can also be selected.

Also, the xy carrier component element +t. Although it is basically desirable that the attenuation characteristic of the IF filter 41 for the component and the components in the vicinity thereof be flat, it is not limited to this. The IF signal processing circuit 62 includes a variable gain amplifier and a wave detector, and sends out a baseband video signal having the characteristics as shown in FIG. 4(C) to the conductor 63.
It is possible to reduce the gain by the amount of change in attenuation for the F carrier, that is, in principle, by 6 dB. The video signal digitized by the human/D converter 6 is flattened in overall frequency characteristics by a characteristic compensation filter 61 as shown in FIG. properties are given. This characteristic compensation filter 61 is constituted by a symmetrical transversal filter or the like, and can satisfactorily compensate the amplitude-frequency characteristic of the residual sideband signal without generating phase distortion. Although a configuration is shown in which the local oscillation control circuit 21 for controlling the local oscillation frequency of the tuner also controls the characteristic compensation filter 61 via the conductor 22 shown by the broken line, by configuring it in this way), It is possible to prevent the overall layer width-frequency characteristic from changing with respect to a change in the local oscillation frequency, that is, a change in the IF multiplied signal carrier frequency.

That is, by making the frequency f250 of the characteristic compensation filter 61 shown in (■) in FIG. 4 follow the change in the 17 frequencies, substantially constant characteristics can be maintained.

Effects of the Invention As described above, in the receiving device according to the present invention, the television signal transmitted in the vestigial sideband is processed by the wideband tuner and IF filter that do not substantially change the amplitude-frequency characteristics of the baseband video signal. Since the configuration detects the IF multiplied signal obtained by using the IF filter, it is possible to reduce undesired loss caused by the IF filter. Therefore, it is possible to reduce the gain of the RF-IF amplifier that operates at high frequencies in the receiving device, which not only improves the operational stability of the device, but also improves the S/N especially when the level of the incoming input signal is high. In addition, after A/D converting the baseband video signal, a digital filter performs the amplitude-frequency characteristic compensation necessary for receiving the residual sideband signal, making it possible to reproduce high-quality baseband video signals and other industrial applications. It has great value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a television signal receiving device according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional television signal receiving device, and FIG. 3 is an explanation of the operation of the conventional receiving device. FIG. 4 is a characteristic diagram used to explain the operation of the receiving apparatus according to the present invention. 3...Tuner, 41...IF filter, 52...IF signal processing circuit, 6...
・A/D, 61...Compensation filter, 21...
...Local control circuit. Castle N Figure 3 (A) (Snake)

Claims (1)

[Claims] An apparatus for receiving a television signal transmitted in an amplitude modulated vestigial sideband, the apparatus comprising: a tuner for converting at least an incoming input signal into a predetermined intermediate frequency (IF) signal;
an IF filter to which the output signal of the tuner is supplied;
An IF signal processing circuit that receives the output signal of this filter as input and sends out a baseband signal, an A/D conversion circuit coupled to this IF signal processing circuit, and an IF signal processing circuit that sends out a baseband signal using the output signal of this filter as an input; and a compensation filter for changing the amplitude-frequency characteristics, the IF filter effectively performs wideband processing on the signal component of the desired channel, and the compensation filter performs wideband processing on both sides of the television signal. A television signal receiving device that compensates relative gains to be approximately the same for baseband video signal bands corresponding to a waveband and a single sideband.