JPH0740728B2 - Television signal receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal receiver, and more particularly to a television signal receiver that is amplitude-modulated and transmitted in the vestigial sideband.

2. Description of the Related Art The related art related to the present invention will be described below with reference to FIG. In Fig. 2, the radio frequency (RF) received by antenna 1
It shows that the television signal is converted into a predetermined intermediate frequency (IF) signal by the tuner 3 controlled by the local oscillator control circuit 2 and then supplied to the IF filter 4. The IF filter 4 receives an incoming RF signal as an RF television signal as shown in FIG. 3 (A).
As shown in, when the carrier frequency is ₁₀ , the upper sideband component up to ₃₀ and the lower sideband component up to ₂₀ are asymmetric so-called vestigial sideband signals. Therefore, when the tuner 2 is the lower heterodyne, Shows the IF carrier frequency ₁₁ as shown in (B).
The gain at 1/2 is set to 1/2 so that the gain of the double sideband transmission part changes substantially linearly, and the amplification and detection circuit 5 that compensates the overall frequency characteristic and processes the IF signal is output. Amplitude-frequency characteristics of baseband video signal
It is arranged for the purpose of being flat as shown in FIG. The baseband video signal sent to the lead wire 51 is currently digitized by the A / D converter 6 and subjected to predetermined signal processing by the luminance Y channel processing circuit 7 and the chromaticity C channel processing circuit 8, and then the matrix. , R, G, B primary color signals are sent to the signal output terminal 10 via the D / A circuit 9. Further, the amplification / detection circuit 5 and the tuner 3 are respectively configured so that the gain of the amplifier can be controlled, and are controlled in the form of a known delayed AGC, and the conductor 51 is controlled in response to a wide range change of the received signal level of the incoming input signal. Keep the video signal level constant.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above-described conventional apparatus, the IF filter 4 is used to compensate for the total amplitude-frequency characteristic of the television signal in the vestigial sideband.
In principle, it is necessary to reduce 6 dB to the center of the IF band. Therefore, the total maximum gain of the tuner 3 and the amplification / detection circuit 5 needs to compensate for the attenuation of 6 dB with respect to the above-mentioned carrier frequency component, and stable operation such as oscillation of an amplifier handling a high frequency signal such as an RF-IF signal. It is a factor that deteriorates the degree.

When the incoming input signal level is high, that is, under the condition that the gain of the tuner 3 is reduced by the control of the delayed AGC described above, the power loss of the IF filter 4 causes the S / N of the video signal sent to the lead wire 51. This is a cause of deterioration of the S / N ratio, and in this case, the S / N is undesired in the configuration of the conventional device that needs to be attenuated by 6 dB for the IF carrier as described above.
Deteriorates.

Further, it is practically difficult to adjust or maintain the vicinity of the IF carrier among the characteristics of the IF filter 4 to a predetermined characteristic, and thus the image quality is deteriorated.

Means for Solving the Problems In a television signal receiving apparatus according to the present invention, a tuner for converting an incoming input signal into a predetermined IF signal and a signal component of a desired channel from an IF signal output by the tuner are selected. The IF filter that attenuates undesired interfering signal components without changing the amplitude-frequency characteristics and the IF that outputs the baseband video signal using the IF output signal as input
At least a signal processing circuit, an A / D conversion circuit coupled to the output of the circuit, and a compensation filter for changing the amplitude-frequency characteristic of the digitized video signal are arranged.

In the above-mentioned device according to the present invention, the IF filter selects only the signal component of the desired channel by substantially wideband processing, and particularly the amplitude-frequency characteristic in the vicinity of the carrier of the IF signal is made substantially flat, and A predetermined filter characteristic is provided so as to remove only the signal component of the unwanted channel which is to be used. Therefore, this IF filter does not generate any special power loss for processing the vestigial sideband television signal when the tuner and the IF signal processing circuit are coupled. The characteristic compensation filter compensates the amplitude-frequency characteristic for the digitized baseband video signal by the asymmetric sideband transmission and the wideband IF filter processing in the receiving device without causing phase distortion. Has an effect.

Embodiments Embodiments of the present invention will be described below in detail with reference to the drawings, but those having the same operation as the conventional device and having no difference in characteristics are denoted by the same reference numerals and detailed description thereof will be omitted. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, the IF signal output from the tuner 3 is subjected to wide band processing on the signal component of the desired channel by the IF filter 41, and the adjacent signal The desired signal is removed. Assuming that the tuner 3 is a lower heterodyne for an incoming input signal having a carrier frequency of ₁₀ as shown in FIG. 4 (A), the IF filter 41 has an IF carrier _{110 as} shown in FIG. 4 (B). The characteristics are set so as to remove the undesired adjacent channel component without substantially attenuating the components in the vicinity thereof. Substantially, the IF filter 41 has, for example, a frequency of _{20 to 10} IF at which the lower sideband component is completely transmitted.
In the frequency range of _{210 to 110} , it is desirable to have the cutoff characteristic as shown by the solid line a in FIG. 4B, but it is also possible to have the characteristic as shown by the broken line b in FIG. Various characteristics can be selected. IF carrier component
The attenuation characteristic of the IF filter 41 with respect to ₁₁₀ and components in the vicinity thereof is basically desirable to be flat, but not limited to this. The IF signal processing circuit 52 includes a variable gain amplifier and a detector, and sends out a baseband video signal having the characteristics as shown in FIG. It is possible to reduce the amount of change in the attenuation amount with respect to, that is, 6 dB in principle. A / D converter 6 digitizes video signal is a flat overall frequency characteristic in the characteristic compensation filter 61 as shown in FIG. 4 (D), the high-frequency enhancement type having a boundary frequency of ₂₃₀ Characteristics are given. The characteristic compensation filter 61 is composed of a symmetrical transversal filter or the like and can favorably compensate the amplitude-frequency characteristic for the vestigial sideband signal without generating phase distortion. Local oscillation control circuit for controlling the local oscillation frequency of the tuner
21 shows a configuration for controlling the characteristic compensation filter 61 also via the conductor 22 shown by a broken line, but by configuring in this way, with respect to a change in the local oscillation frequency, that is, a change in the carrier frequency of the IF signal, It is possible to prevent the total amplitude-frequency characteristic from changing. That is, the frequency ₂₃₀ of the characteristic compensation filter 61 shown in FIG.
By following the change in frequency, a substantially constant characteristic can be maintained.

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 the IF filter that do not substantially change the amplitude-frequency characteristic of the baseband video signal. Since the IF signal obtained is detected, undesired loss due to the IF filter can be reduced. Therefore, it is possible to reduce the gain of the RF-IF amplifier that performs high frequency operation in the receiving device, so that not only the operational stability of the device is improved, but also the S / N is improved especially when the incoming input signal level is large. Also, after the baseband video signal is A / D converted, the digital filter performs the amplitude-frequency characteristic compensation necessary for receiving the signal in the vestigial sideband, so that a high-quality baseband video signal can be reproduced. It is of great value.

[Brief description of drawings]

FIG. 1 is a block diagram of a television signal receiving apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional television signal receiving apparatus, and FIG. FIG. 4 is a characteristic diagram used for explaining 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.

Claims (1)

[Claims] 1. A receiver for a television signal transmitted in the amplitude modulated vestigial sideband, the tuner converting at least an incoming input signal into a predetermined intermediate frequency (IF) signal, and the tuner. Output signal of the IF filter, an IF signal processing circuit that outputs the baseband signal using the output signal of this filter as an input, an A / D conversion circuit that is coupled to this IF signal processing circuit, and is digitized. And a compensation filter for changing at least the amplitude-frequency characteristic of the video signal in the television signal,
The IF filter effectively performs wideband processing on the signal component of the desired channel, and the compensating filter is applied to the baseband video signal band corresponding to each of the double sideband and the single sideband in the television signal. On the other hand, a television signal receiving apparatus in which relative gains are compensated so as to be substantially the same.