JPS607552Y2 - electronic circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic circuit comprising a pair of electronic circuits connected to each other via a photocoupler.

A photocoupler is a means of electrically insulating the signal from one electronic circuit and transmitting it to another electronic circuit, but in reality, a photocoupler completely electrically disconnects the upper electronic circuit. is difficult due to the performance of the photocoupler.

Therefore, when transmitting a signal from a negative electronic circuit to another electronic circuit via a photocoupler, there is a risk that interference signals such as commercial AC signals may be mixed into or superimposed on the signal, resulting in deterioration of the signal-to-noise ratio. There is.

The present invention is proposed to suppress the deterioration of S/N due to such causes.

In the present invention, attention is paid to the fact that interference signals are also generated between the ground conductor of the above-mentioned - electronic circuit and the ground conductor of other electronic circuits,
This interference signal is detected and added to an appropriate location in the electronic circuit or other electronic circuit in order to cancel out the interference signal component in the signal.

That is, for example, an electronic circuit (-) is formed on a so-called hot chassis that does not have an insulating transformer interposed between it and the commercial AC power supply, and other electronic circuits are isolated from the commercial AC power supply by a transformer. .

When formed on a so-called cool chassis, the ground conductor on the hot chassis side is not connected to the ground, whereas the ground conductor on the cool chassis side is connected to the ground.

Therefore, a potential difference occurs between the two ground conductors even though they are the same ground conductor, and a disturbance signal such as a commercial AC signal appears between the two electronic circuits.

Therefore, the present invention improves the signal-to-noise ratio by canceling out the interference signal mixed into or superimposed on the signal by the interference signal based on the potential difference between two ground conductors.

The present invention will now be described in detail with reference to the drawings.

FIG. 1 shows one embodiment of the invention, in which 1 and 2 are a pair of electronic circuits (first and second electronic circuits), and superior electronic circuits 1 and 2 are shown in FIG.
are connected to each other via a photocoupler 3, and a signal from the first electronic circuit 1 is transmitted via the photocoupler 3 to the second electronic circuit 2.

In this example, the first electronic circuit 1 is constituted by a grounded emitter transistor amplification circuit, and a signal source (
For example, a video frequency signal source) e is connected.

Note that 10B□ is the power supply for this first electronic circuit 1.

In this example, the second electronic circuit 2 is constituted by a grounded emitter transistor amplification circuit, and an output terminal 4 is led out from the collector of the transistor Q2.

Togarasu is the power supply for the second electronic circuit 2 (it is electrically isolated from the power supply B1, and G2 is a ground conductor).

The photocoupler 3 is assembled into a package with a light emitting element 5 such as a light emitting diode, and a light receiving element 6 such as a photodiode facing each other.

In this photocoupler 3, a width increasing transistor Q3 is provided on the light receiving element 6 side.

The anode of the light emitting diode 5 is connected to the power source 1a of the first electronic circuit 1, and the cathode is connected to the transistor Q1.
connected to the collector of

The cathode of the photodiode 6 is connected to the staggered power source of the second electronic circuit 2, and the anode is connected to the base of the transistor Q3.

In this case, the second electronic circuit 2 is provided with a load resistor 7 and a capacitor 8 so that the transistor Q3 constitutes a grounded emitter transistor amplifier circuit, and the collector of the transistor Q3 is connected to the power supply staggered through the resistor 7. It is also connected to the base of transistor Q2 through capacitor 8, and its emitter is connected to ground conductor G2.

Furthermore, a detection circuit 10 detects a disturbance signal from the ground groove p□ of one of the pair of electronic circuits 1 and 2.
is provided, and the interference signal detected by this detection circuit 10 is supplied to an appropriate location of the other electronic circuit 2 to cancel the interference signal.

This detection circuit 10 is configured to suppress a commercial AC signal as an interfering signal.

That is, a series circuit of resistors 11 and 12 is connected between the ground conductor G and 02, and the connection midpoint of the resistors 11 and 12 is connected to the emitter of the transistor Q2 of the second electronic circuit 2 through the resistor 13. do.

In this case, the resistance values of the resistors 11, 12, and 13 are, for example, 8.2 MΩ, IKΩ, and 30Ω, and for example, the resistor 13 is a variable resistor.

In the electronic circuit of FIG. 1, if the detection circuit 10 is not provided, the output obtained at the output terminal 4 of the second electronic circuit 2 is equal to the signal from the signal source e of the first electronic circuit 1. The result is a signal in which a commercial AC signal is superimposed on the amplified signal.

However, since the detection circuit 10 is provided as described above, the commercial AC signal is canceled out in the second electronic circuit 2.

In this case, the commercial AC signal obtained from the emitter of transistor Q2 and the commercial AC signal obtained from detection circuit 10 are exactly opposite in phase.

In this case, by adjusting the resistance value of, for example, the resistor 13 of the detection circuit 10, the level of the commercial AC signal obtained from the output terminal 4 can be minimized.

Incidentally, as shown in FIG. 2, the ground conductor G of the second electronic circuit 2
The interference signal from the second electronic circuit 1 may be detected by the detection circuit 10, and the detected interference signal may be supplied to an appropriate location of the first electronic circuit 1 to cancel out the interference signal.

In this case, the detection circuit 10 connects a series circuit of resistors 11 and 12 between the ground conductors G and 02, and connects the midpoint of the connection to the emitter of the transistor Q of the first electronic circuit 1 through the resistor 13. It is composed of

In this case, for example, the resistor 13 is a variable resistor.

When handling a video frequency signal, especially a television signal, as the signal from the signal source e as in the electronic circuit shown in FIG. Since there is also a signal of 100 kHz, in that case, the detection circuit 10 should be as shown in FIG.
In addition to the configuration shown in FIG. 1, the following configuration can be added.

That is, a capacitor (470p
F) A series circuit of 14 and a resistor (1KΩ) 15 is connected, and the midpoint of the connection between the capacitor 14 and the resistor 15 is connected to the collector of the transistor Q3 via the resistor (30Ω) 16.

For example, the resistor 16 is a variable resistor.

Note that the location where the output of the detection circuit 10 of the first or second electronic circuit 1 or 2 is supplied and the configuration of the detection circuit 10 are appropriately selected depending on the frequency of the interference signal.

According to the present invention described above, in an electronic circuit in which a pair of electronic circuits are connected to each other via a photocoupler, deterioration in signal S/N due to mixing or superimposition of interference signals can be effectively suppressed. Can be done.

[Brief explanation of the drawing]

1, 2 and 3 are circuit diagrams showing embodiments of the present invention. 1 and 2 are first and second electronic circuits, 3 is a photocoupler, 5 is a light emitting element, and a detection circuit. 6 is a light receiving element, 10 is

Claims (1)

[Scope of utility model registration request] A first electronic circuit having a first transistor of a common emitter type whose base is connected to a signal source and a second electronic circuit having a second transistor of a common emitter type are connected via a photocoupler. , the ground conductor of the first electronic circuit and the ground conductor of the second electronic circuit are connected through first and second resistors connected in series, and the first and second resistors are connected in series. An electronic circuit in which the connection midpoint and the emitter of the first or second transistor are connected via a third resistor to obtain an output signal from the collector of the second transistor in which the interfering signal is canceled. .