JP2008217934A - Signal processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal processing apparatus capable of suppressing noise, that is generated by a ground potential difference between both apparatuses due to respective signal currents flowing on the ground side of connection cables between both apparatuses, by generating a noise canceling voltage and mixing the voltage into a signal line on which noise is canceled with respect to the signal processing apparatus, which is connected to an apparatus having at least two kinds of signal sources through a plurality of connection cables corresponding to the signal sources and processes signals sent from respective signal sources. <P>SOLUTION: An input part 10 in the signal processing apparatus includes a noise elimination circuit 110 which is capable of generating a noise canceling voltage Ec corresponding to a ground potential difference En from a video signal voltage Ev by using an arbitrary multiplication coefficient and of adding this voltage Ec to a line audio signal voltage Ea. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention provides a signal line between a device having at least two types of signal sources and a signal processing apparatus that is connected via a plurality of signal lines corresponding to the signal sources and processes signals sent from the signal sources. The present invention relates to a technique for reducing a noise voltage appearing in a signal processing device due to a potential difference generated between the devices due to a signal current flowing on the ground side.

  When the signal processing device and the DVD player are connected via the video signal connection cable and the line audio connection cable, a current obtained by adding the video signal current and the line audio signal current flows through the ground line of the connection cable. Since the connection cable connected to the ground has a resistance, a potential difference is generated between the DVD player and the signal processing device, and noise is mixed into the line audio signal, resulting in deterioration of sound quality.

  In order to avoid the ground loop, a method of separating the ground line and the signal line and grounding at one point, and an apparatus for that purpose (see Patent Document 1) have been used.

Japanese Patent Laid-Open No. 11-260435

  However, one-point grounding requires a device for separating the ground line and the signal line of the connection cable, and the ground line tends to be long. As a result, since the signal line and the ground line are far away from each other, a large loop is formed, and external noise jumping into the loop is added to the signal as noise.

  According to the signal processing device of the present invention, the signal current of the connection cable that transmits the signal from the signal source corresponding to the ground line that is assumed to be the noise source is assumed to be a noise source. A signal processing apparatus is provided in which a noise removal circuit is interposed between the signal line to be erased.

  The present invention relates to a potential difference generated between a device having at least two types of signal sources and a signal processing device that is connected via a plurality of signal lines corresponding to the signal sources and processes signals sent from the signal sources. A voltage corresponding to En is generated by the multiplication circuit using the multiplication coefficient, and the addition circuit adds the noise to the signal line to be canceled. As a result, noise is reduced and high-quality audio signal transmission is realized.

  According to the present invention, a conventional connecting device can be used for connecting a device having at least two types of signal sources and a signal processing device connected via a plurality of connecting cables corresponding to the signal sources. It is possible to provide a signal processing device that reduces noise without being affected by the impedance of the ground line that varies depending on the length.

  The best mode for carrying out the present invention will be described with reference to FIG. The signal processing apparatus 1 includes an input unit 10, a video output unit 11, an analog / digital converter (ADC) 12, a digital signal processor (DSP) 13, a digital / analog converter (DAC) 14, an audio output unit 15, A control unit 16 and an operation unit 17 are provided.

  The input unit 10 includes a noise removal circuit 110, a video load resistor 103, and an audio load resistor 104. Further, the video input terminal 101 and the line audio input terminal 102 are electrically connected to the DVD player 20, and are provided with a video signal line 105 and a line audio signal line 106 connected by a cable.

  A video signal connection cable 301 is connected to the video signal input terminal 101. An analog video signal is input from the DVD player 20 via the video signal connection cable 301. A line audio signal connection cable 302 is connected to the line audio signal input terminal 102. An analog audio signal is input from the DVD player 20 via the line audio signal connection cable 302.

  The video signal connection cable 301 includes an internal conductor video signal line 301a and an external conductor ground line 301b. The line audio signal cable 302 includes an internal conductor line audio signal line 302a and an external conductor ground line 302b.

  For audio signals, for example, in the case of multi-channel such as two stereo channels and 5.1 surround channels, an input terminal can be provided for each channel.

  The ADC 12 provided for each channel converts the input analog audio signal of each channel into a digital audio signal, and outputs the converted digital audio signal to the DSP 13. The DSP 13 performs digital signal processing such as surround decoding processing on the digital audio signal.

  The DAC 14 converts the digital audio signal into an analog audio signal and outputs the converted analog audio signal to the audio output unit 15. The audio output unit 15 includes an output terminal corresponding to each channel, and the analog audio signal of each channel is output from the output terminal corresponding to each channel and input to the speaker of each channel.

  The analog video signal input from the video signal input terminal 101 is output from the video output unit 11 and input to a monitor (not shown).

  Alternatively, the input analog video signal may be converted into a digital signal and subjected to signal processing such as resolution conversion, and then the video signal converted into the analog signal may be output from the video output unit 11.

  The noise removal circuit 110 includes an operational amplifier and includes a multiplication circuit 111 and an addition circuit 112. The multiplication circuit 111 multiplies the video signal voltage Ev input from the video signal input terminal 101 by a multiplication coefficient to generate a noise cancellation voltage corresponding to the potential difference En, and the addition circuit 112 mixes into the line audio signal line 106. . The analog audio signal to which the noise cancellation voltage is added is input to the ADC 12.

  Next, with reference to FIG. 4, in order to estimate how the potential difference En is generated and how much the value will be, a description will be given by obtaining based on numerical values.

The potential difference En generated between the DVD player and the signal processing device is
En = Ir x R
= (Iv + Ia) × R
= {[(Ev ÷ (R + Rv)) + (Ea ÷ (R + Ra)}] × R… (1)
It is expressed by the following formula.

Usually R is a sufficiently small value of 0.1 or less.
En ≒ (Ev ÷ Rv) × R = R / Rv ・ Ev (2)
Is obtained.

  Accordingly, En accurately approximates the video signal voltage Ev multiplied by the coefficient (R / Rv) of the ground line total resistance value R of the connection cable used for connecting the signal processing device and the DVD player.

  An example of calculating En generated between a DVD player and a signal processing device assuming a resistance value of a cable assumed to be generally used and a voltage of each unit is shown.

Video signal voltage Ev: 1.0Vp-p (100% screen)
Video load resistance Rv: 75Ω
Line audio signal current Ea: 2.8Vp-p (1.0Vrms)
Line audio load resistance Ra: 47kΩ
Total resistance of connection cable ground wire R: 0.05Ω
Then, the potential difference En is calculated from the equation (1)
En = {(1.0Vp-p ÷ 75Ω) + (2.8Vp-p ÷ 47000Ω)} × 0.05Ω
= (13.333mAp-p + 0.0596mAp-p) × 0.05Ω
= 0.67mVp-p
According to this equation, it can be seen that most of the noise generated between the DVD player and the signal processing device is caused by the video signal current.

  The principle of the present invention will be described with reference to the circuit diagram of FIG.

  In order to cancel the potential difference En, the noise removal circuit 110 generates a noise cancellation voltage Ec corresponding to En using the expression (2) and mixes it with the line audio signal voltage Ea.

The voltage Eai input to the line audio signal input terminal 102 of the signal processing device 1 is
Eai = Ea + Ec-En, where Ec = En,
Eai = Ea (3)
Is guided.

  From Equation (3), the influence of the potential difference En that causes noise mixing can be eliminated, and Ea, which is the line audio signal source of the DVD player, can be directly input to the line audio signal terminal of the signal processing device as Eai. .

  Therefore, the multiplication coefficient is set so that the mixing ratio of the video signal voltage to the line audio signal voltage is optimized in accordance with the ground line total resistance value R of the connection cable used for connecting the DVD player and the signal processing device. Is set.

  Next, an embodiment in which noise is removed using the above-described En will be described with reference to FIG.

  In the first embodiment, an optimum multiplication coefficient is set in advance in the noise removal device 110 from the total resistance R of the connection cable and the value of the video load resistance Rv, and the noise cancellation voltage corresponding to the potential difference En is multiplied by Ev. Ec is generated and mixed into the line audio signal voltage Ea.

  Hereinafter, the optimum multiplication coefficient (R / Rv) when using a device that is generally assumed to be used will be described.

The multiplication coefficient (R / Rv) is assumed to be a generally used value, video load resistance Rv = 75Ω, and line audio load resistance Ra = 47kΩ. From equations (1) and (2),
En = Ir x R = {(Iv + Ia) x R}
= [{(Ev ÷ (R + 75)} + {Ea ÷ (R + 47000)}] × R
Usually, R is a sufficiently small value of 0.1 or less.
En ≒ (Ev ÷ 75) × R = R / 75 ・ Ev
And the multiplication coefficient is R / 75.

  A second embodiment will be described with reference to FIGS. 1 and 3.

  In the second example, the operation unit 17 receives an operation 41 for setting a ratio (multiplication coefficient) for adding the video signal voltage to the line signal voltage in the noise removal circuit 110. In addition, it has an operation unit for inputting various instructions such as a power on / off instruction 42 and a volume control 40. (FIG. 1) Specifically, a user interface is provided for accepting operations. As the user interface, an angularly displaceable rotary knob, a displaceable slide knob, a touch panel, or the like can be used. Of course, these can be used together.

  Each element operated by the user in the user interface includes a switch, a button, and the like for turning on and off the signal processing apparatus 1. Examples include an adjustment button for setting a multiplication coefficient, a volume adjustment button, and the like.

  In the control unit 16, the multiplication circuit 111 multiplies the video signal voltage Ev by the multiplication coefficient (R / Rv) set by the operation unit 17 to generate a noise canceling voltage Ec corresponding to the potential difference En, and the addition circuit 112 , Ec is added to the line audio signal voltage Ea to control the noise removal circuit 110. The setting of the multiplication coefficient (R / Rv) defines a default value, and when there is no operation from the operation unit 17, the default value of the multiplication coefficient (R / Rv) is used. The operation on the operation unit 17 can be configured to change the setting so that the coefficient value is finely adjusted around the default value.

  According to the present embodiment, the noise removal circuit 110 generates a noise cancellation voltage Ec using a default multiplication coefficient, adds the noise cancellation voltage Ec to the line audio signal voltage Ec, removes the noise, and further causes a human hearing problem. If the noise to become is generated, the noise canceling voltage Ec can be finely adjusted by operating the operation unit 17. Further, even when the ground line total resistance value R and the video load resistance Rv of the connection cable used for connection with the signal processing device 1 are different from the default setting values, the user operates the operation unit 17 to set the potential difference En. The corresponding noise cancellation voltage Ec can be adjusted to be optimum.

It is a block diagram of the signal processing apparatus which is an Example of this invention. 1 is a configuration diagram of a signal processing device in Embodiment 1. FIG. It is a block diagram of the signal processing apparatus in Example 2. It is a figure explaining the circuit which simplified about the potential difference. It is a figure explaining the effect of an addition apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Signal processing apparatus, 10 ... Input part, 11 ... Video output part, 12 ... ADC, 13 ... DSP, 14 ... DAC, 15 ... Audio output part, 16 ... Control part, 17 ... Operation part, 20 ... DVD player, DESCRIPTION OF SYMBOLS 101 ... Video signal input terminal, 102 ... Line audio signal input terminal, 103 ... Video load resistance, 104 ... Line audio load resistance, 105 ... Video signal line, 106 ... Line audio signal line, 110 ... Noise removal circuit, 111 ... Multiplication Circuit, 112 ... adder circuit, 301 ... video signal connection cable, 301a ... video signal connection cable signal line, 301b ... video signal connection cable ground line, 302 ... line audio signal connection cable, 302a ... line audio signal connection cable signal line, 302b ... Line audio signal connection cable ground line

Claims (3)

Line audio signals sent from the signal sources connected to the video and audio reproduction equipment having at least two types of signal sources via a plurality of connection cables, each having a signal line and a ground line, corresponding to the signal sources. And a signal processing device for processing a video signal,
An input unit to which a signal from the signal line of the connection cable is input, and a processing unit to process each of the input signals,
The input unit is
A connector for connecting the connection cable;
A multiplication circuit for generating a noise cancellation voltage, and an addition circuit for adding the noise cancellation voltage to a line audio signal line,
The multiplication circuit is configured such that, among the signal sources, a signal current flowing through the ground line is assumed to be a noise source, and the signal source voltage Ev of the video signal line corresponding to the ground line is set to a load resistance of the video signal line. Rv, the total resistance of the ground lines of the plurality of connecting cables is R, and multiplied by a multiplication coefficient (R / Rv) to generate a potential difference En generated in the ground line,
The signal processing apparatus, wherein the adding circuit adds the generated En to the line audio signal line voltage. The signal processing device according to claim 1,
In the multiplication circuit, the multiplication coefficient (R / Rv) is set in advance. The signal processing device according to claim 1,
An operation unit for receiving a user operation and changing the multiplication coefficient (R / Rv);
A signal processing apparatus comprising a control unit that controls the multiplication circuit and the addition circuit.

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