JPH0653788A - Noise elimination circuit - Google Patents

Abstract

PURPOSE:To reduce the cost by simplifying the configuration. CONSTITUTION:The noise elimination circuit is a circuit eliminating a noise pulse whose pulse width is less than a prescribed pulse width, in which a 1st connecting point P1 is connected to an output of a 1st NOR circuit 1 and a 2nd connecting point P2 is connected to both inputs of a 2nd NOR circuit 2 and one input of a 3rd NOR circuit 3. Furthermore, a 3rd connecting point P3 is connected to an output of the 2nd NOR circuit and a 4th connecting point P4 is connected to the other input of the 3rd NOR circuit. Then the output of the 3rd NOR circuit is connected to one input of the 1st NOR circuit, the other terminal of a 1st capacitor C1 and the other terminal of a 2nd capacitor C2 connect to a signal earth, the other input of the 1st NOR circuit is used for a noise elimination input Bin and an output of the 3rd NOR circuit is used for a noise elimination output BOUT.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise removing circuit for removing a pulse having a pulse width smaller than a predetermined width.

[0002]

2. Description of the Related Art In a crime prevention detector, a heat ray incident from a warning area is focused by a lens on a pyroelectric element of a sensor circuit, and a voltage corresponding to a change rate of the heat dose is applied from the pyroelectric element. It is equipped with a passive heat ray crime prevention detector that outputs a signal and outputs a warning when the output voltage exceeds a predetermined level, and a light emitting / receiving device, so that the light from the light emitting device cannot be received by the sensor circuit of the light receiving device. And a light-and-receive type security detector that outputs a warning and an ultrasonic-type security detector that emits an ultrasonic wave and receives a reflected wave with a sensor circuit and outputs a warning when there is a change in the reflected wave. And so on.

By the way, FIG. 3 is a main part circuit diagram showing a sensor circuit of the above-mentioned passive heat ray security detector. Figure 3
In, 1 pyroelectric element, 2 an amplifier, CP _1, CP ₂ respectively comparators, r _1, r _2, r ₃ is the comparison reference voltage of the comparator CP _1, CP ₂ by applying a power supply voltage V _DD min E _{1 ,}
Voltage dividing resistors for generating E ₂ , d _{1 and} d ₂ are diodes for taking an AND output of the outputs of the comparators CP _{1 and} CP ₂ .

The sensor circuit described above is connected as follows.
ing. That is, the output of the pyroelectric element 1 is the input of the amplifier 2.
And the output of the amplifier 2 is connected to the comparator CP.₁Non of
Inverting input terminal and comparator CP₂To the inverting input terminal of
Connected, comparator CP ₁The inverting input terminal of
Anti r_1,r₂Connected to the connection point of the comparator CP₂of
Non-inverting input terminal is voltage dividing resistor r_3,r_FourConnected to the connection point of
ing. Diode d ₁Is the comparator CP
₁Connected to the output of diode d₂The anode of
Parator CP₂Connected to the output of diode d₁Mosquito
Sword and diode d₂Connected to the cathode of
It And the diode d₁Cathode and diode d
₂The connection point with the cathode of is the output part of this sensor circuit.
It is A.

The sensor circuit connected as described above operates as follows. That is, the comparators CP _1, CP
₂ is connected as described above to form a window comparator, and when the output voltage from the amplifier 2 is within the range between the potential E ₁ and the potential E ₂ , the sensor circuit output unit A has a Lo
When w is output and the output voltage from the amplifier 2 is outside the range between the potential E ₁ and the potential E ₂ , the sensor circuit output section A is set to Hi.
Output gh. In other words, the sensor circuit shown in FIG. 3 outputs High from the sensor circuit output section A only when there is a change in the heat dose such that an intruder enters the caution area and the output voltage from the pyroelectric element 1 becomes a predetermined value or more. Is output.

However, from the sensor circuit output section A
If there is a high output, it means that there was an intruder.
If an alert is issued and output by an intruder in the warning area,
High output due to some noise factors other than
It will be output as if there was an intruder.
It Therefore, in order to improve the reliability of the crime prevention detector,
Normal pulse width T generated by an intruder entering₁
Pulse width T shorter than ₁Triggered for pulses less than
Noise removal measures are taken to prevent output.

It should be noted that such noise removal measures are taken not only in the passive heat ray crime prevention detector, but also in the light emitting and receiving type crime prevention detector, the ultrasonic type crime prevention detector and the like.

[0008]

However, in the conventional crime prevention detector, the above-mentioned noise elimination measures are to take the pulse from the sensor circuit output section A through the input port connected to the microcomputer. Read
A method has been adopted in which the pulse width is verified by processing by software, and if the pulse width is less than a predetermined pulse width, the alarm output is not performed. Therefore, the crime prevention detector is expensive and useful, but has not been adopted so much.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a noise elimination circuit which is simple in structure and inexpensive.

[0010]

In order to solve the above problems, the present invention is a noise removing circuit for removing a pulse having a pulse width of less than a predetermined width, which is a noise, and comprises a first NOR circuit and a second NOR circuit. Third NOR circuit, first resistor and second
A resistor, a first capacitor, a second capacitor, a first diode, and a second diode are provided, and one end of the first resistor and the anode of the first diode are connected to form a first connection point. An end, the cathode of the first diode and one end of the first capacitor are connected to form a second connection point, and one end of the second resistor and the cathode of the second diode are connected to form a third connection point, The other end of the second resistor, the anode of the second diode and one end of the second capacitor are connected to form a fourth connection point, and the first connection point is connected to the output terminal of the first NOR circuit,
The second connection point is connected to both input terminals of the second NOR circuit and the third NOR circuit.
Connect to one input terminal of the circuit and connect the third connection point to the second N
Connect to the output terminal of the OR circuit and connect the fourth connection point to the third NOR
The other input terminal of the circuit, the output terminal of the third NOR circuit is connected to one input terminal of the first NOR circuit, and
The other end of the capacitor and the other end of the second capacitor are connected to a signal ground, the other input terminal of the first NOR circuit is a noise elimination input terminal, and the output terminal of the third NOR circuit is a noise elimination output terminal. It is characterized by

[0011]

With the above configuration, it is possible to easily remove the pulse having the pulse width less than the predetermined pulse width by using the NOR circuit, the resistor, the capacitor, and the diode.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a noise removing circuit according to the present invention will be described in detail below with reference to FIGS.

FIG. 1 is a circuit diagram showing a noise removing circuit. This noise removing circuit, as shown in FIG.
NOR circuit 1 corresponding to the OR circuit, NOR circuit 2 corresponding to the second NOR circuit, and N corresponding to the third NOR circuit.
An OR circuit 3, a resistor R ₁ corresponding to the first resistor, a resistor R ₂ corresponding to the second resistor, a capacitor C ₁ corresponding to the first capacitor, a capacitor C ₂ corresponding to the second capacitor, A diode D ₁ corresponding to one diode,
It is composed of a diode D ₂ corresponding to the second diode.

The above-mentioned components are connected as follows. That is, one end of the resistor R ₁ is connected to the anode of the diode D ₁ to form a first connection point P _1, and the other end of the resistor R ₁ is connected to the cathode of the diode D ₁ and one end of the capacitor C _1. Form a second connection point P ₂ and connect one end of the resistor R ₂ to the cathode of the diode D ₂ to form a third connection point P ₃
The other end of the resistor R ₂ , the anode of the diode D ₂ and one end of the capacitor C ₂ are connected to form a fourth connection point P _4, and the connection point P ₁ is connected to the output terminal of the NOR circuit 1. Then, the connection point P ₂ is connected to both input terminals of the NOR circuit 2 and one input terminal of the NOR circuit 3, and the connection point P ₃ is connected to the NOR circuit 2
Connected to the output terminal of the NOR circuit 3, the connection point P ₄ to the other input terminal of the NOR circuit 3, and the output terminal of the NOR circuit 3 to NOR.
It is connected to one input terminal of the circuit 1, and the other end of the capacitor C _{1 and} the other end of the capacitor C ₂ are connected to the signal ground. The other input terminal of the NOR circuit 1 constitutes a noise elimination input terminal B _in, and the output terminal of the NOR circuit 3 constitutes a noise elimination output terminal B _out .

Next, the operation of the noise removing circuit will be described with reference to FIG. 2A and 2B are timing charts showing the operation of the noise removal circuit. FIG. 2A shows a voltage waveform input to the noise removal input terminal B _in , FIG. 2B shows a voltage waveform at the connection point P ₁ , and FIG. The voltage waveform output from the noise elimination output terminal B _out is shown in (d) of the connection point P ₂ (e).
Shows the voltage waveform at the connection point P ₃ , and (f) shows the voltage waveform at the connection point P ₄ .

By the way, the noise elimination input terminal B _in is low.
In the case where the operation of the noise elimination circuit is stabilized in the state of (4) (time point t ₀ ), the connection point P ₁ and the connection point P _{2 are}
Is high, the connection points P ₃ and P ₄ are low, and the noise elimination output terminal B _out is low.

Now, as shown in FIG. 2A, the pulse width
T_bPulse X_bIs the noise elimination input terminal B_inEntered in
Then, pulse X_bWhen t is input₁There
Is the output of the NOR circuit 1 (connection point P₁) Becomes Low.
However, the connection point P₂Is resistance R ₁And capacitor C₁Contact with
Since it is a continuation point, connection point P₂Response of the potential change of
Delay, connection point P₂The potential is gradually changed as shown in Fig. 2 (d).
High to Low. However, pulse X_bThe pal
Width T_bIs short, so connection point P₂Potential of NOR circuit 2
And the threshold value V of the NOR circuit 3_thBefore descending to
Noise elimination input terminal B_inBecomes Low again. This noise
Removal input terminal B_inWhen t becomes Low again t₂There
Is the output of the NOR circuit 1 (connection point P₁) Becomes High again
, Capacitor C₁Is the diode D₁Fast charge through
And the connection point P₂As shown in Fig. 2 (d), the potential of
Crab becomes High. Then, the NOR circuit 2 and NOR times
The output of path 3 does not cause any state change. That is, pal
Short pulse X_bPulse like noise input
Terminal B_inInput to the noise elimination output terminal B_{ou t}Or
Their output remains low and does not change at all.

Next, as shown in FIG. 2A, the pulse width
T_aPulse X_aIs the noise elimination input terminal B_inEntered in
Then, pulse X_aWhen t is input₃There
Is the output of the NOR circuit 1 (connection point P₁) Becomes Low.
However, the connection point P₂Is resistance R ₁And capacitor C₁Contact with
Since it is a continuation point, connection point P₂Response of the potential change of
Delay, connection point P₂The potential is gradually changed as shown in Fig. 2 (d).
High to Low. And time t₃To T₁Time
Time t_FourAnd the connection point P₂The potential of
The threshold value V of the NOR circuit 2 and the NOR circuit 3_thReached
To do. This T₁Is given by the following equation (1).

T ₁ = −C ₁ × R ₁ × Ln (V _th / V _DD ) ... (1) where V _DD is a drive voltage.

Then, the output of the NOR circuit 2 (connection point
P₃) Becomes High. However, the connection point P _FourIs resistance R₂When
Capacitor C₂Since it is a connection point with_FourElectric power
The response of the position change is delayed, and the connection point P_FourFigure 2 shows the potential of
As shown in (f), it gradually rises from Low to High. Only
At time t_FourTo connection point P_FourThe potential of the
P_FourPotential is threshold V_thTo reach T₂Time
It costs. That is, T₂Time period (time t_FourFrom time t
₆Up to), both inputs of the NOR circuit 3
Becomes Low, and the NOR circuit 3 outputs High.
That is, the noise elimination output terminal B_outIs shown in Figure 2 (c)
It becomes High. In addition, T₂Is the following formula (2)
Given.

T ₂ = −C ₂ × R ₂ × Ln (1-V _th / V _DD ) ... (2) where V _DD is a drive voltage.

Then, at time t_FourGradually changes from Low to High
Ascending connection point P_FourIs at time t_FourTo T₂Time passage
Time t₆Becomes threshold V_thReach Do
And connection point P₂The input of NOR circuit 3 connected to is Low
Although there is a connection point P_FourInput of NOR circuit 3 connected to
Becomes high, the output of the NOR circuit 3, that is, noise
Removal output terminal B_outGoes low as shown in Fig. 2 (c).
It Noise elimination input terminal B_inNOR times to connect to
The input of path 1 is already at time t._FiveWhich is low
, The other input of the NOR circuit 1 is at time t₆To Low
It That is, time t ₆Output of NOR circuit 1 (connection point P
₁) Becomes High. Output of NOR circuit 1 (connection point P₁)
Becomes high, the capacitor C₁Is the diode D₁Through
And then charged at high speed, connecting point P₂Potential is shown in Fig. 2 (d).
High as soon as possible. Connection point P₂Potential is High
Then, the output of the NOR circuit 2 (connection point P₃) Is Low
Become. Then, the capacitor C₂Is the diode D₂Through
Is discharged at high speed and the connection point P_FourQuickly goes Low.

In this way, the state of the noise elimination circuit after the time t ₆ is the same as the case where the operation of the noise elimination circuit is stabilized by keeping the noise elimination input terminal B _in in the Low state, that is, Connection point P ₁ and connection point P ₂ are High
Then, the connection point P ₃ and the connection point P ₄ are set to Low, and the noise elimination output terminal B _out is set to Low. That is, the pulse output having the pulse width T ₂ that rises after a delay of T ₁ time from the rising time t ₃ of the pulse X _a is formed from the noise elimination output terminal B _out .

Next, assuming that _a pulse having _a pulse width longer than the pulse X _a and a pulse width of [T ₁ + T ₂ ] time or more is input to the noise removal input terminal B _in , the noise removal output terminal in this case. The output from B _out (detailed description and illustration is omitted because it is a logic similar to the above) has a pulse width T ₂ that rises with a delay of T ₁ time from the rise of the pulse input to the noise elimination input terminal B _in. Pulse output.

As is apparent from the above description, in the noise removing circuit configured as described above, if the pulse width input to the noise removing input terminal B _in is T ₁ or more,
A pulse output having a pulse width T ₂ that rises with a delay of T ₁ is obtained at the noise elimination output terminal B _out . Further, if the pulse width input to the noise removal input terminal B _in is less than T ₁ , the pulse is not output from the noise removal output terminal B _out and is removed.

Therefore, an output containing noise (short pulse) from the sensor circuit as described in the prior art is passed through the noise removing circuit as described above,
Noise removal measures can be easily implemented without using a complicated and expensive microcomputer.

As the NOR circuit element described above, it is preferable to use a CMOS type element instead of a bipolar type element because the output pulse voltage can be fully taken up to the drive voltage V _DD .

The present invention is not limited to the above embodiment, but the first resistor or the first capacitor may be made variable so that the pulse width of the removable pulse can be adjusted. The two resistors or the second capacitor may be made variable so that the output pulse width from the noise elimination output terminal can be adjusted, and the present invention also includes such a variable type.

[0029]

Since the noise removing circuit of the present invention is configured as described above, it is possible to provide a noise removing circuit which is simple in structure and can remove a pulse having a pulse width of less than a predetermined width, which is noise. Has the effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a noise removing circuit according to an embodiment of the present invention.

FIG. 2 is a timing diagram showing the operation of the noise removal circuit according to the exemplary embodiment of the present invention.

FIG. 3 is a main part circuit diagram showing a sensor circuit of a passive heat ray security detector.

[Explanation of symbols]

1 1st NOR circuit 2 2nd NOR circuit 3 3rd NOR circuit B _in Noise elimination input terminal B _out Noise elimination output terminal C ₁ 1st capacitor C ₂ 2nd capacitor D ₁ 1st diode D ₂ 2nd diode P ₁ 1st connection point P ₂ 2nd connection point P ₃ 3rd connection point P ₄ 4th connection point R ₁ 1st resistance R ₂ 2nd resistance

Claims (1)

[Claims] 1. A noise removing circuit for removing a pulse having a pulse width of less than a predetermined width, which is noise, including a first NOR circuit, a second NOR circuit, a third NOR circuit, a first resistor and a second resistor.
A resistor, a first capacitor, a second capacitor, a first diode, and a second diode are provided, and one end of the first resistor and the anode of the first diode are connected to form a first connection point. An end, the cathode of the first diode and one end of the first capacitor are connected to form a second connection point, and one end of the second resistor and the cathode of the second diode are connected to form a third connection point, The other end of the second resistor, the anode of the second diode and one end of the second capacitor are connected to form a fourth connection point, and the first connection point is connected to the output terminal of the first NOR circuit,
The second connection point is connected to both input terminals of the second NOR circuit and the third NOR circuit.
Connect to one input terminal of the circuit and connect the third connection point to the second N
Connect to the output terminal of the OR circuit and connect the fourth connection point to the third NOR
The other input terminal of the circuit is connected, and the output terminal of the third NOR circuit is connected to one input terminal of the first NOR circuit,
The other end of the capacitor and the other end of the second capacitor are connected to a signal ground, the other input terminal of the first NOR circuit is a noise elimination input terminal, and the output terminal of the third NOR circuit is a noise elimination output terminal. A noise removal circuit characterized by the above.