JPH0562864B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an emphasis method used in FM transmission of television signals, and aims 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 configuration of the FM emphasis system in the prior art.In this example, the configuration on the receiving side is simplified and a 3-tap de-emphasis circuit 7 is used, so the amplitude characteristics on the transmitting side cannot be improved.
The pre-emphasis circuit 6 has about 15 taps.

In this method, since the number of taps is large, many relatively large vibrations are generated on both sides of the main tap as shown in the waveforms of FIGS. 4a and 4b in the impulse response. to this waveform
When ringing is added (dotted line) as shown in the waveform in Figure 4c during FM transmission, the non-linear expansion circuit 3 on the receiving side corresponds to the compression part (high amplitude part) of the non-linear compression circuit 2 on the transmitting side. In the extended portion, the added ringing portion is expanded in the amplitude direction.
Moreover, since the ringing located far away from the main tap is expanded in amplitude due to non-linear extension,
It has become difficult to eliminate ringing using a ringing elimination circuit with a simple configuration on the receiving side, causing deterioration in image quality.

(Summary of the Invention) An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional system, and to provide an emphasis system that has a simple circuit configuration on both the transmitting side and the receiving side, and that causes less deterioration in image quality.

That is, the emphasis method of the present invention is an emphasis method for television image signals in which pre-emphasis is performed on the transmitting side using a 3-tap transversal filter, and then FM transmission is performed.
On the receiving side, the image signal is passed through a linking cancellation circuit of a 3-tap transversal filter, and de-emphasis is performed using a 3-tap and 5-tap connected in cascade, and a transversal filter having characteristics opposite to those of the pre-emphasis, to restore the image signal. It is characterized by this.

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

FIG. 1 shows a block diagram of the linking 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 expressed as {1+bcos(ωτ)}{1+c cos(2ωτ)}, but this inverse characteristic filter can be approximated by the 3-tap pre-emphasis filter 1 in Figure 1. . However, b=a, c=a ^z (2-a ^z ) must be satisfied. Here, a, b, and c are the coefficients of the pre-emphasis filter 1 coefficient unit, the 3-tap side coefficient unit, and the 5-tap side coefficient unit of the de-emphasis filter 5, respectively, and τ is the 1-tap delay time. Moreover, in order to set the amount of emphasis to m=B/A, it is sufficient to set a=(10 ^m/zo −1)/(10 ^m/zo +1).

As shown in FIGS. 2a and 2b, the impulse response of the pre-emphasis filter 1 described above generates one vibration on each side of the main tap. FIG. 2c (broken line) shows the situation when ringing occurs in the transmission line after this waveform is non-linearly compressed in the circuit 2. When the waveform of FIG. 2c is non-linearly expanded in the circuit 3 on the receiving side, the ringing is also expanded 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. As shown in Figure 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. The ringing caused by circuit 3
This is because the amplitude is not large enough to cause non-linear expansion.

Next, the amplitude-enlarged ringing at the main tap and adjacent to it can be canceled by a ringing canceling circuit 4 having a simple configuration as shown in FIG. 2d.
Its operation is as shown in FIG. 2e, where the components of the output and in FIG. 2d are used to cancel the ringing (dashed line) in the output.

(Effects of the Invention) By carrying out the present invention, it is possible to realize an emphasis method that efficiently eliminates ringing and has 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 system of the present invention, and FIG. 2 is a diagram showing the impulse response waveforms (a) and (b) of the pre-emphasis filter of the present invention, respectively, and a signal c to which ringing is added. , a ringing cancellation circuit (d), a waveform diagram (e) showing the operation of ringing cancellation, FIG. 3 is a diagram showing the configuration of the FM emphasis method in the prior art, and FIG. 4 is a diagram showing the configuration of the prior art pre-emphasis filter. FIG. 3 is a diagram showing impulse response waveforms a and b and a signal waveform c to which ringing is added in the FM transmission line. 1... Pre-emphasis filter of the present invention, 2...
Non-linear compression circuit, 3... Non-linear expansion circuit, 4... Ringing cancellation circuit, 5... De-emphasis filter of the present invention, 6... Pre-emphasis filter of the prior art, 7... De-emphasis filter of the prior art.

Claims (1)

[Claims] 1 In the emphasis system for television image signals, after pre-emphasis is performed by a 3-tap transversal filter on the transmitting side,
FM transmission is carried out, and on the receiving side, the image is passed through a linking cancellation circuit of a 3-tap transversal filter, and de-emphasis is performed using a 3-tap and 5-tap connected in cascade, and a transversal filter having characteristics opposite to those of the pre-emphasis. An emphasis method characterized by restoring the signal.