JPS61255119A - Optical receiver - Google Patents

Abstract

PURPOSE:To reduce remarkably pulse width distortion by providing a delay circuit retarding a threshold voltage for a prescribed time and a comparison circuit inputting a voltage from the delay circuit and a signal being electric conversion of an optical input and reproducing and outputting the signal. CONSTITUTION:The optical signal is converted into a current by a photodetector 1, converted into a voltage b an amplifier 2 and amplified into a waveform of a signal V4d1 required by a comparison circuit 9. An amplifier 7 generates a reference voltage when no optical signal exists. Since the output of a switching circuit 6 rises at the same time when the waveform of the signal V1 descends, the lower part from the center of the waveform of the signal V1 is sliced and then accurate waveform reproduction is not attained. Thus, a delay circuit 10 is provided after the switching circuit 6 and the entire thresh old voltage V2 is retarded from the waveform of the signal V1 so that a thresh old voltage V2' keeps the center position of the waveform of the signal V1 even if the waveform of the signal V1 descends, a pulse width distortion DELTATw' of an output voltage V3 outputted from the comparator circuit 9 is expressed as DELTATw'=t3-t2, and a signal with less distortion is obtained.

Description

[Detailed Description of the Invention] [Background and Objectives of the Invention] The present invention relates to an optical receiver, and in particular to an optical receiver used for receiving an optical input that performs code transmission of a DC component suitable for significantly reducing pulse width distortion. This invention relates to a digital optical signal device.

2. Description of the Related Art Conventionally, there is a digital optical receiver having a circuit configuration shown in FIG. 3, which is used to receive an optical signal that transmits codes of DC components. The optical signal is converted into a current by the light-receiving element 1, converted into a voltage by the amplifier 2, and amplified to a signal 1 with a waveform necessary for waveform processing in the next stage and subsequent stages.

Further, the above-mentioned signal 1 is divided into 1/2 by the resistors 3 and 4, and the signal is held in the peak detection circuit 5. 6 is a switching circuit which compares the amplitude of the signal Vl with the amplitude of the voltage obtained by adding the voltage of the level shift circuit 8 to the output voltage of the amplifier 7 that generates the DC component, and sets the higher level as the threshold voltage V. '2, this vl and Vz
is input to the comparator circuit 9, and the comparator circuit 9 outputs an output voltage (3) whose waveform is reproduced.

FIG. 4 is an input/output waveform diagram of the comparator circuit 9 in FIG. 3, and (a)
is the input waveform, and (b) is the output waveform. Threshold voltage v2
divides the signal voltage Vt into 1/2 and generates the peak detection circuit 5.
However, as shown in Fig. 4, the signal voltage v
When the waveform of signal voltage ■1 begins to fall, threshold voltage ■2 also falls, so the pulse width of output voltage ■3 becomes t2 relative to the pulse width tl of signal voltage ■1, and the pulse width distortion Δ
7w=tt -11 occurs, resulting in an optical receiver with large distortion.
ing.

The present invention has been made in view of the above, and an object thereof is to provide a digital optical receiver that can significantly reduce pulse width distortion.

[Summary of the Invention] The present invention is characterized by a peak detection circuit that generates a voltage of 172 signal amplitudes obtained by converting optical input into an electrical value, and an amplifier for generating a reference voltage corresponding to the voltage when there is no optical input. a level shift circuit that raises the voltage of the circuit by a predetermined voltage; a switching circuit that compares the voltage from the level shift circuit with the voltage from the peak detection circuit and sets the higher voltage as a threshold voltage; The present invention consists of a delay circuit that delays a voltage for a predetermined period of time, and a comparison circuit that inputs the voltage from the delay circuit and a signal obtained by converting the optical input into an electrical value, and reproduces and outputs the signal.

[Example] The present invention will be described in detail below with reference to the example shown in FIG. 1 and FIG. 2.

FIG. 1 is a circuit block diagram showing an embodiment of the optical receiver of the present invention. FIG. 1 shows a light receiving element 1 that converts an optical signal into a current, an amplifier that converts the current into a voltage and amplifies it,
In order to enable DC transmission, it has the same circuit configuration as amplifier 2, and includes an amplifier 7 that generates a reference voltage, a level shift circuit 8 that adds a predetermined voltage to this reference voltage to raise it, and a resistor 3゜4 to reduce the voltage by 1/2. a detection circuit 5 which detects the peak of the voltage of the amplifier 2 and detects the peak of the voltage of the amplifier 2;
A switching circuit 6 whose threshold voltage is the higher of the output voltage of the peak detection circuit 5 and the output voltage of the level shift circuit 8, a delay circuit 10 which delays the voltage from the switching circuit 6 by a predetermined time, and a signal regeneration circuit. It consists of a comparison circuit 9 that outputs.

FIG. 2 is an input/output waveform diagram of the comparator circuit 9 in FIG. 1, and (a)
is an input waveform when there is no delay circuit, (b) is an input waveform when a delay circuit is provided, and (C) is an output waveform.

The optical signal is converted into a current by the photodetector 1, and then the amplifier 2
The voltage is converted into a voltage by the comparator circuit 9 and amplified to the waveform of the signal Vl required by the comparator circuit 9. Since the amplifier 7 is not connected to a light receiving element, it generates a reference voltage when there is no optical signal. When performing code transmission of a DC component, the level shift circuit 8 raises the reference voltage to a predetermined voltage, thereby making it possible to identify the DC component. In order to roughly and accurately identify the signal, the signal from the amplifier 2 is divided into 1/2 by the resistor 3.4, and the peak detection circuit 5 detects the peak of the signal and holds it. By using the switching circuit 6 which sets the higher of the outputs of the level shift circuit 8 and the output of the level shift circuit 8 as the threshold voltage Vz, the threshold voltage v2 is placed at the center of the waveform of the signal 1. By the way, since the output of the switching circuit 6 falls at the same time as the waveform of the signal V1 falls, it cuts below the center of the waveform of the signal 1, so accurate waveform reproduction cannot be performed. A delay circuit 10 is provided to delay the entire threshold voltage (2) from the waveform of the signal (1) so that even if the waveform of the signal (Vl) falls, the threshold voltage (Vz-) maintains the center position of the waveform of the signal (Vr). , the pulse width distortion ΔTw" of the output voltage v3 output from the comparison circuit 9 is Δl"W --
t3 t2, so that a signal with very little distortion can be obtained.

[Effects of the Invention] As explained above, according to the present invention, pulse width distortion can be significantly reduced, and by providing a delay circuit, the threshold voltage can be reduced for the falling portion of the signal waveform. Since they cross at almost right angles, signal reproduction with less jitter is possible, and signal waveform overshoot and
This has the effect of providing a circuit configuration that is less affected by undershoot.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing one embodiment of the optical receiver of the present invention, FIG. 2 is an input/output waveform diagram of the comparison circuit of FIG. 1, and FIG.
The figure is a circuit block diagram of a conventional optical receiver, and FIG. 4 is an input/output waveform diagram of the comparison circuit of FIG. 3. DESCRIPTION OF SYMBOLS 1... Light receiving element, 2... Amplifier, 3.4... Resistor, 5... Peak detection circuit, 6... Switching circuit, 7... Reference voltage generation amplifier, 8... Level shift circuit, 9... Comparison circuit, 10... Delay circuit. Agent Patent Attorney Fujio Sato r 2

Claims (1)

[Claims] (1) A digital optical receiver that receives an optical input that performs code transmission of a DC component includes a peak detection circuit that generates a voltage that is 1/2 of the signal amplitude obtained by converting the optical input into an electrical value; a level shift circuit that raises the voltage from the reference voltage generation amplifier by a predetermined voltage, which corresponds to the voltage when A switching circuit that sets a threshold voltage, a delay circuit that delays the threshold voltage for a predetermined time, and inputs the voltage from the delay circuit and a signal obtained by converting the optical input into an electrical value, and reproduces and outputs the signal. An optical receiver comprising a comparison circuit.