JPH0422581Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention relates to noise reduction circuits for audio equipment, etc.
In particular, the purpose is to reduce common mode noise.

[Prior Art] When attempting to transmit analog signals between two or more devices powered by commercial AC, it is necessary to determine the difference in leakage impedance between the primary, secondary coil, and core of each power transformer, and the polarity of the primary voltage. etc., the ground potential between devices differs, resulting in a potential difference between the devices.

This potential difference becomes common mode noise, which is extremely harmful in unbalanced transmission circuits.

Conventionally, various ideas have been made to reduce the influence of this common mode noise.

Isolation Transformer Coupling As shown in Figure 2, in a configuration diagram in which an isolation transformer 03 is interposed in the signal path between equipment 01 and equipment 02, e _S is the signal source, R _L is the input resistance or load resistance of equipment 02, e _o is the common mode noise voltage generated between both devices 01 and 02, r ₁ is the output resistance of device 01, r ₂ is the resistance of the transmission line and DC resistance of the primary coil, r ₃ and r ₄ are the secondary coil's These are DC resistance and wiring resistance.

Common Mode Noise Removal Chiyoke Coil As shown in FIG. 3, this is a configuration in which a chiyoke coil consisting of a pair of coils with the same polarity is interposed between equipment 01 and equipment 02.

In the figure, e _S is the signal source, R _L is the input resistance or load resistance of device 02, e _o is the common mode noise voltage generated between both devices 01 and 02, r ₁ is the output resistance of device 01, and r ₂ is These are the resistance of the transmission line and the DC resistance of the coil.

Potential difference positive feedback As shown in Figure 4, common mode noise voltage
The configuration is such that e _o is positively fed back to the signal source and common mode noise is canceled by the input resistor R _L of device 02.

In the figure, 05 is an amplifier circuit with amplification factor K, e _S is a signal source, R _L is input resistance or load resistance of device 02,
e _o is the common mode noise voltage generated between both devices 01 and 02, r ₁ is the output resistance of device 01, and r ₂ is the resistance of the transmission line.

[Problems to be Solved by the Invention] The conventional examples of the above-mentioned configuration each have advantages and disadvantages, and it cannot be said that a sufficient common mode noise reduction effect is obtained.

For example, theoretically, with respect to the common mode noise voltage _eo , since the current circuit is opened by the isolation transformer 03, no current flows, and the influence of _eo does not appear on signal transmission.

However, since there is leakage resistance and coupling capacitance between the primary and secondary coils of the isolation transformer 03, a current circuit of e _o is formed in a high frequency region, and the influence of common mode noise appears.

That is, this configuration is effective against common mode noise of low frequency components, but less effective against high frequency components.

Also, regarding the signal e _S , due to transformer coupling,
Difficult to transmit low frequencies.

In order to transmit signals down to low signal frequencies, the transformer must be made larger, and the larger the transformer, the greater the coupling capacitance between the primary and secondary coils, which reduces the ability to remove common mode noise of high frequency components. descend.

The impedance is low for normal mode signals and high impedance for common mode noise signals, thereby suppressing common mode noise current and suppressing the influence of common mode noise.

In Figure 3, i ₁ is changed to e _S →r ₁ →L→R _L →L→r ₂
→e Current flowing through _S , i ₂ e _o →L→r ₂ →Earth→e _o
If is the current flowing, e _S = {r ₁ + r ₂ + R _L + 2jω
(L-M)}i ₁ +{r ₂ +jω(L-M)}i ₂ ...(1) e _o = {r ₂ +jω(L-M)}i ₁ +(r ₂ +jωL)i ₂ ... …(2) Vo=i ₁ , R _L …(3) ω: Angular frequency of e _S , e _o e _o : Equivalent amount of noise generated between the signal reference points on the signal system side and the load side, This is generally common mode noise.

From equations (1), (2), and (3) above, Vo=e _S , R _L (r ₂ + jωL)/{r ₂ (r ₁ + R _L ) + jωL (r ₁
+r ₂ +R _L )+(jω) ² (L-M)(L+M)} -e _o R _L {r ₂ +jω(L-M)}/r ₂ (r ₁ +R _L )+jωL
(r ₁ +r ₂ +R _L )+(jω) ² (LM) (L+M)}.

Here, if the coupling coefficient of the two coils is approximately 1, it can be approximated that L=M. (A coupling coefficient of 0.99 to 1 can be easily obtained by bifilar winding two wires.) Therefore, if L=M, the above formula is vo=e _S R _L /r ₁ +R _L {1+jω/ω ₁ ′/1+jω/ω ₁
} −e _o R _L /r ₁ +R _L {1/1+jω/ω ₁ } However, ω ₁ = r ₂ (r ₁ + R _L )/L (r ₁ + r ₂ + R _L ) ω ₁ = r ₂ /L .

Furthermore, r ₂ is the DC resistance of the transmission line and coil,
Since r ₂ ≪ r ₁ + R _L is generally small, ω ₁ = r ₂ /L = ω ₁ , and vo = R _L e _S / r ₁ + R _L −R _L e _o /r ₁ + R _L {1 /1+jω/ω ₁ } The e _o component appearing in vo in the above equation has attenuation characteristics when ω>ω ₁ as shown in FIG.

In other words, it is less effective against common mode noise of frequency components lower than ω ₁ , and can be expected to have a reduction effect on common mode noise of frequency components higher than ω ₁ . Therefore, in order to bring ω ₁ to a low frequency, it is necessary to increase L, which increases the capacitance of both coils, which reduces the effect on common mode noise of high frequency components. .

In this case, the voltage Vo generated across the resistor R _L is expressed as Vo = R _L /r ₁ + R _L e _S + R _L /r ₁ + R _L (k-1) e _o , and if k = 1, the influence of e _o can be completely eliminated, but amplifier circuits generally cannot have infinite frequency characteristics and have a finite value of the band ω _O. In the case of a voltage follower amplifier, this ω _O is determined by the open loop characteristics and has the characteristics shown in FIG.

The transfer function k in this case is expressed as 1/(1+jω/ω _O ), so the coefficient of the e _o term in the above equation is R _L /r ₁ + R _L {jω/ω _O /1+jω/ω _O } becomes.

Therefore, as shown in Figure 7, the e _o component is ω<
Although it has a damping effect in the ω _O region, it has a small effect on common mode noise of frequency components above ω _O.

[Means for Solving the Problem] This invention includes a signal source, a feedback amplifier circuit, a device having an amplifier circuit that receives the outputs of the signal source and the feedback amplifier circuit as inputs, and a device having an input resistance or a load resistance. , comprising a chain coil in which primary, secondary and tertiary coils are wound with the same polarity, one winding end of the primary coil is connected to the output of the amplifier circuit,
One winding end of the secondary coil is connected to the ground of the device 1, one winding end of the tertiary coil is connected to the input terminal of the feedback amplifier circuit, and the other winding end of the primary coil is connected to one end of the resistor, The other winding end of the secondary coil and the other winding end of the tertiary coil are each connected to the other end of the resistor, forming a noise reduction circuit.

[Operation] With the above configuration, common mode noise of low frequency components is reduced by the potential difference positive feedback means, and common mode noise of high frequency components is reduced by the common mode noise removing chioke coil means.

[Example] In Fig. 1-a, 1 is a first device, 1a is an amplifier circuit, 1c is a first output terminal connected to the output of the amplifier circuit 1a, 1b is a feedback amplifier circuit, The output of the feedback amplifier circuit 1b is connected to the other input end (one end in the figure) of the amplifier circuit.

1d is a feedback input terminal connected to one input terminal (+ in the figure) of the feedback amplifier circuit, e _S is a signal source connected to one input terminal (+ in the figure) of the amplifier circuit 1a, and 1e is the second terminal connected to the ground of device 1.
Output end, 2 is the second device, 2c is the first input end, 2
e is the second input terminal, 2d is the feedback output terminal, and R _L is the input resistance or load resistance of the device 2, which is connected between the first input terminal 2c, the second input terminal 2e, and the feedback output terminal 2d. There is.

4 is a first coil 4a and a second coil wound with the same polarity.
It is a chain coil consisting of a coil 4b and a third coil 4c, and the first output end 1c is connected to one end of the first coil 4a (indicated by the starting end in the figure), and the feedback input end 1d is connected to the third coil 4c. At one end of the
The second output 1e is connected to one end of the second coil 4b, the other end of the first coil 4a is connected to the first input end 2c, and the other end of the second coil 4b is connected to the second input end. 2e, the other winding end of the third coil 4c is connected to the feedback output end 2d.

An equivalent circuit for common mode noise of the circuit having the above configuration is shown in FIG. 1-b.

In the figure, e _S is the signal source, R _L is the input resistance of device 02, e _o is the common mode noise voltage generated between devices 1 and 2, r ₁ is the output resistance of device 1, and r ₂ is the transmission line resistance. The resistance, L, is the self-inductance of each of the first, second, and third coils, M is the mutual inductance between each coil, M≈L, and k is the amplification factor of the feedback amplifier circuit.

Here, if the voltage of the resistor R _L is Vo, then Vo = R _L / r ₁ + R _L e _S + (k-1) R _L / (r ₁ + R _L ) (1 +
jω/ω ₁ )e _oHowever , if ω ₁ = r ₂ /L and k=1/{1+(jω/ω _O )}, then the previous equation
The coefficient of the term e _o is R _L・jω/ ₀ / (r ₁ + R _L ) (1 + jω/ω ₁ ) (1 + jω
/ω ₀ ), and (jω/ω _O )/{1+(jω/ω _O )} represents the reduction effect by the positive feedback means, and 1/{1+
(jω/ω ₁ )} represents the reduction effect by the chiyoke coil means.

That is, as shown in Fig. 8, the characteristics of the noise reduction circuit of this invention are the overall characteristics (solid line) of the characteristics of the positive feedback means (shown by the dotted line in the figure) and the characteristics of the chiyoke coil (shown by the dashed line in the figure). ).

[Effects of the invention] As is clear from the characteristics shown in Figure 8, the positive feedback means is expected to have a reduction effect on common mode noise of low frequency components, and the chiyork coil is expected to have a reduction effect on noise of high frequency components. We were able to obtain a noise reduction effect over the entire frequency band. In addition, for low frequencies, the reduction effect due to positive feedback can be expected, and the reduction effect of the Chuuk coil only needs to be borne in the high frequency range, so there is no need to make L of the Chuuk coil larger than necessary, and the static of the Chuuk coil can be reduced. The influence of capacitance could be suppressed.

[Brief explanation of the drawing]

Figure 1-a is a noise reduction circuit diagram of the embodiment of this invention, Figure 1-b is an equivalent circuit diagram, Figures 2 and 3 are
Figure 4 is a diagram of a conventional noise reduction circuit, Figure 5 is a frequency characteristic diagram of the reduction circuit shown in Figure 3, Figure 6 is a frequency characteristic diagram of an amplifier circuit, and Figure 7 is a diagram of the reduction circuit shown in Figure 4. FIG. 8 is a frequency characteristic diagram of the noise reduction circuit according to the embodiment of the invention. e _S is the signal source, 1b is the feedback amplifier circuit, 1a is the amplifier circuit, 1 is the equipment, R _L is the load resistance or input resistance,
2 is a device; 4a, 4b, and 4c are primary, secondary, and tertiary coils; and 4 is a chiyoke coil.

Claims (1)

[Scope of utility model registration request] Signal source e _S , feedback amplifier circuit 1b, signal source e _S
and a device 1 having an amplifier circuit 1a whose inputs are the outputs of the feedback amplifier circuit 1b, a device 2 having an input resistance or a load resistance R _L , and a primary 4a, a secondary 4b, and a tertiary coil 4c wound with the same polarity. One winding end of the primary coil 4a is connected to the amplifier circuit 1a output, one winding end of the secondary coil 4b is connected to the ground of the equipment 1, and one winding end of the tertiary coil 4c is connected to the ground of the device 1. one end of the coil is connected to the input end of the feedback amplifier circuit 1b, the other winding end of the primary coil 4a is connected to one end of the resistor R _L , the other winding end of the secondary coil 4b and the other winding of the tertiary coil 4c are connected. A noise reduction circuit characterized in that its ends are respectively connected to the other ends of the resistor R _L.