JPS61201533A - Transmission and reception equipment with collision detecting function - Google Patents

Abstract

PURPOSE:To expand the range of reception level possible for detection of collision by inserting a high pass filter having a required characteristic to the pre- stage of a partial response filter. CONSTITUTION:A high pass filter 22 consists of a resistor 23 and a capacitor 24. Further, the high pass filter 22 and partial response 1, -1 filter 1 are connected by a buffer amplifier 25 whose input impedance is a high impedance and whose output impedance is equal to a characteristic impedance of the analog delay line 14. A midpoint 0 level included in an output of the partial response 1, -1 filter 11 is kept to a prescribed valve even when the received light level is changed by using the high pass filter having a required characteristic and inserted to the pre-stage of the partial response 1, -1 filter 11. Thus, the received light level range possible for collision detection is expanded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention uses C8MA/'CD (C8MA/'CD) as an access method.
arrisr 5ense Multiple Acc
ess with Calision Date-c
AM (Local Area
The present invention relates to a transmitting/receiving device with a collision detection function that performs collision detection (Ca!1iSion Detection) in addition to data transmission in a network.

[Conventional technology]

FIG. 4 is a configuration diagram showing a conventional transmitting/receiving device with a collision detection function. In the figure, (1) is the transmitter, (2) is 1B
2BB2 circuit, (3) is a light emitting element drive circuit.

(4) is a light emitting element, 151 is an optical fiber 161g optical star coupler, (7) is an optical fiber, (8) is a receiver, (
9) is a light receiving element, Ql is a preamplifier, αυ is a partial response (1, -1) filter, C2 is a comparison circuit,
C3 is a coding rule violation detection circuit.

FIG. 5 is a block diagram showing a partial response (1, -1) filter suitable for the transmission/reception device with a collision detection function shown in FIG. 4. In the figure, aυ indicates a partial response (tt-t) filter 'fr.

■ is an analog delay line, αS is an input terminal, ae is an output terminal, (17a) and (17b) are output signals, and 0tsuchi is an input signal.

(19a) and (19b) are reflected waves.

Partial response of Figure 6H, IE5 (1°-1
) is a waveform diagram of each part in the filter. In the figure,
(20a) and (20b) are the threshold values of the comparator circuit α2.

(21a) and (2ib) are DC equilibrium levels.

Next, the operation of the conventional transmitting/receiving device with a collision detection function shown in FIG. 4 will be explained. In the transmitter fi+, at the pit rate. The input signal is encoded and electro-optical converted. The input signal of the transmitter (1) is:

It is encoded into a 51B2B code by the 1B2BB doubling circuit (2) and output to the 9 light emitting element drive circuit (31. Here, l
−j, 1 Consider a biphase code as a B2B code. The light emitting element driving circuit (31) outputs a driving current to the light emitting element (4), and an optical signal corresponding to the driving current is output from the light emitting element (4).A light signal output from the light emitting element (4) is input to the optical star coupler (6) via the optical fiber (5).In the optical star coupler (6), the optical signal input from each input optical fiber is equally distributed to each output optical fiber. The optical signal input to the fiber (7) is equally distributed to each output optical fiber.

The optical signal input to the optical fiber (7) is output to the receiver (8). The receiver (8) performs opto-electrical conversion of the input optical signal and optical signal collision detection. The input optical signal of the receiver (8) is photoelectrically converted in the light receiving element (91).
After being amplified by the preamplifier α1, the filter is
is output to. The partial response (1°-1) filter αυ completely subtracts the signal delayed by this input signal kfo (b) from the input signal, and outputs the result to the output signal full comparison circuit H. The code rule violation detection circuit 0 is a comparison circuit αa
A code rule violation signal caused by a collision is detected in the output of the controller, and the presence or absence of a collision is determined based on the detection result.

As shown in Figure 5, the partial response (t+-t
) The filter αυ is composed of a reflection differentiator circuit using an analog delay line α4. Partial response (1,
-1) The input from the input terminal t1!9 of the filter aυ is
It is driven by a pre-stage circuit having the same output impedance as the analog delay line IO characteristic impedance, and its output is terminated by a high impedance circuit at the output terminal αe. The partial response (t+-1 filter αυO output signal (17a) is the input signal α field and the reflected wave (19
This is the composite signal of a).

In Fig. 6, the partial response (1
, -1) shows the operation waveform of filter fill. First, an ideal case where the attenuation constant of the analog delay line α is 0 will be described. Input signal and reflected wave (19a)
In the output signal (17a) obtained by f combining, a medium level is generated at every other bit. The comparison circuit αa has a threshold value (2) slightly below the intermediate level of the output signal (17a).
Da)? setting, and detects when the received signal is interfered with by the collision signal and falls below the threshold (2)a). At this time, a code rule violation occurs. There are two types of intermediate levels: 09, which is obtained by subtracting the optical signal ON and the optical signal ON, and 0, which is obtained by subtracting between the optical signal 0 and the optical signal OFF. 01 is not used for determining signal collision because it is likely to be erroneously detected when there is no collision due to shot noise generated in the light receiving element (9). The middle 0 level is
DC equilibrium level (M
Since it matches (a), it does not change with respect to changes in the received signal level. Therefore, even if the threshold value (2Qa) is set close to the all-median zero level, a stable collision detection operation can be obtained in a wide range of light reception levels.

[Problem that the invention seeks to solve]

In the conventional transmitting/receiving device with a collision detection function as described above,
During actual collision detection operation, the signal propagating through the analog delay line Q4 is attenuated, so the input signal θ and the reflected wave (
19b), the level difference V between the intermediate O level of the output signal (17b) and the DC equilibrium level (21b),
) changes with respect to changes in the received light level, as expressed by the fi1 equation below.

vom-(1-e)S・・・・・・・・・
(11) Here, α is the attenuation constant of the analog delay line (141), and L is the length of the analog delay line α4 from the input end to the shorted end.

S is an amplitude proportional to the received light level. When α=0, it becomes vO-0. Currently, the bitrate fQ is 32M”
When 7B, analog delay line t141 is connected by coaxial cable.
When configured, the required length of analog delay line a4 is approximately 3 m.
F) *e-””=about 0.93. The threshold value of the comparator circuit α2 is set to about 20% (20 is the amplitude S at the minimum received optical signal level). Therefore, if the amplitude S increases by n times of S(, then vO-(1
2So, the correct collision detection operation cannot be performed because the intermediate 0 level and the threshold value (20b) overlap. in this way.

In a conventional transmitting/receiving device with a collision detection function.

Since the intermediate 0 level generated at the output of the partial response (1, -1) filter αυ changes depending on the received light level, there is a problem that the range of received light levels in which collision detection is possible becomes narrow.

The present invention was made in order to solve this problem, and therefore, the middle 0 level of the output of the partial response (t, -1) filter is made to match the DC equilibrium level, thereby widening the light receiving level range in which collision detection is possible. The overall objective is to obtain a transmitting/receiving device with a collision detection function that can be expanded.

[Means for solving problems]

A transmitting/receiving device with a collision detection function according to the present invention.

By inserting a bypass filter with the required characteristics before the partial response (t, -t) filter! +, partial response (1, -1) The medium A level included in the output of the filter is made not to change depending on the total light reception level.

[Effect]

In the transmitting/receiving device with a collision detection function of the present invention, the bypass filter having the required characteristics is inserted before the herbal response (1, -1) filter, and the output of the partial response (1, -1) filter includes The intermediate 0 level that can be detected can be maintained at a constant value even if the light reception level changes, thereby making it possible to expand the entire range of light reception levels in which collision detection is possible.

〔Example〕

FIG. 1 is a block diagram showing a transmitting/receiving device with a collision detection function i which is an embodiment of the present invention. The same parts as those in FIG. In the figure, the wire is a bypass filter, and this bypass filter @ is inserted before the partial response (1, -1) filter αυ. The rest of the structure is the same as that of the apparatus shown in FIG. 4 above.

Figure 2 shows the bypass filter and partial response (1, -
1) It is a block diagram showing a filter.

In the figure, @ is resistance, c! 4 is a capacitor, (C) is a buffer amplifier, @ is an input signal, (5) is a reflected wave, and @ is an output signal.

Figure 3 shows the partial response (1°-1) of Figure 2.
It is a waveform diagram of each part in a filter. In the figure, the wire is the DC equilibrium level.

Next, the operation of the transmitting/receiving device with a collision detection function, which is an embodiment of the present invention shown in FIG. 1, will be described. As shown in the figure, the transmitting/receiving device with a collision detection function of the present invention has a bypass filter @ inserted between the preamplifier aa toheral response (1, -1) filter αυ shown in FIG. 4 above. The operation of other parts is described in the fourth section above.
The operation is similar to that of the conventional device shown in the figure. Bypass filter (2) is composed of a resistor (to) and a capacitor Q4.

Also.

Bypass filter @ and partial response (1°-1
) The filter αυ is connected to a buffer amplifier (c) whose input impedance is high and whose output impedance is equal to the characteristic impedance of the analog delay line α4. Now, the received signal is subjected to sag distortion due to low frequency cutoff by the bypass filter (2). For this reason,
Sag distortion occurs in the input signal (a) of the partial response (1, , -1) filter αυ and the reflected wave that is reflected at the short-circuited end and returns to the input end.

Output signal obtained by combining these two distortions (to)
The value at the bit center of the amplitude v1 of the middle 0 level of is .

It is expressed by the cylinders (2) and (3) below.

Here, to, J, is the 3 dB low frequency cutoff frequency of the bypass filter (c). Partial response (1°-
1) The DC equilibrium level (to) of the filter αυ is 0, which is 6.

Therefore, from the above formula (21), fcL is expressed as vulgar temperature (4
), the amplitude v1 of the middle 0 level at the center of the bit becomes 0, and the DC equilibrium level (
).

The insertion loss of the analog delay line α core is about e-2dL-053, as explained in the example of the conventional device above. At this time, +fcL becomes 0J)23 fo from the above equation (4).

〔Effect of the invention〕

As described above, the present invention provides a transmitting/receiving device with a collision detection function by inserting a bypass filter having required characteristics before the partial response (1, -1) filter.
) Since the intermediate 0 level included in the output of the filter does not change depending on the total received light level, compared to conventional devices of this type, it is possible to expand the entire range of received light levels in which collision detection is possible. It is effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a transmitting/receiving device with a collision detection function which is an embodiment of the present invention, and FIG. 2 shows a no-pass filter and a partial response (1, - 1) Configuration diagram showing the filter,
Figure 3 shows the partial response (t, -1
) Waveform diagram of each part in the filter, Figure 4 is a configuration diagram showing a conventional transmitting/receiving device with a collision detection function, and Figure 5 is a waveform diagram of each part in the filter.
Figure 8 u
, is a waveform diagram of each part in the partial response (1, -1) filter of FIG. 5. In the figure, (1)...transmitter, (2)...1B2
BB2 conversion circuit, (3)... light emitting element drive circuit, 14)
...Light emitting element, 151. (7)...Optical fiber, (6)...Optical star coupler, (8)...Receiver, (9)...Photodetector, α-to...Preamplifier, α-to...Partial Response (1,
-1) Filter, a3... Comparison circuit, 03... Sign rule violation detection circuit, +14... Analog delay line, α9
...input terminal, txe...output terminal, ■...no\ bus filter, (c)...resistor, (2)...capacitor, 2!9...buffer amplifier. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] Transmission data with a bit rate f_0 is encoded into a 1B2B code and transmitted by a transmitter, and the received 1B2B code is identified through a filter having sin(πf)/(2f_0) characteristics to detect a violation of the coding rule. In a transmitting/receiving device with a collision detection function that detects signal collision on a transmission path, one end is short-circuited and the other end of the analog delay line is used as an input end and an output end.
)/(2f_0) When the attenuation constant of the analog delay line is α and the length from the input end to the shorted end is L, the 3dB low frequency cutoff frequency is (2αL)/π.
A transmitting/receiving device with a collision detection function configured to include a high-pass filter of f_0.