JPS5834976B2 - 3 Houkou Bunki Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a three-way branch circuit used when transmitting and receiving information between three or more parties at the same time.

Conventionally, this type of three-way branch circuit has been put into practical use by combining six hybrid transformers.

This conventional circuit has the drawbacks that there is a transmission loss due to the hybrid transformer and that the reverberation attenuation of the hybrid transformer cannot be sufficiently large.

As a countermeasure, an amplifier was inserted into each arm of the hybrid transformer, and its amplification effect and unidirectionality were used to compensate for transmission loss and improve echo attenuation.

A circuit using this amplifier uses six hybrid transformers and six amplifiers, making it large and uneconomical.

SUMMARY OF THE INVENTION An object of the present invention is to provide a three-way branch circuit that can be made small and inexpensive, compensate for transmission loss, and provide sufficient reverberation attenuation.

According to this invention, six resistors are sequentially connected to form a ring resistance network, and the resistor connection points at symmetrical positions in the ring resistance network are one set of input and output sides, and these three sets are connected to each other. Negative feedback amplifiers are connected in series to each of the input and output sides.

The resistance value of each of the above six resistors is selected to be one step larger than the characteristic impedance of the circuit such as the transmission line or circuit network connected to the input side, and the closed loop gain of each of the above negative feedback amplifiers is It is made small, for example 10 or less.

Furthermore, a capacitor is inserted in series between the input side of each negative feedback amplifier and the resistor connection point to which it is connected, and the frequency band in which the amount of reverberation attenuation is maximized is selected based on the capacitance value of the capacitor.

Next, let's explain with reference to the drawings.

Figure 1 shows a three-way branch circuit using six conventionally used hybrid transformers.
The input from is branched by hybrid transformer 1,
Output ends B in the B direction and C direction pass through hybrid transformers 2 and 3, respectively.

and branches to C8.

Similarly, the input from the input terminal Bi (C1) in the B direction (C direction) is also branched by the hybrid transformer 6.4, passes through hybrid transformers 5 and 3 (5 and 2), respectively, and passes through the A direction and C direction (A direction and B direction) output end A.

and C3 (AO and B.

), allowing mutual transmission in three directions.

However, in this circuit, the transmission loss per hybrid transformer is approximately 3 dB, so from each input end to each output end there is a loss equivalent to two hybrid transformers, which is approximately 6 dB.
This results in a transmission loss of dB.

Further, an important performance in this type of circuit is the amount of reverberation attenuation, but the circuit shown in FIG. 1 cannot sufficiently increase this amount.

That is, in FIG. 1, for example, the amount of echo attenuation is determined by the input from the input end Ai in the A direction being branched at the hybrid transformer 1, and then reaching the hybrid transformer 6 due to leakage from the hybrid transformer 3; Through the A direction output end A.

, the input from the input terminal A1 is similarly branched at the hybrid transformer 1, and then the hybrid transformer 2-
Output end A in direction A through 4-5.

The reverberation attenuation is determined by the balance conditions of the hybrid transformer, and normally a sufficiently large value cannot be obtained.

This often causes singing, etc., and as a countermeasure to this, a hybrid transformer in which unidirectional amplifiers 7 to 12 are inserted in series in each branch arm of the hybrid transformer is often used, as shown in Figure 2. The amplification effect compensated for transmission loss, and the unidirectionality improved the deterioration of echo attenuation.

However, since the circuit shown in FIG. 2 uses six hybrid transformers and six amplifiers, it is expensive and has the disadvantage of being large in size.

FIG. 3 shows an example of a three-way branch circuit according to the present invention,
Six resistors 21 to 26 are sequentially connected in a ring to form a ring resistance network 53.

Those at symmetrical positions in the annular resistance network 53 of the respective resistor connection points 27 to 32 27, 30.29, 32.31° 28
are the input side and output side of the A direction, B direction, and C direction, respectively.

A negative feedback amplifier is connected to each output side via a capacitor.

That is, the connection point 27 is connected to the A direction input end Ai, and the connection points 29 and 31 are connected to the B direction input end Bi and the C direction input side C1, respectively.
are connected to each.

Further, the connection point 30 is connected to the amplifier 3 through the capacitor 33.
A direction output end A through 4.

The connection point 32 is connected to the B direction output terminal B through a capacitor 35 and further through an amplifier 36.

The connection point 28 is connected to the C-direction output terminal C8 through a capacitor 37 and an amplifier 38.

Amplifiers 34, 36 and 38 are connected to negative feedback resistors 39 and 38, respectively.
40°41 are connected to form a negative feedback amplifier.

Further, matching resistors 45 to 47, which are equal to the characteristic impedance of the transmission line or circuit connected to the input terminals, are connected in parallel to each of the input terminals Ai, Bi, and Ci, respectively.

Each resistance value of the resistors 21 to 26 is the same as that of the matching resistors 45 to 47.
is sufficiently smaller than each resistance value of the feedback amplifiers 34 and 36.
, 38 are small, for example, 10 or less.

The input from the A-direction input terminal Ai is branched to resistors 21 and 22, and the signal passing through the resistor 21 is amplified by an amplifier 36 to the B-direction output terminal B.

reached. On the other hand, the signal passing through the resistor 22 is similarly amplified by the amplifier 38 and reaches the output terminal C6 in the C direction.

Similarly, an input from direction B or direction C becomes an output from direction A, direction C, or direction A, direction B, respectively, and is branched into three directions.

Furthermore, the amount of reverberation attenuation leaking from the A-direction input to the input-direction output can obtain a sufficiently large value as described below.

The resistance values R7 and R6 of the resistors 21 and 26 are related to the external gain of the feedback amplifier circuit 36, but as mentioned above, this external gain is not very large, so the resistance value R1-
Re can be increased to 1, for example, usually 104 to 10
It can be set to 5Ω.

The resistor 47 is a matching resistor for input in the C direction, and its resistance value R4 is generally a low resistance of 75Ω for a high frequency line and 600Ω for an audio frequency line.

Therefore, the condition R1, R6>>Ro' is obtained.

From the A direction input end Ai to the A direction output end A.

The reverberation attenuation RLo leaking to the resistor 21-26-
It is a composite value of the component RL1 passing through the path of 25-amplifier 34 and the component RL2 passing through the path of resistors 22-23-24-amplifier 34.

Assume that the input impedance of the amplifier 36, 38 is infinite, and that the resistors 21, 22, 23, 24, 25,
Each resistance value of 26, 39, 46, 47 is R1, R2, R3
, R4, R6, R6, R9°Ro, R□', the amount of echo attenuation can be expressed by the following formula.

The first term on the right side of equation (1) is the amount obtained at the connection point 31 by the voltage division between the resistors 21 and 26, the matching resistor 4γ, and the parallel circuit of the line impedance connected to the input terminal C1, and the second term is the amount obtained at the connection point 31. term is the external gain of negative feedback amplifier 34.

The resistance value R6' of the matching resistor 47 is 75Ω as described above.
or about 600Ω, while the resistance values R1 and R6 are 1
Since it is approximately 0' to 10'Ω, the signal flowing from the input terminal Ai to the resistors 21-26 is greatly attenuated at the connection point 31.

Furthermore, since the external gain of the negative feedback amplifier 34 is small, about 10 or less, even if the signal that is greatly attenuated at the connection point 31 is amplified by the negative feedback amplifier 34, the level is only small.

Similarly, as shown on the right side of equation (2), the output terminal A is output from the input terminal Ai through the resistor 22.

The leakage to the output terminal A is also greatly attenuated at the connection point 29.

The level reached is extremely small.

The reverberation attenuation RLo is, RO'<< R1+ R6゜ Ro(R2 3 Also A large amount of reverberation attenuation RLo can be obtained.

In the above, it is assumed that the input impedance of the amplifiers 36 and 38 is infinite, but in reality, the impedance seen from the connection point 28°30.32 etc. to the amplifier side becomes a low value due to parallel feedback, so even at these connection points, Since the leakage component is attenuated, the amount of echo attenuation is further improved.

For example, the impedance Z when looking at the amplifier 36 from the connection point 32.

, is approximately expressed by the following equation.

However, RIO is the resistance value of resistor 40, and C is the capacitor 35.
The capacitance values of Ao and f are the maximum gain and cutoff frequency of the amplifier 36 when it is open, respectively.

In the frequency range higher than the cutoff frequency, the open gain of the amplifier is A.

It is assumed that the slope decreases from 6 dB to 10 cT.

In this equation (3), the second term in the square root is RIO So, that Z.

1 is approximately -. Ao is usually obtained about 10' times O2, and since the resistor 40 is a feedback resistance of the amplifier 40, its resistance value is about 105 to 106 Ω.

Therefore, Z in f-fo. 1 is approximately several Ω, which is sufficiently low compared to the resistance value of the resistor 21 (usually io' to 10' Ω), so that leakage from the input terminal Ai through the resistors 21-26 is greatly attenuated at the connection point 32. .

As described above, according to the three-way branch circuit of the present invention,
A constant amount of echo attenuation determined by equations (1) and (2) can be obtained from the straight line 50 in FIG. The result is a curve 52.

In the conventional model shown in Figure 1, the reverberation attenuation is 30
Only about dB could be obtained, and at best it was only 40 dB.

However, according to the circuit of the present invention, about 50 dB can be easily obtained just by the attenuation of the straight line 50, and since the attenuation of the curve 51 is added to this, a significantly large reverberant attenuation can be obtained.

The attenuation according to equation (3) is f. As is clear from the formula for fo, it can be changed by changing the capacitance C of the capacitor 35, and the smaller C is, the greater f is.

has a high frequency.

f in the center of the audio frequency band of 0.3-3.4KHz.

, and the attenuation according to equation (3) can be set to 25 dB in this band, so the overall attenuation is 75 dB.
A reverberation damping of B can be obtained.

Basic group in frequency division multiple carrier transmission (60-10
8 KHz), the fractional band becomes narrower (3)
It is easy to set the attenuation to 45 dB or more using the formula,
Significant reverberation attenuation is obtained.

Moreover, the only constituent elements of the circuit of this invention are a resistor, a capacitor, and an amplifier, and if a semiconductor integrated circuit is used as the amplifier, the overall shape can be made compact and economically inexpensive.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a three-way branch circuit using a conventional hybrid transformer, and Figure 2 is a circuit diagram showing a conventional three-way branch circuit in which an amplifier is inserted in each arm of the hybrid transformer to improve echo attenuation. FIG. 3 is a circuit diagram showing an example of a three-way branch circuit according to the present invention, and FIG. 4 is a curve diagram showing frequency characteristics of reverberation attenuation of the three-way branch circuit according to the present invention. Ai: A direction input end, A6: A direction output end, Bi2 B direction input end, Bo: B direction output end, Ci: C direction input end,
Co: C direction output end, 21 to 26: Resistor, 53: Annular resistance network, 33, 35. 37: Capacitor, 34, 36,
38: Amplifier, 39-41: Negative feedback resistor, 45-47
: Matching resistor.

Claims (1)

[Claims] Sixteen resistors are sequentially connected to form a ring resistance network, and the resistor connection points at symmetrical positions in the ring resistance network are respectively set as a set of input ends and an output side. A three-way branch circuit with feedback amplifiers connected in series on each output side.