JPH07135453A - Signal converter - Google Patents

Abstract

PURPOSE:To avoid a DC level fluctuation by converting a pulse signal attended with the DC level fluctuation into a positive/negative signal at a front edge and a tail end edge so as to eliminate the DC level fluctuation and discriminating the level with a comparator means having a hysteresis characteristic for positive and negative threshold levels so as to provide an output of a rectangular wave signal. CONSTITUTION:A series circuit comprising, a PIN photo diode 5 and a resistor 6 is connected between a power supply voltage point Vcc and ground, the diode 5 receives an optical signal and makes photoelectric conversion and the resulting current signal is fed to a high pass filter 7. The filter 7 converts the signal into a positive/ negative signal at the front edge and the tail end edge of the signal similarly to the case with a differentiation circuit 3, the resulting signal is given to an amplifier 8, in which the signal is amplified and the amplified signal is given to a hysteresis comparator 4, in which the level is discriminated from the output of the filter 7 by using positive negative threshold levels thereby providing a rectangular wave signal as an output where the DC level fluctuation is avoided, Thus, the DC level fluctuation giving an adverse effect such as pulse width, error rate and dynamic range onto the decoding of the rectangular wave is avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal converter for converting a pulse signal, which has been subjected to a change in DC level due to external noise or the like, into a predetermined rectangular wave signal.

[0002]

2. Description of the Related Art In optical communication or the like, a multi-value P by a rectangular wave is used.
When using PM (Pulse Position Modulation), etc., the received signal is converted to TTL (Transistor Transistor Lo).
A device as shown in FIG. 6 is used for converting into a gic level. That is, the signal is given to the amplifier 1 in FIG. 6 to be amplified, the level is discriminated by the predetermined threshold voltage Vth by the comparator 2, and the portion exceeding the threshold voltage Vth is output as a rectangular wave signal.

[0003]

FIG. 7 is a diagram showing how the DC level changes due to the pulse density, and FIG. 8 shows how the DC level changes due to the signal strength change.

Multi-valued PP using rectangular waves in optical communication and the like
When M or the like is used, for example, if a rectangular wave with a duty ratio of 50% (the ratio at which the signal is at the “H” level) is used for the preamble part, a significant difference occurs in the pulse density between the preamble part and the data part. When the pulse density is sparse, the DC level, which is the average value of the signal, is at the bottom of the pulse as shown in FIG. 7A, but when the duty ratio is 50%, as shown in FIG. At the center of the pulse, fluctuations in DC level (DC wandering) occur relative to the signal at the input stage of the comparator 2. Further, as shown in FIG. 8, when the input signal strength changes abruptly, the DC level also changes.

Such variations make it impossible to take a large margin between the threshold value and noise, and as a result, SN
It makes the ratio worse. This leads to an increase in bit error rate and a decrease in dynamic range.

Therefore, a main object of the present invention is to provide a signal converter capable of avoiding fluctuations in DC level.

[0007]

The invention according to claim 1 is
A signal conversion device for converting a pulse signal, which has received a change in DC level due to external noise or the like, into a predetermined rectangular wave signal, which removes a change in DC level contained in the pulse signal, and a leading edge of the pulse signal. It comprises a conversion means for converting into a positive / negative signal at the trailing edge, and a comparison means having a hysteresis characteristic of positive / negative threshold values and discriminating the level of the signal converted by the conversion means to output a rectangular wave signal. It

The invention according to claim 2 uses a differentiating circuit or a high-pass filter as the converting means according to claim 1.

[0009]

The signal converter according to the present invention converts positive and negative signals into positive and negative signals at the leading edge and the trailing edge of the pulse signal to eliminate fluctuations in the DC level, and the positive and negative signals have hysteresis characteristics of positive and negative threshold values. Is applied to the comparing means having the above to perform level discrimination, and a rectangular wave signal is output.

[0010]

1 is a block diagram of an embodiment of the present invention. In FIG. 1, the pulse signal that has undergone the fluctuation of the DC level is given to the differentiating circuit 3, its leading edge is converted into a positive signal and its trailing edge is converted into a negative signal, and the DC level fluctuation is removed, It is given to the hysteresis comparator 4. The hysteresis comparator 4 has a hysteresis characteristic of positive and negative threshold values, level-discriminates the output signal of the differentiating circuit 3, and outputs a rectangular wave signal. In this way, by removing the DC level fluctuation by the differentiating circuit 3, even if a pulse signal accompanied by the DC level fluctuation is input, it is possible to avoid the DC level fluctuation and output a rectangular wave signal.

FIG. 2 is a block diagram when the embodiment of the present invention is applied to optical communication. In FIG. 2, the power supply voltage V
A PIN-PD (PIN photodiode) 5 and a resistor 6 are connected in series between cc and ground. The PIN-PD5 receives an optical signal and performs light-current conversion,
The converted signal is given to the high pass filter 7. The high-pass filter 7 converts the leading edge and the trailing edge of the signal into positive and negative signals and applies the same to the amplifier 8 in the same manner as the differentiating circuit 3 in FIG. The amplifier 8 amplifies the signal and supplies it to the hysteresis comparator 4. The hysteresis comparator 4 is shown in Fig. 1.
Similarly, the output of the high-pass filter 7 amplified by the amplifier 8 is level discriminated by the positive and negative threshold values, and the rectangular wave signal which avoids the DC level fluctuation is output.

FIG. 3 is a more specific circuit diagram of the embodiment shown in FIG. In FIG. 3, the high-pass filter 7 includes a capacitor 71 and a resistor 72 and has a cutoff frequency of 10 kHz. The amplifier 8 includes a transistor 81 whose base receives the output of the high-pass filter 7 via a capacitor 80, and a bias voltage is applied to the base of the transistor 81 by resistors 82 and 83 connected between the power supply voltage Vcc and the ground. To be Transistor 81
The resistor 84 is connected between the collector of the transistor 81 and the power supply voltage Vcc, and the resistor 8 is connected between the emitter of the transistor 81 and the ground.
5 and a parallel circuit of the resistor 86 and the capacitor 87 are connected. A signal is output from the collector of the transistor 81 and applied to the comparison input terminal of the comparator 4 via the resistor R41. A resistor 42 is connected between the comparison input end of the comparator 4 and the output, and a reference voltage of 2.5 V, for example, is applied to the reference input end of the comparator 4. A resistor 43 is provided between the output of the comparator 4 and the power supply voltage Vcc.
Are connected.

FIG. 4 is a waveform diagram of each part of FIG. PIN
-When the PD 5 receives the optical signal, it performs light-current conversion and outputs a pulse signal accompanied by DC level fluctuation as shown in Fig. 4A. This pulse signal is the capacitor 71
After passing through a high-pass filter 7 composed of a resistor 72 and a resistor 72, the leading edge of the pulse signal changes positively with respect to the DC level and the trailing edge changes negatively with respect to the DC level as shown in FIG. 4B. It is converted into a signal and the DC level fluctuation is removed. Since the signal output from the high-pass filter 7 is a pulse having substantially the same magnitude in the positive direction and the negative direction, the DC level does not change due to the pulse density or the signal strength. Then, this signal is output by the transistor 81 of the amplifier 8.
As shown in FIG. 4C, it is amplified about 20 times and given to the hysteresis comparator 4. The hysteresis comparator 4 has threshold values of Vth and -Vth as shown by the dotted line in FIG.
A TTL level rectangular wave signal as shown in (d) is output to restore the original signal.

FIG. 5 is a block diagram showing still another embodiment of the present invention. In the embodiment shown in FIG. 5, the amplifier 8 shown in FIG. 2 is connected between the PIN-PD 5 and the high-pass filter 7, and its operation and effect are almost the same as those of the embodiment shown in FIG. Is.

[0015]

As described above, according to the present invention, the positive and negative signals are converted into positive and negative signals at the leading edge and the trailing edge of the pulse signal accompanied by the fluctuation of the DC level to eliminate the fluctuation of the DC level, and the signal is changed to the positive or negative sign. Since the rectangular wave signal is outputted by discriminating the level by the comparing means having the hysteresis characteristic of the threshold value of, the DC level fluctuation which adversely affects the pulse width, the error rate, the dynamic range, etc. in the restoration of the rectangular wave is avoided. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram when an embodiment of the present invention is applied to optical communication.

FIG. 3 is a more specific circuit diagram of the embodiment shown in FIG.

FIG. 4 is a waveform diagram of each part of FIG.

FIG. 5 is a block diagram showing another embodiment of the present invention.

FIG. 6 is a block diagram of a conventional signal conversion device.

FIG. 7 is a waveform diagram for explaining how the DC level varies depending on the pulse density in the conventional signal converter.

FIG. 8 is a waveform diagram showing how a DC level changes due to a change in signal strength.

[Explanation of symbols]

 3 Differentiating circuit 4 Hysteresis comparator 5 PIN-PD 6 Resistor 7 High pass filter 8 Amplifier

Claims (2)

[Claims] 1. A signal conversion device for converting a pulse signal, which has undergone a change in DC level due to external noise or the like, into a predetermined rectangular wave signal, wherein the DC level fluctuation contained in the pulse signal is removed and the pulse signal is removed. A converter that converts positive and negative signals at the leading edge and the trailing edge of the pulse signal, and a hysteresis characteristic of positive and negative threshold values, level-discriminates the signal converted by the converter, and outputs a rectangular wave signal. A signal conversion device comprising a comparison means. 2. The signal conversion device according to claim 1, wherein the conversion means is a differentiating circuit or a high-pass filter.