JPH07226716A - Signal transmitter - Google Patents

Abstract

PURPOSE:To correct the error due to temperature drift of a light emitting element or the fluctuation in a loss due to an optical fiber connector and an optical fiber in the direct intensity modulation system automatically by providing an offset circuit, a variable gain amplifier and a gain control circuit to the transmitter. CONSTITUTION:An electric signal outputted from a photo diode 26 is given to a variable gain amplifier 28, and an electric signal outputted from the amplifier 28 has a DC component corresponding to a DC signal level from an offset circuit 18 added by a light emitting element drive circuit 16. Furthermore, the electric signal from the amplifier 28 is outputted respectively to a DC block circuit 30 and a gain control circuit 32, and a DC extract circuit 34 in the circuit 32 eliminates an AC signal component included in the electric signal from the amplifier 28 to extract the DC component. The DC component reflects on a temperature drift of a light emitting element 19 and a fluctuation due to a loss of optical fiber connectors 20, 24, a loss of an optical fiber 22 and a conversion characteristic or the like of the diode 26 with fidelity when a level of a DC electric signal from the circuit 18 is stable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission device for converting an electric signal into an optical signal for transmission, and more particularly to a signal transmission device for automatically correcting an amplitude error occurring in the transmitted signal.

[0002]

2. Description of the Related Art A signal transmission device for converting an analog electric signal into an optical signal and transmitting the same using an optical fiber cable is capable of transmitting the electric signal over a long distance without deteriorating the electric signal. Because you can
Widely used for transmitting video signals and measurement signals.
There is also a digital method in which an analog signal is digitized and then converted into an optical signal for transmission, but because the frequency bandwidth is limited and the circuit configuration becomes complicated and expensive, the voltage amplitude of the electrical signal is directly output. A direct intensity modulation method in which the signal is converted into an intensity amplitude and transmitted is widely used.

FIG. 2 is a block diagram of a conventional signal transmission device using direct intensity modulated light. The input terminal 100 is E /
The E / O converter 102 is connected to an O (electrical / optical) converter 102, and the E / O converter 102 includes an optical fiber connector 104 and an optical fiber connector 104.
O / E via cable 106 and optical connector 108
It is connected to an (optical / electrical) converter 110. The O / E converter 110 is connected to the amplifier 112, and the amplifier 112 is connected to the output terminal 114.

The operation of the signal transmission device of FIG. 2 will be described below. The electric signal applied to the input terminal 100 is converted by the E / O converter 102 into an optical signal having a light intensity corresponding to its amplitude. . A light emitting diode (LED) is widely used for the E / O converter 102 (light emitting element).
The optical signal from the E / O converter 102 is received by the optical fiber connector 104 and 108.
It is transmitted to the O / E converter 110 by the cable 106. The optical signal transmitted to the O / E converter 110 is converted into an electric signal according to its intensity, amplified by the amplifier 112, and output to the output terminal 114.

However, when an LED is used for the above-mentioned light emitting element 102, the electric / optical conversion efficiency of the LED depends on the temperature, and therefore an error (temperature drift) occurs in the optical output.
The O / E converter 110 also causes a change in conversion efficiency. Also, the splice loss due to the optical fiber connectors 104 and 108 varies with each reconnection. Furthermore, when the length of the optical fiber cable 106 is changed, the loss also changes, so that the optical signal intensity at the O / E converter 110 also changes. Further, the conversion efficiency of the O / E converter 110 also changes.

As a conventional technique for solving the above problems,
When transmitting a signal having a specific standard (for example, a video signal of the NTSC standard), the amplifier 112 is arranged so that the signal output from the output terminal 114 has an amplitude equal to the standard (for the NTSC signal, a vertical synchronizing signal, for example). There has been a signal transmission device that controls the gain of AGC (Automatic Gain Control).

Also, another optical fiber cable is provided between the light emitting element side and the O / E converter side to provide O / E.
There is a signal transmission device that performs a self-calibration by transmitting a control signal from the converter side to the light emitting element side and switching an electric signal applied to the input terminal 100 to a reference signal.

However, the above-mentioned signal transmission device for applying AGC can be applied only to a signal having a specific format (standard) to be transmitted (for example, an NTSC standard video signal), and the accuracy is low (10%). However, there was a problem.

Further, the signal transmission device for self-calibration has a problem that not only the circuit structure becomes complicated and expensive, but also a time (dead time) during which a signal cannot be transmitted occurs during self-calibration.

Therefore, an object of the present invention is to perform signal transmission in a direct intensity modulation type signal transmission device, which automatically corrects an error caused by a temperature drift of a light emitting element (LED) and a loss variation due to an optical fiber connector and an optical fiber. It is to provide a device.

[0011]

SUMMARY OF THE INVENTION A signal transmission device of the present invention includes an offset circuit for adding a DC electric signal of a predetermined level to an AC component of an inputted electric signal, and an electric signal from an O / E converter. By including a variable gain amplifier that amplifies, a DC extraction circuit that extracts a DC component from an electric signal from the variable gain amplifier, and a gain control circuit that controls the gain of the variable gain amplifier according to the DC component from the DC extraction circuit. In the direct intensity modulation method, the error due to the temperature drift of the light emitting element and the fluctuation of the loss due to the optical fiber connector and the optical fiber is automatically corrected.

[0012]

1 is a block diagram of a signal transmission device according to the present invention. The input terminal 10 is connected to the input amplifier 12, and the input amplifier 12 is connected to the DC blocking circuit 14. The DC blocking circuit 14 is connected to the light emitting element drive circuit 16. An offset circuit 18 is also connected to the light emitting element drive circuit 16. The light emitting element drive circuit 16 is connected to the light emitting element (LED) 19. The light output from the light emitting element 19 is output to the optical fiber connector 20. Optical fiber 22 with one end connected to optical fiber connector 20
An optical fiber connector 24 is connected to the other end of the. The optical signal from the optical fiber connector 24 is sent to the O / E converter (photoelectric conversion element) 26. The O / E converter (hereinafter referred to as a photodiode) 26 includes a variable gain amplifier 28.
The variable gain amplifier 28 is connected to the DC blocking circuit 30.
Also, it is connected to the DC extraction circuit 34 in the gain control circuit 32. The DC blocking circuit 30 is connected to the output amplifier 36, and the output terminal 36 is connected to the output amplifier 36.
The DC extraction circuit 34 is also connected to an error amplifier 42 that detects a difference from the reference potential 40. The output of the error amplifier 42 is connected to the variable gain amplifier 28.

The operation of the signal transmission device of FIG. 1 will be described below. The electric signal applied to the input terminal 10 is amplified by the input amplifier 12. The DC signal is removed by the DC blocking circuit 14 from the electric signal amplified by the input amplifier 12. The electric signal including only the AC signal component is added to the DC electric signal of a predetermined level by the light emitting element drive circuit 16 and the offset circuit 18. In the light emitting element 19, the voltage amplitude of the electric signal of the light emitting element drive circuit 16 is directly converted into the intensity change of the optical signal (direct intensity modulation). The electric signal can take either positive or negative values, but since there is no negative value in the light intensity, a direct current electric signal of a predetermined level is given by the offset circuit 18 and added by the light emitting element drive circuit 16. Therefore, a constant optical signal is output even when the electric signal is zero. The optical signal output from the light emitting element 19 is passed through the optical fiber connector 20, the optical fiber cable 22, and the optical fiber connector 24, and then the photodiode 26.
Be transmitted to.

The intensity of the optical signal transmitted to the photodiode 26 fluctuates due to the temperature drift of the light emitting element (LED) 19, the loss due to the optical fiber connectors 20 and 24, and the transmission loss due to the optical fiber 22. Furthermore, the fluctuation of the conversion efficiency of the photodiode 26 is added to the fluctuation of the electric signal output from the photodiode 26. The electric signal output from the photodiode 26 is input to the variable gain amplifier 28. The electric signal output from the variable gain amplifier 28 has a DC component corresponding to the DC signal level from the offset circuit 18 added by the light emitting element drive circuit 16. The electric signal output from the variable gain amplifier 28 is input to the DC blocking circuit 30 and the gain control circuit in the gain control circuit 32, respectively. The DC extraction circuit 34 in the gain control circuit 32 removes the AC signal component contained in the electric signal from the variable gain amplifier 28 and extracts the DC component. If the DC electric signal of the offset circuit 18 is stable, this DC component causes temperature drift of the light emitting element (LED) 19, loss of the optical fiber connectors 20 and 24,
The loss due to the optical fiber 22 and the variation due to the conversion characteristics of the photodiode are faithfully reflected. DC extraction circuit 34
The DC signal extracted in is input to the error amplifier 42,
The difference from the reference potential 40 is compared. Error amplification circuit 42
Outputs to the variable gain amplifier 28 an error signal corresponding to the difference between the DC signal from the DC extraction circuit and the reference potential. The amplification factor of the variable gain amplifier 28 is controlled so that the magnitude of the error signal is constant or zero. The output signal from the variable gain amplifier 28 removes the DC component and is also input to the AC signal blocking circuit 30 that passes only the AC component. The output signal from the DC blocking circuit 30 is applied to the output amplifier 36, amplified, and output from the output terminal 38.

The electric signal output from the output terminal 38 is
Since the amplitude variation is corrected by the variable gain amplifier 28, it faithfully corresponds to the electric signal at the input terminal 10.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described herein, and various modifications and modifications can be made as necessary without departing from the gist of the present invention. It will be apparent to those skilled in the art that changes can be made.

For example, in the above-described embodiment, the light emitting element 19 is a light emitting diode (LED), but any device such as a laser diode that converts an electric signal into an optical signal may be used.

Similarly, the O / E converter 26 may be a phototransistor, a solar cell, or the like that converts light into an electric signal.

[0019]

According to the present invention, in a direct intensity modulation type signal transmission device, a signal transmission for automatically correcting an error due to a temperature drift of a light emitting element (LED or the like) and a loss variation due to an optical fiber connector and an optical fiber. A device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of a signal transmission device according to the present invention.

FIG. 2 is a block diagram of a conventional signal transmission device using direct intensity modulated light.

[Explanation of symbols]

 18 Offset Circuit 19 Light Emitting Element 26 O / E Converter 28 Variable Gain Amplifier 32 Gain Control Circuit 34 DC Extraction Circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04B 10/152 10/142

Claims (1)

[Claims] 1. A signal transmission device comprising a light emitting element for converting an AC electric signal into an optical signal, and a photoelectric conversion element for converting the optical signal from the light emitting element back into an electric signal, wherein the AC electric signal has a predetermined level. Offset circuit for adding the DC electric signal of, a variable gain amplifier for amplifying the electric signal from the photoelectric conversion element, a DC component of the output signal from the variable gain amplifier is extracted, and a DC component is extracted according to the DC component. And a gain control circuit for controlling the gain of the variable gain amplifier.