JPH0193931A - Noise suppressing system - Google Patents

Abstract

PURPOSE:To suppress noise at the time of the absence of a digital signal, by setting an encoded output to zero when the absolute value of the level of the digital signal outputted from an A/D converter is lower than the level of an encoded output limiting signal. CONSTITUTION:For example, when a binary-coded value corresponding to the level of the digital signal outputted from an A/D converter 10 is 001 or 010 and that corresponding 10 the level of the encoded output limiting signal is 010, the encoded output of the digital signal corresponding to binary-coded output 001 or 010 is set to zero by an encoded output limiting means 14 because the level of the digital signal is equal to or lower than the level of the encoded output limiting signal. The signal outputted from the encoded output limiting means 14 is subjected to various signal processings by a digital signal processing means 16. When signal levels of a noise input waveform A and a noise input waveform B are lower than the level of the encoded output limiting signal, encoding is not performed and the encoded output is set to zero. Thus, the noise at the time of the absence of the digital signal is suppressed.

Description

[Detailed Description of the Invention] Summary: Regarding a method for suppressing noise when there is no signal in the digital signal output from an analog-to-digital converter, suppressing noise when there is no signal in the digital signal output from the analog-to-digital converter. For the purpose of and encoding output limiting means for converting the encoded output value to zero in accordance with the level of the encoded output limit signal, and the absolute value of the digital signal level output from the analog-to-digital converter is the encoded output limit signal. When the level is smaller than the level of , the encoded output is set to zero.

INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to a noise suppression method for a digital signal output from an analog-to-digital converter (hereinafter referred to as an A/D converter) when there is no signal.

Digital telephone networks are a field of communication in which analog signals are used as information and transmitted over digital lines, and the voice information transmission method in digital telephone networks uses digital transmission using digital exchanges and the like. Also, since the voice itself is an analog signal, it is necessary to perform A/D conversion on the calling side and D/A conversion on the receiving side, but it is necessary to perform A/D conversion on the calling side and D/A conversion on the receiving side. The digital signal contains noise generated from each converter, but this noise occurs even when there is no call, which poses a problem of deteriorating voice quality.

It is desired to suppress the adverse effects on information transmission signals caused by noise generated from such electronic layer devices such as A/D converters.

BACKGROUND OF THE INVENTION FIG. 8 is a block diagram of a conventional analog-to-digital conversion system.

A sample-and-hold circuit device 24 that samples an analog signal and holds the sampled value, an A/D converter 10 that performs hanging, quantization, and encoding, and a digital signal that performs encoding and various signal processing. It is constituted by processing means 16.

When converting an analog signal into a digital signal, the analog signal is first sampled in the sample-and-hold circuit device 24, and the value of the sampled signal is held for a certain period of time. The output of the sample and hold circuit device 24 is A
The /D converter 10 performs quantization, but may also perform further encoding. The signal that has been quantized only by the A/D converter 10 is encoded by the digital signal processing means 16, and then subjected to various signal processing.

FIG. 9 is an input/output characteristic diagram using the above-mentioned analog-to-digital conversion method. By adjusting the output code to the position where it is zero even if there is a noise input waveform when the input level is zero,
The output waveform is set to zero. However, as shown in Figure 10, A
When the input/output characteristic curve fluctuates on the coordinate axes due to temperature fluctuations or aging of the /D converter 10, even if the input level of the analog signal is zero, if there is a noise input waveform, two of a and b will occur.
An output waveform with a value is output.

This is the problem that the invention aims to solve.In the analog-to-digital conversion method described above, the A/
If the input/output characteristic curve of the D converter deviates due to temperature fluctuations or the like, there is a problem in that if a noise input waveform exists when there is no signal, an output waveform due to noise will occur.

The present invention has been made in view of these points, and its purpose is to provide a noise suppression method capable of suppressing noise when there is no signal in a digital signal output from an A/D converter. It is to provide.

Means to solve problems FIG. 1 shows a block diagram of the configuration of the present invention.

In FIG. 1(A), an encoded output limit signal that generates an encoded output limit signal for setting a signal level for converting the encoded output value of the digital signal output from the A/D converter 10 to zero is shown. A generating means 12 is provided, as well as an encoding output limiting means 14 for converting the encoded output value to zero in accordance with the level of the encoded output υ11 signal.

Further, as another aspect of the present invention, as shown in FIG. A signal level number determining means 20 is provided for determining whether the number of signal levels of a signal is binary.

Further, a signal level unifying means 22 is provided for unifying the binary digital signals into one value.

Operation FIG. 2 shows an input/output characteristic diagram of the noise suppression method according to the present invention shown in FIG. 1(A). However, the dotted line is the input/output characteristic curve of the A/D converter.

The binary encoded value corresponding to the level of the digital signal output from the A/D converter 10 is, for example, OOl, 010, and the binary encoded value corresponding to the level of the encoded output limit signal is 010. At some point, since the level of the digital signal is equal to or lower than the level of the encoded output limiting signal, the encoding output limiting means 14 encodes the digital signal corresponding to 2 Brigadier encoded output OO1,010. The output will be zero. The signal output from the encoded output limiting means 14 is subjected to various signal processing by the digital signal processing means 16. Further, for example, when the signal level of noise input waveform A1 and noise input waveform B is smaller than the level of the encoding output limit signal, encoding is not performed and the encoding output becomes zero.

FIG. 3 is a comparison table of the binary encoding output according to the present invention and the binary encoding output according to the conventional method.
3 is encoded as is as 0OO1001,010,011, but in the noise suppression method shown in Fig. 2, when the signal input value is Oll and 2, the encoded output is encoded as OOO, and the is encoded as 011 as is.

Further, FIG. 4 shows a flowchart of another noise suppression method of the present invention shown in FIG. 1(B).

The digital signal output from the A,/D conversion '510 is stored for a certain period of time in the signal storage means 18, and the signal level number determining means 20 determines whether the signal level number is binary. And when the number of signal levels is binary,
The digital signal is sent to the signal level unifying means 22, unified to the lower of the two signal levels, and further subjected to various signal processing in the digital signal processing means 16. When the number of signal levels is three or more, the A/D converter 10
The digital signal outputted from the digital signal processing means 16 directly undergoes various signal processing. FIG. 5 shows an input/output waveform diagram when the number of signal levels is multi-valued, and the input waveform is output as is.

FIG. 6 shows an input/output characteristic diagram of the noise suppression method according to another aspect of the present invention shown in FIG. 1(B). In the figure, when binary values a and b are alternately output by a small signal such as a noise input waveform, the signal level stored in the signal storage means 18 is a
, b, and the signal level number determining means 20 determines that the signal level is binary, and the signal level number unifying means 22 unifies the signal level to the value b. FIG. 7 shows an input/output waveform diagram at this time.

Effects of the Invention Since the present invention is configured as detailed above, analog
It is possible to suppress noise in the digitally converted digital signal when there is no signal, and it is possible to generate a digital signal with a good S/N ratio.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the configuration of the present invention, Fig. 2 is an input/output characteristic diagram of the noise suppression method according to the present invention shown in Fig. 1 (Δ), and Fig. 3 is a diagram according to the present invention shown in Fig. 1 (A). FIG. 4 is a flowchart of the noise suppression method according to another aspect of the present invention shown in FIG. 1 ([3)]; FIG. FIG. 6 is an input/output waveform diagram when the number of signal levels is multi-level; FIG. 6 is an input/output characteristic diagram of the noise suppression method according to another aspect of the present invention shown in FIG. 1(B); FIG. 7 is the diagram of FIG. (B) is an input/output waveform diagram of the noise suppression method according to another aspect of the present invention, FIG. 8 is a block diagram of the conventional analog-to-digital conversion method, and FIG. Output Characteristic Diagram FIG. 10 shows an input/output characteristic diagram when the input/output characteristic curve changes ωJ in the conventional system. 10... A/D converter, 12... Encoded output limiting signal generation means, 14... Encoded output limiting means, 16... Digital signal processing means, 18... Signal storage means, 20 ...Signal level number determining means, 22. Signal level unification means, 24. Sample and hold circuit device. z′〕Representative: Patent Attorney Igeta Sada, ′−ゝ・,昌＼ 7 7′ (A) (B) Hon Meguri Month 0 S [Receipt]′ 口・り Ｇａ １ Ｇｕｒｅ １ 圀（ A) 1 niho ne horizontal 5 light J' 7) spicy all tone F turquoise 1 f) entering the poetic figure 2 J' ro 2 acquisition manzai b comparison with water power Figure 3 (Telegraph), 1st day (B)
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Claims (2)

[Claims] (1) Encoding output limit signal generating means (12) that generates an encoding output limit signal for setting a signal level for converting the encoded output value of the digital signal output from the analog-to-digital converter (10) to zero. ) and encoding output limiting means (14) for converting the encoded output value to zero in accordance with the level of the encoded output limiting signal, the digital signal output from the analog-to-digital converter (10) A noise suppression method characterized in that when the absolute value of the level is smaller than the level of the encoded output limiting signal, the encoded output value is set to zero. (2) Signal storage means (18) for storing the digital signal output from the analog-to-digital converter (10) for a certain period of time
and signal level number determining means (20) for determining whether the number of signal levels of the digital signal stored by the signal storage means (18) is binary; and converting the binary digital signal into one value. A signal level unifying means (22) is provided to unify the signal level, and the signal level number determining means (20) determines that the number of signal levels of the digital signal output from the analog-to-digital converter (10) is binary. The noise suppression method is characterized in that the digital signal is sent to a signal level unifying means (22) and the signal level is unified to the lower of the two values.