JPS6240887A - Emphasis system - Google Patents

Abstract

PURPOSE:To realize an emphasis system which hardly causes picture deterioration with a simple circuit configuration, by restoring a picture signal by performing de-emphasis with a transversal filter with characteristics opposite to those of the pre-emphasis filter. CONSTITUTION:Video input on the transmission side is FM-transmitted through a nonlinear compression circuit 2 after it is subjected to preemphasis by means of the 3-tap transversal filter of a preemphasis filter 1. On the reception side, the video input is passed through the ringing eliminating circuit 4 of a 3-tap transversal filter through a nonlinear expanding circuit 3. Moreover, by cascade- connecting three taps and five taps in a de-emphasis filter 5 and performing de-emphasis by means of the transversal filter of the de-emphasis filter 5 having characteristics opposite to those of the filter 1, picture signals are restored.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an emphasis method used in FM transmission of television signals, and is intended to obtain better waveform transmission characteristics than conventional methods.

(Prior art) In the conventional emphasis method, in order to reduce the burden on the receiving side, pre-emphasis is performed on the transmitting side using a filter with a large number of taps, amplitude is limited using a non-linear compression circuit, and then FM modulation is applied. On the sending and receiving sides, de-emphasis was performed after passing through FM demodulation and non-linear expansion circuits.

Figure 3 shows an overview of the FM emphasis system configuration in the prior art.In this example, the configuration on the receiving side is simplified.
Since a tap de-emphasis circuit 7 is used, a pre-emphasis circuit 6 of about 15 taps is used on the transmitting side in order to improve the amplitude characteristics.

In this method, since the number of taps is large, the impulse response
As shown in the waveforms in Figures (a) and (b), many relatively large vibrations occur on both sides of the main tap. When ringing (broken line) is added to this waveform as shown in the waveform in FIG.
In the extended portion of the nonlinear expansion circuit 3 on the receiving side corresponding to the high amplitude portion), the added ringing portion is expanded in the amplitude direction. Furthermore, since the ringing is located far away from the main tap and the amplitude is expanded by non-linear expansion up to the ringing, it is difficult to eliminate the ringing with a simple ringing elimination circuit on the receiving side, which can cause image quality deterioration. It had become.

(Summary of the Invention) The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional system,
It is an object of the present invention to provide an emphasis method with a simple circuit configuration on both the transmitting side and the receiving side, and with little deterioration in image quality.

In other words, in the emphasis method of the television image signal, the emphasis method of the present invention performs pre-emphasis with a 3-tap transversal filter on the transmitting side (S side), then performs FM transmission, and on the receiving side, ringing cancellation of the 3-tap transversal filter is performed. pass through the circuit,
Furthermore, the image signal is restored by performing de-emphasis using a transversal filter having 3 taps and 5 taps connected in cascade and having characteristics opposite to those of the pre-emphasis.

(Example) The system of the present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 1 shows a block diagram of the ringing cancellation type emphasis system of the present invention. In this structure, the pre-emphasis filter and the de-emphasis filter are well known.

The transfer function of this de-emphasis filter 5 is (1+b cos(ωτ) ) (1+c C03(2
ωτ)), this inverse characteristic filter is shown in Figure 1, 3.
It can be approximated by a tap pre-emphasis filter 1.

However, b = a, c = a2 (2-a'') must be satisfied. Here, a, b, and c are the coefficient unit of the pre-emphasis filter 1, the 3-tap side coefficient unit and the 5-tap side coefficient unit of the de-emphasis filter 5, respectively. In the coefficient of the side coefficient multiplier, τ is one tap delay time. Also, to set the emphasis amount to m=B/A, a-(10""-1)
/(10''+1) may be used.

As shown in FIGS. 2(a) and 2(b), the impulse response of the pre-emphasis filter 1 described above generates one vibration on each side of the main tap. FIG. 2C (broken vA) shows what happens when ringing occurs in the transmission line after this waveform is non-linearly compressed in the circuit 2. Figure 2(c)
When the waveform of is non-linearly expanded in circuit 3 on the receiving side,
Ringing is also magnified in the amplitude direction. However, in this case, the only ringing caused by the non-linear extension is the ringing that appears at the main tap and immediately adjacent to it. If anything,
As shown in Figures 2 (a) and (b), large vibrations occur only on both sides of the main tap in the impulse response, and are flat in the part that is more than τ away from the main tap, and the vibrations are superimposed on this part. This is because the amplitude of the resulting ringing is not large enough to cause non-linear expansion in the circuit 3.

Next, the ringing whose amplitude has been expanded at the main tap and its neighbor can be canceled by a ringing canceling circuit 4 having a simple configuration shown in FIG. 2(d).

The operation is as shown in Fig. 2(e), and Fig. 2(d)
The components of output ■ and ■ at are the ringing of output ■ (
dashed line).

(Effects of the Invention) By carrying out the present invention, it is possible to efficiently eliminate ringing and realize an emphasis method having good waveform transmission characteristics. As a result, image quality can be improved compared to conventional television FM transmission.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the ringing-cancelling emphasis method of the present invention, and FIG. 2 is a waveform of the impulse response of the pre-emphasis filter of the present invention (a), (b) a signal to which ringing is added (C ), ringing cancellation circuit diagram 4 (d)
, a waveform diagram (e) showing the ringing cancellation operation, FIG. 3 is a diagram showing the configuration of the FM emphasis method in the prior art, and FIG. 4 is a waveform (a) of the impulse response of the pre-emphasis filter in the prior art. , (b) and a signal waveform (c) with ringing added in the FM transmission path. 1... Pre-emphasis filter of the present invention 2... Non-linear compression circuit 3... Non-linear expansion circuit 4... Ringing cancellation circuit

Claims (1)

[Claims] 1. In the emphasis system for television image signals, on the transmitting side, after performing pre-emphasis with a 3-tap transversal filter, FM transmission is performed, and on the receiving side, the signal is passed through a ringing cancellation circuit of a 3-tap transversal filter, and then An emphasis system characterized in that an image signal is restored by performing de-emphasis using a transversal filter which connects a tap and five taps in cascade and has a characteristic opposite to that of the pre-emphasis.