JPH1022934A - Signal conversion method for optical communication receiving circuit and signal conversion circuit applied with the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optically received signal conversion circuit optimum for the preceding stage of a TTL circuit unnecessitating the adjustment of reference voltage by the circuit constitution of a small scale by inexpensive parts. SOLUTION: A photoelectric conversion transducer output circuit is connected to an amplifier circuit 12 with a prescribed amplifying characteristic and the output of this amplifier circuit 12 is supplied as a comparing signal input for the input terminal (m) of a comparing circuit 15 operating with an applied voltage corresponding to the signal voltage of a digital signal processing circuit connected to a postage and supplied for a first delay circuit 14. The output of the first delay circuit 14 is supplied as the input of a reference signal for the second input terminal (n) of the comparing circuit 15. The output of the comparing circuit 15 is supplied for the digital signal processing circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal conversion method in an optical communication receiving circuit that modulates a predetermined signal into light and transmits the signal using an optical fiber or the like. The present invention relates to a conversion method and a signal conversion circuit to which the method is applied.

[0002]

2. Description of the Related Art Optical communication is widely used for industrial and general communication because of its advantages that it is hardly affected by noise due to electromagnetic induction and the like and that it can secure many communication lines on one communication line. It is becoming. As a means for transmitting a signal between electric circuits having electrically different reference levels, an optical coupling function element (photocoupler) for converting the signal into an electric signal / optical signal / electric signal has been put to practical use. In a receiving circuit for an optical signal transmitted using an optical fiber or the like, it is necessary to convert the optical signal into an electric signal corresponding to the signal processing circuit. For example, if the electric circuit is a TTL optical signal of 10 MHz, the low signal of the received signal is 0.8
Below V, the high signal is shaped into a signal above 2V.

A conventional optical / electrical conversion and shaping circuit is configured as shown in FIG. 3 and has characteristics as shown in FIG. In FIG. 3, an optical signal transmitted through an optical fiber (not shown) or the like is converted into an electric signal by a photoelectric conversion circuit 1 configured by a photoelectric conversion element such as a photodiode, and is converted to a predetermined level by a high-speed operational amplifier 2. After being amplified, the signal is input to a first terminal p which is a comparison signal input of a comparison circuit 3 having a high-speed comparator function. A reference voltage preset by a voltage setting device 4 such as a battery is input to a second terminal q which is a reference signal input of the comparison circuit 3.

FIG. 4 shows the operation of the circuit shown in FIG. A curve a shown in FIG. 4A shows a signal current waveform output from the photoelectric conversion circuit 1, and a signal current a output from the photoelectric conversion circuit 1 is a high-speed operational amplifier 2 and a signal shown in a curve b in FIG. It is amplified like a current waveform. Vc shown in FIG. 2B indicates a signal voltage waveform output from the high-speed operational amplifier 2, and Vs indicates a reference voltage set by the voltage setting device 4. Accordingly, the comparison circuit 3 compares the signal voltage Vc with the reference voltage Vs, and outputs a signal waveform as shown by Ve in FIG. 4C in a range where the signal voltage Vc is higher than the reference voltage Vs. You. When a digital signal processing circuit (not shown) provided on the output side of the comparison circuit 3 operates at a TTL level with a 5-volt power supply, a voltage conversion function of the signal Vs is provided.

[0005]

By the way, in the case of high-speed communication, it is required to perform high-speed processing as a high-speed operational amplifier and to reduce drift, so that in the case of a circuit as shown in FIG. It is necessary to employ expensive semiconductor functional elements. further,
It is necessary to preset the value of the reference voltage Vs in accordance with the offset amount obtained by integrating the characteristics of the photoelectric conversion circuit 1 and the high-speed operational amplifier 2. If a low-cost transistor amplifier is used for the high-speed operational amplifier described above, there is a problem that the reference voltage Vs cannot be fixed because the drift varies. The present invention solves the above-mentioned problems (problems) of the prior art, and employs a signal conversion method for an optical communication receiving circuit which does not require adjustment of a reference voltage with a small-scale circuit configuration using inexpensive components, and applies this signal conversion method. It is an object of the present invention to provide a signal conversion circuit according to the above.

[0006]

In order to solve the above-mentioned problems, a signal conversion method for an optical communication receiving circuit according to the present invention is provided. After that, the amplified signal is compared with the amplified signal that has passed through the first-order delay circuit, and the output of the comparison result corresponding to the set comparison characteristic is shaped and amplified in a square shape, and the peak value of the shaped signal is determined at least in the subsequent stage. Is set to a value larger than the level value at which the semiconductor logic circuit to be input to is determined to be a high signal. A signal conversion circuit to which this method is applied is a digital signal processing circuit in which a photoelectric conversion transducer output circuit is connected to an amplification circuit having predetermined amplification characteristics, and an output of the amplification circuit is connected to a subsequent stage. Is supplied as a comparison signal input to a first input terminal of a comparison circuit that operates with an applied voltage corresponding to the signal voltage of the first comparison circuit, and is also supplied to a first-order lag circuit. An input terminal is supplied as a reference signal input, and an output of the comparison circuit is supplied to the digital signal processing circuit. With the above configuration, even if a low-priced transistor amplifier circuit having a drift is used for the amplifier circuit that amplifies the light reception signal after converting the light reception signal to an electric signal, the comparison signal and the reference signal input to the comparison circuit are similarly generated. Because it does, it is not affected by drift.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a circuit configuration example of a signal conversion circuit to which a signal conversion method of an optical communication reception circuit according to the present invention is applied. In FIG. 1, reference numeral 1 denotes a photoelectric conversion circuit, which is an optical signal transmitted inside an optical fiber or the like. Is converted into an electric signal, for example, a photoelectric conversion element such as a photodiode. The output of the photoelectric conversion circuit 1 includes a transistor 11a as an amplifying element and a resistor 1
1b, the output of the amplifier circuit 12 is supplied to a first input terminal m of a comparator circuit 15 as a comparison signal input, and the first-order lag circuit 14
The output of the primary delay circuit 14 is supplied to the second input terminal n of the comparison circuit 15 via the buffer circuit 13.
Is supplied as a reference signal input. In addition,
The output terminal r of the comparison circuit 15 is connected to a digital signal processing circuit (not shown). The comparison circuit 15 may use a semiconductor element with a processing speed corresponding to the frequency to be used, for example, a rise / fall response speed of 10 ns or less and a voltage of 5 V, for example, a so-called line receiver. The resistor 11b has a function of converting an optical signal current, which is converted into an electric signal by the photoelectric conversion circuit 1 and amplified by the transistor 11a, into a voltage value.

The operation of the above-described circuit configuration will be described with reference to a characteristic diagram shown in FIG. In FIG. 2A, Ia indicates the waveform of the current output from the photoelectric conversion circuit 1, and Ib indicates the waveform of the collector current of the transistor 11a. 2B, a curve Vf represents a waveform of a voltage generated at a terminal such as the resistor 11b by the current Ib shown in FIG. 2A, that is, a first input terminal m as a comparison signal input of the comparison circuit 15. Shows the input voltage. Vf is
The signal is input to the primary delay circuit 14. The primary delay circuit 14 is composed of, for example, a resistor R and a capacitor C. If the time constant T of the circuit is T = 1 / 2πf (π = pi, f = frequency), the AC passing through the primary delay circuit 14 When the frequency of the signal is f, for example, the amplitude is attenuated by 3 dB and the phase is 4
5 degrees late. Therefore, if the time constant is appropriately set for the signal frequency, the output signal of the primary delay circuit 14 is
The waveform shown in the curve Vg of FIG.

If the input impedance of the comparison circuit 15 is set to a high impedance so as not to affect the output voltage change of the primary delay circuit 14, and the output is output in the same phase as the input, the gain may be almost 1, so that it is sufficient. By applying the feedback, the drift can be suppressed to a necessary range without using an expensive and highly stable amplifier element. The comparison circuit 15 appropriately corrects the attenuation characteristic at a high frequency while maintaining the required characteristics of the primary delay circuit 14 so as to obtain the characteristic shown in FIG. 2B by combining with the primary delay circuit 14. It may be configured as follows.

With the above configuration, the output signal of the transistor 11a is input to the two input terminals of the comparison circuit 15 at the same phase and the same level, so that the output drift of the transistor 11a is canceled out by mutual characteristics. . Further, a digital signal of 5V level shown in FIG. 2C is input to the input terminal n of the comparison circuit 15 as an output from the buffer circuit 13. Therefore, when the output of the comparison circuit 15 is input to a digital logic circuit functioning in TTL, the ON signal becomes 2 V or more and the low signal becomes 0.8 V or less, so that the digital logic circuit can be operated stably. The above description shows one embodiment for explaining the basic configuration for realizing the technical idea of the present invention and the operation thereof, and if the above technical idea can be realized, the functions other than those shown in FIG. It goes without saying that the element may be appropriately configured.

[0011]

According to the present invention, the above-described method and a configuration to which the method is applied have the following excellent effects. Since inexpensive components can be used and the number of components can be reduced, a low-cost product with a small circuit scale can be obtained. Since the output of the primary delay circuit is used as the reference signal, it is not necessary to adjust the offset of the reference signal. Since the output of the primary delay circuit is used as the reference signal, it is not affected by output deviation characteristics due to temperature drift or the like of an amplification function included in the photoelectric conversion unit.

[Brief description of the drawings]

FIG. 1 is a schematic block circuit diagram showing a configuration of a signal conversion circuit to which a signal conversion method for an optical communication reception circuit according to the present invention is applied.

FIG. 2 is a signal waveform diagram of a main circuit portion in the circuit configuration shown in FIG. 1; FIG. 2A shows an input current Ia and an output current I of an amplifying element for amplifying a photoelectrically converted signal;
3B shows the waveforms of the input voltage Vf and the output voltage Vg of the primary delay circuit, and FIG.
Represents the waveform of the output voltage of the comparison circuit.

FIG. 3 is a schematic block circuit diagram illustrating a configuration example of a signal conversion circuit in a conventional optical communication receiving circuit.

4 is a signal waveform diagram of a main circuit portion in the circuit configuration shown in FIG. 3; FIG. 4A shows a waveform of a signal current a output from a photoelectric conversion circuit and a high-speed operational amplifier for amplifying the signal; FIG. 4B shows the waveform of the output signal current b of the amplifier, and FIG. 4B shows the waveform of the output signal voltage Vc of the high-speed operational amplifier and the waveform of the reference voltage Vs set by the voltage setting function. 7 shows an output waveform Ve of the comparison circuit.

[Explanation of symbols]

 1: photoelectric conversion circuit 12: amplification circuit 13: buffer circuit 14: primary delay circuit 15: comparison circuit

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04L 25/03

Claims (2)

[Claims] In a photoelectric conversion circuit, a light receiving signal is converted into an electric signal to obtain an amplified signal of a predetermined level, and then the amplified signal is compared with the amplified signal passed through a first-order delay circuit. The output of the comparison result corresponding to the characteristic is shaped and amplified in a square shape, and the peak value of the shaped signal is set to a value that is at least larger than the level value determined by the semiconductor logic circuit input to the subsequent stage to be a high signal. A signal conversion method for an optical communication receiving circuit, comprising: 2. In a photoelectric conversion circuit, a photoelectric conversion transducer output circuit is connected to an amplifier circuit having a predetermined amplification characteristic, and an output of the amplifier circuit is applied to a signal voltage of a digital signal processing circuit connected to a subsequent stage. A first input terminal of a voltage-operated comparison circuit is supplied as a comparison signal input to a first-order delay circuit, and the output of the first-order delay circuit is supplied to a second input terminal of the comparison circuit as a reference signal input. A signal conversion circuit for an optical communication receiving circuit, wherein the signal is supplied to the digital signal processing circuit.