JPS5942704Y2 - Signal discrimination circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal discrimination circuit for converting a signal into a binary value.

In optical reading devices, optical communications, and the like, the amount of light is detected by converting the amount of light into an amount of electricity using an opto-sensor or the like, and measuring this amount of electricity.

However, the potential level of this quantity of electricity is indefinite, and when calculating it on the next stage electronic computer, it is better to convert this quantity of electricity into a digital quantity of 1"70" at a constant level, which simplifies the calculation and Preferable in terms of accuracy.

However, conventional signal level discrimination circuits have various drawbacks.

This will be explained below. FIG. 1 shows a conventional signal discrimination circuit.

First, the potential level of the signal source 1 fluctuates in response to the amount of light from the outside.

This changed amount of electricity is input to one terminal of the comparator circuit 2 via the resistor 3.

This amount of electricity is also input to other terminals of the comparator circuit 3 via the diode 4 and the resistor 5.

A capacitor 6 is further connected to the other terminal of the comparator circuit 3, and at the same time, it is also connected to a potential supply terminal 8 via a resistor T.

Next, we will outline the operation of this circuit.

First, when the potential of the signal source 1 rises in accordance with the amount of external light, this signal is input to one terminal of the comparator circuit 2.

At this time, the potential of the other terminal of the comparator circuit 2 becomes a potential lower than the increased potential by the forward voltage drop of the diode 4, and the output of the comparator circuit 2 reaches a high level.

Next, when the potential of signal source 1 decreases, one terminal of comparator circuit 2 becomes the potential of signal source 1, but the other terminal changes depending on the time constant determined by the capacitance of capacitor 6 and the resistance value of resistor 7. Potential decreases.

These values are determined so that the potential decreases more slowly than the potential decrease of the signal source 1.

This is because the signal from the signal source 1 is cut by the diode 4, and the charge stored in the capacitor 6 is discharged according to the time constant.

At this time, the output of the comparator circuit 2 becomes Low level because the potential of one terminal of the comparator circuit 2 is lower than the potential of the other terminal.

Then, when the potential of the signal source 2 starts to rise again, the potential of one terminal of the comparator circuit 2 becomes higher than the potential of the other terminal by the forward voltage drop of the diode 4 as described above, so the output of the comparator circuit 2 becomes High level.

Since this circuit automatically follows the potential fluctuations of the signal source 1, there is no need to adjust the reference voltage according to the type of light, as is the case when comparing the signal with a reference voltage.
It is used in various fields because it can obtain output corresponding to

However, since this circuit always responds to potential fluctuations of the signal source 1, it may follow fluctuations in noise signals that have not reached the reference potential and may output an erroneous output.

The present invention aims to correct this drawback and provide a signal discrimination circuit that cuts all signals below a predetermined potential level and automatically tracks and distinguishes all signals above a predetermined potential level. do.

The present invention will be explained with reference to the drawings.

FIG. 2 shows an embodiment of the present invention.

A signal to be determined is generated at the signal source 11 .

A specific example of the signal source 11 is an opto-sensor, which generates a variable signal depending on the amount of light from the outside.

This signal is input to one end of the comparator circuit 13 via a resistor 12, and at the same time is input to the other terminal of the comparator circuit 13 via a diode 14 and a resistor 15.A capacitor 17 is connected to the node 16 between the diode 14 and the resistor 150. A resistor 18 is connected, the former to ground and the latter to potential supply terminal 1.
Connected to 9.

A potential supply terminal 19 of this circuit is connected to a negative potential power source.

Further, a reference potential source 2 is connected to the node 16 via a diode 20.
1 is also connected.

The comparison circuit 13 has two input terminals and one output terminal, and has a function of comparing the potentials of the two input terminals.

For example, if the potential of one input is higher than the potential of the other input, the output will be High level, and in the opposite case, the output will be Low level.

A circuit with such a function is Toshiba's OP amplifier TA7.
504M etc.

Next, the operation of the circuit shown in FIG. 2 will be explained with reference to FIGS. 3 and 4.

In FIG. 3, a solid line 22 represents a signal from the signal source 11, and a dotted line 23 represents potential fluctuations at the node 16.

FIG. 4 shows a comparison circuit 13 corresponding to the signals shown in FIG.
This is the output of

These figures show transient phenomena and the like in a somewhat simplified manner for the sake of explanation.

First, when the potential of the signal source 11 is high at time t1, this signal is directly input to one end of the comparison circuit 13, and the other end receives a signal that is lower than the potential of this signal by the forward voltage drop VFI of the diode 14. enters.

The output of the comparator circuit 13 from time t1 to t2 when the potential of the signal source 11 is high is High as shown in FIG.
h level.

When the potential of the signal source 11 decreases at time t2, one terminal of the comparison circuit 13 changes to the same potential, but the potential of the other terminal changes according to a time constant determined by the capacitance of the capacitor 17 and the resistance value of the resistor 18. Since the charge stored in node 17 is discharged, the potential of node 16 becomes higher than the potential of signal source 11.

The rate of potential drop at the node 16 is designed in advance to be lower than the rate of potential drop at the signal source 11.

Therefore, the output of the comparison circuit 13 from time t2 to time t3 becomes Low level as shown in FIG.

In this way, when the potential of the signal source 11 is high, current flows through the diode 14 and charges the capacitor 17, but when the potential decreases, the diode 14 becomes reverse biased and no current flows from the signal source 11 to the node 16. is not supplied.

This is because the potential at node 16 at this time is
The electric charge stored in the capacitor 17 is discharged according to a time constant determined by the capacitance of This is because it is designed.

The operation from time t3 to t4 is also the same as above, and the output of the comparison circuit 13 becomes High level.

Next, when the potential of the signal source 11 decreases, the potential of the node 16 also decreases according to the amount of discharge of the capacitor 17.
The potential changes from the potential VA of the reference potential source 21 to the diode 2.
The potential vA- is obtained by subtracting the forward voltage drop VF2 of 0.
■When F2=■c, the potential does not drop any further.

This is because, at this potential, current flows from the reference potential source 21 through the diode 20 and begins to charge the capacitor 17.

In this way, the potential of the node after time t5 is. It is held at Vc.

Even if the potential of the signal source 11 rises from time t6 to t7, if the potential rises above VC, the output of the comparator circuit 13 remains unchanged and remains at the Low level.

The potential fluctuation from time t6 to t7 is not a signal to be discriminated, but is noise that does not reach a predetermined potential level.

In the conventional circuit shown in Fig. 1, even this signal is recognized,
Although the output of the comparator circuit 13 is at a high level, this signal is not discriminated by this circuit, and the output of the comparator circuit 13 is at a low level.

Then, only when the potential of the signal source 11 exceeds the potential of the reference potential source 21 at time t8 does the diode 20
becomes reverse biased, diode 14 becomes forward biased, and the potential at node 16 becomes a potential level corresponding to the signal from signal source 11.

As described above, according to the circuit of the present invention, reliability is improved because noise and the like that do not reach the reference potential are not discriminated.

At the same time, signals having a reference potential or higher can be discriminated according to the signal from the signal source.

The present invention is not limited to the above-mentioned embodiments, and various embodiments are possible.

[Brief explanation of the drawing]

FIG. 1 is a conventional signal discrimination circuit, FIG. 2 is a signal discrimination circuit according to the present invention, and FIGS. 3 and 4 are explanatory diagrams for explaining the operation of the circuit in FIG. 2. . 11... Signal source, 13... Comparison circuit, 1
4...Diode, 16...Node, 1
7... Capacitor, 18... Resistor, 1
9...- Potential supply terminal, 20... Diode, 21... Reference potential source.

Claims (1)

[Claims for Utility Model Registration] A comparator circuit that has two input terminals and compares the potential levels of two human input signals applied to the input terminals, and a signal that is applied to seven input terminals of the comparator circuit. a signal source; a capacitive element connected to the other input terminal of the comparison circuit; a diode connected between the other input terminal of the comparison circuit and the signal source; a reference potential source that generates a reference potential; A signal discrimination circuit comprising: a control device that connects the reference potential source and the other input terminal only when the other input terminal of the comparison circuit is within a predetermined potential level range.