JPS60201720A - Code reproducing circuit with automatic threshold value control function - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a code regeneration circuit with automatic threshold adjustment function used in optical data links and the like.

(Conventional configuration and its problems) In recent years, the introduction of optical communication systems has progressed, and it is thought that the development of optical data links for di-notal data transmission will influence the development. An optical data link consists of a transmitter that converts an electrical signal into an optical signal and radiates it into an optical fiber, and a receiver that converts the optical signal transmitted through the optical fiber into an electrical signal. This receiving section includes a section that converts minute light attenuated by propagation within an optical fiber into an electrical signal, an amplifying section, and a specified electrical level (for example, TT
(L level).

A code regeneration circuit with an automatic threshold adjustment function is used in the receiving section of an optical data link to convert an amplified signal to a specified electrical level, and it can be used without adjustment regardless of the level of optical input to the receiver. Code reproduction can be realized.

The conventional code reproducing circuit with an automatic threshold value adjustment function described above will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of a conventional code reproducing circuit with an automatic threshold value adjustment function. In FIG. 1, 1 is a comparator, 2
is the negative phase input terminal of the comparator, 3 is the positive phase input terminal of the comparator,
4 and 5 are resistors, 6 is a capacitor, 7 is an input terminal, and 8 is an output terminal.

The operation of the code reproducing circuit with automatic threshold adjustment function configured as above will be explained below.

The high-level voltage of the comparison input input from input terminal 7 is V, H.
The +lower voltage is VlL, and the higher voltage at the output terminal 8 is V.

H2 low voltage ■. Let it be L. Let resistor 4 be R1° and resistor 5 be R2. At the positive phase input terminal 3, the comparison input is vi
At H, the output is V. The voltage when it is L is V, (L→H), the comparison input is vlL, and the output is V. The voltage at H is vT(H→
L). FIG. 2 illustrates this voltage level. In FIG. 2, 11 is an input terminal 7. That is, the voltage waveform of the negative phase input terminal 2 is the voltage waveform of the negative phase input terminal 2, and 12 is the voltage waveform of the positive phase input terminal 3. VT(L-+H).

VT(H-+L) is given by the following equation.

Also, V, L<vT(H→L), vT(L-+H)<vthH
If R1 and R2 are determined so as to satisfy (3), an output voltage waveform 13 as shown in FIG. 2 is obtained, and code reproduction becomes possible. The capacitor 6 is intended to make the change in the positive phase input gentler than the change in the negative phase input, and to ensure the operation of the comparator 1.

However, with the above configuration, there were problems such as large fluctuations in signal width when using a single signal, and when reproducing up to DC, the front stage amplification section required a DC amplifier, which limited the dynamic range. . Figure 3 shows the waveform for a single pulse. In addition, in Figure 2, to make the explanation easier to understand,
Although the input waveform is shown as an ideal rectangular wave, the input waveform also has a delay time as shown in FIG. 3 during high-speed operation. In FIG. 3, 21 is an input terminal 7. That is, 22 is the voltage waveform of the negative phase input terminal 2, 22 is the voltage waveform of the positive phase input terminal 3, and 23 is the output voltage waveform of the output terminal 8. Input waveform 2 as shown in Figure 3
1, when it is rounded, the comparison potential of the positive phase input terminal 3 is further rounded because of the capacitor 6, and therefore the output voltage waveform 23 becomes a waveform with a wider pulse width than the input voltage waveform 21. Next, let's talk about the dynamic range. If you want to reproduce a signal up to the DC level, you cannot use an AC coupling type amplifier system using a capacitor, and it is necessary to connect a DC amplifier. Since there are two types of optical signals: lighting and non-lighting, the input section of the amplifier uses the non-lighting time as the bias point, and when the light is on, it only touches one side of the center value (bias point) of the amplifier's operating range. For this reason, the amplifier system does not saturate when the input is large, and the dynamic range becomes narrow.

(Object of the Invention) In view of the above-mentioned drawbacks, the present invention provides an A
The present invention provides a code regeneration circuit with an automatic threshold adjustment function that is capable of C-coupling.

(Structure of the Invention) The code regeneration circuit with automatic threshold adjustment function of the present invention supplies a bias potential to the negative phase input terminal, connects the negative phase input terminal and the input of the present code regeneration circuit with a capacitor, and connects the positive phase input terminal to the positive phase input terminal. A resistor is connected between the output terminal and the positive phase input terminal, and a resistor is connected between the positive phase input terminal and another reference voltage having a voltage equal to the bias potential of the negative phase input terminal, thereby forming a seamit circuit.

(Description of Examples) Examples of the present invention will be described below with reference to the drawings. FIG. 4 is a circuit configuration diagram showing an embodiment of the present invention. In FIG. 4, 31 is a comparator, 32 is an input terminal, 33 is a negative phase input terminal of the comparator, and 34 is a positive phase input terminal of the comparator. ,
35 is an output terminal, 36 is a reference potential, 37 is a capacitor,
38, 39.40°, 41, 42, and 43 are resistors, 44 is a power supply, and 45 is a ground.

The operation of the code reproducing circuit with automatic threshold value adjustment function configured as described above will be explained below.

Let the resistor 42 be R4 and the resistor 43 be R2. The bias potential of the negative phase input terminal 33 of the comparator and the voltage level of the reference potential 36 are set to VB, and the high level of the output voltage is set to V. H1 low level is V. Let's call it L. Capacitor 3 when input terminal is high level
7, the input waveform is differentiated, but at this time the positive phase input terminal 33
A voltage greater than VB is applied to. At this time, output terminal 3
5 is low level V. If it becomes L, the positive phase input terminal 34
The input voltage of is stopped. Conversely, when the input terminal is at low level, the output terminal is at high level V. If it becomes H, the input voltage at the positive phase input terminal is stopped.

Let ν be the alternating current portion of the potential that appears at the negative phase input terminal when the minimum voltage is input within the comparator operating range.
If 1, R2 is selected, code reproduction becomes possible. This is shown in Figure 5. In FIG. 5, 51 is the waveform of the input terminal 32, 52 is the waveform of the negative phase input terminal 33 of the comparator, and 53 is the waveform of the input terminal 33 of the comparator.
54 shows the waveform of the positive phase input terminal 34, and 54 shows the waveform of the output terminal 35. Since the waveform 53 of the positive phase input terminal 34 changes its level at the moment of rising and falling of the negative phase input waveform 52, even if the negative phase input waveform 52 converges to the IA level after a long period of time. , the code can be played. Therefore, AC coupling is possible using a capacitor. Note that since ACAC coupling is performed by the capacitor at the input of the comparator, the code regeneration circuit with automatic threshold adjustment function of this embodiment operates even if AC coupling exists in the amplifier section.

Figure 6 shows the waveform when a single sys input. In FIG. 5, the waveform 51 of the input terminal 320 is assumed to be an ideal rectangular wave to make the explanation easier to understand, but during high-speed operation, the input waveform 51 becomes dull due to the influence of the band of the amplifier. In FIG. 6, 61 shows the waveform of the input terminal 32, 62 shows the waveform of the negative phase input terminal 33 of the comparator, 63 shows the waveform of the positive phase input terminal 34, and 64 shows the waveform of the output terminal 35. As shown in FIG. 6, the waveform 64 at the output terminal 35 is the same as the waveform 62 at the negative phase input terminal.
oscillates symmetrically with respect to the bias potential VB, the influence of sluggishness will have an equal effect on rising and falling, and the pulse width will not be affected.

(Effects of the Invention) As described above, the present invention supplies a bias potential to the negative phase input terminal, connects a resistor to the positive phase input terminal and the output terminal, and connects the input terminal and the negative phase input terminal. Connect a resistor between the bias potential and another reference voltage with equal voltage,
Since it is configured as a Schmitt circuit, the pulse width fluctuation during a single pulse is small, and AC coupling is possible.
The dynamic range can be increased, and its practical effects are great.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional code regeneration circuit with automatic threshold adjustment function, Figure 2 is an input/output voltage level diagram of a conventional code regeneration circuit with automatic threshold adjustment function, and Figure 3 is a diagram of a conventional code regeneration circuit with automatic threshold adjustment function. An input/output voltage level diagram when a single pulse is input to the code regeneration circuit, FIG. 4 is a configuration diagram of the code regeneration circuit with automatic threshold adjustment function according to the present invention, and FIG. 5 shows the code regeneration circuit with automatic threshold adjustment function according to the present invention. FIG. 6 is an input/output voltage level diagram of the code reproducing circuit with automatic threshold adjustment function according to the present invention when a single pulse is input. 1... Comparator, 2... Comparator negative phase input terminal, 3...
...Comparator positive phase input terminal, 4, 5...Resistor, 6...
・Capacitor, 7...Input terminal, 8...Output terminal,
11... Voltage waveform of negative phase input, 12... Voltage waveform of positive phase input, 13... Output voltage waveform, 21... Voltage waveform of negative phase input, 22... Voltage of positive phase input Waveform, 23.
... Output voltage waveform, 31... Comparator, 32... Input terminal, 33... Negative phase input terminal of comparator, 34... Positive phase input terminal of comparator, 35... Output terminal , 36...
Reference potential, 37... Capacitor, 38.39.40.
41.42.43...Resistance, 44...Power supply, 45.
... Earth, 51 ... Input voltage waveform, 52 ... Comparator negative phase input waveform, 53 ... Positive phase input waveform, 54 ...
・Output waveform, 61... Input voltage waveform, 62... Comparator negative phase input waveform, 63... Positive phase input waveform, 64...
・Output waveform. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] A comparator having two input terminals, a positive phase and a negative phase, is provided, a bias potential is supplied to the negative phase input terminal of the comparator, and the negative phase input terminal and the input of the present code regeneration circuit are connected by a capacitor. a resistor is connected between the positive phase input terminal and the output terminal, and a resistor is further connected between the positive phase input terminal and another reference voltage having a voltage equal to the bias potential of the negative phase input terminal. A code regeneration circuit with automatic threshold adjustment function configured as a Schmitt circuit.