JPH0234216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In a digital optical communication system that uses pulse width as a signal, the present invention generates a sub-pulse train whose width is narrower than the pulse to be transmitted, and transmits and receives the sub-pulse train by the signal pulse width. This invention relates to an optical transmitter/receiver circuit.

In an optical signal transmission system using light emitting diodes, photodiodes, etc., when transmitting digital signals, a method as shown in FIG. 5, for example, has been used. This is a voltage “L” signal corresponding to “0” and a voltage “H” signal corresponding to “1” at every fixed time ΔT.
The signal is generated selectively.

In this example, the first voltage signal is "H", the next is also "H", the third is "L", etc., representing the digital signal 110.... This is the simplest method.

FIG. 6 shows another conventional example, which is called pulse width modulation (PWM). They are the same in that one signal corresponds to each fixed time ΔT, but the pulse width corresponding to "1" is wide and the pulse width corresponding to "0" is narrow. “0” or “1” depending on pulse width
represents the value of

In addition to this, several other methods of transmitting digital signals are known.

A similar method is also effective in communication systems that handle optical signals made of optical fibers, light emitting diodes, semiconductor lasers, photodiodes, avalanche photodiodes, etc. instead of electrical signals.

These switch the output of the light source into two stages, and depending on the light intensity and pulse width, the signal is "0" or "1".
shows. In any case, the output of the light source was kept constant within the pulse width of the signal. In other words, there was a correspondence between one signal and one pulse.

In order to increase the S/N ratio of the transmission system, it is effective to increase the light intensity of a light emitting diode, semiconductor laser, etc. on the transmitting side. However, if a relatively large current is continuously passed through these light sources, the life of the device will be shortened and power consumption will be large.

Rather, these light sources are preferably energized and emit light for only a short period of time. It does not need to be driven with a constant current during the pulse width of the signal. For example, power consumption can be reduced by generating an appropriate number of sub-pulse trains each with a duty cycle of 1/10 to express one signal pulse. Furthermore, since a larger current can be passed through the light source than when the current is applied continuously (for ΔT time), the S/N ratio is also increased.

Of course, when the transmission capacity is large, the response speed of the element, the dispersion of the optical fiber, etc. become limitations, making it difficult to accurately transmit and receive sub-pulses narrower than the signal pulse.

However, if the transmission capacity is small, there is sufficient margin, so optical communication can be performed using sub-pulses.

For example, if the transmission capacity is 1 to 20 kb/s, 1
Transmission time required per bit is 50μsec to 1msec
It is. The delay in response speed of the element is at most
Since it is 0.1 μsec, the pulse width is narrow (e.g.
1μsec~10μsec) to accurately generate sub-pulses,
Can send and receive.

The inventor of the present invention has thus discovered that it is useful to transmit a digital signal by means of a train of sub-pulses.

To do this, for example, the following circuit may be considered. That is, it is a circuit that constantly generates sub-pulses with a width of 3 μsec, for example every 30 μsec, calculates the product of the digital signal voltage to be transmitted and the sub-pulse train, and drives a light emitting diode with the product signal.

Although this is simple, since there is no synchronization between the rise of the signal voltage and the oscillation of the sub-pulses, an error occurs that makes the repetition period Ts of the sub-pulse train the maximum value.

It is desirable that the transmitted signal (SD) and received signal (RD) be exactly the same. Although both are required to be the same, there is often no problem even if there is a delay in transmission time.

The present invention responds to such demands by replacing the pulse signal of the transmission signal (SD) with a sub-pulse train, modulating and driving the light source, propagating it directly through space or transmitting it within an optical fiber, and transmitting it to a light receiving element. It relates to an optical transmitting/receiving circuit that reproduces a pulse signal with the same width as the original pulse signal from a sensed sub-pulse train and generates a received signal (RD).

EMBODIMENT OF THE INVENTION Hereinafter, the structure, operation, and effect of the present invention will be explained in detail with reference to drawings showing examples.

FIG. 1 is a diagram of an optical transmitter/receiver circuit according to an embodiment of the present invention, in which the left half of the diagram shows the transmitting side and the right half shows the receiving side.

First, the sending side will be explained. The transmitting circuit has two monostable multivibrators IC1 and IC2.

The monostable multivibrator IC1 produces a one-shot pulse with a pulse width T1 determined by the product of a capacitor C1 connected between its two pins and a resistor R1 connected between the power supply V+ and one of its pins. For example, assume that the pulse width T1 is 27 μsec.

Monostable multivibrator IC2 similarly produces a one-shot pulse with a pulse width T2 determined by capacitor C2 and resistor R2.

The Q terminal is normally at an "L" (low) potential, and when a trigger input is input, it generates an "H" potential with a predetermined pulse width. The opposite is true for terminals.

The A and B terminals are trigger terminals.

In the monostable multivibrator IC1, when the B terminal is at H level and a change from H to L is applied to the A terminal, IC1 is triggered. In other words, a positive pulse and a negative pulse of width T1 are generated at the Q terminal.

Furthermore, when the A terminal is at L level, when the B terminal changes from L to H, IC1 is triggered. Similarly, a pulse output Q, of width T1 is produced.

In other words, the A terminal is triggered at the falling edge, and the B terminal is triggered at the rising edge.

Further, the clear terminal CLR clears IC1 when it is at L level. In other words, the Q output is always L,
Q output holds H.

When the clear terminal CLR is at H level, when pulse input is given to the aforementioned trigger terminals A and B,
IC1 produces a pulse output.

Also, when the A terminal is at L level and the B terminal is at H level, if the clear terminal CLR changes from L to H,
A one-shot pulse of pulse width T1 occurs at Q.

The above changes are summarized in the input/output correspondence diagram of the monostable multivibrator shown in FIG.

The monostable multivibrator IC2 also produces a one-shot pulse with a pulse width T2 determined by _C2 and _R2 . For example, T2 is 3 μsec.

The functions of the Q, output, and CLR terminals of monostable multivibrator IC2 are the same as those of IC1.

However, the functions of the trigger terminals A and B are opposite to those of the monostable multivibrator IC1 described above.

In other words, when the B terminal is at L level, the A terminal is at L level.
→ When changing H, Q produces a positive pulse with a pulse width T2, and Q produces a negative pulse.

In other words, monostable multivibrator IC2 is
Trigger terminal A is triggered when it rises, and trigger terminal B is triggered when it falls.

FIG. 3 is an input/output correspondence diagram of the monostable multivibrator IC2.

The monostable multivibrator IC3 on the receiving side is
Pulse width T3 determined by capacitor C3 and resistor R3
This produces a one-shot pulse. For example, T3
Set to 60μsec.

Another monostable multivibrator IC4
produces a pulse of width T4 determined by capacitor C4 and resistor R4. For example, T4 is 57 μsec.

Monostable multivibrator IC3, like IC2, is triggered when the A terminal rises and the B terminal falls.

Monostable multivibrator IC4 operates in the same way as IC1.

For example, CMOS 4528B can be used as the monostable multivibrators IC2 and IC3. That is, CMOSICs such as MC14528B (Motorola), F4528B (Fairchild), TC4528BP (Toshiba), μPD4528C (Nichiden), etc. Also, CMOS 4538B
But that's fine. i.e. MC14538B (Motorola),
F4538B (Fairchild), HD14538B (Hitachi)
CMOSIC such as can be used.

As the monostable multivibrators IC1 and IC4, for example, TTLIC's 74123 and 74LS123 can be used. Namely, SN74123, SN74LS123 (Texas Instruments), 74123 (Fairchild),
DM74123, DM74LS123 (National Semiconductor), MC74123 (Motorola), N74123,
N74LS123A (signatetics), 74123,
74LS123 (Raytheon), HD74123, HD74LS123
(Hitachi), M53323, M74LS123 (Mitsubishi), MB440,
Uses MB74LS123 (Tomidotsu), μPB2123 (Nichiden), etc.

In this example, monostable multivibrator
All of IC1 to IC4 may be TTL, or all may be CMOS ICs.

Also, you can use a TTL IC such as 74122.

Now, in the circuit shown in FIG. 1, the transmission signal SD passes through the resistor R5 and is smoothed by the capacitor C5 before entering the clear terminal CLR of the monostable multivibrator IC1.

FIG. 4 illustrates input and output waveforms of each element. Assume that the transmission signal SD is a long positive pulse of ΔT, as shown in (a).

The output of IC1 is connected to trigger terminal A of IC2. If necessary, terminal A is pulled up to the positive power supply V+ using resistor R6.

The other trigger terminal A of IC1 is grounded. IC2
The other trigger terminal B is connected to the power supply V+.
The clear terminal CLR of IC2 is also connected to the power supply V+.

The Q output of monostable multivibrator IC2 is
Through the resistor R7, the switching transistor Tr
Connected to the base of 1. A light emitting diode LED is connected to the collector of the transistor Tr1.
A resistor R8 is connected to the base of Tr1.

The light output of the light emitting diode LED is transmitted by an optical fiber OF.

On the receiving side, a photodiode PD receives the optical output and performs photoelectric conversion. The current through resistor R9 is
It is amplified by an amplifier Amp whose amplification factor is determined by resistors R10 and R11.

A comparator Comp to which a reference voltage Vr is applied by resistors R12 and R13 shapes the output of the amplifier Amp into L level and H level.

Transistor that drives light emitting diode LED
The configuration of Tr1 and the circuit that amplifies and shapes the output of the photodiode PD is arbitrary.

When the transmission signal SD is at L level, the clear terminal CLR of IC1 is at L level, so the inverted output is at H level.
level.

Also, the Q output of IC2 is at L level and the light emitting diode LED is off. Since the output of IC2 is at H level, the B terminal of IC1 is also at H level.

When the transmission signal SD rises at ta, the clear terminal CLR of IC1 changes from L to H, generating a one shot pulse. In other words, the output changes from H to L at this moment. The A terminal of IC2 is not sensitive to this change.

After a time T1 (eg 27 μsec) the pulse ends.
Q output returns from L to H. With this change, A of IC2
Terminal is triggered. IC2 produces a short (3 μsec) pulse with T2 time.

Since the Q output of IC2 drives the LED, the LED emits light for T2 time.

When the pulse of IC2 ends, the output rises, so
The B terminal of IC2 is triggered.

The output of IC1 goes down from H to L. After time T1, the output rises from L to H, triggering the A terminal of IC2.

Then, IC2 generates a one-shot pulse with a pulse width T2, causing the LED to emit light. At the end of the pulse,
IC1 is triggered.

In this way, IC1 and IC2 sequentially trigger each other in turn to generate pulses T1 and T2.
The LED emits light during T2 pulse.

When the transmission signal SD changes from H to L at tb, IC1
is cleared. The output of IC1 rises. IC2
Since the A terminal of is triggered by the rising pulse,
Generates a T2 pulse.

That is, the light emitting diode LED is T2 after tb
It emits light for a period of time. This is assumed to be the nth pulse. The SD end point tb may come in the middle of the immediately preceding pulse ((n-1)th). However, since the monostable multivibrator IC2 is retriggerable, the Q of IC2 for T2 time after tb is
The output becomes H level.

In other words, the light emitting diode generates the first pulse with a delay of T1 from the starting point ta of the transmission signal SD, and (T
The pulse continues to be generated with a repetition period of 1+T2), and the final pulse n is generated after the end point tb.

Thus, the SD pulse of width ΔT is (T1+T
2) is replaced with a sub-pulse train having a period of T2 and a pulse width of T2.

The duty Dt of the sub-pulse is given by Dt=T2/T1+T2...(1). In this example, the repetition period is 30μsec
The duty is 0.1.

The number n of sub-pulse trains is determined by the inequality ΔT/T1+T2≦n<ΔT/T1+T2+1 …(2) It is a natural number determined by .

Next, the operation on the receiving side will be explained.

The output waveform of photodiode PD is shown in c. The pulse is deformed into a slightly rounded shape due to the delay in the response of the element. The shaped waveform is shown in d. This is a well-formed square wave.

This input signal is connected to the B terminal of IC3 and the B terminal of IC4.
guided to the terminal. The former is triggered by a falling edge, and the latter by a rising edge.

Furthermore, the output of IC3 is connected to the A terminal (falling edge) of IC4.

Initially, Q is at L level and Q is at H level in both IC3 and IC4. Therefore, the A terminal of IC4 is at H level. At this time, even if a rising pulse is applied to the B terminal of IC4, it will not be triggered. (See the truth table in Figure 2) Therefore, at the rising edge of the first sub-pulse of the square wave d, IC4 is not triggered.

At the falling edge of the first pulse, IC3 is triggered. This is because it is received at the B terminal (falling edge). Then, the output of IC3 changes from H to L as shown in FIG. 4e.

Then, the A terminal of IC4 connected to the output changes to L level.

At the rising edge of the second sub-pulse, it is triggered by the B terminal input of IC4. I C
The Q output of 4 rises here. As shown in FIG. 4f.

From the rising time ta of the transmission signal, the falling change of IC3 is delayed by 30 μsec (T1+T2), and the rising change of IC4Q is delayed by 57 μsec (2T1+T2).

Thereafter, IC3 continues to be re-triggered at the falling edge of the 2nd, 3rd, .

The pulse width ΔT(3) of IC3 is ΔT(3)=ΔT+T3−T1……(3) becomes.

Similarly, IC4 continues to be re-triggered at the rising edge of the 3rd, 4th, .

The pulse width ΔT(4) of IC4 is ΔT(4)=ΔT+T4−2T1−T2……(4). In the present invention, the pulse width is determined as T4-2T1-T2=0 (5). Then, ΔT(4)=ΔT...(6). In other words, the pulse width of IC4 is the transmission signal
Equal to the SD pulse width. In this example, T1=
Since 27μsec, T2=3μsec, T4=57μsec,
(5) is satisfied.

Then, the Q output of IC4 is taken as the received signal RD.

In this example, two monostable multivibrators are used in combination on both the transmitting and receiving sides. However, it should be noted that their roles are not the same.

The transmitting side sends sub-pulses with a narrow width T2 at intervals
Two multivibrators are required to generate each T1. IC1 and IC2 have equal functions.

On the receiving side, IC3 is triggered by the first sub-pulse and is only needed to create the conditions for IC4 to be triggered by the second sub-pulse. Therefore, the characteristic pulse width T3 of IC3 should just be (T1+T2) or more. That is, T3>T1+T2...(7). It can be said that the smaller T3 of IC3, the better. This is because if this is long, it may not be possible to follow fast changes in the transmission signal SD.

If the minimum interval during which the actual transmission signal SD is at L level is Δm, then T3<T1+T2+Δm (8) must be satisfied.

As explained above in detail, the circuit of the present invention is suitable for transmitting digital signals by optical communication.
Replace the signal pulse ΔT with a narrow sub-pulse train and then convert it into light and propagate it directly in space, or
After transmitting through optical fiber and converting it into electricity again,
The sub-pulse train is restored to obtain the signal pulse ΔT.

The effects obtained by this are as follows.

The time the light source is energized becomes shorter. The duty is reduced by Dt. In this example it is 1/10.
Therefore, the current flowing through the light emitting diode and semiconductor laser can be increased. The amount of light that directly propagates through space or passes through an optical fiber becomes subpulses, and the peak value of each subpulse is large. Therefore, the signal-to-noise ratio increases. In this case, the light-receiving elements, optical fibers, etc., will no longer be required to be of very high quality. The life of the light source is also long.

Furthermore, the power used to drive the light source can also be saved.

Furthermore, no matter what value the pulse width ΔT of the transmission signal has, it can be transmitted such that the pulse width ΔT4 of the reception signal and the pulse width ΔT of the transmission signal are always equal.

In this way, it is a useful invention.

[Brief explanation of drawings]

FIG. 1 shows an optical transceiver circuit according to an embodiment of the present invention.
Figure 2 is a monostable multivibrator input/output correspondence diagram in which the B terminal is triggered by the rising edge and the A terminal is triggered by the falling edge. Figure 3 is a monostable multivibrator input/output correspondence diagram in which the A terminal is triggered by the rising edge and the B terminal is triggered by the falling edge. FIG. 4 is a waveform diagram of each part of the optical transmitter/receiver circuit in the embodiment. FIG. 5 is an example of a digital signal transmission waveform according to a conventional example. FIG. 6 is an example of digital signal transmission waveforms according to another conventional example. IC1~IC4...monostable multivibrator,
T1 to T4...One shot pulse width of IC1 to IC4, SD...Transmission signal, RD...Reception signal, ΔT
... Pulse width of transmission signal, T2 ... Pulse width of sub-pulse, T1 + T2 ... Repetition period of sub-pulse, LED ... Light emitting diode, PD ... Photo diode.

Claims (1)

[Claims] 1 Consists of a transmitting side equipped with at least a transmitting circuit and a light emitting element, and a receiving side equipped with a receiving circuit and a light receiving element.The transmitting signal SD is transmitted as an optical signal by the transmitting circuit and the light emitting element, and the receiving side receives the optical signal. This is an optical transmitter/receiver circuit for serial digital signal transmission that receives a signal and generates a received signal RD, and on the transmitting side, a plurality of sub-pulse trains are generated corresponding to one pulse of the transmitted signal pulse, and the sub-pulses are short. A pulse train having a pulse width T ₂ and a pulse interval T ₁ longer than T ₂ , in which the first pulse of the sub-pulse train is generated with a delay of a pulse interval T ₁ from the starting point t _a of the transmission signal SD pulse, and The final pulse of the sub-pulses is generated at the end point t _b of the transmitted signal SD pulse, and the receiving side receives the sub-pulse train and determines the time T ₁ after the end of the first received sub-pulse. The start point of the received signal RD pulse is set as the end point of the received signal RD pulse, and the end point of the received signal RD pulse is set to a time delayed by a fixed time T ₄ from the start of the final pulse of the received sub-pulse, and the transmission is performed by setting T ₄ −2T ₁ −T ₂ = 0. An optical transmitting/receiving circuit characterized in that the pulse width ΔT of the signal and the pulse width ΔT4 of the received signal are set to ΔT=ΔT(4).