JPH10178398A - Potential insulation device between input and output - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a miniaturizable inexpensive potential insulation device between input and output in simple constitution. SOLUTION: The primary circuit of a high frequency core T2 is constituted of the secondary side winding 1 of a first high frequency core T1, the primary side winding 2 of a second high frequency core T2 and a balanced modulation circuit network (for instance, SBDB) 3 and high frequency modulates the input signals ei. Also, the secondary circuit of the high frequency core T2 is constituted of the secondary side winding 5 of the first high frequency core T1, the secondary side winding 2 of the second high frequency core T2 and the balanced modulation circuit network 7 and high frequency demodulates the input signals es. A local oscillator 8 is a high frequency oscillator and is connected to the primary side winding 9 of the high frequency core T1. Thus, since magnetic coupling is performed by the second high frequency core T2, high frequency noise generated by an inter-device potential difference is effectively suppressed. Also, the two pieces of high frequency transformers and one piece of a local oscillator are sufficient and miniaturization and cost reduction are performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input / output potential insulating device, and more particularly to a simple and inexpensive input / output potential insulating device capable of effectively suppressing noise generated by a potential difference between devices.

[0002]

2. Description of the Related Art Conventionally, various proposals have been made for a method of suppressing noise generated when there is a difference in potential between input / output devices. When the potential difference between the input / output devices is extremely small, a method using a common-mode noise loop is adopted. When the potential difference between the input / output devices is large,
When the input signal is a DC or low-speed signal, a method using a photocoupler or an insulating amplifier is adopted. A transformer is used for an AC input signal.

On the other hand, for a wideband signal including DC,
There is a method in which a band is treated as an AC signal in the frequency domain and transmitted using a high frequency modulation method. One example is shown in FIG.
This will be briefly described with reference to FIG. Now, the signal Si of the device A is
For example, it is assumed that the data is transmitted to the device B that is about 100 meters away. The high-frequency modulator 31 of the device A mixes the wideband signal Si including the direct current with the local oscillation signal supplied from the local oscillator 32 via the transformer 33,
The wideband signal Si is modulated at a high frequency. High frequency modulator 31
The high-frequency modulated signal output from is transmitted to the transmission line 35 via the transformer 34.

[0004] The receiving device B receives the high-frequency modulated signal via the transformer 36. The high-frequency demodulator 41 demodulates the high-frequency modulated signal by mixing with a local signal supplied from a local oscillator 42 via a transformer 43, and the reproduced signal is reproduced by a reproducing device 44 into an image, a sound, or the like. Here, the local oscillators 32 and 42 output local oscillation signals of the same frequency.

[0005]

There is no quantitative solution for the potential between the devices due to the installation work method, the distance between the devices, the arrangement of other facilities, and the wiring method of the earth bus. For this reason, the prior art requires an ad-hoc response. For wideband signals including direct current, there is a method using the high-frequency modulation method as described above. However, two local oscillators and four transformers are required, and high-frequency demodulation is required on the receiving side. However, there has been a problem that the device configuration is complicated and large, the number of parts is increased, and the cost is not reduced.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned problems of the prior art, to provide a simple and compact structure, to provide a low-cost device.
An object of the present invention is to provide an input / output potential insulating device.

[0007]

In order to achieve the above-mentioned object, the present invention relates to an input / output potential isolating device for connecting a plurality of devices having different potentials to perform high-frequency modulation and convert a frequency of an input signal into a band. And a secondary circuit of the high-frequency transformer that performs high-frequency demodulation and reproduces an input signal, and magnetically couples by the high-frequency transformer, so that the influence of the potential between devices occurs between the devices. There is a first feature in that the operation is prevented.

Another aspect is that a balanced modulation network is used for the high-frequency modulation device, a balanced modulation network is used for the high-frequency demodulation device, and a DC power supply is not used for each device. The third feature is that the number of local oscillators required for the high-frequency modulation and the high-frequency demodulation is one.
A fourth feature is that the device for performing the high-frequency modulation and the high-frequency demodulation is provided only in one device connected by an unbalanced transmission line.

According to the present invention, since the primary circuit and the secondary circuit are magnetically coupled by the high-frequency transformer, the influence of the potential between the devices is prevented from occurring between the devices, and the influence of the potential difference between the devices is prevented. Noise can be effectively suppressed. Further, a DC power supply is unnecessary for a device that performs high-frequency modulation and high-frequency demodulation, a local oscillator is provided, and a device that performs high-frequency modulation and high-frequency demodulation is provided only on one device connected by an unbalanced transmission line. As a result, it is possible to provide an inexpensive input / output potential insulating device having a simple configuration, a small size, and a low price.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of one embodiment of the present invention. In the figure, a primary circuit to which an input signal ei is inputted includes a secondary winding 1 of a first high-frequency core T1, a primary winding 2 of a second high-frequency core T2, and a balanced modulation network (ring ring). And an SBDB (Schottky barrier diode bridge) 3 which is a modulator. The secondary circuit that outputs the output signal eo is composed of the secondary winding 5 of the first high-frequency core T1,
Of the high-frequency core T2 and an SBDB 7 having the same configuration as the SBDB 3. The first
A high-frequency oscillator 8 as a local oscillator is provided on the primary side of the high-frequency core T1, and is connected to the primary winding 9 of the high-frequency core T1. The first and second high-frequency cores T1
, T2 are small, for example, about 5 turns.

Next, the operation of this embodiment will be described in detail. The input signal ei can be expressed by the following equation (1). ei = Vs.Cos (pt) [V] (1) On the other hand, the output signal ec of the high-frequency oscillator 9 is expressed by the following (2).
It can be represented by an equation. ec = Vc · Sin (ω ·
t) [V] (2) where p = 2πfp [rad / sec], ω = 2πfc
[Rad / sec]. Fp is the frequency of the input signal (1 / second), and fc is the oscillation frequency of the high-frequency oscillator 8 (1 / sec).
Vs is the maximum value [V] of the amplitude of the input signal, and Vc is the maximum value [V] of the amplitude of the output signal of the high-frequency oscillator 8.

Next, the voltage es on the secondary side of the high-frequency core T2 generated by the primary-side circuit of the high-frequency core T2 is as follows:
Equation (3) is obtained. es = k · ei · ec [V] = k · (・) · Vs · Vc · {Sin (ω + p) t + Sin (ω−p) t} (3) where k is a proportional constant Represents the constant loss of the circuit. In addition, the first term Sin (ω +
p) t is the upper wave whose lower limit is fc,
(Ω-p) t represents a lower side wave whose upper limit is fc.

If these relationships are expressed in the frequency domain, they are as shown in FIGS. Where fpmax
Represents the maximum frequency of the input signal. Further, since p = 0 when the input signal is direct current, the voltage es on the secondary side of the high-frequency core T2 is expressed by the following equation (4). es = kVsVcSin ([omega] t) (4) When this relationship is expressed in the frequency domain, it becomes as shown in FIG.

Next, the output signal eo obtained from the secondary circuit of the high-frequency core T2 can be expressed by the following equation (5). eo = k · es · ec = k 2 · ei · ec 2 = k 2 · Vs · Vc 2 {Sin (ω · t) 2 · Cos (p · t)} = k 2 · Vs · Vc 2 · (1 / 2) · Cos (p · t) −k ² · Vs · Vc ² · (1/4) · {Cos (2ω + p) t + Cos (2ω−p) t} (5) The second of the formula (5) When the term is removed with a low-pass filter,
The output signal eo is expressed by the following equation (6). FIG. 5 shows this processing in the frequency domain.
The characteristic a indicates the low-pass filter characteristic.

Eo = k ² · Vs · Vc ² · (1/2) · Cos (p · t) (6) In the above equation (6), if k ² and Vc are constant, the constant value is It can be ignored and expressed as the following equation (7). eo = Vs · Cos (pt) (7) Comparing the expressions (1) and (7), the input signal ei
It is clear that both the frequency and voltage components are preserved.

According to the above-described embodiment, the primary circuit and the secondary circuit of the second high-frequency core T2 perform signal transmission by the magnetic coupling of the first and second high-frequency cores T1, T2. Therefore, connection is possible even if the input and output have different potentials. Further, by selecting the frequency of the high-frequency oscillator 8 to be equal to or higher than the VHF band, the first and second frequencies can be adjusted.
Of the high-frequency cores T1 and T2 can be extremely miniaturized, and the required number of windings can be reduced, so that stray capacitance between lines is reduced and AC coupling is minimized. In addition, high frequency noise generated by the potential difference between the devices can be effectively suppressed. Further, as is clear from the above description, transmission of a DC signal is also possible.

Next, the potential isolation device 10 between the input and output of the present invention will be described.
Will be described with reference to FIG. 6 for an embodiment in which the present invention is applied to, for example, a surveillance camera system. In the figure, 11
Is an input terminal of a 75Ω coaxial cable, for example, to which CVBS (composite video base band signal) of an image is input. Reference numeral 12 denotes a fixed attenuator, which is inserted for the purpose of reducing the amount of mismatch attenuation. The fixed attenuator 12 reduces the reflection of the CVBS, and can efficiently supply the CVBS to the input-output potential isolator 10.

Reference numeral 13 denotes a low-pass filter having the characteristics described with reference to FIG. As the low-pass filter 13, an inexpensive filter having a Butterworth characteristic can be used. Reference numerals 14 and 15 denote first and second amplifiers.
The amplifier 14 is inserted for the purpose of compensating for the insertion loss of the input-output potential isolator 10, and the second amplifier 15 is connected to the CVBS
Is inserted for the purpose of driving 75Ω. Reference numeral 16 denotes an output terminal to a coaxial cable to which, for example, a television for monitoring is connected.

When the input-output potential isolator 10 of the present invention was evaluated using this system, the in-band ripple was 0.1 dB in a wide band from DC to 7 MHz. The insulation between the input and output of the input-output potential insulating device 10 was 10 MΩ or more.

[0020]

As is apparent from the above description, according to the present invention, since the primary circuit and the secondary circuit are magnetically coupled by a high-frequency transformer, high-frequency noise generated by a potential difference between devices can be effectively reduced. Can be suppressed.
Also, only two high-frequency transformers and one local oscillator are required, and the device for performing the high-frequency modulation and the high-frequency demodulation is provided only in one device connected by an unbalanced transmission line. Therefore, it is possible to provide an inexpensive input / output potential insulating device which is simple, compact, and inexpensive.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating an input signal in a frequency domain.

FIG. 3 is a diagram illustrating a voltage of a secondary circuit in a frequency domain.

FIG. 4 is a diagram illustrating, in the frequency domain, a signal appearing in a secondary circuit when an input signal is DC.

FIG. 5 is a diagram showing an output signal eo obtained from a secondary side circuit in a frequency domain.

FIG. 6 is a system diagram showing an application example of the present invention.

FIG. 7 is a circuit diagram showing an example of a conventional device.

[Explanation of symbols]

1. Secondary winding of the first high-frequency core T1, 2. Primary winding of the second high-frequency core T2, 3. Balanced modulation network (SB
DB), 5 ... secondary winding of the first high-frequency core T1, 6 ...
Secondary winding of the second high-frequency core T2, 7: Balanced modulation network (SBDB), 8: High-frequency oscillator, 9: High-frequency core T
1 primary winding, 12: fixed attenuator, 13: low-pass filter, 14, 15: amplifier.

Claims (6)

[Claims] An input / output potential isolator for connecting between devices having a plurality of different potentials, a primary circuit of a high-frequency transformer for performing high-frequency modulation and band-converting an input signal, and reproducing an input signal by performing high-frequency demodulation. A secondary circuit of the high-frequency transformer, and magnetically coupled by the high-frequency transformer to prevent the influence of the inter-device potential from being generated between the devices. Insulation device. 2. The input / output potential insulating device according to claim 1, wherein a balanced modulation network is used for the high-frequency modulation device, and a balanced modulation network is used for the high-frequency demodulation device.
A potential isolation device between input and output, wherein a DC power supply is not used for each device. 3. The potential insulating device between input and output according to claim 1, wherein the high frequency modulation and the high frequency demodulation are performed simultaneously. 4. The potential isolation device between input and output according to claim 1, wherein one local oscillator is required for said high-frequency modulation and high-frequency demodulation. 5. The potential isolation device between input and output according to claim 1, wherein said plurality of devices having different potentials are connected by an unbalanced transmission line, and common-mode noise is removed. A potential isolation device between input and output characterized by the following. 6. The input / output potential insulating device according to claim 5, wherein the device for performing the high-frequency modulation and the high-frequency demodulation is provided only in one device connected by the unbalanced transmission line. Input-output potential insulation device.