JPH047610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a noise removal device used in digital signal processing.

(b) Prior art Conventional noise removal devices are essentially low-pass filters, which have a noise reduction effect on small-amplitude impulsive random noises, but cannot be expected to be effective on large-amplitude noises. . Moreover, since it is a low-pass filter, the frequency characteristics in the high frequency range deteriorate, and when used in a television receiver, the screen resolution deteriorates.

(c) Purpose of the Invention The present invention has been made in view of the above-mentioned drawbacks, and provides a noise removal device that can sufficiently cope with large-amplitude noise without causing deterioration of the original signal. The purpose is to propose.

(d) Configuration of the invention The noise removal device of the invention converts analog signals into A/D
Difference calculation means for calculating the difference between successive digital values of digital values existing at regular time intervals of the digital signal obtained by conversion, and a difference level obtained by the difference calculation and a reference level. a level comparing means for comparing, a measuring means for generating a plurality of pulses and measuring the pulse period when the difference level is greater than or equal to a reference level by the level comparing means, and a measuring means for measuring the pulse period by the measuring means. time comparison means for comparing the pulse period and a reference time; and a comparison output of the time comparison means to remove at least one digital signal relating to the first pulse period when the pulse period is less than or equal to the reference time; and means for outputting a digital value immediately before the pulse in place of the removed digital signal, and it is possible to determine whether the digital signal is noise or not depending on the level of the digital value of the digital signal and the time that the level is maintained. If it is noise, the digital signal is removed, and the removed area is interpolated with the previous digital signal.

(e) Examples Embodiments of the present invention will be described with reference to the drawings.

Fig. 1 shows a block diagram of the noise removal device of the present invention, and input terminal 1 receives an analog signal which is sampled at regular time intervals and which is converted into a digital signal by an A/D converter. be done. 2 is a difference calculation circuit that calculates the difference between successive digital values existing at each fixed time interval; 3 is a difference level obtained by the difference calculation and a reference level (Vref);
4 is a level comparison circuit that generates a plurality of pulses when the difference level is greater than or equal to a reference level (Vref) by the level comparison circuit 3, and a measurement circuit that measures the pulse period; 5 6 is a time comparison circuit that compares the pulse period measured by the measurement circuit 4 with the reference time (τref), and 6 is the time comparison circuit 5 connected to one input terminal.
This is an AND gate circuit to which the output signal of 1 is input and the clock signal (CLOCK) is input to the other input terminal. 7 is a D-FF (D flip-flop), and the D terminal of this D-FF 7 delays the digital signal input from the input terminal 1 by a predetermined time, and outputs the digital signal to be removed and the digital signal to be removed. The output of the delay circuit 8 for computation time correction is input to synchronize the timing with the output signal from the time comparator circuit 5, and the output of the AND gate circuit 6 is applied to the clock terminal (CLK). It's summery.

The basic concept of the noise removal device of the present invention is that when an input digital signal satisfies the following conditions, the signal is determined to be noise and is removed.

｜Y _o −Y _o-1 ｜Vref (1) Tτref (2) Here, Y _o and Y _o-1 are times n and (n-1), respectively.
Vref indicates a reference level used to determine whether the value of the digital signal is noise. Further, τref is a reference time used to determine whether or not the time T is noise.

Next, the operation of the noise removal device shown in FIG. 1 will be explained with reference to the time chart shown in FIG. 2.

FIG. 2a shows an input signal, which is, for example, a video signal detected by a television receiver, sampled at regular time intervals and A/D converted, and expressed as a level. , ... Y _o-1 , Y _o , Y _o+1 , Y _o+2 ... respectively indicate digital values at times ... n-1, n, n+1, n+2, etc. Below are the digital values to be removed as noise. will be explained as Y _o and Y _o+1 .

This input signal is input to a difference calculation circuit 2, where a difference calculation between successive digital values is performed and output in the form of a difference signal as shown in FIG. 2b.
Then, the difference level |Y _o −Y _o-1 | and the reference level (Vref) are compared in the next level comparison circuit 3,
As a result of this comparison, if the difference level |Y _o −Y _o-1 | is a level value greater than the reference level (Vref), a pulse P1 as shown in FIG. 2c is output. As a result of the next difference calculation, the difference level |Y _o+1 −Y _o | is smaller than the reference level (Vref), so in this case, no pulse is output from the level comparison circuit 3. Similarly, since the differential level |Y _o+2 -Y _o+1 | is a level value higher than the reference level (Vref), a pulse P2 as shown in FIG. 2c is generated.

Then, the next time measurement circuit 4 measures the pulse period T of the pulses P1 and P2 output from the level comparison circuit 3, and the time comparison circuit 5 compares this pulse period T with a reference time (τref). When the pulse period T is less than the reference time (τref), the time comparison circuit 5 outputs a low level signal only during the pulse period T, as shown in FIG. 2e. As a result, only the pulse period T period
Since the AND gate circuit 6 is closed and the clock signal corresponding to the pulse period T is not supplied to the D-FF7 as shown in FIG _.
This is why Y _o+1 is not output from the D-FF7, and instead, the digital value Y _o-1 is output. Second
Figure g shows the digital signal output from D-FF7, and the removed digital value Y _o ,
Instead of Y _o+1 , digital values Y′ _o and Y′ _o+1 at the same level as the digital value Y _o−1 are interpolated.

If the pulse period T is longer than the reference time (τref), the output of the time comparison circuit 5 remains at a high level and a clock signal is supplied to the D-FF7, and the digital values Y _o and Y _o+1 are judged to be noise. It is output from D-FF7 as it is without being processed.

(F) Effects of the Invention The noise removal device of the present invention has the effect of substantially completely removing large amplitude noise without causing deterioration of frequency characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the noise removal device of the present invention.
FIG. 2 is a diagram showing a time chart for explaining the operation. 2...Difference calculation circuit, 3...Level comparison circuit, 4...
Time measurement circuit, 5... Time comparison circuit, 6... AND gate circuit, 7... D flip-flop, 8... Delay circuit for computation time correction.

Claims (1)

[Scope of Claims] 1. Difference calculation means 2 that calculates the difference between successive digital values of digital values that exist at regular time intervals of a digital signal obtained by A/D conversion of an analog signal; Level comparison means 3 for comparing the difference level obtained by the calculation means 2 and the reference level
and a measuring means 4 for measuring the time interval when the difference level is large based on the output of the level comparing means 3; and a time comparison means for comparing the time interval measured by the measuring means 4 with a reference time. A noise removal device comprising: means 5; and means 7 which, based on the comparison output of the time comparison means 5, determines that the time interval is noise when the time interval is small and removes the noise.