JPH04369127A - 2 wire/4 wire conversion circuit - Google Patents

Abstract

PURPOSE:To reduce sneak of a transmission signal to a reception line by connecting a transfer circuit having a frequency characteristic equivalent to an inductance component of a transformer between an output stage of a transmission circuit and an input stage of a reception circuit so as to allow the transfer circuit to be close to a change in the impedance of the transformer. CONSTITUTION:An equivalent circuit 6 having a component equivalent to an inductive component of a transformer 2 is connected between an output stage of a transmission circuit 3 and an input stage of a reception circuit 4 of the 2 wire/4 wire conversion circuit 5. The inductance L' of the equivalent circuit 6 is adjusted to be equivalent to the inductive component of the transformer 2 with respect to the secondary side and a ratio of a resistor R' to the inductance L' is adjusted so as to be equal to a ratio of the equivalent resistor R to the inductance component L of the transformer 2, then a voltage division ratio of the transmission signal inputted respectively to an inverting input terminal and a noninverting input terminal of an operational amplifier in the reception circuit 4 is made close to each other thereby decreasing a transmission signal added to a reception signal.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a 2-wire/4-wire conversion circuit, and more specifically, it is connected between a 2-wire full-duplex line and a communication terminal, and transmits and receives signals to both the line and the communication terminal. This invention relates to a two-wire and four-wire conversion circuit that separates and transmits signals.

0002

[Prior Art] Conventionally, in facsimile machines and the like that transmit and receive image information using a telephone line as a two-wire full-duplex transmission line, even though the transmission procedure itself is half-duplex, However, in some facsimile communication procedures, it is necessary to separate the transmitting path and receiving path to perform full-duplex operation. For this reason, traditional facsimile machines
A two-wire/four-wire conversion circuit 1 as shown in FIG. 4 is connected between the secondary side of a transformer 2 to which a line is connected and the transmission path and reception path of a communication terminal.

In FIG. 4, a transmission signal outputted from a transmission path is transmitted from a transmission circuit 3 and an equivalent resistance R, which constitute a buffer circuit including an operational amplifier OP1 and a resistor r, to a line via a transformer 2. The received signal received through the terminal is sent to the communication terminal by subtracting the transmitted signal added to the received signal by the receiving circuit 4, which constitutes a differential circuit consisting of an operational amplifier OP2 whose input terminals are connected to both ends of an equivalent resistor R, and a resistor r. is transmitted to the receiving path.

Note that the equivalent resistance R is set so that the impedance component of the transformer 2 is equivalent to the pure resistance R, and the transmission signal is transmitted to the input terminal of the receiving circuit 4 at the voltage division ratio between this impedance value and the equivalent resistance R. The transmitted signal that is added to the received signal by inputting the signal to the received signal is subtracted.

[0005]

[Problem to be Solved by the Invention] However, in such a conventional 2-wire 4-wire conversion circuit, the impedance component of the transformer 2 is assumed to be equivalent to a pure resistance R, and the equivalent resistance R is connected for transmission. Since the circuit configuration was designed to prevent signals from going around to the reception path, there was a problem in that in a frequency range that cannot be approximated by the equivalent resistance R, the roundabout of the transmitted signal could not be sufficiently suppressed.

That is, since the impedance component of the transformer 2 is originally equivalent to the inductance L, the impedance value changes depending on the frequency of the transmitted signal, and the equivalent resistance R alone cannot change the impedance value at this frequency. Unable to respond to the change, the balance between the impedance value of the transformer 2 and the voltage division ratio by the equivalent resistance R is disrupted, and the transmitted signal that is added to the received signal input to the receiving circuit 4 is not subtracted, causing the communication terminal to A situation occurs in which the signal is transmitted to the receiving path.

Accordingly, the present invention connects a transfer circuit having frequency characteristics equivalent to the inductance component of the transformer between the output stage of the transmitter circuit and the input stage of the receiver circuit, thereby controlling the change in the impedance value of the transformer over a wide frequency range. It is an object of the present invention to provide a two-wire and four-wire conversion circuit that approximates the following and reduces the looping of a transmission signal into a reception path.

[0008]

[Means for solving the problem] The invention according to claim 1 includes:
The secondary side of the transformer to which the two-wire line is connected is connected to both the transmitting end and receiving end of the communication terminal, and the input terminal is connected to the transmitting end of the communication terminal, and the output terminal is connected to the secondary side of the transformer. a transmitting circuit that connects and transmits a transmission signal output from the transmitting end to the line via the transformer; an input terminal is connected to the secondary side of the transformer; and an output terminal is connected to the receiving end of the communication terminal; a receiving circuit that separates a received signal received from the line via a transformer from a transmitted signal and transmits it to the receiving end, and transmits communication simultaneously between the two-wire line and the communication terminal via the transformer. In a two-wire four-wire conversion circuit that separates a signal and a received signal and transmits them to both a line and a communication terminal, a transmission circuit having frequency characteristics equivalent to the inductance component of the transformer is connected to an output terminal of the transmitting circuit and the receiving circuit. Connect between the input terminals of
The transmission circuit is characterized in that the transmission signal is reduced from going around to the reception circuit, and the invention according to claim 2 is characterized in that in the invention according to claim 1, the transmission circuit is formed by an amplifier circuit having a predetermined transfer function. and setting the frequency characteristics by connecting a resistor, a capacitor, etc. as a transfer coefficient of the amplifier circuit, and making it possible to integrate a 2-wire and 4-wire conversion circuit including the transfer circuit, The invention according to claim 3 is characterized in that, in the invention according to claim 2, a resistor, a capacitor, etc. for setting the frequency characteristics are externally attached to the transmission circuit, so that the resistors and capacitors can be changed. There is.

[0009]

[Operation] In the invention as claimed in claim 1, two
In a 2-wire and 4-wire conversion circuit in which a transmitting signal and a receiving signal that are communicated simultaneously between a wire line and a communication terminal are separated and transmitted to both the line and the communication terminal, frequency characteristics equivalent to the inductance component of the transformer are A transmission circuit having a transmission circuit is connected between an output terminal of the transmitting circuit and an input terminal of the receiving circuit. Therefore, the transfer circuit can reduce the loop of the transmitted signal to the receiving circuit in a wide frequency range, and improve the separation performance of the 2-wire and 4-wire conversion circuit between the transmitted signal and the received signal.

In the invention as set forth in claim 2, the transfer circuit as set forth in claim 1 is constituted by an amplifier circuit having a predetermined transfer function, and a resistor, a capacitor, etc. are connected as a transfer coefficient of the amplifier circuit, and Frequency characteristics are set. Therefore, it is possible to reduce the leakage of the transmitted signal to the receiving circuit, and also to
The line conversion circuit can be easily integrated into an integrated circuit, and the 2-wire/4-wire conversion circuit can be installed in a communication terminal such as a facsimile machine at low cost.

[0011] According to the third aspect of the invention, by externally attaching a resistor, a capacitor, etc. for setting the frequency characteristics of the transfer circuit according to the second aspect, it becomes easy to change the resistors and capacitors. Therefore, the frequency characteristics of the transfer circuit can be changed in accordance with the frequency characteristics of the transformer to which it is connected, and a highly versatile 2-wire 4-wire conversion circuit can be integrated at low cost. Adjustment work of a communication terminal such as a facsimile machine equipped with a conversion circuit can be facilitated.

0012

EXAMPLES The present invention will be specifically explained below based on examples. 1 to 3 are diagrams showing an embodiment of a 2-line and 4-line conversion circuit to which the inventions of the present application are applied. FIG. 1 shows a circuit configuration for explaining the basic principle of a 2-wire 4-wire conversion circuit 5 according to the present invention. have the same numbers and symbols. In FIG. 1, an equivalent circuit (transfer circuit) 6 equivalent to the inductance component of the transformer 2 is connected between the output stage of the transmitting circuit 3 and the input stage of the receiving circuit 4 of the two-wire and four-wire conversion circuit 5. The inductance L' in the equivalent circuit 6 is
It is adjusted to be equivalent to the inductance component when looking at the transformer 2 from the secondary side, and the ratio of the resistance R' and the inductance L' is the same as the ratio of the equivalent resistance R and the inductance component L in the transformer 2. By adjusting as shown in FIG. do.

However, if the inductance L' in the equivalent circuit 6 in FIG. 1 is constructed from an actual inductance component, when constructing the 2-wire 4-wire conversion circuit 5, not only will the cost increase, but it will also be difficult to adjust the impedance value. Therefore, FIG. 2 shows a two-wire and four-wire conversion circuit in which an equivalent circuit is connected by a circuit equivalent to this inductance component. In the 2-wire 4-wire conversion circuit 11 shown in FIG. 2, in the equivalent circuit 12, the resistor R' shown in FIG. In addition, the equivalent resistance R is replaced by a resistance r1 and a resistance r2.

Now, if the impedance seen from the secondary side of the transformer 2 in FIG. 2 is approximated by a uniform inductance L, the transfer function in the transmission signal transmission path (a→b in the figure) becomes the following equation (■). .

[0015]

[Equation 1] However, s: Laplace operator On the other hand, the transfer function in the signal path (a→c in the figure) of the transmission signal subtracted by the differential circuit in the receiving circuit 4 is expressed by the following equation (2).

[0016]

[Mathematical 2] Here, if we compare formulas ■ and ■, we can see that the differential circuit in the receiving circuit 4, that is, the inputs b and c of the operational amplifier OP3, can be subtracted from the received signal by subtracting the transmitted signal from the received signal, regardless of the frequency of the transmitted signal. The conditions for For example, if the values of each resistor and capacitor are determined to satisfy r1 = r3, r2 = 2r, and L = cr2, then Hab(s) = Hbc(s), which means that the received signal can be changed from the transmitted signal regardless of the frequency. can be subtracted. In reality, the values of the resistors r1, r2, r3, r2 and the capacitor c do not need to be the same as the conditions, and may be determined so that the voltage division ratios for the transmission signals are the same. In addition, the values of resistors r1, r2, r3, r, and capacitor c take into consideration the recent error when approximating the impedance seen from the secondary side of transformer 2 to L, and adjust the transfer function in a wider frequency range. It is desirable to determine it so that it can be approximated.

Therefore, by connecting an equivalent circuit 12 having frequency characteristics equivalent to the inductance component of the transformer 2 as shown in FIG. 2 between the output terminal of the transmitting circuit 3 and the input terminal of the receiving circuit 4, The transmitted signal added to the received signal can be subtracted regardless of the signal frequency, and the separation performance of the transmitted signal and received signal of the 2-wire 4-wire conversion circuit can be greatly improved. By connecting the line conversion circuit to a communication terminal such as a facsimile machine, it is possible to improve the transmission performance of transmitted and received signals exchanged during facsimile communication. Furthermore, since the equivalent circuit 12 is composed of an operational amplifier OP3, two resistors r, a capacitor c, and a resistor r3, it can be easily integrated into an IC, and can be easily built into a communication terminal such as a facsimile machine.

FIG. 3 shows a configuration in which the 2-wire/4-wire conversion circuit 11 of FIG. 2 is incorporated into a communication control analog IC 21 built into a communication terminal such as a facsimile machine to form a single chip. In the communication control analog IC 21 shown in FIG. 3, the control logic section 22 receives a control signal from a control section not shown.
However, the modem transmission signal transmitted from the modem is passed through the transmission filter section 23, adjusted to a predetermined level by the reception level adjustment section 24, and transmitted from the transmission circuit 3, and the reception signal inputted from the reception circuit 4 is transmitted through the reception filter section 25. The equalizer section 26 performs adjustment for each predetermined frequency band and transmits it to the modem as a modem reception signal.

Furthermore, the communication control analog IC 21 in FIG.
Then, the resistor r1 that determines the transfer function of the 2-wire 4-wire conversion circuit
, r2, and r3 can be changed externally. Therefore, in the communication control analog IC 21, the resistance r
The impedance adjustment procedure can be completed by simply changing the values of 1, r2, and r3, the communication control analog IC 21 can be made into a versatile IC, and the manufacturing cost of the communication control analog IC 21 can be reduced. Can be done. By mounting this communication control analog IC 21 on a communication terminal such as a facsimile machine, it becomes possible to reduce the manufacturing cost of the communication terminal.

[0020]

According to the invention as claimed in claim 1, the transmission signal and the reception signal that are communicated simultaneously between the two-wire line and the communication terminal via the transformer are separated and transmitted to both the line and the communication terminal. In the 2-wire 4-wire conversion circuit, a transfer circuit with frequency characteristics equivalent to the inductance component of the transformer is connected between the output terminal of the transmitting circuit and the input terminal of the receiving circuit. In this case, it is possible to reduce the leakage of the transmitted signal to the receiving circuit in the region, and improve the separation performance of the 2-wire and 4-wire conversion circuit between the transmitted signal and the received signal.

According to the invention set forth in claim 2, the transfer circuit set forth in claim 1 is constituted by an amplifier circuit having a predetermined transfer function, and a resistor, a capacitor, etc. are connected as a transfer coefficient of the amplifier circuit. Since the frequency characteristics are set, it is possible to reduce the loop of the transmitted signal to the receiving circuit, and it is also possible to easily integrate the 2-wire 4-wire conversion circuit including the transmission circuit, The line conversion circuit can be installed in a communication terminal such as a facsimile machine at low cost.

According to the invention set forth in claim 3, since the resistor, capacitor, etc. for setting the frequency characteristics of the transmission circuit set forth in claim 2 are externally attached, it is easy to change the resistor and capacitor, and the The frequency characteristics of the transfer circuit can be changed according to the frequency characteristics of the transformer to which it is connected, and a highly versatile 2-wire 4-wire conversion circuit can be integrated into a low-cost integrated circuit. Adjustment work for communication terminals such as facsimile machines to be mounted can be facilitated.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a circuit configuration for explaining the basic principle of a 2-wire/4-wire conversion circuit according to the invention as claimed in claim 1;

FIG. 2 is a diagram showing an actual circuit configuration of a 2-wire 4-wire conversion circuit according to the invention as claimed in claim 1.

FIG. 3 is a diagram showing a circuit configuration of a 2-wire/4-wire conversion circuit according to the invention according to claims 2 and 3;

FIG. 4 is a circuit configuration diagram of a conventional 2-wire 4-wire conversion circuit.

[Explanation of symbols]

3 Transmission circuit 4 Receiving circuit 5 2-wire 4-wire conversion circuit 6, 12 Equivalent circuit

Claims (3)

[Claims] Claim 1: The secondary side of the transformer to which the two-wire line is connected is connected to both the transmitting end and the receiving end of the communication terminal, the input terminal is connected to the transmitting end of the communication terminal, and the secondary side of the transformer is connected to the transmitting end and receiving end of the communication terminal. a transmitting circuit having an output terminal connected to the side thereof and transmitting a transmission signal outputted from the transmitting end to the line via the transformer; and an input terminal connected to the secondary side of the transformer;
a receiving circuit that connects an output terminal to a receiving end of a communication terminal, separates a received signal received from a line via a transformer from a transmitted signal, and transmits the signal to the receiving end, and transmits the signal to the receiving end via the transformer. In a two-wire four-wire conversion circuit that separates a transmitting signal and a receiving signal that are communicated simultaneously between a line and a communication terminal and transmits the separated signals to both the line and the communication terminal, the transmission has frequency characteristics equivalent to the inductance component of the transformer. A two-wire four-wire conversion circuit, characterized in that a circuit is connected between an output terminal of the transmitting circuit and an input terminal of the receiving circuit, and the transfer circuit reduces the loop of the transmitted signal to the receiving circuit. 2. In the invention according to claim 1, the transfer circuit is configured by an amplifier circuit having a predetermined transfer function, and the frequency characteristics are set by connecting a resistor, a capacitor, etc. as a transfer coefficient of the amplifier circuit. A 2-wire 4-wire conversion circuit, characterized in that the 2-wire 4-wire conversion circuit including the transmission circuit can be integrated into an integrated circuit. 3. The invention as claimed in claim 2, wherein a resistor, a capacitor, etc. for setting the frequency characteristics are externally attached to the transmission circuit, so that the resistors and capacitors can be changed. 4-wire conversion circuit.