JPH07250042A - Low frequency conversion type frequency multiplex transmission device - Google Patents

Abstract

(57) [Abstract] [Purpose] To lower the relaxation oscillation frequency of the laser diode on the transmitting side, prevent signal loss on the receiving side, and improve the S / N ratio. [Configuration] An RF signal input to an input terminal 1 is converted to a low frequency by mixers 4 and 5 after passing through bandpass filters 2 and 3. The converted signal is passed through the low pass filters 6 and 7
After passing through, couple on the same signal line by the coupler 8,
The laser diode 10 is driven and converted into an optical signal. At the time of conversion, the distortion is corrected by the output correction photodiode 12 or the like. The optical signal is transmitted by the optical fiber 13 and converted into an electric signal by the photodiode 14. The converted signal is amplified by the operational amplifier 15, branched by the coupler 17, and converted into the frequency of the original RF signal by the mixers 18, 19. After conversion, the bandpass filters 20, 21
To pass through and output from the RF output terminals 22 and 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low frequency conversion type frequency multiplex transmission device for converting an RF signal into a low frequency signal, performing a photoelectric conversion operation, and transmitting the optical fiber cable as a transmission medium.

[0002]

2. Description of the Related Art In a conventional optical transmission device, for example, when transmitting an input signal existing in two frequency bands having different frequency ranges, a laser diode 29 and an optical fiber cable 30 are mainly used as shown in FIG. , A photodiode 31.

The RF signals input to the RF input terminals 26 and 27 of the transmission device are bandpass filters 26 and 2, respectively.
After passing through 7, the signal is transmitted on the same signal line by the coupler 28, driven by the laser diode 29 to be converted into an optical signal, and transmitted by the optical fiber cable 30.

The signal transmitted through the optical fiber cable 30 is received by the photodiode 31, and the signal after the reception is transmitted by the coupler 34 via the operational amplifier 32.
By branching into two and passing through the band-pass filters 35 and 36, excess frequency components are removed and output from the RF output terminals 37 and 38.

[0005]

In the above-mentioned conventional transmission device, the frequency of the signal to be transmitted is in the high frequency region and has a wide band, so that the signal is transmitted to the laser diode 2.
9 makes matching difficult during photoelectric conversion, and the distortion characteristics of the laser diode 29 in the high frequency region are determined from the relaxation oscillation frequency, so the relaxation oscillation frequency must be extremely high. On the receiving side, the drive current of the photodiode 31 is extremely small, and the feedback resistor 33 for amplifying this signal needs to have a large value. However, in this case, since it is difficult to perform lossless matching of signals up to two bands, the S / N ratio deteriorates.

The present invention solves the above-mentioned conventional problems. The relaxation oscillation frequency of the laser diode on the transmitting side can be lowered, and signal loss on the receiving side can be prevented to reduce S. An object of the present invention is to provide a low frequency conversion type frequency multiplex transmission device capable of improving the / N ratio.

[0007]

The technical means of the present invention for attaining the above-mentioned object is a conversion means for converting an input RF signal having a high frequency into a low frequency signal and a laser diode for converting the low frequency signal. A photoelectric conversion optical transmission means for converting the optical signal into an optical signal and transmitting the optical signal and converting the transmitted optical signal into an electric signal by a photodiode, and a conversion means for converting the converted low frequency signal into the frequency of the RF signal. It is a thing.

A mixer can be used as each of the above conversion means.

[0009]

Therefore, according to the present invention, the RF signal input on the transmitting side is converted into the low frequency signal and the low frequency signal is converted into the frequency of the original RF signal on the receiving side. It is possible to improve the generated distortion and prevent signal loss on the receiving side.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, 1 is an RF input terminal, 2 and 3 are band pass filters, 4 and 5 are mixers for converting RF signals into low frequency signals, and 6 and 7 are for removing excess frequency components of signals. Low-pass filter, 8 coupler, 9 operational amplifier, 10 laser diode, 11 circuit for correcting output of laser diode 10, 12 laser diode output correction photodiode, 13 optical fiber cable, 14 photodiode Reference numeral 15 is an operational amplifier, 16 is a feedback resistor for signal amplification, 17 is a coupler, 18 and 19 are mixers for returning a low frequency signal to the original frequency again, 20 and 21 are band pass filters, and 22 and 23J are RF signal outputs. It is a terminal.

The operation of the above configuration will be described below. The frequency of the RF signal (several 100 MHz to several GHz) input from the RF signal input terminal 1 is divided into two frequency bands by the bandpass filters 2 and 3. Next, the RF signal is converted into a low frequency of several MHz by the mixers 4 and 5. Here, Lo of Mixers 4 and 5
A frequency signal lower than the frequency of the RF signal by the frequency of the signal output from the IF terminal is input to the input.
That is, when expressed by an equation, (frequency of signal input to RF terminal) ± (frequency of signal input to Lo terminal) = (frequency of signal obtained from IF terminal)

From the two signals generated by the mixers 4 and 5, low-pass filters 6 and 7 remove high frequency component signals. Next, they are coupled on the same signal line by the coupler 8, drive the laser diode 10, undergo photoelectric conversion, and then are transmitted to the receiving side through the optical fiber cable 13.

Here, the optical signal from the laser diode 10 is the laser diode output correction photodiode 1.
2 is also received, and then fed back to the original signal line by the operational amplifier 9 through the laser diode output correction circuit 11. In this way, the distortion of the optical signal generated by the laser diode 10 is corrected.

The signal transmitted by the optical fiber cable 13 is received by the photodiode 14.
Here, since the driving current of the photodiode 14 is small, it must be amplified by the operational amplifier 15. Here, in order to perform amplification, it is desirable that the feedback resistance 16 is large. However, if the resistance value is increased, as shown by reference numeral 41 in FIG.
It has its own component of capacitance. As a result, the receiving side has the characteristics of the low-pass filter as shown in FIG.

Since the transmitted signal passes through the coupler 17 and remains at a low frequency until it passes through the mixers 18 and 19, it can pass without loss.

When the signal passes through the mixers 18, 19,
To the Lo inputs of the mixers 18 and 19, the frequency having the same value as the input frequency of Lo in the mixers 4 and 5 is input. Therefore, the frequencies of the signals immediately after passing through the bandpass filters 2 and 3 are reproduced from the IF outputs of the mixers 18 and 19, respectively. These signals are passed through the bandpass filter 2
It is outputted from the RF output terminals 22 and 23 via 0 and 21.

As described above, according to this embodiment, the low frequency,
By taking advantage of the narrow band, the relaxation oscillation frequency of the laser diode 10 can be lowered, and the distortion can be corrected by using the feedback operation, so that a low distortion system can be easily realized. Further, the system that amplifies the output light from the receiving photodiode 14 has the characteristics of a low-pass filter, but since the signal transmitted through this system has a low frequency, the S / N ratio of the signal is not lost,
Can be amplified.

[0019]

As described above, according to the present invention, the RF signal input at the transmitting side is converted into the low frequency signal, and the low frequency signal is converted into the frequency of the original RF signal at the receiving side.
Improve the distortion generated by the laser diode on the transmission side,
The relaxation oscillation frequency of the laser diode can be lowered, and signal loss on the receiving side can be prevented to reduce the S / N ratio.
The ratio can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a low frequency conversion type frequency multiplex transmission device in one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a receiving device side in the transmission device.

FIG. 3 is a characteristic diagram of a low-pass filter.

FIG. 4 is a configuration diagram showing a conventional optical transmission device.

[Explanation of symbols]

 4 Mixer 5 Mixer 10 Laser Diode 12 Laser Diode Output Correction Photodiode 13 Optical Fiber 14 Photodiode 18 Mixer 19 Mixer

Claims (2)

[Claims] 1. A conversion means for converting an input RF signal having a high frequency into a low frequency signal, the low frequency signal converted into an optical signal by a laser diode and transmitted, and the transmitted optical signal is electrically converted by a photodiode. A low-frequency conversion type frequency multiplex transmission device comprising photoelectric conversion optical transmission means for converting into a signal and conversion means for converting the converted low-frequency signal into the frequency of the RF signal. 2. The low frequency conversion type frequency multiplex transmission device according to claim 1, wherein each conversion means is a mixer.