JPH05235692A - Optical signal coupling circuit - Google Patents

Abstract

PURPOSE:To propagate an AC signal to a wide range of DC input current by controlling the DC of an output voltage by providing a DC negative feedback circuit at an amplifier circuit for a photoelectric current in an optical signal coupling circuit. CONSTITUTION:Only the DC component of an electrical signal can be propagated to a light receiving element 2b by connecting a capacitor Co for AC grounding and a light emitting element 16 for DC feedback to the emitter of a transistor Q1 which amplifies the photoelectric current of the light receiving element 2 and adjusting a resistor R0, and it is negative-fed back from the collector of a transustor Q2 to the base of the transistor Q1. An AC component can be propagated by DC negative feedback even when the DC component of an input signal is increased. Also, when no input signal exists, no consumption current flows.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal coupling circuit.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional transistor output type optical signal coupling circuit (photocoupler) includes a light emitting diode (light emitting element) 1, a light receiving photodiode (light receiving element) 2, a transistor Q1 and a load resistor R. _{Has L.}

A conventional transistor type photocoupler is used for inputting a pulse current, and a light receiving photocoupler is used for inputting a pulse current, and a pulsed photocurrent flowing through a light receiving photodiode 2 is used to output voltage V ₀ of a transistor Q1. _{Is the} power supply voltage V _CC and the saturation voltage V _{CE (sat) of the} transistor Q1
To switch between.

[0004]

This conventional transistor output type photocoupler requires a circuit for setting the current value in order to drive the light emitting diode with current. Further, the light emitting efficiency of the light emitting diode differs depending on the light emitting diode used, and the photocurrent of the light emitting photodiode varies. Therefore, it is difficult to set the DC voltage of the output voltage V ₀ to an appropriate value. Further, since the transistor Q1 is saturated, there is a problem that the analog AC signal does not propagate when a DC current of the light emitting diode is passed.

Further, if a current mirror circuit is constructed using the transistors Q1 and Q2 and the resistor R _B as shown in FIG. 3, the DC voltage of the output voltage V ₀ can be set to an appropriate value, but it is always 2 ×. _{(V CC -V bE (Q2)} ) / R B becomes current consumption, there is a problem that flowed even no signal input state.

[0006]

The optical signal coupling circuit of the present invention comprises a circuit for negatively feeding back the DC component of the electric signal of the light receiving element.

[0007]

FIG. 1 shows an optical signal coupling circuit according to an embodiment of the present invention. Light emitting diode 1a and light receiving photodiode 2a
And the transistor Q1 has a light receiving photodiode 2a
The photocurrent of is amplified and the voltage is output from the collector. The negative feedback circuit includes a light emitting diode 1b, a light receiving photodiode 2b, and a transistor Q2. The emitter voltage of the transistor Q1 is negatively fed back from the collector of the transistor Q2 to the base of the transistor Q1. Since the capacitance C ₀ is connected to the emitter of the transistor Q1, only the AC component of the electric signal is propagated from the light emitting diode 1b to the light receiving photodiode 2b and negative feedback is applied. The amount of negative feedback can be adjusted by changing the resistance R ₀ .

In the non-input state where no current flows through the light emitting diode 1a, the transistors Q1 and Q2 are in the off state, and no current consumption occurs.

FIG. 2 shows an optical signal coupling circuit according to the second embodiment of the present invention. It has a light emitting diode 1 and a light receiving photodiode 2, and the transistor Q1 is a light receiving photodiode 2
The photocurrent of is amplified and the voltage is output from the collector. The emitter voltage of the transistor Q1 is negatively fed back from the collector of the transistor Q2 to the base of the transistor Q1.
Since the resistor R ₀ and the capacitor C ₀ are connected to the emitter of the transistor Q1, the AC component of the electric signal is grounded, and the transistor Q2 feeds back only the DC component. The DC negative feedback amount of the electric signal can be adjusted by changing the resistance R ₀ . Further, in the non-input state in which no current flows in the light emitting diode 1, the transistors Q1 and Q2 are in the off state, and no current consumption flows.

The second embodiment is similar to the embodiment of FIG.
Light-emitting diode 1b and light-receiving photodiode 2b of the second set
Since the circuit is not used, the circuit on the light receiving side including the light receiving photodiode can be built in one IC chip.

[0011]

As described above, since the present invention has the DC negative feedback circuit for the electric signal, it has the effect that the AC signal can be propagated in a wide range of the DC current of the light emitting element, and there is no signal. In the input state, there is an effect that current consumption does not flow.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a second embodiment of the present invention.

FIG. 3 is a circuit diagram in which a current mirror circuit is applied to a conventional transistor output type photocoupler.

FIG. 4 is a circuit diagram of a conventional transistor output type photocoupler.

[Explanation of symbols]

1, 1a, 1b Light emitting diode 2, 2a, 2b Light receiving photodiode Q1, Q2 Transistor _RL Load resistance R _B Current mirror circuit bias resistance R ₀ Feedback amount setting resistance C ₀ AC grounding capacitance

Claims (1)

[Claims] 1. A light emitting element for converting an electric signal into an optical signal, a light receiving element for converting an optical signal from the light emitting element into an electric signal, and a signal processing for processing and outputting the electric signal obtained by the light receiving element. In an optical signal coupling circuit having a circuit,
The optical signal coupling circuit is characterized in that the signal processing circuit includes a negative feedback circuit for a direct current component of an electric signal and does not flow current consumption in a signal non-input state.