JPS63248256A - Light reception circuit for burst data - Google Patents

Abstract

PURPOSE:To prevent the condition that an error pulse is outputted by a noise at the time of a silence and the condition is held by detecting the condition that a signal input is eliminated and setting the threshold voltage of a comparator to an initial value then. CONSTITUTION:When a signal detecting circuit 11 detects the absence of a light signal, an initial value setting circuit 12 switches the threshold of a comparator 4 for a constant time and sets the signal output of the comparator to either of '1' or '0' specified beforehand. When the signal detecting circuit detects the absence of the light signal, a noise pulse occurs, thus, an erroneous action is executed, the signal output of the comparator is inverted to the condition opposite to the condition specified beforehand, and then, the threshold of the comparator is switched in accordance with the inverting output and the signal detecting circuit also detects the presence of the light signal temporarily. Thereafter, the signal detecting circuit outputs the detecting signal of a signal, this is operated to the initial value setting circuit and the threshold switched in accordance with the inverting output is switched again and returned to an original initial level. After the threshold returned to the original level and the differential output at the time of the silence are compared, the comparator changes the output inverted by the erroneous action and sets it to an '1' or '0' condition specified beforehand.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application J] The present invention relates to an optical receiving circuit, particularly an optical receiving circuit for burst data that transmits intermittent data.

[Prior Art] A fourth conventional example of an optical receiving circuit that receives burst signals is
As shown in the figure. Further, the waveform at the point A-D in the figure is shown in FIG. The output current of the photodiode 1 that receives optical input is converted into a voltage by the preamplifier 2, and amplified by the main amplifier 3 to the amplitude necessary for processing the stage invasion. capacitor 7
A differentiating circuit 5 consisting of a resistor 8 and a resistor 8 functions to extract the rising and falling edges of the main amplifier output A, as shown in FIG. 5B. The negative phase output of the comparator 4 is connected to the resistor 1.
A feedback loop through a hysteresis circuit 6 consisting of 0 and 9 adds sterisis to the threshold voltage of the comparator 4. FIG. 5C shows a threshold voltage waveform with hysteresis. That is, when the output is "1", the threshold voltage is low, and when D is "0", the threshold voltage is high. Since the differentially processed signal B becomes a positive pulse at the rising edge and a negative pulse at the falling edge, input data can be accurately reproduced and output by adding the above-mentioned hysteresis to the threshold value.

Also, at this time, the threshold voltage change voltage Δv1. By selecting a value larger than the tl& level, malfunctions due to noise can be prevented.

By the way, the circuit shown in FIG. 4 has the following problem.

As shown in FIG. 5, when a noise pulse N exceeding Δv/2 is generated, the output is erroneously inverted and at the same time the threshold value C is lowered, so that this state is maintained thereafter.

In particular, in a system (such as a bus-type LAN) that determines a no-signal state when the rOJ state continues for a certain period of time and moves on to the next process, if "0" is incorrectly held as [IJ], this process will not be possible. This could cause the system to stop.

Therefore, it became necessary to take measures to prevent such mistakes from continuing.

[Problems to be Solved by the Invention] As described above, the conventional optical receiving circuit has the disadvantage that when a noise pulse occurs and the output is erroneously inverted, the state 'hX' is maintained.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical receiver circuit for burst data that can eliminate the drawbacks of the prior art described above and effectively prevent malfunctions caused by noise without deteriorating circuit characteristics. .

Means for Solving the L Problem] The optical receiver circuit for burst data of the present invention converts an optical signal and differentiates the amplified electrical signal, applies the differential output to a comparator, and applies the differential output to the comparator. Detecting the presence or absence of the optical signal in a burst data optical receiving circuit that compares the output with a threshold whose level is switched according to the comparator output and identifies the optical signal into NJ and rOJ digital levels. a signal detection circuit, and when the signal detection circuit detects the absence of an optical signal, the threshold value of the comparator is switched for a certain period of time, and the signal output of the comparator is set to a predetermined "1" or rO.
An initial value setting circuit for setting one of J is added.

Here, burst data is data that has a limit on the pulse width of the signal pulse and prohibits continuous "o" or "1" for longer than a predetermined time, and when handling such data, The present invention is realized.

[Function 1: When the optical signal disappears and the signal is cut off, the signal detection circuit acts on the initial 1 self-setting circuit to switch the threshold value of the comparator for a certain period of time, but at this time, the signal output of the comparator changes to the predetermined value. If the threshold value is set to "1" or the rOJ state, there will be no change in the signal output even if the threshold value is switched to the initial level.

On the other hand, when the signal detection circuit detects no optical signal, a noise pulse is generated, which malfunctions, and the signal output of the comparator is reversed to the opposite state to the predetermined state. The threshold value of the comparator is changed according to the signal, and the signal detection circuit also temporarily detects the presence of optical signal. However, the signal detection circuit then outputs the signal detection signal again, which acts on the initial 1a SQ constant rotation to switch the threshold value that was switched according to the inverted output again and return it to the original initial level. As a result of comparing the restored threshold with the differential output when there is no signal, the comparator changes the output that was inverted due to the malfunction and sets it to a predetermined "1" or rOJ state.

In this way, the threshold value is set to an initial value so that the threshold value is not held in an incorrect state, and the signal output does not settle to a state opposite to the predetermined state. .

[Example] An example of the present invention will be described below based on FIGS. 1 to 3.

FIG. 1 shows an example of an optical receiving circuit for burst data according to the present invention. In the figure, parts having the same functions as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

A retriggerable monostable multivibrator (hereinafter referred to as Simply called monomulti)'11.
12 are additionally connected in series. The front-stage monomulti 11 functions as a signal detection circuit, and the rear-stage monomulti 12 functions as an initial 111 value setting circuit. The inverted output of the front stage mono multi 11 is added to the rear stage mono multi 12, and the rear stage mono multi 1
The normal output of No. 2 is wire-OR-connected with the negative phase output of comparator 4 which is led to hysteresis circuit 6.

Figure 2 shows the operating waveforms of each part. Monomulti 11.12
is a circuit for detecting the presence or absence of burst data, that is, a carrier, and initializing hysteresis, and operates as follows.

As mentioned above, the monomulti 11 is of a retriggerable type, and its output pulse width T (is selected to be larger than the maximum length of the optical signal pulse to be transmitted).

Therefore, while the normal input continues, that is, while the signal is present, the normal output of the monomulti 11 is always "1".

Now, if the signal stops at the time tl, that is, there is no signal, the inverted output E of the monomulti 11, which was rOJ until then, changes to FlJ after the time T1. The normal output F of the monomulti 12 generates a T2 pulse and returns to rOJ again. Since a wired OR is configured with the 12 normal outputs of the monomulti and the negative phase output of comparator 4, in a normal state where the negative phase output of comparator 4 is always "1", the negative phase output There is no change in , therefore,
The threshold voltage C also remains positive without any change.

That is, during normal operation, there is no change in the state due to the addition of the monomultis 11 and 12.

Next, consider the case where a noise pulse N occurs at time t2. When the noise pulse N exceeds the threshold value, the positive phase output of the comparator 4 changes to "1" due to a malfunction, and from this, the monomulti 11 generates a pulse of T1. Furthermore, the monomulti 12 generates a pulse of T2.Threshold voltage C
At time 1, ttz, the output of the comparator 4 is inverted by the pulse N, and the output F of the monomulti 12 changes to a negative value.
becomes "1", this [mono multi 12 which became 1J]
Since the output F of the comparator 4 and the negative phase output of the comparator 4, which is ``○'' due to a malfunction, are wired OR, the wire OR output becomes ``Ll'', and this ``1'' is added to the hysteresis circuit 6. Therefore, the threshold value C returns to positive at time t3. Therefore, comparator output D1. The output pulse FA does not remain at "1" and returns to "0" within a certain period of time. At this time, the length of the applied pulse is determined by the output pulse width T1 of the monomulti 11.

The output pulse width T1 of this monomulti 1'1 is selected to be larger than the maximum length of the optical signal pulse to be transmitted as described above, but the output pulse width T2 of the monomulti 12, that is, the fixed time for switching the threshold 1, is The minimum time required for the threshold to return and stabilize is sufficient.

In this way, when there is no optical signal, the output is set to "0" without error.
Even if there is a system that determines that there is no signal when the "○" state continues for a certain period of time and transfers it to the next process, this process may not be possible or the system may stop. There is no.

Note that the present invention can also be applied to a system in which the output is a series of "1"s when there is no optical signal.

By the way, since the monomultis 11 and 12 have the function of detecting the signal carrier and initializing the hysteresis, the same effect can be expected with the circuit shown in FIG. 3.

In this circuit, in place of the monomulti 11 at the front stage, the negative phase output of a comparator 16 derived from the output of the peak hold circuit 14 connected to the preamplifier 2 is added to the mono multi 12 at the rear stage. 15 is a holding capacitor. The peak hold circuit 14 is a circuit for detecting the output amplitude of the preamplifier 2, and is a circuit for detecting the output amplitude of the preamplifier 2.
Generates ffi pressure. This voltage is compared to a reference voltage ref by comparison 816. That is, the negative phase output of the comparator 16 is "OJ" when a signal is input, and rIJ when no signal is input.The monomulti 12 is the same as that shown in FIG.

Therefore, when the signal disappears, the threshold voltage of the comparator 4 is set to "positive" by the monomulti 12, so that the same effect as in FIG. 1 can be maintained.

[Effects of Light] In summary, according to the present invention, the following effects are achieved.

(1) Detects the state where no signal input is present, and then sets the comparator's threshold voltage to the first i! I] value, so
It is possible to prevent a situation in which an erroneous pulse is output due to noise when there is no signal and that state is maintained.

(2) The added circuit does not cause deterioration of characteristics such as pulse width distortion and receiving sensitivity.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the optical receiver circuit for burst data according to the present invention, FIG. 2 is a block diagram showing the circuit operation shown in FIG. 1, and FIG. 3 is a modification of the present invention. FIG. 4 is a block diagram showing a conventional optical receiver circuit, and FIG. 5 is a time chart showing the operation of the conventional circuit shown in FIG. In the figure, 1 is a light receiving element, 2 is a preamplifier, 3 is a main amplifier, 4.16 is a comparator, 5 is a differential circuit, 6 is a hysteresis circuit, 7.15 is a capacitor, 8 and 9.10 are resistors,
11 and 12 are monostable multivibrators, and 14 is a peak hold circuit. Patent Applicant Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinutani Figure 3

Claims (1)

[Claims] Converting the optical signal and differentiating the amplified electrical signal, applying the differentiated output to a comparator, and comparing the differentiated output applied to the comparator with a threshold whose level is switched according to the comparator output, In the burst data optical receiving circuit that identifies the optical signal into digital levels of "1" and "0," there is a signal detection circuit that detects the presence or absence of the optical signal, and when the signal detection circuit detects the absence of the optical signal. , the threshold value of the comparator is switched for a certain period of time, and the signal output of the comparator is set to a predetermined value.
1. An optical receiving circuit for burst data, comprising: an initial value setting circuit for setting either "1" or "0".