JP2867396B2 - 2-wire 4-wire conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention transmits a signal from a two-wire line to a four-wire line, and supplies a signal from the four-wire line to the two-wire line. The present invention relates to a four-wire conversion circuit.

[Conventional technology]

As shown in FIG. 3, the two-wire to four-wire conversion circuit has a function of transmitting a signal transmitted from the two-wire line to the four-wire line and a function of transmitting a signal supplied from the four-wire line to the two-wire line. In addition to the supply function, a terminating impedance combining function for canceling a signal reflected when a signal is input from a two-wire line, an insertion loss correction function for reducing insertion loss caused during conversion from a four-wire system to a two-wire system, and a two-wire system A balance function is provided for canceling a signal reflected at the time of outputting a signal to the four-wire line and going around the four-wire line.

[Problem to be Solved by the Invention] In the above-described conventional two-wire / four-wire conversion circuit, when realizing the termination impedance synthesis function, the insertion loss correction function, and the balance function, it is necessary to configure each of them with a different circuit, which is complicated. In addition, there is a disadvantage that the chip area increases.

[Means for solving the problem]

A two-wire / four-wire conversion circuit according to the present invention transmits a signal from a two-wire line to a four-wire line and supplies a signal from the four-wire line to the two-wire line. A termination impedance combining circuit that cancels a signal reflected when a signal is input from a two-wire line, an insertion loss correction circuit that reduces insertion loss caused by conversion from a four-wire line to a two-wire line, and a four-wire line And a balance circuit for canceling a signal reflected by the two-wire line and wrapping around the four-wire line when a signal is output from the two-wire line, the termination impedance combining circuit and the insertion loss correction circuit viewed from the two-wire line. , Arranged in the order of the balance circuit, further equalizing the poles of the transfer function of the termination impedance synthesis circuit and the insertion loss correction circuit, and the termination impedance synthesis circuit and the insertion loss correction circuit are configured by a common circuit It is.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of the invention, where v _S indicates the transmission source ZL of a two-wire line and _{L L} indicates the nominal impedance of the two-wire line.
H _Z , H _O , and H _B represent transfer functions having a termination impedance synthesis function, an insertion loss correction function, and a balance function, respectively. Further A
Represents a unity gain amplifier, and _R0 represents a reference resistor.

Next, the relationship between v _S , v _X , and v _R is analyzed. When the output voltage of the unity-gain amplifier v _0, 2-wire line side connection point of the two-wire four-wire conversion circuit and a voltage and v _i, v _0, v _i is given by the following equation.

The following equation is obtained from the equations (1) and (2).

Now, if v _R = 0 And the necessary and sufficient conditions for impedance matching Than That is, And it is sufficient.

Next, if v _S = 0 in the equation (3), the following equation is obtained.

Here, assuming that the equation (4) is satisfied and impedance matching is achieved, the following equation is obtained by substituting the equation (5).

Therefore, the following equation should be satisfied in order for the insertion loss to be 0 dB.

Next, in order to obtain the H _B v _S = 0 as v when guiding the relationship between _R and v _X becomes as follows.

Here, Z _L ′ is the line impedance of the two-wire line.

 The following equation is obtained from the equations (9) and (10).

The following equation is obtained by substituting into the equations (11) and (8).

Therefore, the necessary and sufficient condition for eliminating the wraparound of v _R → v _X is given by the following equation.

Here, when the termination impedance is matched and the insertion loss is 0 dB, the expressions (4) and (7) are satisfied. By substituting into the expression (13), the following expression is obtained. .

Where the term in equation (4) is When considered separately, the result is as shown in FIG. At this time,
As is clear from the comparison between H ₀ shown in the equation (7) and H _Z2 shown in the equation (15), they are completely the same except for the constants.

〔The invention's effect〕

As described above, the present invention, when viewed from a two-wire line,
By installing the terminating impedance synthesis function, insertion loss correction function, and balance function in this order, it is possible to configure a common circuit with the poles of the transfer function that realizes the impedance synthesis function and insertion loss correction function exactly equal to each other. Has the effect of reducing

[Brief description of the drawings]

1 and 2 are block diagrams showing embodiments of the present invention, and FIG. 3 is a block diagram of a conventional example. v _S …… Source signal, H _Z …… Terminal impedance synthesis function, H _O
...... insertion loss compensation function, H _B ...... Equilibrium, v _R ...... 4-wire line feed signal, v _X ...... 4-wire line transmission signal, the nominal impedance of Z _L ...... 2-wire line.

Claims (1)

(57) [Claims] 1. A two-wire to four-wire conversion circuit for transmitting a signal from a two-wire line to a four-wire line and supplying a signal from the four-wire line to the two-wire line. A termination impedance combining circuit for canceling a signal reflected when a signal is input, an insertion loss correction circuit for reducing insertion loss caused by converting from a four-wire line to a two-wire line, and a signal A balance circuit for canceling a signal reflected by the two-wire line at the time of output and going around the four-wire line.
The terminating impedance combining circuit, the insertion loss compensating circuit, and the balancing circuit are arranged in this order as viewed from the line, and the poles of the transfer functions of the terminating impedance combining circuit and the insertion loss compensating circuit are made equal to each other. A two-wire / four-wire conversion circuit, wherein the impedance synthesis circuit and the insertion loss correction circuit are configured by a common circuit.