JPH02192248A - Transmission interface circuit - Google Patents

Abstract

PURPOSE:To use one and same printed wiring board even for a line with a different impedance by setting an output level of a bipolar signal attended with a change in an output impedance while revising a winding ratio of a transformer. CONSTITUTION:A positive and a negative trigger signal from a switching control circuit 3-1 are inputted to transistors(TRs) 3-2, 3-3. The TRs 3-2, 3-3 supply a current to the primary windings (C-D, C-E) of a transformer 3-5 only for a moment conducted with the trigger signal and a bipolar signal is outputted at the secondary side (A-B). Thus, the transformer 3-5 acts like converting a unipolar signal into a bipolar signal through the change in the winding ratio and outputting a specified signal level with a specified output impedance. Thus, one and same printed wiring board is usable for a line even with a different impedance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmission interface circuit, and particularly to a transmission interface circuit for a communication device that outputs a bipolar signal.

[Conventional technology]

7 and 8 are block diagrams and circuit diagrams showing an example of a conventional transmission interface circuit.

(+) side trigger signal 7-2 and H side trigger signal 7-3 from switching control circuits 7-1 and 8-1
unipolar signal (7-5° on the + side, 7-6° on the - side)
) output switching circuit 7-4 (transistor 8
-2.8-3), converts the unipolar signal into a bibo 2 signal and changes the output impedance to 7 through the transformer 8-5.
5Ω or 120Ω, the voltage Vcc applied to the primary side of the transformer 8-5 is adjusted by the resistor 8-4, and the signal level is adjusted as the output impedance is changed, and the output (8 -6, 8-7) Yes.

[Problem to be solved by the invention]

The conventional transmission interface circuit described above has, for example, 7
Since the 5Ω interface circuit or the 120Ω interface circuit is set independently, the circuit configurations, circuit components, and circuit constants are different, resulting in the following drawbacks.

L Printed wiring boards must be designed and manufactured for each different interface.

2 Since the circuits are different, these parts must be manufactured and managed individually.

[Means to solve the problem]

A transmission interface circuit of the present invention includes a switching circuit that outputs a unipolar 2 signal in response to a trigger signal from a switching control circuit, and a conversion circuit that converts the unipolar signal into a biborder 2 signal and outputs it via a transformer. The present invention is characterized in that the winding ratio between the input side and the output side of the transformer is changed to match the impedance of the output circuit.

〔Example〕

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

1 and 2 are block diagrams of first and second embodiments of the present invention, and FIGS. 3 and 4 are circuit diagrams of the first and second embodiments of the present invention.

1 and 2 show a switching control/control circuit 1
-1.2-1 (+) side switching trigger signal 1-2.2-2 and (C) side switching trigger signal 1
-3. Unipolar signal by 2-3 (+ side is 1-5.
2-5, - side is U-B for 75Ω which has a switching circuit 1-4.2-4 that outputs 1-6.2-6> and a transformer that converts a unipolar signal into a bipolar signal and has an output impedance of 75Ω. The circuit includes a circuit 1-7 and a 120Ω U-B circuit 2-7 having a transformer with an output impedance of 120Ω.

In the first embodiment shown in FIG. 3, the (+) side and (to) side trigger signals from the switching control circuit 3-1 are input to the transistors 3-2, 3-3.

Transistors 3-2, 3-3 connect to the primary side (C-ri, C-E
) to output a Bibo 2 signal to the secondary side (A-B).

In this way, the transformer 3-5 can play the role of converting a unibo 2 signal into a bipolar 2 signal by changing the winding ratio, and can output a predetermined signal level at a predetermined output impedance.

The second embodiment shown in FIG. 4 differs from the first embodiment shown in FIG. 3 in that the secondary side of the transformer 4-5 (4-6 and 4-
7) is short-circuited, for example, the transistor 4-2.4-
Overcurrent protection element 4 that prevents damage to 3 due to overcurrent
-4 (for example)) is inserted between the midpoint of the winding of the transformer 4-5 and the power supply Vce.

Note that the transformer is now transformer 3- as shown in Figure 3.
The winding ratio of 5 is 1:n (n is a positive rational number) and A-8
When the impedance when looking at the output side from between is 2, D-
The impedance Z' appearing between E is expressed by equation (1).

Therefore, the impedance 2' appearing between the midpoint C and D or between C and E is expressed by equation (2).

Here, if the secondary side A-B is short-circuited, impedance 2 becomes O, and impedance 2' also becomes O at the same time.When the transistor becomes conductive, overcurrent flows from the collector to the emitter of the transistor. Become.

5 and 6 are circuit diagrams for explaining the turns ratio of the transformer of this embodiment. FIG. 5 shows an example of an output impedance of 75Ω, and FIG. 6 shows an example of an output impedance of 120Ω. In FIG. 5, the turns ratio of the transformer is 1:α25. As a signal level voltage value, this is −order @
Secondary aO to IK.

5, so it is output at a ratio of 1:0.5. for example,
If the potential applied to the 0 point is 5■, and the voltage drop at the drive transistor is about 0.3■, the voltage value output to A-B is as follows: (3) Equation 7 % (3) It almost matches the voltage value Z37V recommended by CCITT. Similarly, in Figure 6, the turns ratio of the transformer is 1:
It is α32. As a voltage value, this is - side 1
Since the secondary side is 0.64, the ratio is 1:α64. In this case, the voltage value output to A-B is
(4) Formula ■A-B=(5,0-α3)×α64=3.00V
...(4) fi, which matches the voltage value &Ov recommended by CCITT.

〔Effect of the invention〕

As explained above, the present invention sets the output level of the pi-indicator signal in accordance with a change in output impedance by changing the turns ratio of the transformer. If you do this, you can use exactly the same circuits, so the circuit configuration and circuit constants are not common, and the same printed wiring board can be used even with different impedances, making production management easier. It also has the effect of being effective.

FIG. 2 is a block diagram and a circuit diagram showing an example of a circuit.

1-1, 2-1, 3-1, 7-1, 8-1...
・Switching control circuit, 1-4, 2-4
, 7-4... switching circuit, 1-7.2-7...
・75Ω, 120Ω U-B circuit, 3-2, 3-3
, 4-2 , 4-3 , 8-2 .

8-3...Transistor, 3-5.5-5.6-5゜8-5...Transformer, 4-4...Overcurrent protection element,
7-7...U-B circuit (for 75Ω, 120Ω).

Claims (1)

[Claims] A transmission interface circuit comprising a switching circuit that outputs a unipolar signal in response to a trigger signal from a switching control circuit, and a conversion circuit that converts the unipolar signal into a bipolar signal and outputs it via a transformer, the input side and the output side of the transformer. A transmission interface circuit that matches the impedance of an output circuit by changing the winding ratio of the transmission interface circuit.