JPH02244877A - noise reduction circuit - Google Patents

Abstract

PURPOSE:To improve residual noise at a signal edge and deterioration in the waveform transmission characteristic due to the noise by connecting a high frequency band reduction circuit having an inverse characteristic with the characteristic of a high frequency emphasis circuit to a post stage of a nonlinear de-emphasis circuit. CONSTITUTION:A circuit correcting a change in a signal waveform caused by a high frequency emphasis circuit is connected to the post-stage of a nonlinear de-emphasis circuit and the high frequency emphasis circuit 2 is connected to a pre-stage of a nonlinear pre-emphasis circuit 3. Since the time when the signal edge to be sent acts on a low impedance region of a diode included in the nonlinear de-emphasis circuit is considerably reduced, the resident time when a noise caused in the transmission system resides in the signal edge is considerably reduced and the deterioration in the transmission waveform due to noise is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to processing of video signals, and is intended to improve the deterioration of transmission characteristics caused by noise generated in the transmission system.

Conventional technology When transmitting a video signal, as a means to improve the signal-to-noise ratio (hereinafter abbreviated as S/N ratio) of the video signal due to noise generated in the transmission system, it is possible to reduce the amplitude of the signal to be transmitted. In addition, for large amplitude parts of the signal, a process called non-linear emphasis is performed to greatly reduce the degree of emphasis, or conversely, to reduce the degree of emphasis. A method is used to restore the .

FIG. 6 shows a conventional example of the pre-emphasis side of this non-linear emphasis circuit. In Fig. 5, 9 is a signal input terminal, 10 is a capacitor C1, 11 is a resistor R, 12 is a resistor R2, 13 is a capacitor C2, and 14 is a diode D.
1.16 is a diode D2.16 is a signal output terminal. It is suitable for the circuit shown in Fig. 5.
I), 13 (C2) is made almost the same as the resistance value ratio of the resistors 11 (R,), j 2 (Fl, 21), the signal output level of the output terminal of 16 becomes the same as that of the diode 14.15 When the level of the amplitude-limited signal is sufficiently large, the transfer characteristic of the circuit shown in FIG. 6 becomes the characteristic shown as "at the time of large signal input" in FIG.

In the circuit of FIG. 6, even if the circuit constants are the same as in the case described above, when the signal output level at the output terminal 16 is sufficiently lower than the level at which the amplitude is limited by the diodes 14 and 15, the other capacitors 13 Since the influence on the circuit elements becomes negligible, the transfer characteristics of the circuit can be as shown in FIG. 6 as "when a small signal is input".

In a system that transmits a signal, when the maximum amplitude of the signal is limited, in this way, the high frequency range of the signal is emphasized only when the amplitude of the small signal is small, without emphasizing the high frequency range for large signals. If the inverse conversion is performed, the influence of noise generated in the transmission system can be reduced, and signal transmission with a good S/N ratio becomes possible.

Next, the operation of the circuit shown in FIG. 6 will be explained from the viewpoint of signal waveform transmission.

FIG. 7 shows the forward current and voltage characteristics of a typical diode. From this figure, it can be seen that the impedance of the diode changes continuously depending on the current value in the forward direction. Therefore, when a signal having the waveform shown in FIG. 8 is input to the circuit shown in FIG. 5, the diode 14 of the circuit shown in FIG.
At the connection point between 15 and capacitor 13, a waveform shown in FIG. 9 is obtained. The waveform shown in FIG. 9 is mainly controlled by the impedance of capacitors 10, 13 and diodes 14, 15 in the circuit of FIG. It has already been mentioned that after the signal is transmitted, the signal is restored by a circuit (hereinafter referred to as nonlinear de-emphasis circuit) having the opposite characteristics to the circuit shown in Figure 6. A waveform similar to the waveform shown in Fig. 9 can be obtained in the part corresponding to the part where the waveform shown in Fig. 9 is obtained, but the purpose of using this nonlinear pre-emphasis and non-linear de-emphasis circuit is as described above. Since the objective is to reduce the S/N drop in the transmission system, the operation of the nonlinear de-emphasis circuit must be performed under the condition that noise is added to the signal.

Fig. 10 (7) Fi is an enlarged waveform diagram of the signal waveform shown in Fig. 8 with noise added to the part shown in Fig. 10. (b) K decreases as shown. Figure 10 (2) is an enlarged view of the waveform shown in Figure 9 with noise added to part A';
As can be seen from Figure 10(a)K, the signal potential applied to the diode exists in the region where the impedance of the diode is low at the edge of the signal, so the noise reduction effect is low, and as shown in Figure 10(a)K. Similarly, noise remains at the edges of the signal. In addition, since the impedance of the diode is non-linear to the above-mentioned curve, the waveform shown in Figure 10) differs from the waveform in the noise-free state shown by the solid line to the waveform with the average value shown by the dotted line when there is noise. Change. That is, in such a non-linear de-emphasis circuit, the waveform transmission characteristics deteriorate due to the addition of noise to the input. Also, in Figure 10 (1), the average value is shown with noise added, but since noise is usually random, the occurrence of such a waveform change means that the edge noise is converted to low frequency noise. It also means that.

Problems to be Solved by the Invention It is an object of the present invention to provide a noise reduction circuit that greatly improves the residual noise at the signal edge portion and the deterioration of waveform transmission characteristics due to noise in the nonlinear deemphasis circuit described above. do.

Means for Solving the Problems In order to solve the above-mentioned problems, the noise reduction circuit of the present invention includes a signal high-frequency emphasis circuit at a stage before a non-linear pre-emphasis circuit, and a signal high-frequency emphasis circuit at a stage after the non-linear de-emphasis circuit. It is constructed by connecting a high-frequency reduction circuit with the opposite characteristics.

Effect: By adding this high frequency enhancement circuit, the time during which the edge portion of the signal applied to the diode is involved in the low impedance region of the diode is greatly shortened.

Embodiment FIGS. 1 and 2 show an embodiment of the present invention. Figures 1 and 2
The figures show an example on the non-linear pre-emphasis side, but on the non-linear de-emphasis side, the process opposite to the process shown in these figures is performed.

In FIG. 1, 1 is an input terminal, 2 is a high-frequency emphasis circuit, 3 is a nonlinear pre-emphasis circuit similar to that shown in FIG. 5, and 4 is an output terminal. Figure 2 shows a specific configuration example of the high frequency enhancement circuit shown in Figure 1 and 2, where 6 is an input terminal, 6 is a resistor R5, γ is a capacitor C3, 8 is a resistor R4, and 9 is an output terminal. It is.

FIG. 3 shows an example of the output signal waveform obtained at the output terminal 9 of the circuit shown in FIG. 2 when the signal waveform shown in FIG. 8 is input to the input terminal 5 of the circuit shown in FIG. ,
The high-frequency emphasis circuit shown in FIG. 2 causes an overshooter at the edge of the signal. Even if the amount of high-frequency emphasis necessary to obtain the effects described later in the high-frequency emphasis circuit shown in FIG. 2 is a relatively small value of around 2 dB, a sufficient effect can be obtained. Fig. 4 f'i When the signal obtained by the circuit of Fig. 2 is input to the nonlinear pre-emphasis circuit shown in Fig. 1, the portion corresponding to the connection point of the capacitor 13 and diode 14, 15 in Fig. 5 This figure shows the waveform obtained at . In the waveform shown in Figure 4, an overshoot occurs in the input signal waveform at the edge of the signal as shown in Figure 3, so the diode can be turned off in a much shorter time than the waveform shown in Figure 9. Enter the high impedance region. This also applies to non-linear de-emphasis circuits.

Effects of the Invention As described above, in the present invention, the time during which the edge portion of the transmitted signal acts in the low impedance region of the diode included in the nonlinear de-emphasis circuit is greatly shortened, so that the noise generated in the transmission system is reduced. The time that the signal remains at the edge portion can be greatly shortened, and the noise at the edge portion of the signal can be reduced. Furthermore, since deterioration of the transmission waveform due to noise can be prevented, visual deterioration due to noise in the video signal transmission system can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a high frequency emphasizing circuit of the present invention, and FIG. 3 is a waveform showing an example of a signal waveform obtained at the output of the circuit of the present invention. figure,
FIG. 4 is a waveform diagram showing an example of a signal waveform obtained in a specific part of a non-linear emphasis circuit to which the circuit of the present invention is added, FIG. 6 is a circuit diagram showing a conventional non-linear pre-emphasis circuit, and FIG. A characteristic diagram showing an example of the characteristics of the circuit shown in the figure, FIG. 7 is a characteristic diagram showing an example of the characteristics of the diode, FIG. 8 is a waveform diagram showing an example of the input signal waveform of the circuit shown in FIG.
FIG. 9 is a waveform diagram showing an example of a signal waveform obtained in the specific section of the circuit of FIG. 5 when the signal shown in FIG. 8 is input to the circuit of FIG. 6, and FIG. 10 (7). (A) and (Y) are waveform diagrams showing examples of noise waveforms at signal edge portions. 2...High frequency emphasis circuit, 3...Nonlinear pre-emphasis circuit, 6.8...Resistor, 7.
9... Capacitor. Name of agent: Patent attorney Shigetaka Awano and 1 other person 1st
Figure 4 Figure Kazu/Tile Figure Voice fI and (LO (3r) Figure 10 (In (Back Figure Figure VF (L/N No--Figure 8 Figure 9)

Claims (1)

[Claims] A non-linear pre-emphasis circuit transmits a signal that emphasizes the high frequency range of a minute signal by applying the signal to an element having non-linear impedance via a capacitor, and a non-linear pre-emphasis circuit that reduces the high frequency range of the minute signal of the transmitted signal. an emphasis circuit, a high-frequency emphasis circuit at a stage before the non-linear pre-emphasis circuit, and a circuit for correcting a change in signal waveform caused by the high-frequency emphasis circuit at a stage after the non-linear de-emphasis circuit. A noise reduction circuit characterized by connecting.