JPH0551214B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a CSMA/CD, anti-collision carrier detection multiple access type transmitter/receiver with a collision detection function. [Prior Art] FIG. 7 shows a conventional CSMA/CD access control device. In Figure 7, 1 is a signal input terminal, 2 is a dipulse encoding circuit, 3 is an LED driver, and 4 is a
LED, 5a, 5b, 5c, 5d, 5e, 5f,
6c, 6d, 7c and 7d are optical fibers, 8a,
8b is an optical connector, 9a and 9b are splice points,
10 is a star coupler, 11 is an APD (avalanche photodiode), 12 is a preamplifier, and 13 is a
PR (1, -1) filter (partial response (1, -1) filter), 14 is a signal discriminator, 15
is a threshold voltage generation circuit, 16 is a first current source, 17
is a resistor, 18 is a collision detection circuit, 19 is a data reproduction output terminal, 20 is a collision detection pulse output terminal, 21
2 is a timing extraction circuit, and 22 is a block synchronization circuit. The transmission signal input to the signal input terminal 1 in FIG. 7 is represented by four 2-bit patterns shown in the signal series in Table 1. Dipulse encoding circuit 2
converts the signal sequence shown in Table 1 into a corresponding dipulse sequence.

[Table] The discrimination level is assumed to be −Δ, which is slightly lower than zero. ×: Depends on the preceding code 0 ^* : Noisy 0 level

【table】

[Problem that the invention seeks to solve]

The conventional transmitting/receiving device with a collision detection function is configured as described above, so the LED driver 3,
Preamplifier 12 and PR (1, -1) filter 1
3 had the problem of requiring an extremely low distortion circuit and requiring a lot of test and adjustment time. Furthermore, there is a problem in that the range of received light power in which erroneous collision detection does not occur is limited by waveform distortion and cannot be widened on the large side of received light power. This invention was made in order to solve the above-mentioned problems, and it is possible to shorten the test adjustment time of a transmitting/receiving device with a collision detection function, and to widen the range of received light power without causing erroneous collision detection. The purpose is to obtain a transmitting and receiving device. [Means for solving the problem] In a transmitting/receiving device using a communication channel using CSMA/CD control, a carrier-off detection circuit 29 outputs a carrier-off detection pulse when receiving a packet, and a partial response (1, -1) is used. ) one or more comparison circuits 25 which are supplied with the output signal of the filter 13 and a preset specified voltage, and which output a level detection pulse when the peak value of the output signal exceeds the specified voltage; , a flip-flop 26 is provided corresponding to one or more comparison circuits, and is set by the output pulse of the comparison circuit 25 and reset by the output of the carrier-off detection circuit 29; and a threshold voltage generation circuit 15 that outputs different threshold voltages to the signal discriminator 14. [Operation] The flip-flop 26 is set by the output pulse of the comparison circuit 25, and the threshold voltage output from the threshold voltage generation circuit 15 is changed by the output signal of the flip-flop 26. This changed threshold voltage and partial response (1, -1) filter 1
3 to the signal discriminator 14 to reduce the signal collision detection level difference. After data reception, the flip-flop 26 is reset by a carrier-off detection pulse from the carrier-off detection circuit 29, and the threshold voltage output from the threshold voltage generation circuit 15 is returned to its original value, thereby obtaining stable collision detection operation in a region where the received light power is large. [Embodiment] Hereinafter, a first embodiment of the present invention will be described based on FIGS. 1 to 3. In the figure, 1 is a signal input terminal, 2 is a dipulse encoding circuit, 3 is an LED driver, 4 is an LED,
5a, 5b, 5c, 5d, 5e, 5f, 6c, 6
d, 7c and 7d are optical fibers, 8a and 8b are optical connectors, 9a and 9b are splice points, 10 is a star coupler, 11 is an APD (avalanche photodiode), 12 is a preamplifier, and 13 is a PR (1, -
1) Filter (partial response (1, -1)
14 is a signal discriminator, 15 is a threshold voltage generation circuit, 16 is a first constant current source, 17 is a resistor,
18 is a collision detection circuit, 19 is a data reproduction output terminal, 20 is a collision detection pulse output terminal, 21 is a timing extraction circuit, and 22 is a block synchronization circuit. 23 is a level detector, 24 is a specified voltage input terminal, 25 is a comparison circuit, 26 is a flip-flop,
27 is a second constant current source, 28 is a switch, and 29 is a carrier off detection circuit. Figure 2 shows partial response (1, -1)
FIG. 3 is a waveform diagram of the output of the filter 13. In the figure, 1
5b is a controlled threshold. FIG. 3 is a graph showing the signal collision detection level difference and threshold versus received light power characteristics. Next, the operation of the present invention will be explained. The level detector 23 monitors the output level of the PR (1, -1) filter 13, and when the output level peak value exceeds the specified voltage input to the terminal 24,
The comparator circuit 25 outputs a pulse signal “H”. The flip-flop 26 is set by this pulse signal. When the output of the flip-flop 26 is set, a switch 28 connecting the second constant current source 27 and the resistor 17 in the threshold voltage generation circuit 15 is activated.
is in a closed state, and the current I 2 is added to the current I ₁ of the first constant current source 16, causing a current I ₁ + _{I 2 to} flow through the resistor 17. As a result, the threshold values of the comparator circuit 25 are set as shown in FIG.
Move away from the zero level of 3 outputs. Now, suppose that the specified voltage input to terminal 24 is the received light power -35.5 dB.
m, and the current value of the second constant current source I ₂
If is set to a value such that the threshold 15b is separated until the signal collision detection level difference reaches 8 dB at the received light power of -35.5 dBm, the relationship between the signal collision detection level difference, the threshold, and the received light power is as shown in FIG.
The threshold value changes from threshold value 15a to threshold value 15b when the received light power exceeds -35.5 dBm. Along with this, the signal collision detection level difference increased from 9.5 dB to 8 dB. When the received light power exceeds -35.5 dBm, the signal collision detection level difference increases again with the received light power and reaches 9.5 dB again at -34.0 dBm. Compared to a conventional transmitting/receiving device with a collision detection function, the difference in signal collision detection level at -35.5 dBm or higher is
However, the threshold value and the "0" level at the output of the PR (1, -1) filter 13 are significantly different by 1.5 dB, and more stable operation can be performed against erroneous collision detection. Even if the threshold value changes from threshold value 15a to threshold value 15b, the signal collision detection level difference is maintained at 8 dB, which is required in the configuration example of the optical local network, and system performance will not deteriorate. The level detector 23 monitors the peak output of the PR (1, -1) filter 13. PR (1, -1)
Since the optical signal is a unipolar signal, the filter 13 cancels the DC offset voltage that occurs at the start of packet reception, so it can monitor immediately after the start of packet reception, and when the received light level is high, the The thresholds can be separated at the beginning (eg, within the synchronization pull-in time). In the threshold voltage generation circuit 15, the threshold value is set to threshold value 1.
The operation of separating from 5a to 15b is performed by the second constant current source 2.
7 is controlled by opening and closing the switch 28, it is possible to move the threshold value more smoothly compared to methods such as selecting a plurality of constant voltage sources by a switch, which also contributes to stable operation. After the packet reception is completed, a carrier-off detection signal is output from the carrier-off detection circuit 29 monitoring the output of the preamplifier 12 to the level detector 23, and the flip-flop 26 is reset. When the output of the flip-flop 26 is reset, the switch 28 becomes open, and the threshold value returns to the initial value determined by the current value of the first constant current source 16. Therefore, reception can be started at a threshold of 15 for any reception level. 4 to 6 show a second embodiment of a transmitting/receiving device with a collision detection function according to the present invention. In the figure,
30 is a second specified voltage input terminal, 31 is a second comparison circuit, 32 is a second flip-flop, 33 is a third constant current source, and 34 is a second switch.
In this second embodiment, the specified voltage input terminal 24, comparator circuit 25, flip-flop 26, switch 27, and threshold value 15 described in the first embodiment are used.
b is applied as a first specified voltage input terminal, a comparison circuit, a flip-flop, a switch, and a threshold value. Further, in the case of this embodiment, flip-flops are provided on the output sides of the first and second comparison circuits 25 and 31, respectively, corresponding to the first and second comparison circuits 25 and 31, and Comparison circuits 25, 31
has first and second specified voltage input terminals 24 and 30.
Different specified voltages are supplied through the respective terminals. FIG. 5 is an output waveform diagram of the partial response (1, -1) filter 13. 15c in the figure
is a controlled second threshold. FIG. 6 is a diagram showing the signal collision detection level difference and threshold versus received light power characteristics. For other configurations, please refer to the first
Since this is almost the same as the embodiment, the explanation will be omitted. The second specified voltage input to the terminal 30 is set for the received light power -34 dBm, and the third constant current source 3
Assume that the threshold value is set to be apart from the second threshold value 15c until the signal collision detection level difference becomes 8 dB when the current value I ₃ of No. 3 is set to -34 dBm with the received light power (see FIG. 5). Third comparator 31 and second set/reset flip-flop 32 operate similarly to second comparator 25 and first set/reset flip-flop 26. The second switch 34 opens and closes the connection state between the third constant current source 33 and the resistor 17, as in the embodiment shown in FIG. At this time, the signal collision detection level difference, threshold value, and received light power range are as shown in FIG. Compared to a conventional transmitting/receiving device with collision detection function, the difference in signal collision detection level is small when the received light power is -34 dBm or more
4dB decrease but threshold PR (1, -1) filter 13
Since the distance of the output zero level is increased by 3 dB, stable operation can be obtained against erroneous collision detection. In addition, the third, fourth...Nth specified voltage input terminals, the third, fourth...Nth comparison circuits, the third, fourth...
. . . an Nth flip-flop, a fourth, a fifth, . . . N+1 constant current source, and a third, a fourth, . Good too. In the above embodiment, the signal discriminator 14 is provided with a threshold value only between the zero level and the lower (negative) level of the partial response (1, -1) filter 13 output. Vessel 1
4 between the upper (positive) level and zero level of the output of the partial response (1, -1) filter 13, the current source from the first to the other (N+1)th current source of the threshold voltage generation circuit 15 A similar effect can be achieved by making the current flow in the opposite direction. A similar effect can also be obtained when two signal discriminators are used and the thresholds are simultaneously located above (positive) and below (negative) the zero level of the partial response (1, -1) filter 13 output. , the switch can be shared by the threshold voltage generation circuits above and below the zero level. [Effects of the Invention] The present invention includes a carrier-off detection circuit that outputs a carrier-off detection pulse when receiving a packet, and an output signal of the partial response (1, -1) filter, and a preset specified voltage. one or more comparison circuits that output a level detection pulse when the peak value of the output signal is given and the peak value of the output signal exceeds the specified voltage; a flip-flop that is set by the output pulse of the carrier-off detection circuit and reset by the output of the carrier-off detection circuit; and a threshold voltage generation circuit that outputs a plurality of different threshold voltages to the signal discriminator based on the output signal of the flip-flop. Since the threshold value of the signal discriminator is automatically changed according to the received light level, it operates stably against false collision detection in the region of high received light power, and it is possible to maintain a received light power range in which false collision detection does not occur. Can be expanded. Further, there is an effect that the test and adjustment of this device can be easily performed without using a special PR (1, -1) filter having low loss, wide band, and low distortion characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a transmitting/receiving device with a collision detection function according to a first embodiment of the present invention, FIG. 2 is a partial response (1, -1) filter output waveform diagram of the first embodiment, and FIG. FIG. 4 is a diagram showing the signal collision detection level difference and threshold value versus received light power characteristics of the first embodiment, FIG. Partial response (1, -1) filter output waveform diagram, FIG. 6 is a signal collision detection level difference and threshold value versus received light power characteristic diagram of the second embodiment, and FIG. 7 is a diagram of a conventional transmitter/receiver with collision detection function. Fig. 8 is a diagram showing the collision detectable level difference and threshold versus received light power characteristic of a conventional transmitting/receiving device with a collision detection function, and Fig. 9 is an output waveform diagram of a conventional partial response (1, -1) filter. It is. 1... Signal input terminal, 2... Dipulse encoding circuit, 3... LED driver, 4... LED, 1
1...APD, 12...Preamplifier, 13...Partial response (1, -1) filter, 14
... Signal discriminator, 15 ... Threshold voltage generation circuit, 1
6...First current source, 17...Resistor, 18...Collision detection circuit, 19...Data reproduction output terminal, 20
... Collision detection pulse output terminal, 21 ... Timing extraction circuit, 22 ... Block synchronization circuit, 23 ...
... Level detector, 24 ... Specified voltage input terminal, 2
5...Comparison circuit, 26...Flip-flop, 2
7...Second constant current source, 28...Switch, 29
...Carrier off detection circuit, 30...Second specified voltage input terminal, 31...Second comparison circuit, 32...
...Second flip-flop, 33...Third constant current source, 34...Second switch.

Claims (1)

[Scope of Claims] 1 A transmitter that performs 1B2B code conversion on packet transmission data, modulates its intensity, and transmits the signal to a communication channel; a partial response (1, -1) filter that receives this transmission signal and converts it into AC; a signal discriminator that is supplied with the output signal of the partial response (1, -1) filter and identifies a signal using a threshold voltage slightly deviated from the zero level in the output signal;
After establishing block synchronization for decoding the 1B2B code, a collision detection circuit is provided which detects a code transition rule violation based on the code string output from the signal discriminator and detects that a received packet is in a collision state. The transmitting/receiving device includes a carrier-off detection circuit that outputs a carrier-off detection pulse upon completion of receiving a packet, and a carrier-off detection circuit that outputs a carrier-off detection pulse when receiving a packet, and a carrier-off detection circuit that outputs a carrier-off detection pulse when receiving a packet.
1) one or more comparison circuits that are supplied with the output signal of the filter and a preset specified voltage, and output a level detection pulse when the peak value of the output signal exceeds the specified voltage; A flip-flop is provided corresponding to one or more comparison circuits and is set by the output pulse of the comparison circuit and reset by the output of the carrier-off detection circuit, and a plurality of different threshold voltages are set by the output signal of the flip-flop. A transmitting/receiving device comprising: a threshold voltage generating circuit that outputs an output to the signal discriminator. 2. The threshold voltage generation circuit includes a resistor connected in series with the first constant current source, a switch opened and closed by the flip-flop, and a switch connected in parallel with the first constant current source by the switch. 2. The transmitting/receiving device according to claim 1, wherein the transmitting/receiving device is constituted by a constant current source.