JPH0782055B2 - Noise detector - Google Patents

Description

The present invention relates to noise detection for detecting a level of noise generated in a processing circuit for analog signals such as video signals and audio signals and mixed in an output signal of the processing circuit. Regarding the device.

[Conventional technology]

Conventionally, in the field of video equipment and audio equipment, performance evaluation of video and audio signal processing circuits such as amplifiers and filter circuits is performed. Therefore, video signals and audio signals generated in the processing circuits and passed through the processing circuits are used. The level (magnitude) of relatively minute noise such as white noise mixed in is detected.

By the way, conventional detection of this kind of noise is often
This is performed using an oscilloscope, and for example, a video signal (composite signal) whose luminance level is fixed at 50% (gray level) or a sine wave audio signal is input to a detection target processing circuit, and the output of the processing circuit is detected. This is done by observing the signal waveform with an oscilloscope.

On the other hand, on page 14-10 of "Television Engineering Handbook" (edited by The Television Society of Japan, published by Ohmsha Co., Ltd.), the level of high frequency noise mixed in the video signal is detected by the noise detection device having the configuration shown in FIG. It is described to do.

In the case of the detection device of FIG. 3, the input video signal to be detected (hereinafter referred to as the input video signal) is divided into three by the video distribution circuit (1), and the high-pass filtering circuit (2) It is input in parallel to the level hold circuit (3) and the sync separation circuit (4), and the input video signal of the input video signal is input from the filtering circuit (2) to the threshold detection circuit (6) through the preamplification circuit (5) for level clamping. High frequency components are output.

Further, the hold circuit (3) holds the threshold E as a reference for noise detection based on the level hold of the input video signal.
A signal of the level is formed, and the signal is output to the detection circuit (6).

Then, only when the level of the output signal of the amplifier circuit (5) exceeds the level of the threshold value E of the output signal of the hold circuit (3), the signal is output from the detection circuit (6) to the gate circuit (7). .

Further, based on the sync signal in the input video signal separated by the sync separation circuit (4), the noise gate pulse generation circuit (8) causes the gate circuit (7) to have a preset noise detection period of one field each. A gate pulse of width is output.

The gate circuit (7) is turned on only when the gate pulse is output from the generation circuit (8) to output the input signal to the counter circuit (9), and at this time, the synchronization signal of the synchronization separation circuit (4). Based on the above, the counter gate pulse generation circuit (10) outputs to the counter circuit (9) a gate pulse having a width of a predetermined counting period within the noise detection period, and only while the gate pulse is input, With the counter circuit (9), the signal output period of the gate circuit (7),
That is, the signal period exceeding the threshold value E is counted.

Therefore, the counter circuit (9) outputs the count signal of the number of times that the level of the high frequency component of the input video signal exceeds the level of the threshold value E to the display hold circuit (11) during a fixed period set by the count period. However, at this time, the value of the count signal increases as the level of high-frequency noise included in the input video signal increases, and the count repeat count (total sampling count) of the counter circuit (9) during the certain period is also increased. The level of high frequency noise included in the input video signal can be calculated based on the number of count signals of the counter circuit (9) (the number of samplings exceeding the threshold value E).

Therefore, for example, the hold circuit (11) calculates and displays the level of the high frequency noise included in the input video signal based on the input count signal.

[Problems to be solved by the invention]

By the way, as described above, when observing the waveform of the output signal of the processing circuit with an oscilloscope and detecting relatively small noise such as white noise mixed in the output signal of the processing circuit, the high impedance of the oscilloscope is detected. There is a problem that various external noises are easily mixed in the probe and cannot be detected accurately.

On the other hand, when detecting the noise mixed in the output signal of the processing circuit by using the detection device of FIG. 3 instead of the oscilloscope, by connecting the processing circuit and the detection device with a low-impedance coaxial cable or the like, Mixing of extraneous noise, such as when using a detection probe, is prevented.

However, when the detection device of FIG. 3 is used, the analog level detection of the input video signal based on the threshold value E of the hold circuit (3) formed from the input video signal and the generation circuit (formed from the input video signal In order to detect noise by counting the number of times of detection based on the gate pulse of 8) and (10), a hold circuit (3), a sync separation circuit (4),
Detection circuit (6), gate circuit (7), generation circuit (8),
(10), requires a large number of circuits such as a counter circuit (9),
There is a problem that the detection device becomes complicated and expensive, and cannot be detected easily and inexpensively.

Further, in the case of the detection apparatus of FIG. 3, since only the high frequency component is extracted by the filtering circuit (2) and only the high frequency noise is detected, it is difficult to detect the noise in all bands, and Since the generation circuit (8), (10) forms a gate pulse based on the synchronization signal in the video signal, it is applicable to the detection of noise generated in the processing circuit for analog signals other than video signals such as audio signals. There is a problem that can not be done.

[Means for solving problems]

The present invention has been made with the above points in mind, and the present invention will be described below with reference to FIG. 1 corresponding to the embodiment.

Circuit for processing analog signals such as video and audio signals (1
In the noise detection device for detecting the level of noise generated in 2) and mixed in the output signal of the processing circuit, in the present invention, a periodic sawtooth reference signal is used as an input signal of the processing circuit (12) at the time of detection. And a reference signal generation circuit (13) for generating a signal, and an analog / digital conversion circuit (14) for sequentially converting the output signal of the processing circuit (12) into an N-bit digital signal.
And a delay circuit (15) for delaying and outputting all bits or lower K bits (1 ≦ K <N) of the converted digital signal of the conversion circuit (14) for a period of an integer multiple of the reference signal, A comparison circuit (16) for repeatedly comparing the conversion digital signal and the delayed digital signal of the delay circuit (15) for all the bits or the K bits and outputting a detection signal obtained by converting the noise level into time. .

[Work]

Therefore, according to the noise detecting device of the present invention, at the time of detection, the level of the input signal of the processing circuit (12) is based on the reference signal of the generating circuit (13) as shown by the solid line A in FIG. 2 (a). It changes repeatedly with a sawtooth shape, at this time,
The level of the output signal of the processing circuit (12) is changed to the processing circuit (12).
Based on comparatively small noise such as white noise generated inside, it fluctuates randomly within the range of broken lines B and B ′ in FIG.

Then, the output signal of the processing circuit (12) is digitally converted by the conversion circuit (14). At this time, the converted digital signal output from the conversion circuit (14) corresponds to the noise level mixed with the lower K bits. Fluctuate.

Further, all bits or lower K bits of the converted digital signal of the conversion circuit (14) are delayed by the delay circuit (15), and the converted digital signal of the conversion circuit (14) and the delay circuit (15) are delayed by the comparison circuit (16). ) All the bits of the delay digital signal or the matching or mismatching of the lower K bits are detected, so that the detection signal output from the comparison circuit (16) is time-multiplexed in synchronization with the cycle of the sawtooth reference signal. Then, as shown in FIG. 2 (b), for example, the converted digital signal is changed to the lowest bit (LSB) according to the change of the unit level DZ of the reference signal.
For a certain period of time Ta required to change
A signal that has a level indicating that there is continuous noise due to a mismatch for a period Tb proportional to the noise level HZ of is obtained, and at this time, the noise of the entire band is obtained from the formula of NZ = DZ × (Tb / Ta). Level is easily detected.

Then, the reference signal of the generation circuit (13) is input to the processing circuit (12), and the output signal of the processing circuit (12) is converted into a digital signal by the conversion circuit (14), the delay circuit (15) and the comparison circuit (16). In addition to converting the digital signal to the delayed digital signal to obtain a detection signal in which the amplitude of noise such as white noise generated in the processing circuit (12) is converted into time, Compared to the detection device shown in the figure, the configuration is simple and inexpensive, and moreover,
Since the detection signal of the comparison circuit (16) is a binary change signal, even if an oscilloscope or the like is used for the multiplex synthesis, accurate detection can be performed without being affected by external noise and the like. Since the detection apparatus shown in the figure does not require the threshold value E and the gate pulse, it can be applied to various analog signal processing circuits.

〔Example〕

Next, the present invention will be described in detail with reference to FIGS. 1 and 2 showing one embodiment thereof.

FIG. 1 shows a case where a video signal processing circuit is used as a detection target circuit. In FIG. 1, (12) is a detection target processing circuit, such as a video signal (composite signal) amplifier circuit, a filter circuit, or the like. It consists of a single circuit or a combination of multiple single circuits, and the input and output signal levels are relatively low.

Reference numeral (13) is a reference signal generation circuit provided before the processing circuit (12), for example, a ROM storing waveform pattern data, an address generator for reading the ROM, and the read pattern data. Is converted into an analog signal and is output to the processing circuit (12). The digital-to-analog converter converts the signal into an analog signal and outputs a comparatively gentle sawtooth wave for each horizontal scanning period of the video signal (hereinafter, the horizontal scanning period is referred to as H). The changing reference signal of the waveform of the solid line A in FIG. 2A is output.

(14) is an analog / circuit provided after the processing circuit (12)
A digital conversion circuit that continuously repeats sampling and quantization to sequentially convert an output signal of the processing circuit (12) into an N-bit (N is an integer) digital signal and convert each digital signal into a converted digital signal. Output as.

Reference numeral (15) is a delay circuit to which the converted digital signal is input, and the lower K bit (1
It is formed by using a 1H delay circuit of K bits for delaying only .ltoreq.k <N), and delays and outputs only a preset lower K bit among all the bits (= N bits) of the converted digital signal.

Reference numeral (16) is a comparison circuit connected to the conversion circuit (14) and the delay circuit (15), which is composed of a 2-input match / mismatch detection circuit, and is a lower order of the converted digital signal output from the conversion circuit (14). Output from the K bit and delay circuit (15)
Compare the K bit of the 1H delayed digital signal, and if the signals of both K bits become exactly the same and there is no level difference between adjacent 2H, it is considered that there is no noise and the output is held at 0 and both K bits are If there is a difference in level between adjacent 2H signals due to different signals, it is considered that there is noise, the output is inverted to a high level, and the detection signal shown in FIG. 2B is repeatedly output. (17) is a noise detection device having a broken line configuration.

Then, at the time of detection, the processing circuit (12) and the detection device (17) are connected as shown in FIG. 1 using a coaxial cable or the like,
At this time, the generation circuit (13) repeatedly reads the pattern data of the ROM, converts it into an analog signal, and processes the reference signal of the waveform of the solid line A in FIG. Output to 12).

The reference signal changes to almost the maximum input level of the processing circuit (12) during 1H.

Further, the K bit described above is set in anticipation of the maximum number of bits of the converted digital signal that fluctuates due to noise generated in the processing circuit (12), and based on white noise,
When the output signal of the processing circuit (12) fluctuates within the width of the broken lines B, B'in FIG. 2 (a), the lower K bit of the converted digital signal changes.

Then, when the reference signal of the generation circuit (13) passes through the processing circuit (12), the signal output from the processing circuit (12) to the conversion circuit (14) includes a white signal generated in the processing circuit (12). A relatively small amount of noise such as noise is mixed, and at this time, the level of the mixed noise is the broken line B in FIG.
If the noise level (amplitude) NZ is in the width of B ', the output signal of the processing circuit (12) fluctuates randomly within the noise level NZ range with reference to the level of the solid line A in FIG.

On the other hand, in the conversion circuit (14), the unit level DZ in FIG. 2 (a) corresponding to the minimum bit (LSB) is set to be larger than twice the expected maximum noise level, and the interval is sufficiently smaller than 1H. At, the input signal is sampled and quantized, and N-bit converted digital signals (parallel signals) are sequentially output.

Then, the converted digital signal randomly fluctuates below the lower K bit depending on the noise level NZ, and the processing circuit (12)
When the output signal of the processing circuit (12) is at the level of the broken line B in FIG. 2 (a), compared to the case where the output signal of FIG. 2 is at the level of the reference signal of the solid line A in FIG. Indicates that the converted digital signal changes rapidly only during the period corresponding to the half width of the noise level NZ, and when the output signal of the processing circuit (12) reaches the level indicated by the broken line B ′ in the figure, the converted digital signal indicates the noise level NZ. It changes slowly only during the period corresponding to the half-value width of.

Further, the converted digital signal is input to the delay circuit (15) and the comparison circuit (16), and the comparison circuit (16) outputs a delayed digital signal obtained by delaying the lower K bits of the converted digital signal by 1H.

Then, the comparison circuit (16) compares the lower K bit of the converted digital signal with the delayed digital signal. At this time, if both K bits are the same, the comparison circuit (16) considers that there is no noise. Hold the output level at 0, and if both K bits are different, it is considered that there is noise and the output level is inverted to the high level.

Therefore, the detection signal of the comparison circuit (16) is as shown in FIG.
Of the solid line A, the broken lines B, and B'in the constant period Ta required for the unit level DZ to change, a period Tb proportional to the noise level NZ
Continuously becomes a high level indicating that there is noise, and at this time, the formula of NZ = DZ × (Tb / Ta) is established.

That is, the detection signal of the comparison circuit (16) is the processing circuit (12).
It becomes the signal which converted the level of the white noise etc. which occurred in the time, and the period Ta, Tb of the detection signal of the comparison circuit (16).
The noise level is detected from the length of the noise.

In the present embodiment, for example, assuming that the Kth bit to be compared with the AD conversion bit number being 8 is the fifth bit from the lower order of the AD conversion bit, the maximum AD conversion input is 256 steps in FIG. 2A. Separated. The unit level DZ is 16
It is separated by step intervals, and the fifth bit from the lower order is inverted every 16 steps. TA corresponds to a period in which the sawtooth wave indicated by A in FIG. 2 (a) changes by a unit level, and when the signal in which the white noise is superimposed on the sawtooth wave is AD-converted, FIG.
In the Tb period of (a), depending on white noise, 5
AD conversion timing occurs when the bit number changes. In this period Tb, the time width changes in proportion to the white noise level. Therefore, assuming that the white noise level is 6 steps, Tb / Ta = 6/16 in FIG. 2B, and the noise level can be known by measuring the time width of Tb.

By the way, the lengths of the periods Ta and Tb are measured, for example, by using an oscilloscope and displaying the waveform of the detection signal of the comparison circuit (16) on the screen based on the sweep trigger synchronized with the reference signal. , Ta and Tb are measured from the multiple composite waveform obtained by superimposing the detection signals of the comparison circuit (16) for one field or one frame which is visible at one time by the afterimage effect, and the comparison circuit (16)
The detection signal of 2 changes greatly in two values depending on the presence / absence of noise regardless of the level of the output signal of the processing circuit (12), so that the continuity of the period Tb is clearly displayed and external noise etc. The noise level NZ can be easily and accurately detected by accurately measuring the periods Ta and Tb without being affected by.

From the waveform displayed on the oscilloscope, the period Ta, Tb
When measuring, the length between the centers of the periods Tb becomes equal to the period Ta, so in reality, the length between the centers of the periods Tb and the period Tb
And the length of is measured.

In the case of FIG. 1, the reference signal is supplied to the processing circuit (12), the output signal of the processing circuit (12) is converted into a digital signal, and the lower K of the digital signal delayed by 1H from the digital signal is supplied. Since the configuration is such that bits are compared,
The detection device (17) is formed easily and inexpensively without the need to amplify the input signal, separate the synchronization and create the gate pulse like the detector shown in the figure, and to detect the noise level NZ easily and inexpensively. You can

Furthermore, since the filtering circuit (2) of FIG. 3 is not used,
Since the noise level NZ of the entire band can be detected and it is not necessary to form a gate pulse for detection from the synchronizing signal in the output signal of the processing circuit (12), for example, Even if replaced with a signal processing circuit,
It can be detected in the same manner as described above, and can be used for detecting noise generated in various analog signal processing circuits.

All bits of the converted digital signal of the conversion circuit (14) are delayed by the delay circuit (15), and all bits (= N) of the digital signals of both circuits (14) and (15) are delayed by the comparison circuit (16). The same effect as described above can be obtained by comparing (bit).
In the case of the figure, K of digital signals of both circuits (14) and (15)
Since only the bits are compared, the configurations of the delay circuit (15) and the comparison circuit (16) are simplified, and the configuration of the detection device (17) is significantly simpler and less expensive than the case of comparing all the bits. .

By the way, it goes without saying that the above-mentioned N bit and K bit can be arbitrarily set according to the application, the noise level NZ and the like.

Also, the unit level DZ of the conversion circuit (14) can be variably set. In this case, for example, when the noise level NZ becomes larger than the expected level,
By increasing the unit level DZ and decreasing the resolution of the conversion circuit (14), the period Ta becomes longer, the periods Ta and Tb can be measured, and the noise level NZ in a wide level range can be detected.

Furthermore, the periods Ta and Tb of the detection signal of the comparison circuit (16) can be automatically measured using, for example, a counter instead of using the oscilloscope.

In the case of the above-mentioned embodiment, the video signal processing circuit (12)
In order to apply to the signal generator circuit (13), the reference signal of the generation circuit (13) is a video signal format signal with a sync signal added. However, when applied to an audio signal processing circuit, etc., add a sync signal etc. In this case, the variable level range of the reference signal, the cycle length, etc. can be set arbitrarily.

Further, it goes without saying that the generating circuit (13) may be formed by a sawtooth signal generator having various configurations, and further, the delay circuit (15)
Of course, the delay period may be set to an arbitrary period that is an integral multiple of the period of the reference signal such as a plurality of Hs.

〔The invention's effect〕

As described above, according to the noise detecting device of the present invention, the periodic sawtooth signal of the reference signal generating circuit is input to the processing circuit, and the output signal of the processing circuit is converted into a digital signal to be formed. , The converted digital signal is delayed for a period of an integral multiple of the period of the reference signal, and all bits of the delayed digital signal or lower K bits are repeatedly compared,
By repeatedly outputting a signal obtained by converting the level of noise such as white noise generated in the processing circuit into time as a detection signal, the white noise of the entire band can be obtained with a simple and inexpensive configuration based on the waveform of the multiple synthesis of the detection signal. It is possible to easily and accurately detect the level of comparatively small noise such as, and moreover, even if the processing circuit is various processing circuits such as video signals and audio signals, detection can be performed.
It is possible to provide a highly versatile noise detection device.

[Brief description of drawings]

FIGS. 1 and 2 (a) and (b) show an embodiment of the noise detecting device of the present invention. FIG. 1 is a block diagram and a second diagram.
FIGS. 3A and 3B are waveform diagrams for explaining the operation, and FIG. 3 is a block diagram of the conventional noise detecting device. (12) …… Processing circuit, (13) …… Reference signal generating circuit,
(14) …… Analog / digital conversion circuit, (15) …… Delay circuit, (16) …… Comparison circuit.

Claims (1)

[Claims] 1. A noise detection device for detecting the level of noise generated in a processing circuit for analog signals such as video signals and audio signals and mixed in an output signal of the processing circuit, wherein the input signal of the processing circuit is detected. A reference signal generation circuit for generating a periodic sawtooth reference signal, an analog / digital conversion circuit for sequentially converting the output signal of the processing circuit into an N-bit digital signal, and all of the conversion digital signals of the conversion circuit. A delay circuit for delaying and outputting a bit or lower K bits (1≤K <N) for a period of an integer multiple of the reference signal; and all bits of the converted digital signal and the delayed digital signal of the delay circuit, or And a comparison circuit that outputs the noise detection signal by repeating the detection comparison of the K bit coincidence and non-coincidence.