JPH02243040A - Isolation method for differential signal transmission line - Google Patents

Abstract

PURPOSE:To use an inexpensive demodulation circuit having an unbalanced input characteristic by providing a 2nd pulse transformer between a 1st pulse transformer and a demodulation circuit in the reception of a differential signal and connecting one of transmission lines between the 1st and 2nd pulse transformers to the demodulation circuit. CONSTITUTION:A demodulation circuit 4A having an unbalanced input characteristic and high input impedance with inexpensive constitution is used as a demodulation circuit. Moreover, a pulse transformer 3 with the transformation ratio of 1:1 is newly inserted between the circuit 4A and the pulse transformer 2. A transmission line 11a being one side of transmission lines 11 between the transformers 2 and 3 is connected to the reference point 4P of the circuit 4A via a potential coupling line 12. By such a constitution, since the fluctuation of the potential between the transmission line 11 and the circuit 4A is eliminated, the invasion of noise to the circuit 4A via an inter-line capacitance of the transformer 3 is avoided and only a differential signal component is sent.

Description

[Detailed description of the invention]

[Industrial Application Field 1] The present invention relates to a method of insulating between a transmission line that performs differential signal transmission and a circuit that receives the signal.
The present invention relates to a method for insulating a differential signal transmission line, which enables the use of a demodulation circuit in which the impedances of two input lines to ground are unbalanced, and the input impedance is high. Note that in the following figures, the same reference numerals indicate the same or corresponding parts. 2. Description of the Related Art FIG. 3 shows an example of a circuit configuration of a receiving section of this type of differential signal transmission path. In the same figure, l is a transmission line, 5 is a transmission device on the receiving side, and transmission line 1 is a modulated signal (for example, logic "1", "0") from a signal transmitting means (sequencer, etc.) not shown in the figure. A signal converted into a different rectangular wave) is transmitted to the transmission device 5 side. Reference numeral 2 denotes a pulse transformer for insulating the transmitted modulated signal and transmitting it to the demodulation circuit in the transmission device 5. The demodulation circuit 4 demodulates the modulated signal thus received into a digital signal. In such a receiving circuit, when viewed from the demodulation circuit 4, the transmission path 1
are completely insulated and exhibit constantly changing potential fluctuations of tens to hundreds of volts to ground, usually due to external induction. On the other hand, the pulse transformer 2 has line capacitances 7 and 8 between the primary and secondary windings, and the demodulation circuit 4 usually has a high impedance to ground. In this case, if the input impedance of the demodulation circuit 4 is high,
The potential fluctuation of the transmission line l transmitted through the line capacitances 7 and 8 (
The noise signal) causes a potential difference of several tens to hundreds of millivolts between the input terminals of the demodulating circuit 4, and the demodulating circuit 4 cannot operate normally. For this reason, conventionally, the demodulation circuit 4 has been of a balanced differential type (i.e. 2
The input line (terminal) has a balanced impedance to ground), and the influence of the above-mentioned potential fluctuations on the transmission line 1 is prevented by using a demodulation circuit with a low input impedance.

[Question B that the invention attempts to solve]

However, the above-mentioned transmission signal receiving circuit has a problem in that it has a complicated configuration and is expensive. Therefore, the present invention connects two pulse transformers in series and inserts them between the transmission line and the demodulation circuit, and connects one side of the transmission line sandwiched between the two pulse transformers to a part of the demodulation circuit, so that the input impedance is high. It is an object of the present invention to solve the above problem by making it possible to use a demodulation circuit having unbalanced input characteristics.

[Means to solve the problem]

In order to solve the above problems, the method of the present invention isolates the differential signal transmitted via the r transmission path (such as 1) through a first pulse transformer (such as 2) and connects it to a receiving circuit (demodulation circuit). 4A, etc.), a second pulse transformer (3, etc.) is inserted between the first pulse transformer and the receiving circuit, and one of the transmission lines between the first and second pulse transformers is inserted. (118, etc.) is connected to at least a portion of the receiving circuit (potential reference point 4P, etc.) (via potential coupling line 12, etc.).

[For use]

By matching the potential of the transmission line between the two pulse transformers to the demodulation circuit, the demodulation circuit is not affected by potential fluctuations of the transmission line even with unbalanced input characteristics.

【Example】

The present invention will be described in detail below with reference to FIGS. 1 and 2. FIG. 1 is a configuration circuit diagram of a first embodiment of the present invention, and corresponds to FIG. 3. In contrast to FIG. 3, FIG. 1 shows a demodulation circuit 48 with an inexpensive configuration that has non-balanced input characteristics (that is, characteristics in which the impedances of the two input lines to the ground are not balanced) and high input impedance. At the same time, a new pulse transformer 3 with a transformation ratio of 1:1 is inserted between the demodulation circuit 4^ and the pulse transformer 2, and the pulse transformer 2
The transmission line lla on one side of the transmission line 11 between and 3 is newly connected via a potential coupling line 12 to a potential reference point 4P as a part of the demodulation circuit 4A. The potential coupling line 12 is for preventing relative potential fluctuations between the transmission line 11 and the demodulation circuit 4A. With this configuration, even if the potential of the transmission line 1 to ground changes, the input impedance of the transmission line 11 is low (tA).
Since the impedance between the transmission lines lla and llb is small, the differential component of the noise signal that enters the transmission line 11 via the line capacitances 7 and 8 of the pulse transformer 2 (i.e., the transmission lines lla, llb)
The component generated between the two lines is extremely small, and almost only a differential signal based on normal magnetic coupling between the lines of the transformer 2 is transmitted from the transmission line 1 to the transmission line 11. On the other hand, since potential fluctuations between the transmission line 11 and the demodulation circuit 48 are prevented by the potential coupling line 12, the line-to-line capacity of the pulse transformer 3! There is no noise signal entering the demodulation circuit 4A side via (not shown). In this way, only the differential signal component as a correct signal is transmitted from the transmission line 1 to the demodulation circuit 4A. FIG. 2 shows a modification of FIG. 1 as a second embodiment of the present invention. The difference from FIG. 1 is that the transmission line on one side of the transmission line 11 sandwiched between pulse transformers 2 and 3 is lla
is connected to the 0■ of the power supply 6 of the demodulation circuit 4^ by a thick potential coupling wire 12 so as to have a low impedance. Noise can be removed more effectively.

【Effect of the invention】

According to the present invention, in a device for insulating a differential signal transmitted via a transmission line 1 via a pulse transformer 2 and transmitting it to a demodulation circuit 4A, a pulse transformer is provided between the pulse transformer 2 and the demodulation circuit 4A. 3, and one side 11a of the transmission line between the pulse transformers 2 and 3.
is connected to at least the reference potential point 4P as a part of the demodulation circuit 4A via the potential coupling line 12, so that the inexpensive demodulation circuit 48 with high input impedance and non-balanced input characteristics can be connected to the transmission line. It becomes possible to use it more insulated than 1.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of this invention, FIG. 2 is a block diagram showing a second embodiment of this invention, and FIG. 3 is a block diagram showing a first embodiment of this invention.
FIG. 2 is a conventional configuration diagram corresponding to FIG. 1, +1: transmission line, lla, llb: transmission line,
2゜3: Pulse transformer, 4A: Demodulation circuit, 5: Transmission device, : Power supply, 12: Potential coupling line. Pulse transformer Pulse transformer ■ Figure 3, ? Figure 2

Claims (1)

[Scope of Claims] 1) A device for insulating a differential signal transmitted via a transmission line and transmitting it to a receiving circuit via a first pulse transformer, wherein: between the first pulse transformer and the receiving circuit; A second pulse transformer is inserted into the differential signal transmission, and one of the transmission lines between the first and second pulse transformers is connected to at least a part of the receiving circuit. road insulation method.