JPS6372247A - Optical receiver - Google Patents

Abstract

PURPOSE:To decrease the fluctuation of a recovered pulse width caused by the change in the optical signal level by changing the identification level corresponding to the output of an amplifier amplifying the output of a photodetector. CONSTITUTION:A clamp circuit 20 is connected between an output of the amplifier 2 amplifying the output of the photodetector 1 and a voltage division point 6 of the resistance voltage division circuit 4. When the level of the optical signal is small, a guard voltage decided by a reference voltage generating circuit and the circuit 4 is used as a identification level, which is given to a comparator 8, and when the optical signal level is larger than a prescribed level, the clamp circuit 20 recovers the pulse at the identification level larger than the identification level formed by the voltage division ratio of the circuit 4. Moreover, when the level of the optical signal is large, the clamp circuit 20 is not operated and the pulse is recovered at the identification level formed by the voltage division ratio of the circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an optical receiver that converts an optical signal into an electrical signal.

(Prior Art) In general, in an optical receiver that receives a digital optical signal and converts it into an electrical signal, the reproduced waveform of the optical signal converted by the light receiving element is distorted from the original rectangular pulse waveform. .

Therefore, pulse regeneration is performed after waveform shaping. In this case, the level of the optical signal input to the optical receiver differs depending on the type of optical receiver connected to the optical receiver and the length of the optical fiber between them. Also, an automatic discrimination level circuit is provided in the comparator circuit of the pulse regeneration circuit in order to reduce the change in the width of the output pulse to be reproduced.

As such an optical receiver, Japanese Patent Application Laid-Open No. 57-1 filed by the present applicant
92155 discloses a structure shown in FIG. 5. That is, in this optical receiver, between the amplifier ■ that amplifies the output of the light receiving element ■ and the reference voltage generation circuit ■,
A pair of resistors (5a) and (5b) having equal resistance values constituting a resistive voltage dividing circuit (2) are connected, and a peak value detection circuit (2) is connected to the voltage dividing point 0 thereof. In addition, the output terminal of this peak value detection circuit ■ and the output terminal of the amplifier ■ are connected to a comparator ■
In addition, a constant current source ■ and a reference voltage generation circuit ■
A resistor (10) for applying a card voltage to prevent the comparator (c) from malfunctioning when there is no signal is connected between the two.

In this optical receiver, the output voltage of the reference voltage generating circuit (■) is the output signal (A) of the amplifier (■) when there is no signal as shown in FIG.
DC voltage V. It is also set to be a straight line (G
) is set to a predetermined voltage v3 higher than the DC voltage V of the output signal (A) of the amplifier (2) when there is no signal. Then, the output signal (A
) is smaller than a predetermined level, the guard voltage ■ζ becomes the discrimination level Vth of the comparator circuit.

To prevent malfunction of the optical receiver, and if the amplitude of the output signal (A) of the amplifier A) is set to 172 to perform pulse reproduction.

However, in this optical receiver, when the optical signal is large, the discrimination level Vch is set to 172 of the output signal (A) of the amplifier ■, even though the reproduced waveform converted by the light receiving element ■ is distorted. Therefore, as shown in FIG. 7 corresponding to FIG.
) The problem is that the width is much wider than the width of .

(Problems to be Solved by the Invention) As mentioned above, in the conventional optical receiver, when the optical signal is large, the discrimination level is set to 172 of the output signal of the amplifier based on the output signal of the amplifier. Another problem is that the reproduction pulse width is wider than the transmission pulse width.

The present invention was made to solve this problem, and an object of the present invention is to construct an optical receiver in which fluctuations in reproduction pulse width are small with respect to fluctuations in the level of an optical signal.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides an arrangement between the output end of an amplifier that amplifies the output of a light-receiving element and a reference voltage generation circuit that generates the same voltage as the DC voltage of this amplifier when there is no signal. A resistor voltage divider circuit is connected,
A constant current source is connected to the output terminal of the peak value detection circuit that detects the peak value at the voltage division point of this resistor voltage divider circuit, and a resistor is connected between this constant current source and the reference voltage generation circuit. In an optical receiver configured to compare the output with the output of the peak value detection circuit using a comparison circuit, a clamp circuit is connected between the output terminal of the amplifier and the voltage division point of the resistor voltage division circuit. .

(Function) When a clamp circuit is connected between the output end of the amplifier that amplifies the output of the light receiving element and the voltage dividing point of the resistive voltage dividing circuit as described above, if the level of the optical signal is small, the above circuit configuration The guard voltage determined by is used as the discrimination level to prevent malfunction of the optical receiver, and if the level of the optical signal is higher than the predetermined level, the above-mentioned clamp circuit sets the guard voltage to be higher than the discrimination level created by the voltage division ratio of the resistor voltage divider circuit. If pulse reproduction is performed at a large discrimination level and the optical signal level is also large, the clamp circuit will not operate, and pulse reproduction will be performed at the discrimination level created by the voltage division ratio of the resistor voltage divider circuit, and the optical signal will be It is possible to reduce fluctuations in reproduction pulse width with respect to fluctuations in level.

(Example) Hereinafter, the present invention will be described based on an example with reference to the drawings.

FIG. 1 shows the configuration of an optical receiver according to an embodiment of the present invention. This optical receiver includes a light-receiving element (2) consisting of a PIN photodiode, and an amplifier (2) for amplifying the output of this light-receiving element (2).
, a reference voltage generation circuit ■ that generates a voltage equal to the output voltage of this amplifier ■ when no signal is present, and a pair of series resistors (5a) connected between this reference voltage generation circuit ■ and the output terminal of the amplifier ■. ), (5b), and a peak value detection circuit (2) connected to the voltage division point 0 of this resistance voltage divider circuit 0).

The constant current source (9) connected to the output end of this peak value detection circuit (■), this constant current source (■), and the base +1! Voltage generation circuit■
a resistor (10) connected between the resistor (10) and a comparator (
), and in this example, a resistive voltage divider circuit (a)
A clamp circuit (2
0) is connected.

In FIG. 1, (21) is a differential amplifier that constitutes the peak value detection circuit, (22) is a diode, and (23) is a differential amplifier that constitutes a peak value detection circuit.
is a capacitor.

In this optical receiver, as in the conventional example, the output voltage of the reference voltage generation circuit (3) is set equal to the DC voltage v0 of the output signal (A) of the amplifier (2) shown in FIG. Due to the output voltage of circuit 0 and the voltage generated via the resistor (10) by the constant current source (9), the voltage shown by the straight line (G) in Fig. 2, that is, when there is no signal, the comparator (8)
A guard voltage v3 is applied to prevent the device from malfunctioning. That is, this guard voltage V is defined by the resistance value of the resistor (10) as Ro, and the current of the constant current source (9) as E.

VK=V, +IR.

It becomes.

In such an optical receiver, an optical signal is input to the light receiving element (2), and the potential (1) at the voltage dividing point 0 of the resistor voltage divider circuit (to) is greater than the output of the peak value detection circuit (2), and both ends of the resistor (5a) If the voltage between them is smaller than the clamp voltage v0 of the clamp circuit (20), the output voltage of the peak value detection circuit ■ is Vi
Therefore, the discrimination level Vth is the output signal (A
) is the peak value of VP, resistance (5a).

Let the resistance values of (5b) be R1 and R, respectively. Further, when the level of the optical signal becomes even higher, the voltage across the resistor (5a) is fixed to the clamp voltage Vc of the clamp circuit (20), and the discrimination level Vth becomes Vth=vp v.

becomes.

Therefore, with the above configuration, the discrimination level Vth becomes ■ depending on the level of the optical signal. +IR,,(
vpR□+ Va Rz )/ (Ri + Rz)
, VP-Vo, the difference between the width of the transmission pulse (13) and the width of the reproduction pulse (12) is small, as shown in FIG. 3 corresponding to FIG. The optical receiver can faithfully regenerate pulses even if the signal varies.

Next, another embodiment shown in FIG. 4 will be described.

This optical receiver is particularly suitable for the voltage dividing point (0) of the resistive voltage dividing circuit (A).
A clamp circuit (
20) is composed of diodes.

The rest of the configuration is the same as that of the previous embodiment, so the same parts are given the same numbers and the explanation thereof will be omitted.

When the clamp circuit (20) is configured with diodes in this way, the clamp voltage v0 can be easily changed by changing the type of diodes, the number of diodes, etc. An optical receiver with small fluctuations can be easily manufactured.

〔Effect of the invention〕

A resistive voltage divider circuit is connected between the output terminal of the amplifier that amplifies the output of the light receiving element and the reference voltage generation circuit, and a constant current source is connected to the output terminal of the peak value detection circuit that detects the peak value at the voltage division point. A resistor is connected between the constant current source and the reference voltage generation circuit, and the output of the amplifier is compared with the output of the peak value detection circuit using a comparison circuit. A clamp circuit is connected between the output terminal and the voltage division point of the resistor voltage divider circuit, so that the discrimination level changes according to the magnitude of the optical signal level, that is, the output of the amplifier, so the optical signal level It is possible to reduce fluctuations in the width of the reproduction pulse caused by changes in the width of the reproduction pulse.

[Brief explanation of the drawing]

Figures 1 to 4 are detailed explanatory diagrams of this invention.
FIG. 2 is a waveform diagram of an optical signal to explain its operation, and FIG. 3 is a waveform diagram showing the relationship between its transmission pulse and reproduction pulse. Figure 4 is a diagram showing the configuration of another embodiment, Figure 5 is a configuration diagram of a conventional optical receiver, Figure 6 is a waveform diagram of an optical signal to explain its operation, and Figure 7 is its transmission. FIG. 3 is a waveform diagram showing the relationship between pulses and reproduction pulses. ■... Light receiving element ■... Amplifier ■...
Reference voltage generation circuit @)... Resistance voltage divider circuit (5a)
, (5b)...Resistance 0...Voltage division point ■...
・Peak value detection circuit (8)... Comparator (9)...
・Constant current source (10)...Resistance (12)・
... Reproduction pulse (13) ... Transmission pulse (A
)... Amplifier output signal agent Patent attorney Inoue - Male - Darkness Figure 2 → Darkness Figure 3 Figure 4 Figure 5 Figure 11 Time Figure 6 Figure 7

Claims (1)

[Claims] a light-receiving element; an amplifier that amplifies the output of the light-receiving element;
a reference voltage generation circuit that generates the same voltage as the DC voltage of the amplifier when there is no signal; a resistor voltage divider circuit connected between the reference voltage generation circuit and the output terminal of the amplifier; and the resistor voltage divider circuit. a clamp circuit connected between the voltage division point of the resistor voltage divider circuit and the output terminal of the amplifier, a peak value detection circuit that detects the peak value of the voltage division point of the resistor voltage divider circuit, and an output terminal of the peak value detection circuit. , a resistor connected between the constant current source and the reference voltage generation circuit, and a comparison circuit that compares the output of the peak value detection circuit and the output of the amplifier. An optical receiver characterized by: