JPH0884114A - Signal transmitting equipment - Google Patents

Abstract

PURPOSE: To convert an analog electric signal into an optical signal with low distortion in a wide input current range, to attain long distance transmission and to improve on SN ratio of a receiving side equipment by compensating non-linear distortion included in a light emitting element by a reverse logarithmic amplifier arranged on the prestage of the light emitting element. CONSTITUTION: A transmitting side equipment 1 is arranged in a TV broadcast receiving station or the like and provided with a light emitting element 4 such as a light emitting diode for converting an analog electric signal into an optical signal and a distortion compensating circuit 6 is provided on the prestage of the element 4. The circuit 6 is constituted of a reverse logarithmic amplifier 8 and a proportional amplifier 10. In such a configuration when an analog electric signal is inputted to the circuit 6 in the equipment 1, the electric signal is outputted as a power number by the amplifier 8, so that the non-linear distortion included in the element 4 is compensated by the amplifier 8. An output from the amplifier 8 is proportionally amplified by the amplifier 10 and then converted into an optical signal by the element 4.

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 analog electric signal into an optical signal and transmitting it through an optical fiber.

[0002]

2. Description of the Related Art Generally, in a signal transmission device, an analog electric signal (for example, a video signal) from a transmission side device is converted into an optical signal by a light emitting element, and then this optical signal is sent to each terminal via an optical fiber. There is a device in which an optical signal is transmitted to a receiving side device and a light receiving element in the receiving side device converts an optical signal into an electric signal and outputs the electric signal.

By the way, a light emitting diode (LED) or the like is used as a light emitting element used in such a device. In such a light emitting element, the relation between the light output and the input current is represented by the reference numeral in FIG. It has a non-linear characteristic like the solid line indicated by a.

Therefore, when the light emitting element directly converts an analog electric signal into an optical signal, the analog signal is distorted. In particular, a light emitting diode (LED) that emits light on the long wavelength side (about 1.3 μm) has a remarkable feature.

As a result, for example, inconvenience occurs such that a faithful video cannot be reproduced with a video signal.

As a countermeasure, in the prior art, the low distortion range of the light emitting element is investigated in advance, and the electric signal is converted into the optical signal within the low distortion range.

[0007]

However, in the above measures, the input current range that can be converted as a low distortion optical signal in the light emitting element is narrowed, and the output power of the optical signal is limited. Therefore, long-distance transmission is not possible.

Further, in the receiving side device for receiving a weak optical signal, the amplification factor of the analog signal after photoelectric conversion by the light receiving element must be set high, which deteriorates the S / N ratio.

The present invention has been made in order to solve the above-mentioned problems, and is capable of converting an analog electric signal into an optical signal having a low distortion in a wide input current range, thereby enabling long-distance transmission. It is an object to improve the S / N ratio at the receiving side device.

[0010]

In order to solve the above problems, the present invention provides a light emitting element for converting an analog electric signal into an optical signal, and an optical fiber for transmitting an optical signal output from the light emitting element. A signal transmission device including a light receiving element for converting an optical signal transmitted through the optical fiber into an electric signal has the following configuration.

That is, according to the present invention, an antilogarithmic amplifier which outputs an analog signal as a power multiplier according to the non-linear distortion of the input current-optical output characteristic of the light emitting element is provided in front of the light emitting element.

[0012]

In the above configuration, since the non-linear distortion of the light emitting element is compensated by the antilogarithmic amplifier provided in the preceding stage of the light emitting element, an analog electric signal can be converted into a low distortion optical signal in a wide input current range. it can.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a main part of a signal transmission device.

In the figure, reference numeral 1 is a transmitting side device, 2 is a receiving side device, and 3 is an optical fiber connecting both devices 1 and 2.

The transmitting device 1 is installed in, for example, a receiving station for TV broadcasting, and has a light emitting element 4 such as a light emitting diode (LED) for converting an analog electric signal into an optical signal.
The distortion compensation circuit 6 is provided in front of the light emitting element 4.

The distortion compensation circuit 6 is composed of an antilogarithmic amplifier 8 and a proportional amplifier 10 in this example.

When the optical signal output with respect to the input current of the light emitting element 4 has a non-linear characteristic as indicated by the symbol a (solid line) in FIG. 2, the inverse logarithmic amplifier 8 accordingly responds to the symbol in FIG. As indicated by b (dashed-dotted line), it is set so as to have an output characteristic of an exponential function that outputs an input signal as a power.

On the other hand, the receiving-side device 2 is arranged, for example, in a house or the like, and is provided with a light-receiving element 12 including a photodiode for converting an optical signal from the optical fiber 3 into an electric signal.

In the signal transmission device having the above configuration, when an analog electric signal (for example, a video signal) is input to the distortion compensating circuit 6 of the transmitting side device 1, this electric signal is supplied to the antilogarithmic amplifier 8 as shown in FIG. As indicated by the symbol b (dashed-dotted line), it is output as a power.

The output of the antilogarithmic amplifier 8 is further proportionally amplified by the proportional amplifier 10 and then converted into an optical signal by the light emitting element 4.

In this case, the light emitting element 4 has a non-linear characteristic as shown by the symbol a (solid line) in FIG. 2, but the analog electric signal to be inputted is controlled by the antilogarithmic amplifier 8 according to its signal level. Light-emitting element 4 because it is a power
The power of the optical signal emitted from is the reference sign c (broken line) in FIG.
As shown in, the output has linearity.

That is, since the antilogarithmic amplifier 8 compensates for the non-linear distortion of the light emitting element 4, the analog electric signal can be converted into a low distortion optical signal in a wide input current range.

Then, this optical signal is transmitted to the receiving side device 2 at the end through the optical fiber 3, and the optical signal is converted into an electric signal by the light receiving element 12 and output.

Therefore, when the analog electric signal is, for example, a video signal, a faithful video is reproduced without causing distortion.

[0025]

According to the present invention, since the non-linear distortion of the light emitting element is compensated by the antilogarithmic amplifier, an analog electric signal can be converted into a low distortion optical signal in a wide input current range.

Therefore, long-distance transmission becomes possible and the S / N ratio at the receiving side device is improved.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an input current versus light output characteristic of a light emitting element.

[Explanation of symbols]

1 ... Transmitting side device, 2 ... Receiving side device, 3 ... Optical fiber, 4
... Light emitting element, 6 ... Distortion compensation circuit, 8 ... Inverse logarithmic amplifier, 12
…Light receiving element.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display part H04N 7/22

Claims (1)

[Claims] 1. A light emitting element for converting an analog electric signal into an optical signal, an optical fiber for transmitting an optical signal output from the light emitting element, and an optical signal for transmitting the optical signal transmitted through the optical fiber. In a signal transmission device comprising a light receiving element for converting to, in the preceding stage of the light emitting element, the inverse logarithm for outputting an analog signal by exponentiation according to the nonlinear distortion of the input current vs. optical output characteristics of the light emitting element. A signal transmission device comprising an amplifier.