JPH01251475A - Digital emphasis circuit - Google Patents

Abstract

PURPOSE:To prevent a phase characteristics from being lost by setting the phase characteristic of a digital phase correction filter so as to be equal to that of a digital HPF. CONSTITUTION:An input digital phase correction video signal is supplied via the digital phase correction filter 4. The filter 4 is constituted of a coefficient multipliers (5a-5c), an adder 6, a delay circuit 7, and an adder 8, and it is possible to change the phase of an output signal obtained from the adder 8 by varying the coefficients of the coefficient multipliers (5a-5c). The coefficients of the coefficient multipliers (5a-5c) are set so that the phase characteristic of the output signal from the adder 8 can be set equal to the phase of the digital HPF1. In such a way, since two digital video signals supplied to an adder circuit 3 are supplied in a state where their phase characteristics are arranged on a line, no phase shift is generated at the adder circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a digital emphasis circuit used in a video signal recording circuit such as a VTR when performing digital signal processing.

(2) Prior Art In video signal recording circuits such as digital VTRs, a digital emphasis circuit is used before FM modulation in order to reduce high-frequency noise.

When emphasizing the high-frequency components of a video signal, the digital emphasis circuit increases the amount of emphasis in low-level areas where noise is more noticeable, and decreases the amount of emphasis in higher-level areas where noise is less noticeable. . As such a digital emphasis circuit, the circuit shown in FIG.
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In FIG. 3, a two-complement code signal of one sample (n pixels) (n is a natural number) is supplied as an input digital phase-corrected video signal. The digital video signal is supplied to a digital high-pass filter 1, and the output of the digital high-pass filter 1 is supplied to a digital compression circuit 2. The output signal of the digital compression circuit 2 is supplied to the adder circuit 3, and the digital video signal as the input signal is also supplied as is, and the two signals are added here. The addition output of the addition circuit 3 is output to the outside as an output of the digital emphasis circuit.

As shown in FIG. 4, the digital high-pass filter 1 has a frequency characteristic in which the gain increases as the frequency increases. Furthermore, as shown in FIG. 5, the digital compression circuit 2 has a compression characteristic in which the gain is relatively large when the amplitude of the input signal is small, and the gain is relatively small when the amplitude of the input signal is large.

As a result, as shown in FIG. 6, when the amplitude of the input digital phase-corrected video signal is small, the output of the digital emphasis circuit shown in FIG. The louder the sound, the more emphasis will be placed on it.

(3) Problems to be Solved by the Invention In the digital high-pass filter 1 shown in FIG. 3, amplitude control is performed for the purpose of reducing high-frequency noise.

However, in terms of phase, although the input digital phase-corrected video signal undergoes a phase change in the digital high-pass filter 1, the adder circuit 3 does not change the phase of the input digital phase-corrected video signal, which does not undergo a phase change. The received output digital video signal of the digital high-pass filter 1 is added.

Therefore, by adding two signals with different phases,
Since phase information is lost in the output signal of the adder circuit 3, which is output from the adder circuit 3, there is a problem in that a signal having a phase different from that of the currently used analog emphasis circuit is output.

(4) Means for Solving the Problems The present invention has been made in view of the above points, and aims to prevent an input digital phase correction video signal from undergoing a phase change, and achieves this object. a digital high-pass filter to which an input digital phase-corrected video signal is supplied; a digital phase-correction filter to which the input digital phase-corrected video signal is supplied; and an output of the digital high-pass filter to which the input digital phase-corrected video signal is supplied; a digital compression circuit having a compression characteristic in which the gain is relatively large when the amplitude of the input digital phase correction video signal is small and the gain is relatively small when the amplitude of the input digital phase correction video signal is large; and the output of the digital phase correction filter and the digital compression circuit. The configuration is such that an adder circuit is provided for adding the outputs of the .

(5) Effect In this configuration, by setting the phase characteristics of the digital phase correction filter to be equal to the phase characteristics of the digital high-pass filter, digital video signals with the same phase characteristics are supplied to the adder circuit, and the phase It works so that information is not lost.

(6) Examples Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a block diagram showing one embodiment of a digital emphasis circuit according to the present invention. Figures 3 to 6 in the figure
Components that are the same as those in the figures are given the same reference numerals and redundant explanations will be omitted.

In FIG. 1, as an input signal, a two's complement code signal of 1 sample and n bits (n is a natural number) is supplied as a digital video signal, similar to the circuit shown in FIG. Digital high-pass filter 1, digital compression circuit 2, adder 5! ! 33 is also similar to the circuit shown in FIG.

In the digital emphasis circuit shown in FIG. 1, the input digital phase correction video signal is not directly supplied to the adder circuit 3, but is supplied via the digital phase correction filter 4.

The digital phase correction filter 4 is a well-known digital phase correction filter having a circuit configuration as shown in FIG. 2 or FIG. 8. The digital phase correction filter shown in FIG. 2 is composed of coefficient units 5 a - c, an adder 6, a delay circuit 7, and an adder 8, and an output signal obtained from the adder 8 by changing the coefficients of the coefficient unit 5 azc. The phase of can be changed. The coefficients of the coefficient multipliers 5a to 5C are such that the phase characteristics of the output signal obtained from the adder 8 are
The phase characteristics are set to be equal to the phase characteristics of the digital high-pass filter 1 shown in the figure.

The same applies to the coefficient units 5a to 5C shown in FIG.

As a result, the two digital video signals supplied to the adder circuit 3 are supplied with the same phase characteristics, so that no phase shift occurs in the adder circuit 3.

FIG. 7 is a block diagram showing another embodiment of the digital emphasis circuit according to the present invention. In the drawings, the same components as those in FIGS. 1 to 6 are given the same reference numerals, and detailed explanations will be omitted.

In the digital emphasis circuit shown in FIG. 7, the digital phase correction filter 9 does not output directly from the adding circuit 3.
I am trying to output it via .

This digital phase correction filter 9 is a well-known digital phase correction filter having a circuit structure as shown in FIG. 2 or FIG. 8. That is, the digital phase correction filter 9 is configured similarly to the digital phase correction filter 4.

This digital phase correction filter 9 is used to obtain the same phase characteristics as the analog emphasis circuit currently used. The other configurations are similar to the circuit shown in FIG. 1 described above. Therefore, even in the circuit shown in FIG. 7, the two digital video signals supplied to the adder circuit 3 are supplied with the same phase characteristics, so that no phase shift occurs in the adder circuit 3. . Furthermore, by using the digital phase correction filter 9, it is possible to obtain the same phase characteristics as the analog emphasis circuit currently used.

(7) Effects of the Invention As explained above, the present invention provides a digital high-pass filter to which an input digital phase correction video signal is supplied, a digital phase correction filter to which an input digital phase correction video signal is supplied, and a digital phase correction filter to which the input digital phase correction video signal is supplied. The output of the high-pass filter is supplied, and the gain is relatively large when the amplitude of the input digital phase-corrected video signal is small.
A digital compression circuit having compression characteristics with a relatively small gain when the amplitude of the input digital phase correction video signal is large, and an addition circuit for adding the output of the digital phase correction filter and the output of the digital compression circuit are provided. It is composed of

In this configuration, by setting the phase characteristics of the digital phase correction filter to be equal to the phase characteristics of the digital high-pass filter, a digital video signal with the same phase characteristics is supplied to the adder circuit, and phase information is This will ensure that nothing is lost.

[Brief explanation of the drawing]

1 is a block diagram showing an embodiment of a digital emphasis circuit according to the present invention; FIG. 2 is a block diagram illustrating digital phase correction filters 4 and 9 shown in FIGS. 1 and 7; FIG. is a block diagram showing a conventional digital emphasis circuit; FIG. 4 is a characteristic diagram explaining the operation of the circuit shown in FIG. 3; FIG. 5 is a characteristic diagram explaining the operation of the circuit shown in FIG. 3; 6 is a characteristic diagram illustrating the operation of the circuit shown in FIG. 3, FIG. 7 is a block diagram showing an embodiment of the digital emphasis circuit according to the present invention, and FIG. FIG. 2 is a block diagram illustrating digital phase correction filters 4 and 9 shown in the figure. l...Digital high pass filter 2...Digital compression circuit 3...Addition circuit 4...Digital phase correction filter 5a...Coefficient unit 5b...Coefficient unit 5c...Coefficient unit 6...Adder 7...Delay circuit 8...Adder 9...Digital phase correction filter patent applicant
NEC Home Electronics Co., Ltd. Agent Patent Attorney Yama 1) Takeki Figure 1 Figure 2 Figure 3 Figure 4 Image L Figure 5 Item (

Claims (1)

[Claims] A digital high-pass filter to which an input digital phase-corrected video signal is supplied; a digital phase-correction filter to which the input digital phase-corrected video signal is supplied; and an output of the digital high-pass filter to which the input digital phase a digital compression circuit having compression characteristics in which the gain is relatively large when the amplitude of the corrected video signal is small and the gain is relatively small when the amplitude of the input digital phase correction video signal is large; A digital emphasis circuit that includes an adder circuit that adds the output of the digital compression circuit and the output of the digital compression circuit.