JPH11243365A - Parallel optical receiver used for parallel optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a parallel optical receiver with a reduced skew. SOLUTION: Photo-detectors 111 to 11n photoelectrically convert optical signals transmitted through plural optical transmission circuits corresponding to plural channels 1 to (n) to electric signals, and plural comparators 161 to 16n and 171 to 17n to which 1st set value of relatively high voltage is fed in common compare each rise and fall signal with the set value respectively by making the electric signals pass through differential circuits 151 to 15n. And, each output signal of the comparators 161 to 16n and 171 to 17n respectively changes the states of output signals of plural flip-flop circuits 191 to 19n corresponding to each channel and also returns it to its original respectively to acquire an output signal corresponding to each channel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parallel optical receiver for use in a parallel optical transmission system for transmitting and receiving optical signals via a plurality of optical transmission circuits corresponding to a plurality of channels, and more particularly to a method for fixing parallel synchronous transmission. The present invention relates to a parallel optical receiving device that operates at an identification level.

[0002]

2. Description of the Related Art Conventionally, there is serial transmission as one of optical interconnects. In this serial transmission, when transmitting a parallel signal, first, the parallel signal is subjected to parallel / serial conversion (abbreviated as P / S) by an electric circuit,
After serial transmission of this signal by an optical transmission module, the received signal must be converted back to the original parallel signal by serial / parallel conversion (abbreviated as S / P). In this case, since the serially transmitted signal is multiplexed,
A high-speed transmission rate of “at least one channel transmission rate × the number of multiplexed channels” is required, and an optical transmission module capable of high-speed transmission is required. Therefore, in serial transmission, technically advanced high-speed optical transmission module,
A P / S circuit and an S / P circuit are required, which makes the system expensive. In addition, the P / S circuit and the S / P circuit
Since a dedicated circuit corresponding to the format of the parallel signal to be transmitted must be formed, there is also a problem that versatility is poor.

On the other hand, there is an optical interconnect using an optical fiber array based on parallel synchronous transfer. The basic method of such parallel optical transmission is multi-channel parallel synchronous transmission using electric / optical (abbreviated as E / O) and optical / electric (abbreviated as O / E) and an optical fiber array. The delay time between inputs must be the same.

[0004]

However, in the above-mentioned parallel optical transmission system, there is a problem that a skew, which is a variation in delay time, occurs fundamentally. Such a skew occurs in each of the parallel optical transmitter, the optical fiber array, and the optical receiver that constitute the optical transmission system. In particular, the optical receiver has a problem that the skew varies depending on the magnitude of the reception power. This skew occurs in the fixed discrimination level method because the discrimination point of the pulse amplitude for the fixed discrimination level differs depending on the input power. That is, as shown in FIG. 5, when the input signals IH and IL having different powers are input to the identification circuit having the fixed identification level TH, the pulse amplitude of the reproduction output OH of the high power signal IH and the low power signal IL Is different from the pulse amplitude of the reproduction output OL corresponding to the rising edge skew Sk11 and the falling skew Sk12.

In order to reduce such skew,
It is necessary to equalize the optical input power, reduce the rise time and fall time of the optical signal, and widen the bandwidth of the analog section of the receiver. In order to make the optical input power uniform, it is necessary to reduce the variation in the optical transmission level of each channel and the connection loss of the optical fiber array. In order to achieve this, high-performance parts and high-precision assembly technology are required, and there are technical difficulties and high costs.

Next, in order to reduce the rise time and the fall time of an optical signal, it is necessary to use a high-speed light emitting element and to increase the speed of a driving circuit. is there. With regard to the broadening of the final receiver analog section, since the bandwidth and the gain of the amplifier are in a trade-off relationship, the widening of the amplifier causes a decrease in the gain, and the S / N ratio is deteriorated due to an increase in the nozzle bandwidth. And the problem of deteriorating the reception performance.
In order to solve this, a higher-performance amplifier is required, and there are technical difficulties and higher costs. Furthermore, skew cannot be fundamentally solved due to problems such as variations in the length of the transmission path for each channel of the optical fiber array.

[0007] For example, Japanese Patent Application Laid-Open No. 5-206943 discloses that a wide band is obtained by amplifying a received signal of each channel by a feedback differential amplifier having a DC feedback circuit for generating a reference DC voltage based on a reference signal. Although an optical parallel signal receiving circuit that solves this problem is disclosed, this technique is based on the premise that the powers of received signals are equal, and does not solve the problem regarding skew.

In view of such circumstances, the present invention provides a parallel optical receiving apparatus used in a parallel optical transmission system capable of reducing skew in a parallel optical receiving apparatus that performs parallel synchronous transmission at a fixed identification level with a simple configuration. The task is to provide

[0009]

According to a first aspect of the present invention, there is provided an optical communication system for transmitting and receiving an optical signal through a plurality of optical transmission lines corresponding to a plurality of channels. A receiving apparatus, wherein an optical signal transmitted through each of the optical transmission paths is subjected to optical-electrical conversion by a light receiving element to obtain an electrical signal corresponding to each of the channels, and each of the electrical signals is passed through a differentiating circuit. Thus, a rising and falling signal corresponding to the rising and falling is obtained, and a plurality of first comparators corresponding to the respective channels to which a relatively high voltage first set value is commonly supplied are used. Each rising signal is compared with the first set value, and a plurality of second comparators corresponding to the respective channels to which a relatively low voltage second set value is commonly supplied are used. Falling signal comparing each said second set value, respectively to change the state of the output signals of the plurality of flip-flop circuit corresponding to each channel on each output signal of said first comparator, said second
Wherein the state of the output signal of each of the flip-flop circuits is returned to the original state by each output signal of the comparator to obtain an output signal corresponding to each channel.

According to a second aspect of the present invention, in the parallel optical transmission system according to the first aspect, an electric signal from the light receiving element is amplified by a variable gain amplifier at a stage preceding each of the differentiating circuits. The parallel optical receiver used. According to a third aspect of the present invention, in the first or second aspect, the first and second set values are respectively set at half positions of the pulse amplitudes of the rising signal and the falling signal. And a parallel optical receiving apparatus used for a parallel optical transmission system.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the first and second set values are set based on a division ratio of a serially connected resistor. And a threshold generation circuit that adjusts at least one of the first and second set values by connecting an external resistor appropriately in parallel with each of the resistors. In a parallel optical transmission system.

According to the present invention, an electric signal obtained from the light receiving element is differentiated by a differentiating circuit to obtain a rising and falling signal, and the rising and falling signal is compared with the first and second set values, respectively. I decided to
Rise and fall skews are significantly reduced, and at the same time, pulse width distortion is reduced, and the reliability of the parallel optical receiver is improved. When the parallel optical receiving device of the present invention is used, the optical transmitting side can perform transmission in the normal mode without performing special processing such as high performance and high functionality, thereby reducing the burden on the transmitting side. can do.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of a parallel optical receiving device according to one embodiment. As shown in the figure,
A plurality of light receiving elements 111 to 11n arranged in parallel for each of a plurality of channels (n channels in the figure) receive parallel received optical signals, convert each received optical signal into an electric signal, and output the electric signal. The electric signal converted into the optical signal is supplied to the preamplifier 1
To the preamplifiers 121 to 12n, respectively.
Outputs of 12n are variable gain amplifiers 131 to 13n, respectively.
, Whereby the electric signal is amplified with a predetermined amplification factor. A gain input terminal 14 is connected to each of the variable gain amplifiers 131 to 13n.
3n gain can be adjusted.

Next, each of the variable gain amplifiers 131 to 13n
Are input to differentiating circuits 151 to 15n provided for channels 1 to n, respectively, to obtain rising and falling signals corresponding to the rising and falling of the respective electric signals. The falling signal is supplied to the first comparators 161 to 16n provided for the respective channels 1 to n and the second comparator 161 to 16n.
Of the comparators 171 to 17n.

Here, the first comparators 161 to 16
n corresponds to the input signal S1 with respect to the relatively high voltage first set value THHIGH input from the threshold generation circuit 18.
Rises only while S1> THHIGH (for example, the output signal is in the “1” state). On the other hand, the second comparator 1
Similarly, the input signal S2 rises only when S2 <THLOW with respect to a relatively low voltage second set value THLOW input from the threshold generation circuit 18 (for example, when the output signal is “1”). ”State).

The threshold voltage generation circuit 18
Although the details will be described later, the first set value set to a predetermined value
This circuit outputs the voltage of THHIGH and the second set value THLOW. The values of the first set value THHIGH and the second set value THLOW can be arbitrarily set via the THHIGH control terminal 18a and the THLOW control terminal 18b. Is available.

The outputs of the first comparators 161 to 16n and the second comparators 171 to 17n are supplied to a set / reset flip-flop circuit (abbreviated as SR-FF) 19
1 to 19n. Here, SR-FF
The output signals of 191 to 19n are output to the first comparator 17
The second comparator 18 sets and rises according to the rise of the signal input from each of the first to 17n.
It is reset and falls by the rise of the signal input from 1 to 18n. That is, during that time, the state “1” is maintained. Then, each SR-FF 191
To 19n are output buffers 211 to 211, respectively.
21n. In addition, these SR-FF
A reset terminal 20 for bringing 191 to 19n into a reset state is connected. The reset terminal 20 is used to set an initial value when there is no signal, such as after power-on.

With the above configuration, the rise and fall corresponding to each received signal are differentiated by the differential circuits 151 to 15n.
As a result, the data is converted into a rising signal and a falling signal, respectively, and the data is reproduced by detecting the rising edge and the falling edge via the rising signal and the falling signal, so that the so-called skew variation is significantly reduced.

Considering the case where signals IH and IL having different powers are input to the differentiating circuit, as in FIG. 5 described in the related art, the output of the differentiating circuit includes rising signals DH1 and DL1 and falling signal, respectively. Signals DH2 and DL2 are output. When these edges are detected at the fixed identification levels THHIGH and THLOW, respectively, an output pulse OH corresponding to the high power signal IH and an output pulse OL corresponding to the low power signal IL are obtained. In this case, some rising skew Sk1 and falling skew Sk2 occur due to the difference in power, but are significantly smaller than the skews Sk11 and Sk12 (see FIG. 5) when the edge is detected directly without passing through a differentiating circuit. .

Further, since the rising and falling edges are detected by the rising signals DH1 and DL1 and the falling signals DH2 and DL2 by the differentiating circuit, the rising skew Sk1 and the falling skew Sk2 are added. Therefore, the pulse width does not vary. Thus, pulse width distortion can be reduced, and reliability can be improved. Here, it is preferable that the fixed identification levels THHIGH and THLOW for detecting the rising signal and the falling signal, which are the outputs of the differentiating circuit, be about one-half of the respective pulse amplitudes of the rising signal and the falling signal. When the rise time and the fall time of the signal input to the differentiating circuit are different, the pulse amplitudes of the rise signal and the fall signal corresponding thereto are different, and accordingly, the fixed identification level THHIGH is set to correspond to the difference. And THLOW must be set to predetermined levels, respectively.

FIG. 3 shows an example of a signal whose rise time and fall time are different. As shown, the rise time Tr is usually slow and the fall time Tf is fast, so that the pulse amplitude of the rise signal D1 is relatively small and the pulse amplitude of the fall signal D2 is relatively large. Therefore, in this case, the differences ΔTHHIGH and ΔTHLOW between the fixed identification levels THHIGH and THLOW set to about one-half of the respective pulse amplitudes and the reference voltage V0 are different,
ΔTHLOW is relatively large.

Therefore, in the above-described embodiment, the threshold voltage generation circuit 18 is connected to the external control terminal 18.
Through the controls via a and 18b, the set values THHIGH and
Although THLOW can be arbitrarily adjusted, an example of this circuit configuration is shown in FIG. As shown in FIG. 4, the threshold voltage generation circuit 18 converts the power supply voltage VDD to the resistors R1 to R1.
By dividing the resistance by R3, the set values THHIGH and
The threshold values THHIGH and THLOW are output through the unity gain buffers 22a and 22b to suppress fluctuations in the threshold voltage due to load fluctuations.

Here, normally, by setting R1 = R3, ΔTHHIGH = ΔTHLOW = VDD × R2 / 2 (R1 + R2 + R
3) When ΔTHHIGH and ΔTHLOW are reduced, the resistor R5 is externally connected between the control terminals 18a and 18b. When ΔTHHIGH and ΔTHLOW are increased, the resistor R5 is connected between the control terminals 18b and 18a and the power supply voltage VDD and the ground GND. , The resistors R4 and R6 may be externally provided. It should be noted that resistors R4 to R6 are externally connected and R4 =
Assuming R6, ΔTHHIGH = ΔTHLOW. Note that FIG.
As shown in the above, if ΔTHHIGH> ΔTHLOW,
W Resistor R between control terminal 18b and ground GND
6 may be connected so that R1> (parallel resistance of R3 and R6). As described above, according to the threshold generation circuit of FIG. 4, an arbitrary threshold voltage can be easily set by connecting a resistor to the control terminal.

[0024]

As described above, according to the present invention, according to the present invention, the rise and fall corresponding to each received signal are converted into a rise signal and a fall signal by a differentiating circuit, respectively. Since the data is reproduced by detecting the rising edge and the falling edge through the falling signal, the so-called skew variation is significantly reduced, and the rising skew and the falling skew are cancelled. Therefore, the skew and the pulse width distortion are reduced, the reliability of data reproduction can be improved, and there is no need to prepare a special device on the transmission side. Can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a parallel optical receiving device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation and effect of the present invention.

FIG. 3 is a diagram for explaining the operation and effect of the present invention.

FIG. 4 is a block diagram illustrating an example of a threshold generation circuit.

FIG. 5 is a diagram for explaining a problem of the related art.

[Explanation of symbols]

111-11n Light receiving element 121-12n Preamplifier 131-13n Variable gain amplifier 14 Gain setting input terminal 151-15n Differentiating circuit 161-16n First comparator 171-17n Second comparator 18 Threshold generation circuit 18a, 18b Control terminal 191-19n set reset flip-flop circuit 20 reset terminal 211-21n output buffer

Claims (4)

[Claims] 1. A parallel optical receiver for use in a parallel optical transmission system for transmitting and receiving optical signals via a plurality of optical transmission lines corresponding to a plurality of channels, wherein the parallel optical receiver is transmitted through each of the optical transmission lines. An optical signal is converted from light to electricity by a light receiving element to obtain an electric signal corresponding to each of the channels, and each electric signal is passed through a differentiating circuit to obtain a rising and falling signal corresponding to its rising and falling. A plurality of first comparators corresponding to the respective channels to which a relatively high voltage first set value is commonly supplied, each of the rising signals is compared with the first set value, The falling signal is compared with the second set value by a plurality of second comparators corresponding to the respective channels to which the second set value of the low voltage is commonly supplied. Changing the states of the output signals of the plurality of flip-flop circuits corresponding to the respective channels with the respective output signals of the first comparator, and changing the output signals of the respective flip-flop circuits with the respective output signals of the second comparator. A parallel optical receiving apparatus for use in a parallel optical transmission system, wherein the state is restored to the original state to obtain an output signal corresponding to each channel. 2. The parallel optical receiving apparatus according to claim 1, wherein an electric signal from the light receiving element is amplified by a variable gain amplifier before each of the differentiating circuits. 3. The parallel processing method according to claim 1, wherein the first and second set values are respectively set at half positions of pulse amplitudes of the rising signal and the falling signal. A parallel optical receiver used for optical transmission systems. 4. The method according to claim 1, wherein the first and second set values are obtained based on a division ratio of a resistor connected in series, and the first and second set values are obtained. A parallel connection for use in a parallel optical transmission system, wherein the parallel connection is supplied via a threshold generation circuit that adjusts at least one of the first and second set values by connecting an external resistor appropriately in parallel with each resistor. Optical receiver.