JPH0685412A - Feedback wiring pattern for electronic circuit - Google Patents

Abstract

PURPOSE:To prevent the mixing of noise into a feedback circuit and also to prevent the superpositioning of noise on the output by a method wherein the earth pattern, with which the earthing wires on the former stage and the latter stage of an electronic circuit are connected, are provided side by side, and at the same time, they are connected to the earthing wire of the electronic circuit at one point. CONSTITUTION:As the ground plane 4, which is stratified on a feedback wiring pattern 3, is connected to an earthing wire at a point 10 on the former stage, and the ground plane 4 is insulated an earth pattern on the other points, the current between machines is allowed to flow to the earth pattern 5, and it is not allowed to flow on the ground plane 4. Accordingly, no induced electromotive force is generated on the feedback wiring pattern 3, the and mixing of noise is prevented. Also, the earth pattern 5 is symmetrically provided side by side to the feedback wiring pattern 3. Accordingly, the induced electromotive force by the electromagnetic flux becomes equal, no noise is generated on the voltage between an output terminal 8a and the earthing wire 8b of the output terminal, and the superposition of noise can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedback wiring pattern for electronic circuits.

[0002]

2. Description of the Related Art Conventionally, feedback wiring patterns for electronic circuits are
It cannot be said that sufficient consideration has been given to noise mixed therein and noise appearing in the output voltage. Therefore, the drawbacks of the conventional feedback wiring pattern will be described with reference to the drawings, taking the case of an audio negative feedback amplifier as an example.

When electronic devices having a power transformer are connected to each other, an inter-device current containing a high frequency component flows as a noise current between the grounds. This inter-device current flows from the ground of the input of the electronic device to the AC power source via the capacitance of the primary winding and the secondary winding of the power transformer. Alternatively, it flows from the ground of the input of the electronic device to the output of the electronic device. Therefore, the inter-device current passes through the grounds at the front and rear of the electronic circuit.

In many negative feedback amplifiers for audio, since the feedback wiring pattern is connected from the latter stage to the former stage, noise due to induced electromotive force is generated in the feedback wiring pattern due to the inter-device current flowing between the former stage and the latter stage. Occurs. For example, when a double-sided board having a ground plane on one side as shown in FIG. 2 is used, noise due to induced electromotive force is generated in the feedback wiring pattern by the inter-device current flowing through the ground plane. For this reason, this induced electromotive force causes noise to be superimposed on the output signal at the output point. It should be noted that FIG. 2 and FIG. 1 to be described later are illustrated by omitting the components mounted on the wiring board except those necessary for explanation.

On the other hand, due to the electromagnetic flux generated in the housing of the amplifier, noise is generated in the return wiring pattern and the ground due to the induced electromotive force. A large amount of electromagnetic flux is generated in the housing from the power transformer and the output stage, but since the conventional amplifier did not pay attention to the induced electromotive force generated in the return wiring pattern and the ground, the electromagnetic flux generated especially from the output stage. There was a drawback that the output voltage was affected by the noise.

The above will be described with reference to the equivalent circuit diagram of FIG. The amplifier 13 is an ideal operational amplifier. Let Vn1 be the noise voltage induced in the feedback wiring pattern by the inter-device current flowing in the ground plane. The amplifier then produces noise -Vn1.

Further, the input voltage is Vin and the resistor 11a is R
Letting a be Rb, the resistance 11b be Rb, the induced electromotive force generated in the feedback circuit by the electromagnetic flux be Vn2, and the induced electromotive force generated at the ground be Vn3, Vn3 is not equal to Vn3. appear. When the above is expressed by a mathematical expression, the output voltage Vout is expressed by Expression 1. Vout = Vin (1 + Rb / Ra) -Vn1 + Vn3-Vn2 Equation 1

[0008]

The problem to be solved by the present invention is a drawback of the conventional feedback wiring pattern.
Noise is mixed in the feedback circuit due to the induced electromotive force of the current between devices. And to prevent noise from appearing in the output voltage due to the electromagnetic flux generated in the housing of the electronic circuit.

[0009]

In order to achieve the above-mentioned object, a ground plane is layered on a return wiring pattern on a printed circuit board, and an earth pattern for connecting a ground at a front stage and a rear stage of an electronic circuit is used as a return wiring pattern. Insulate from the stacked ground planes and install them side by side. The ground patterns that connect the grounds of the front and rear stages of the electronic circuit should be installed substantially symmetrically with respect to the return wiring pattern. The ground plane that is layered on the return wiring pattern is connected to the ground of the electronic circuit concerned at one place.

[0010]

[Operation] With the above configuration, the ground plane that is layered on the return wiring pattern is connected to the ground at one place, and the others are insulated from the ground pattern, so noise current due to inter-device current causes the ground plane to pass through. Since it does not flow, an induced electromotive force due to an inter-device current does not occur in the feedback wiring pattern, and noise is not mixed in the feedback circuit.

Further, since the ground pattern is provided in parallel with the return wiring pattern, the induced electromotive forces Vn3 and Vn2 due to the electromagnetic flux generated in the housing can be made substantially equal, and Vn3-Vn2 = 0. No noise appears in the output voltage.

[0012]

FIG. 1 shows an embodiment of the present invention, in which 1 is a wiring board, 2 is an insulating material for the wiring board, 3 is a return wiring pattern, and 4 is a wiring pattern.
Is a ground plane that is layered on the return wiring pattern, 5
Is a grounding pattern arranged in parallel with the feedback wiring pattern to connect the grounds of the front and rear stages of the electronic circuit. Ground, 9 is an output transistor, 10 is a point where a ground plane laminated on the feedback wiring pattern is connected to the ground at one place, 11a is a feedback resistor, 11b is a feedback resistor, 12a is an input terminal, and 12b is an input terminal. It is earth.

Due to such a structure, the ground plane 4 layered on the return wiring pattern 3 is only connected to the ground at one place 10 in the previous stage, and the others are insulated from the ground pattern 5. Therefore, the inter-device current flows through the ground pattern 5 and does not flow through the ground plane 4. Therefore, an induced electromotive force due to an inter-device current does not occur in the feedback wiring pattern 3, and the equation 1 is Vn1 = 0.
Therefore, the noise due to the current between devices is not mixed in the feedback circuit.

Further, a large amount of electromagnetic flux is generated in the housing from the power transformer and the transistor 9 in the output stage. However, since the ground pattern 5 is symmetrically arranged with respect to the return wiring pattern 3, induction induced by the electromagnetic flux is caused. The electric powers Vn3 and Vn2 are equal to each other, the expression 1 is Vn3-Vn2 = 0, and noise does not appear in the voltage between the output terminal 8a and the ground 8b of the output terminal.

[0015]

As described above, noise is not mixed in the feedback circuit and noise is not superimposed on the output. Furthermore, distortion caused by noise input to the feedback circuit can be prevented. Further, with respect to the electromagnetic flux generated in the housing, the feedback circuit and the ground pattern generate the same induced electromotive force, so that they cancel each other out, and noise does not appear in the output.

Therefore, when this feedback wiring pattern is adopted in the electronic equipment, it is possible to reduce the noise.
Especially when applied to audio amplifiers, high-frequency noise induced by inter-device current is less likely to be input to the feedback circuit, so distortion of audio amplifiers caused by high-frequency noise, such as TIM distortion, is also reduced. It can be an audio amplifier that has low noise and very good sound quality in terms of hearing.

The present invention is not limited to the above-described embodiment, but the ground planes which are superposed on the return wiring pattern may be two layers, and the return wiring pattern may be sandwiched therebetween. Further, the ground pattern is not only arranged on both sides of the ground plane layered on the return wiring pattern, but also applicable to a configuration in which a multi-layer substrate is used to layer on the outside of the ground plane. Further, although the present invention has been described only for the negative feedback amplifier for audio, it can be applied to a general electronic circuit having a feedback circuit.

The following are references regarding the current between devices. "MJ radio and experiment Seibundo Shinkosha 199
June 2nd year p. 133 Amplifier manufacturing techniques that surpass manufacturer's products (2) Consideration of power supply and earth potential Seiichi Tokuhisa ”

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a return wiring pattern according to the present invention.

FIG. 2 is a perspective view showing a conventional return wiring pattern.

FIG. 3 is an equivalent circuit diagram showing a noise source.

[Explanation of symbols]

1 wiring board 2 insulating material 3 return wiring pattern 4 ground plane layered on the return wiring pattern 5 ground pattern arranged in parallel with the return wiring pattern 6 ground plane at the front stage 7 ground plane at the rear stage 8a output terminal 8b output terminal ground 9 Output Transistor 10 Point where the ground plane laminated to the feedback wiring pattern is connected to the ground at one place 11a Feedback resistor 11b Feedback resistor 12a Input terminal 12b Input terminal ground 13 Ideal operational amplifier

Claims (1)

[Claims] 1. In an electronic circuit having a feedback circuit, a ground plane is layered on a feedback wiring pattern on a wiring board, and a ground plane is connected to the feedback wiring pattern so as to connect the grounds of the preceding and subsequent stages of the electronic circuit. A return wiring pattern for an electronic circuit, characterized in that the ground planes, which are insulated from each other and arranged in parallel, are connected to the ground of the electronic circuit concerned at one place.