JPH09119864A - Signal processor for pyroelectric infrared sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal processor by which only an AC signal out of input signals to be input from a pyroelectric infrared sensor is amplified at a prescribed amplification factor. SOLUTION: A signal processor is constituted of a low-pass filter circuit 11 which outputs only a DC portion in an input signal Vin to be input from a pyroelectric infrared sensor 1 and of a differential amplifier circuit 21 which amplifies and outputs only an AC portion in the input signal Vin on the basis of a DC signal VDC to be output from the low-pass filter circuit 11 and on the basis of the input signal Vin to be input from the pyroelectric infrared sensor 1. The input signal Vin to be input from the pyroelectric infrared sensor 1 and the DC signal VDC obtained by passing the input signal Vin through the low-pass filter circuit 11 are input to the differential amplifier circuit 21. In the differential amplifier circuit 21, an output voltage Vout in which only an AC signal VAC is amplified at an amplification factor α to be set on the basis of the relationship of a resistance value by amplifying a (Vin-VDC) signal is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing device for a pyroelectric infrared sensor for amplifying an output signal of a pyroelectric infrared sensor.

[0002]

2. Description of the Related Art Generally, a pyroelectric infrared sensor is known as an infrared sensor for detecting infrared rays radiated from a heating element. Here, the pyroelectric infrared sensor is a sensor that uses a pyroelectric material having a pyroelectric effect such as lead titanate (PbTiO ₃ ) as an infrared detection element. The pyroelectric effect means that when infrared rays enter and a temperature change occurs on the surface of the infrared detecting element, spontaneous polarization occurs in the element which has been stable until now, the neutralization state of the charge collapses, and it is electrically changed. It is the property of becoming unbalanced and generating charges. Further, since the impedance of the pyroelectric material is as high as several hundreds of GΩ, the charges generated in the infrared detecting element are extracted as an output signal by voltage by impedance conversion.

FIG. 1 shows an infrared detecting element and an impedance conversion circuit which constitute an infrared sensor as a prior art.
4 will be described.

In the figure, reference numeral 101 denotes a pyroelectric infrared sensor, which is composed of an infrared detection element 102 and an impedance conversion circuit 103. The impedance conversion circuit 103 is provided on the output side of the infrared detection element 102. Field effect transistor (F
ET) 104 and a gate resistance Rg connected between the gate terminal of the field effect transistor 104 and ground.
And a drain resistance Rd connected between the drain terminal of the field effect transistor 104 and the ground.
The power supply voltage Vcc is input to the source terminal of the field effect transistor 104, and the output signal Vs from the infrared sensor 101 is output from the drain terminal of the field effect transistor 104.

Further, the impedance conversion circuit 10
The output signal Vs output from 3 is the infrared detection element 10
The weak AC component from 2 and the field effect transistor 10
4 and two components (output signal =
AC component + DC component).

Next, FIG. 15 shows an example of a conventional signal processing device for a pyroelectric infrared sensor for amplifying the output signal Vs.

In the figure, reference numeral 111 denotes an inverting amplifier circuit as a signal processing device. The inverting amplifier circuit 111 is an OP amplifier (operational amplifier) 112, an inverting input terminal of the OP amplifier 112 and an input of the inverting amplifier circuit 111. It is composed of a coupling capacitor Ca and an input resistance ra connected in series with a terminal T1, and a negative feedback resistance rb connected between an output terminal and an inverting input terminal of the OP amplifier 112. The non-inverting input terminal of the amplifier 112 is grounded.

The output signal Vs output from the infrared sensor 101 is the input terminal T1 of the inverting amplifier circuit 111.
Is input as an input signal Vin to the inverting input terminal of the OP amplifier 112 through a series circuit including a coupling capacitor Ca for removing a direct current component of the input signal Vin and an input resistance ra. Is entered.

Further, in the OP amplifier 112, since the output terminal T2 of the OP amplifier 112 is connected to the inverting input terminal through the negative feedback resistor rb, the output voltage Vout is fed back to the inverting input terminal and the input signal Vin The output voltage Vout can be obtained by the following equation 1, where f is the frequency.

[0010]

(Equation 1)

As is clear from the equation 1, the input signal Vin
As the frequency f becomes smaller, the amplification factor becomes smaller, so that the output voltage Vout becomes smaller. Therefore, in order to use the inverting amplifier circuit 111 with a constant amplification factor, the frequency f
The band is limited.

Further, regardless of the frequency f of the input signal Vin,
In order for the inverting amplifier circuit 111 to obtain a constant amplification factor, the impedance of the capacitor Ca (1 / 2πfCa)
Whether to increase the resistance value of the input resistance ra compared to (Ω),
A method of increasing the capacitance of the capacitor Ca can be considered. For example, if the capacitance of the capacitor Ca is 22 (μ
F), the amplification factor is 60 (dB), and the reduced cutoff frequency f is 0.
When set to 1 (Hz), the resistance value of the input resistance ra is 70 (KΩ) and the resistance value of the negative feedback resistance rb is 70.
(MΩ) is required.

Further, in order to expand the detection visual field, a pyroelectric infrared sensor 101a having a plurality of pyroelectric infrared sensors,
101b, ..., 101n may be used. In this case, as shown in FIG. 16, a plurality of pyroelectric infrared sensors 101
The input signal Vin obtained from a to 101n is switched to the switch 11
3a to 113n are sequentially switched, and the signal amplified by one inverting amplifier circuit 111 can be detected.
It is desirable because the number of circuit components used is small, the circuit configuration is simple, and the manufacturing cost is low.

[0014]

However, when the resistance value of the negative feedback resistance rb of the inverting amplifier circuit 111 is set to a high resistance value of 70 MΩ, not only the resistance itself is expensive but also the resistance value There is a drawback that the variation is large and the characteristics of the amplifier circuit vary when such a resistor is used.

When a coupling capacitor Ca having a large electrostatic capacitance is used, it is necessary to use an electric field capacitor, but the electric field capacitor has a large leakage current due to its characteristics. Since this leakage current flows through the input resistance ra and the negative feedback resistance rb,
There is a drawback that a voltage drop occurs and an offset voltage is generated in the output voltage Vout after amplification.

Further, when the negative feedback resistor rb having a resistance value of 70 (MΩ) is used and a standard electrolytic capacitor is used, the output voltage Vou is affected by the leakage current.
t will be saturated and will not function as an inverting amplifier circuit. Therefore, it is difficult to amplify the input signal Vin having a low frequency f with a high amplification factor.

Further, when a coupling capacitor Ca is connected to the inverting input terminal of the OP amplifier 112, a DC potential difference is generated between both electrodes of the capacitor Ca, so that a charge corresponding to this potential difference is accumulated in the capacitor Ca. It takes a long time before the power is turned on, and the inverting amplifier circuit 111 does not function normally immediately after the power is turned on.

For example, in the inverting amplifier circuit 111 of FIG. 15, even if the charging time of the capacitor Ca can be shortened, at least 20 due to the time constant before charging because of the large capacitance of the capacitor Ca. It takes about a second. As a result, the plurality of pyroelectric infrared sensors 10
It was difficult to sequentially switch the input signals Vin obtained from 1a to 101n and to speed up and amplify the output signals Vs from the plurality of infrared sensors 101a to 101n with one inverting amplifier circuit 111.

The present invention can amplify a low-frequency input signal output from a pyroelectric infrared sensor with a predetermined amplification factor without using a resistor having a high resistance value and a coupling capacitor. An object is to provide a signal processing device for a pyroelectric infrared sensor.

[0020]

In order to solve the above-mentioned problems, a signal processing device for a pyroelectric infrared sensor adopted by the invention according to claim 1 is a signal processing device for a pyroelectric infrared sensor. A low-pass filter circuit that outputs only a direct-current component, based on a direct-current signal output from the low-pass filter circuit and an input signal input from the pyroelectric infrared sensor, amplifies only the alternating-current component in the input signal. It is composed of a differential amplifier circuit for outputting the output.

With this configuration, the low-pass filter circuit outputs only the DC component of the input signal input from the pyroelectric infrared sensor. The differential amplifier circuit outputs only the AC component of the input signal based on the DC signal and the input signal input from the pyroelectric infrared sensor. As a result, the differential amplifier circuit can output only the AC component of the input signal input from the pyroelectric infrared sensor as an output signal to the outside.

A signal processing device for a pyroelectric infrared sensor employed by the invention according to claim 2 is a low-pass filter circuit for outputting only a direct current component in an input signal input from the pyroelectric infrared sensor, and the low-pass filter circuit. A differential amplifier circuit that amplifies and outputs only the AC component in the input signal based on the DC signal output from the input signal and the input signal input from the pyroelectric infrared sensor; It is composed of a DC bias adding means connected to the next stage and adding a DC bias to the AC signal output from the differential amplifier circuit.

With this configuration, the low-pass filter circuit outputs only the DC component of the input signal input from the pyroelectric infrared sensor. The differential amplifier circuit can amplify and output only the AC component based on the DC signal and the input signal input from the pyroelectric infrared sensor. And from the differential amplifier circuit,
Only the AC component of the input signal input from the pyroelectric infrared sensor is output as an AC signal. Furthermore, by adding a DC bias to the AC signal output from the differential amplifier circuit by the DC bias adding means, not only the AC signal but also the DC bias added output signal can be output to the outside from the DC bias adding means. it can.

A signal processing device for a pyroelectric infrared sensor employed by the invention according to claim 3 is a plurality of low-pass filter circuits for outputting only DC components in input signals input from a plurality of pyroelectric infrared sensors. And, based on each DC signal output from each low-pass filter circuit and each input signal input from each pyroelectric infrared sensor,
It consists of one differential amplifier circuit that amplifies and outputs only the AC component of the input signal.

With this configuration, the plurality of low-pass filter circuits individually output only the DC component of the input signal input from the corresponding pyroelectric infrared sensor. The differential amplifier circuit can output only the AC component of the input signal based on the DC signals and the input signals input from the pyroelectric infrared sensors. As a result, the differential amplifier circuit can output only the AC component of the input signal input from each pyroelectric infrared sensor as an output signal to the outside.

A signal processing device for a pyroelectric infrared sensor employed by the invention according to claim 4 is a plurality of low-pass filter circuits for outputting only DC components in input signals input from a plurality of pyroelectric infrared sensors. And, based on each DC signal output from each low-pass filter circuit and each input signal input from each pyroelectric infrared sensor,
One differential amplifier circuit that amplifies and outputs only the AC component in the input signal, and a DC bias that is connected to the next stage of the differential amplifier circuit and that outputs the AC component signal from the differential amplifier circuit. It is composed of a DC bias adding means for adding.

With this configuration, the plurality of low-pass filter circuits individually output only the DC component of the input signal input from the corresponding pyroelectric infrared sensor. The differential amplifier circuit can output only the AC component of the input signal based on the DC signals and the input signals input from the pyroelectric infrared sensors. Furthermore, by adding a DC bias to the AC signal output from the differential amplifier circuit by the DC bias adding means,
The DC bias adding means can output not only an AC signal but also an output signal added with a DC bias to the outside.

In the invention according to claim 5, switching connection means for switching and connecting between the pyroelectric infrared sensor and the differential amplifier circuit and between the low-pass filter circuit and the differential amplifier circuit, respectively. It is provided.

With this configuration, by operating the switching connecting means, the switching connecting means can simultaneously switch the pyroelectric infrared sensor and the low-pass filter circuit to the differential amplifier circuit. Therefore, when a plurality of pyroelectric line sensors and a plurality of low-pass filter circuits are connected to one differential amplifier circuit, a pair of infrared sensors and low-pass filter circuits are simultaneously and sequentially arranged. You can switch.

According to a sixth aspect of the invention, the DC bias adding means comprises an inverting amplifier circuit composed of an OP amplifier and a reference voltage circuit for adding a reference voltage as a bias, and the inverting input terminal of the inverting amplifier circuit is The differential amplifier circuit is connected to the output side, and the non-inverting input terminal of the inverting amplifier circuit is connected to the output side of the reference voltage circuit and the output side of the low pass filter circuit.

With this configuration, the AC signal in the input signal input from the pyroelectric infrared sensor via the differential amplifier circuit is input to the inverting input terminal of the inverting amplifier circuit. In addition, a DC signal in the input signal input from the pyroelectric infrared sensor is input to the non-inverting input terminal via the low-pass filter circuit. Thus, the output signal of the inverting amplifier circuit can be output to the outside by adding the DC reference voltage output from the reference voltage circuit to the AC signal.

According to a seventh aspect of the present invention, the low-pass filter circuit is located between the output side of the pyroelectric infrared sensor and the ground, and is composed of a resistor and a capacitor connected in series. ) Is cut off and only the DC component can be output.

In the invention according to claim 8, a switching element is connected to both ends of the resistor forming the low-pass filter circuit.

With this configuration, when the switching element is closed at the time of starting the low-pass filter circuit, a relatively large current (input signal) flows from the infrared sensor to the capacitor without passing through a resistor, Shorten the charging time with the capacitor. As a result, the startup time of the low pass filter circuit can be shortened.

According to a ninth aspect of the present invention, in the low-pass filter circuit, an OP amplifier, a resistor connected between an output terminal and an inverting input terminal of the OP amplifier, and a capacitor connected in parallel to the resistor. By connecting the non-inverting input terminal of the OP amplifier to the output side of the infrared sensor, it is possible to block the AC component (high frequency) and output only the DC component.

According to a tenth aspect of the invention, the differential amplifier circuit comprises an OP amplifier, the inverting input terminal of the OP amplifier is connected to the output side of the pyroelectric infrared sensor, and the non-inverting input terminal is a low-pass filter. It is connected to the output side of the circuit.

With this configuration, the differential amplifier circuit can be configured as an inverting amplifier circuit, and the differential amplifier circuit amplifies only the AC component of the input signal input from the pyroelectric infrared sensor. Above, it can be output to the outside as an output signal obtained by adding a DC signal to this AC signal.

In the invention according to claim 11, the differential amplifier circuit comprises an OP amplifier and a series resistance circuit connected between the output side of the low-pass filter circuit and the ground, and the non-inverting input of the OP amplifier. The terminal is connected to the voltage dividing point of the series resistance circuit, and the inverting input terminal is connected to the output side of the infrared sensor.

With this configuration, the differential amplifier circuit can be configured as an inverting amplifier circuit, and among the input signals input from the pyroelectric infrared sensor, only the AC component is amplified and then the DC signal is converted. Only the removed AC signal can be output to the outside as an output signal.

In the invention according to claim 12, a buffer circuit is provided between the low-pass filter circuit and the differential amplifier circuit, and in the invention according to claim 13, the buffer circuit is provided between the pyroelectric infrared sensor and the differential amplifier circuit. In the invention according to claim 14, a buffer circuit is provided between the low-pass filter circuit and the DC bias applying means to prevent electrical interference between the circuits. You can

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION In order to describe the present invention in detail, an embodiment will be described with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technology are denoted by the same reference numerals, and description thereof will be omitted.

First, FIG. 1 and FIG. 2 show a first embodiment of the present invention.
The following shows an example. In the first embodiment, a case where one infrared sensor is used will be described.

In the figure, reference numeral 1 denotes a pyroelectric infrared sensor, which is the same as the infrared sensor 101 described in the prior art, and the infrared detecting element 2 and the field effect transistor 4 are provided.
And the impedance conversion circuit 3 having A gate resistance Rg is connected to the gate terminal of the field effect transistor 4 and a resistance Rd is connected to the drain terminal thereof. Then, an output signal Vs corresponding to the amount of infrared rays received by the infrared detecting element 2 is output from the drain terminal. The output signal Vs is a weak AC component from the infrared detection element 2 and the field effect transistor 4
It is composed of two components, a direct current component and a direct current component.

Reference numeral 10 shows a signal processing device for a pyroelectric infrared sensor according to this embodiment. The signal processing device 10 is connected to the next stage of the pyroelectric infrared sensor 1, and has a low-pass filter circuit 11 and a differential amplifier which will be described later. The circuit 21 and the switch 31 are generally configured.

Reference numeral 11 shows a low-pass filter circuit according to this embodiment, and the low-pass filter circuit 11 has a structure in which a resistor R11 and a capacitor C11 are connected in series. That is, the low-pass filter circuit 11 is configured as an L-type low-pass filter circuit in which one end of the capacitor C11 is grounded and the other end of the resistor R11 is connected to the input terminal T1 of the signal processing device 10. The low-pass filter circuit 11 removes the AC signal VAC from the input signal Vin input from the pyroelectric infrared sensor 1 through the input terminal T1 and the switch 31 and removes only the DC signal VDC from the differential amplifier circuit. It outputs to 21. On the other hand, at the input terminal T1, the output signal Vs output from the pyroelectric infrared sensor shown in FIG. 2A is input signal Vin.
Is entered as The input signal Vin is the AC signal VAC
And DC signal VDC, Vin = (VAC + VD
It can be represented as C).

Reference numeral 12 denotes a switching element. The switching element 12 is connected to both ends of the resistor R11 so as to be connected in parallel with the resistor R11. By closing the switching element 12, the resistor R11 is short-circuited.

Reference numeral 21 denotes a differential amplifier circuit, which is composed of an OP amplifier 22, an input resistor R21, a negative feedback resistor R22, and another input resistor R23. Here, the input resistor R21 is between the resistor R11 of the low-pass filter circuit 11 and the voltage dividing point A of the capacitor C11, and the OP amplifier 2
2 non-inverting input terminals. Negative feedback resistor R22
Is connected between the output terminal and the inverting input terminal of the OP amplifier 22. The other input resistor R23 is connected between the inverting input terminal of the OP amplifier 22 and the input terminal T1.

The inverting input terminal of the OP amplifier 22 has an AC signal VAC and a DC signal V output from the pyroelectric infrared sensor 1 via the input terminal T1 and the switch 31.
The input signal Vin including DC is input, and the DC signal VDC is input from the low-pass filter circuit 11 to the non-inverting input terminal of the OP amplifier 22, so that the differential amplifier circuit 21 receives the AC signal in the input signal Vin. Amplifies only VAC.

Reference numeral 31 denotes a switch, and the switch 31 comprises a first switching element 32 and a second switching element 33. The first switching element 32
Is connected between the infrared sensor 1 and the differential amplifier circuit 21, and the second switching element 33 is connected between the low-pass filter circuit 11 and the differential amplifier circuit 21. Further, the switching elements 32 and 33 are simultaneously opened in conjunction with each other,
Close.

Next, the operation of the signal processing device 10 for the pyroelectric infrared sensor will be described.

First, when the circuit (not shown) for operating the switching element 12 is turned on by turning on the power source of the signal processing device 10 for the pyroelectric infrared sensor, both ends of the resistor R11 are short-circuited. Therefore, the electric charge corresponding to the DC signal VDC of the input signal Vin can be quickly accumulated in the capacitor C11. Furthermore, after a certain period of time, the switching element 1
The low-pass filter circuit 11 can be quickly set to the operable state by turning OFF the switch 2.

Then, in the low pass filter circuit 11,
Since the frequency lower than the cutoff frequency in the input signal Vin can be considered as the direct current component, the direct current signal VDC as shown in FIG. 2B can be taken out. For example, when the low-pass filter circuit 11 is set to extract a frequency component of 0.1 (Hz) or less, the resistance R11 is set to approximately 2 (M
Ω), and the capacitance of the capacitor C11 may be as small as about 1 (μF). These circuit parts can be obtained at low cost, and a ceramic capacitor or a film capacitor having a small leakage current can be used as a capacitor, and the leakage current from the capacitor C11 can be suppressed. Further, the DC signal VDC is input to the non-inverting input terminal of the OP amplifier 22 of the differential amplifier circuit 21 by using the input resistor R21 having a resistance value sufficiently smaller than the input impedance of the OP amplifier 22. As a result, since this DC signal VDC can be considered to be a DC component of the input signal Vin, only the difference from the DC signal VDC, that is, the AC signal VAC in the input signal Vin, is the resistance R22, R.
It is amplified with an amplification factor α determined by the ratio of the resistance values of 23 (R22 / R23).

As a result, as shown in FIG. 2 (c), the output voltage Vout output from the differential amplifier circuit 21 is obtained by the equation (2).

[0054]

(Equation 2)

As described above, the output voltage Vout output from the differential amplifier circuit 21 becomes the second amplified signal obtained by amplifying only the AC signal VAC in the input signal Vin as shown in the first term of the equation 2.
The DC bias shown in section is added.

Therefore, the signal processing apparatus 10 according to the present embodiment.
Then, the input signal Vin input from the input terminal T1 is input to the low-pass filter circuit 11 and the differential amplifier circuit 21, and in the low-pass filter circuit 11, the DC component of the input signal Vin is set as the DC signal VDC. And the differential amplifier circuit 21 outputs the input signal Vin
Only the inside AC signal VAC is amplified by the amplification factor α of (R22 / R23), and then output to the outside as an added output voltage Vout with the DC signal VDC as a DC bias.

Therefore, the signal processing apparatus 10 according to the present embodiment.
Since it is composed of the low-pass filter circuit 11 and the differential amplifier circuit 21, the output obtained by amplifying only the AC component of the input signal Vin including the AC signal VAC and the DC signal VDC without using the coupling capacitor according to the conventional technique. It can be output as the voltage Vout. Moreover, unlike the prior art, since the coupling capacitor Ca is not used, even if the input signal Vin is a low frequency signal,
Accurate amplification corresponding to the input signal Vin can be performed with the amplification factor α of (R22 / R23). Further, since the coupling capacitor is not used, it is possible to use a feedback resistor having a small impedance, eliminate the impedance variation, and perform highly accurate amplification.

As a result, the output voltage Vout is the DC signal V
Although DC is added, only the AC signal VAC is amplified, so fluctuations in DC bias can be prevented,
A change in the peak value of the AC component corresponding to the amount of heat received by the pyroelectric infrared sensor 1 can be detected as a change in α × VAC.

Further, the resistance R of the low-pass filter circuit 11
Since the switching element 12 is connected to both ends of 11, the switching element 12 is closed when the signal processing device 10 is started up, so that the DC signal VDC stored in the capacitor C11 can be quickly supplied without passing through the resistor R11. Can
The low-pass filter circuit 11 can be quickly set to the operation start state.

If it is not necessary to make the pyroelectric infrared sensor signal processing device 10 operable immediately after the power is turned on, the switching element 12 may not be provided.

The switch 31 connects the front-stage and rear-stage differential amplifier circuits 21 each including the infrared sensor 1 and the low-pass filter circuit 11.
In the case of individual pieces, they may not be connected.

Next, the second embodiment will be described with reference to FIG. 3. The characteristics of the signal processing apparatus 10 'according to this embodiment are as follows.
A low-pass filter circuit is connected to each infrared sensor in order to amplify input signals input from a plurality of pyroelectric infrared sensors, and a signal for each infrared sensor and a signal from the low-pass filter circuit are respectively provided as one differential signal. The reason is that a plurality of switching elements are connected for input to the amplifier circuit.

In this embodiment, the same components as those in the prior art and the first embodiment described above are designated by the same reference numerals and the description thereof is omitted. However, in this embodiment, a plurality of pyroelectric elements are used. , 1n, and low-pass filter circuits 11a, 11b,
, 11n, and the description thereof is omitted.

In FIG. 3, 31a, 31b, ..., 31n denote switches as switching connection means, and the switches 31a.
˜31n are first switching elements 3 that connect the pyroelectric infrared sensors 1a to 1n and one differential amplifier circuit 21.
2a to 32n and low pass filter circuits 11a to 11n
And second switching elements 33a to 33n that connect the differential amplifier circuit 21 and the differential amplifier circuit 21.

Reference numeral 34 represents an oscillator, which generates a signal for sequentially switching the switches 31a to 31n at a predetermined frequency f0.

The basic operation of the signal processing device 10 'for a pyroelectric infrared sensor according to this embodiment, which is constructed in this way, is the same as that of the first embodiment.

The drain terminals of the pyroelectric infrared sensors 1a-1n are low-pass filter circuits 11a.
~ 11n. And the pyroelectric infrared sensor 1
Each low-pass filter circuit 1 connected to a to 1n
1a to 11n are in a state in which the operation can be swiftly switched by the switching operation of the switching element 12 described above.

Thereafter, the switches 31a to 31n are sequentially switched based on the frequency f0 of the oscillator 34 while synchronizing the first switching elements 32a to 32n and the second switching elements 33a to 33n. As a result, the input signal Vin and the DC signal VDC obtained from the plurality of pyroelectric infrared sensors 1a to 1n are sequentially input to one differential amplifier circuit 21. As a result, a plurality of pyroelectric infrared sensors 1a
Only the AC component of the input signal Vin obtained from 1n can be rapidly amplified by the single differential amplifier circuit 21.

Further, the low-pass filter circuits 11a to 11n having capacitors in front of the switches 31a to 31n.
Since one differential amplifier circuit 21 is provided in the subsequent stage, the capacitors C11 of the low-pass filter circuits 11a to 11n are always charged by the signals from the infrared sensors 1a to 1n. And the switch 31a
When the infrared sensors 1a to 1n and the low-pass filter circuits 11a to 11n are sequentially connected to the differential amplifier circuit 21 by switching between .about.31n, the low-pass filter circuit 11a.
Since the capacitors C11 of a to 11n are already charged, the input signal V input from the infrared sensors 1a to 1n
The output voltage Vout corresponding to in can be immediately obtained. Furthermore, the switches 31a to 31n by the oscillator 34
Even if the switching frequency f0 is increased, the charging time in the capacitor C11 of each of the low-pass filter circuits 11a to 11n becomes unnecessary.
You can get out.

Next, FIG. 4 and FIG. 5 show the third embodiment. The feature of this embodiment is that a buffer circuit is connected between the low-pass filter circuit and the differential amplifier circuit and the differential amplifier is used. This is because the inverting input terminal of the OP amplifier of the circuit was grounded.

In this embodiment, the same components as those in the first embodiment described above are designated by the same reference numerals and the description thereof will be omitted.

In the figure, reference numeral 40 denotes a signal processing device for a pyroelectric infrared sensor according to this embodiment. The signal processing device 40 is
The low-pass filter circuit 11 connected to the subsequent stage of the infrared sensor 1 includes a buffer circuit 41, which will be described later, connected via a switch 31, and a differential amplifier circuit 51.

Reference numeral 41 denotes a buffer circuit, which is composed of an OP amplifier 42 and resistors R41 and R42. Here, the non-inverting input terminal of the OP amplifier 42 is connected to the resistor R11 of the low-pass filter circuit 11 and the voltage dividing point A of the capacitor C11 via the resistor R41 and the second switching element 33. A resistor R42 is connected between the output terminal and the inverting input terminal of the OP amplifier 42, and the output voltage of the OP amplifier 42 is fed back to the inverting input terminal. The buffer circuit 41 can prevent the direct current signal VDC output from the low-pass filter circuit 11 and the alternating current signal VAC output from the differential amplifier circuit 51 from affecting each other and causing interference.

Reference numeral 51 denotes a differential amplifier circuit according to this embodiment. The differential amplifier circuit 51 includes an OP amplifier 52 and an OP amplifier 52.
The non-inverting input terminal of the amplifier 52 has an input resistor R51, a grounding resistor R52 connected between the connection point of the input resistor R51 and the non-inverting input terminal, and the ground, the output terminal of the OP amplifier 52, and the inverting input terminal. Negative feedback resistor R53 connected between
Input resistance R connected to the inverting input terminal of the OP amplifier 52
It consists of 54 and. The input resistance R51 and the ground resistance R52 form a series resistance circuit, and the non-inverting input terminal of the OP amplifier 52 is connected to the voltage dividing point B of the series resistance circuit.

Also in the signal processing device 40 for the pyroelectric infrared sensor of the present embodiment constructed as described above, it is possible to obtain the same effects as those of the first embodiment described above.

Therefore, in the present embodiment, the buffer circuit 41
Since the input impedance of is set to be extremely large, almost no current flows, and the operation that removes the mutual influence of the low-pass filter circuit 11 and the differential amplifier circuit 51 can be performed. That is, the DC signal VDC at the voltage dividing point A of the resistor R11 and the capacitor C11 of the low pass filter circuit 11 is shown in FIG.
With the characteristics shown in (b), by providing the buffer circuit 41, this DC signal VDC can be directly supplied to the input resistor R51 of the differential amplifier circuit 51.

Further, a divided voltage obtained by dividing the DC signal VDC by the input resistance R51 and the ground resistance R52 is input to the non-inverting input terminal of the OP amplifier 52 which constitutes the differential amplifier circuit 51. For this reason, the difference between the input signal Vin and the divided voltage of the DC signal VDC, which can be considered as a DC component, is the resistance R5.
It is amplified with an amplification factor determined by the resistance values of 1, R52, R53, and R54. The output voltage Vout after the amplification is obtained as shown in Expression 3.

[0078]

(Equation 3)

Here, the input resistors R51, R52, R53, R54
When the resistance values of R51 = R54 and R52 = R53 and the amplification factor β is (R53 / R54), the following expression 4 is obtained.

[0080]

(Equation 4)

Then, the signal processing device 40 according to the present embodiment.
From, it is possible to extract the output voltage Vout obtained by amplifying only the AC signal VAC with respect to the input signal Vin as shown in FIG. Therefore, the output voltage Vout has the characteristic shown in FIG.

Further, in the signal processing device 40 of this embodiment,
Since the buffer circuit 41 is connected between the low-pass filter circuit 11 and the differential amplifier circuit 51, the DC signal VDC output from the low-pass filter circuit 11 and the differential amplifier circuit 51 are connected.
It is possible to prevent signals from each other from interfering with each other and causing an electrical failure.

Further, the differential amplifier circuit 51 according to the present embodiment.
Is a DC signal VDC in the input signal Vin depending on its configuration.
Can be output as a signal obtained by amplifying only the AC signal VAC with the amplification factor β without adding to the output voltage Vout.

Next, a fourth embodiment will be described with reference to FIG. In this embodiment, the same components as those in the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

Therefore, the signal processing circuit 4 according to the present embodiment.
The feature of 0'is that low-pass filter circuits 11a to 11n are connected to each of the infrared sensors 1a to 1n in order to amplify the output signal Vs (input signal Vin) output from the plurality of pyroelectric infrared sensors 1a to 1n. , Infrared sensors 1a-1n
Input signal Vin from low-pass filter circuits 11a to 1
The DC signal VDC output from 1n is connected to one differential amplifier circuit 51 via a plurality of switches 31a to 31n. In addition, the low-pass filter circuit 1
The buffer circuit 41 is connected between 1a to 11n and the differential amplifier circuit 51.

In this embodiment having such a configuration, the first
Of the switch 31 while synchronizing the switching elements 32a to 32n and the second switching elements 33a to 33n.
a to 31n are sequentially switched. As a result, the input signal Vin obtained from the pyroelectric infrared sensors 1a to 1n and the DC signal VDC obtained from the low-pass filter circuits 11a to 11n are input to one buffer circuit 41 and one differential amplifier circuit 51, respectively. To be done. As a result, only the AC signal VAC of the input signal Vin obtained from the plurality of pyroelectric infrared sensors 1a to 1n is output to the outside as the output voltage Vout rapidly amplified by the common buffer circuit 41 and the differential amplifier circuit 51. be able to.

Next, FIG. 7 to FIG. 9 show a fifth embodiment of the present invention.
The present embodiment is characterized in that a DC bias addition circuit is connected to the next stage of the differential amplifier circuit.

In this embodiment, the same components as those in the above-mentioned respective embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 60 denotes a signal processing device for a pyroelectric infrared sensor according to this embodiment, and the signal processing device 60 is
Low-pass filter circuits 11a to 11n, which are respectively connected to the subsequent stages of the plurality of infrared sensors 1a to 1n, and the first switching elements 32a to 3 of the switches 31a to 31n.
One buffer circuit 41A connected to the infrared sensors 1a to 1n via 2n and another buffer connected to the low pass filter circuits 11a to 11n via the second switching elements 33a to 33n of the switches 31a to 31n. The circuit 41B, a differential amplifier circuit 21 connected to the buffer circuits 41A and 41B, and a DC bias adding circuit 61 as a DC bias adding means connected to the subsequent stage of the differential amplifier circuit 21 are generally configured. There is.

The switches 31a to 31n are connected to the oscillator 3
The switching frequency is set according to the frequency f0 output from No. 4.

Here, the low-pass filter circuit 11a
8 to 11n are low-pass filter circuits 11a and 11n shown in FIG.
As shown by two as n, the low-pass filter circuit 11 has the same configuration as that of the low-pass filter circuit 11 described in the first embodiment. That is, the low-pass filter circuit 11a is configured as an L-type low-pass filter circuit in which a resistor R11a and a capacitor C11a are connected in series, and the low-pass filter circuit 11n is also configured as an L-type low-pass filter circuit in which a resistor R11n and a capacitor C11n are connected in series. In all the low-pass filter circuits 11a to 11n, the resistors R11a to R11n have the same resistance value and the capacitors C11a to C11n have the same capacitance.

Further, the buffer circuits 41A and 41B are constructed similarly to the buffer circuit 41 described in the third embodiment, and the buffer circuit 41A is connected to the OP amplifier 42A and the non-inverting input terminal of the OP amplifier 42A. Resistor R41A
And a resistor R42A connected between the output terminal and the inverting input terminal of the OP amplifier 42A. Further, the buffer circuit 41B includes an OP amplifier 42B and an OP amplifier 4B.
A resistor R41B connected to the non-inverting input terminal of 2B and OP
It is composed of a resistor R42B connected between the output terminal and the inverting input terminal of the amplifier 42B. And the resistor R41A
And R41B and resistors R42A and R42B are set to have the same resistance value.

The differential amplifier circuit 21 is constructed similarly to the differential amplifier circuit 21 described in the first embodiment, and includes an OP amplifier 22, an input resistor R21, a negative feedback resistor R22, and another input resistor R23. It consists of

The differential amplifier circuit 21 obtains the output voltage Vout shown in the following equation 5 as in the equation 2, and the output voltage Vout has the characteristic shown in FIG. 9C.

[0095]

(Equation 5)

Next, the DC bias adding circuit 61 according to this embodiment will be described.

The DC bias adding circuit 61 includes an inverting amplifier circuit 63 having an OP amplifier 62 and a reference voltage circuit 64.
Consists of Here, the inverting amplifier circuit 63 has an input resistance R
61, resistor R62, negative feedback resistor R63 and other input resistor R64
It is composed of The input resistor R61 is connected to the non-inverting input terminal of the OP amplifier 62. Resistor R62
Is connected between a connection point of the input resistor R61 and the non-inverting input terminal and a reference voltage circuit 64 described later. The negative feedback resistor R63 is connected between the output terminal and the inverting input terminal of the OP amplifier 62. The other input resistor R64 is connected to the inverting input terminals of the differential amplifier circuit 21 and the OP amplifier 62. The input resistance R61 and the resistance R62 form a series resistance circuit, and the non-inverting input terminal of the OP amplifier 62 is connected to the voltage dividing point C of the series resistance circuit.

Reference numeral 64 indicates a reference voltage circuit, and the reference voltage circuit 64 directs the reference voltage Vre toward the inverting amplifier circuit 63.
It outputs f.

The additional circuit 61 thus constructed obtains an output signal Vout 'according to the following equation 6, and is shown in FIG.
It has the characteristics shown in (d).

[0100]

(Equation 6)

Then, by rearranging Equation 6, Equation 7 is obtained.

[0102]

(Equation 7)

Here, assuming that the resistance value R61 = R64,
Becomes

[0104]

(Equation 8)

As described above, in the DC bias load circuit 61, the DC signal V output from the low-pass filter circuit 11 is output from the output voltage Vout output from the differential amplifier circuit 21.
Since the DC is subtracted and the reference voltage Vref of the reference voltage circuit 64 is added, the output voltage Vout 'output from the signal processing circuit 60 is as shown in the equation (8).

Although the present embodiment is configured in this way, in the signal processing device 60 according to the present embodiment, the output voltage Vout 'does not depend on the DC signal VDC output from the low pass filter circuit 11 as shown in the equation (8). It can be output, and the fluctuation of the output voltage Vout can be suppressed.

Therefore, even if the DC signal VDC included in the output signal Vs varies for each infrared sensor 1a-1n,
Output voltage Vout ′ output from the signal processing device 60
Infrared sensor 1a-
An accurate output voltage Vout 'is obtained by changing the AC signal VAC every 1n.
Can be obtained as

Further, when the switches 31a to 31n are switched at the frequency f0, the infrared sensors 1a to 1n are switched.
When the difference of the DC signal VDC included in the input signal Vin input from is reduced, if the allowable value of this difference is ΔV, the allowable value ΔV is set to each value as defined by the following equation 9. Set.

[0109]

(Equation 9)

As described above, the switching frequency f0, the difference ΔVDC between the maximum value and the minimum value of the DC signal VDC, the amplification factors of the differential amplifier circuit 21 and the inverting amplifier circuit 63, and the resistance value Rf of the low-pass filter circuits 11a to 11n. By setting, it is possible to suppress the variation of the allowable value ΔV of the disparity within a small range and to switch the switches 31a to 31n at high speed.

Next, FIG. 10 shows a sixth embodiment according to the present invention. The feature of the signal processing circuit 60 'according to the present embodiment is that the position of the buffer circuit 41B is brought closer to the DC bias adding circuit 61 side. , OP of the differential amplifier circuit 21
Non-inverting input terminal of amplifier 22 and low-pass filter circuit 1
1 is connected via the second switching element 33.

The signal processing device 60 'constructed as described above.
In this case as well, the buffer circuits 41A and 41B can obtain the same effects as those of the fifth embodiment, and prevent electrical interference between the low-pass filter circuit 11 and the DC bias adding circuit 61. it can.

11 and 12 show the seventh embodiment according to the present invention. The signal processing device 70 according to the present embodiment is characterized in that the AC amplifying means has the differential amplification described in the third embodiment. This is because the circuit 51 is used and a DC bias adding circuit 71 as a DC bias adding means is provided at the final stage.

In this embodiment, the same components as those in the above-mentioned respective embodiments are designated by the same reference numerals and the description thereof will be omitted.

Here, the differential amplifier circuit 51 can obtain the output voltage Vout as shown in the following formula 10, and the output voltage Vout has the characteristic as shown in FIG. 12 (c).

[0116]

(Equation 10)

Next, the DC bias adding circuit 71
Similar to the embodiment described above, it is composed of an inverting amplifier circuit 73 having an OP amplifier 72 and a reference voltage circuit 74. Here, the inverting amplifier circuit 73 is composed of a resistor R71, a negative feedback resistor R72 and an input resistor R73. And the resistor R71
Is the non-inverting input terminal of the OP amplifier 72 and the reference voltage circuit 7.
4 is connected. The negative feedback resistor R72 is connected between the output terminal and the inverting input terminal of the OP amplifier 72. The input resistor R73 is connected to the inverting input terminals of the differential amplifier circuit 51 and the OP amplifier 72.

Then, the DC bias adding circuit 71 outputs the amplification factor γ (R72 / R7) to the input output voltage Vout.
It is possible to obtain the output voltage Vout 'which is obtained by adding the reference voltage Vref after the integration in 3).

As a result, the output voltage Vout 'output from the DC bias adding circuit 71 is as shown in equation 11, and the output voltage Vout' has the characteristic shown in FIG. 12 (d).

[0120]

[Equation 11]

As described above, in the DC bias adding circuit 71, since the reference voltage Vref from the reference voltage circuit 74 is added to the output voltage Vout output from the differential amplifier circuit 51, it is output from the signal processing device 70. Output signal Vou
t'is as shown in the above equation 11.

Therefore, the signal processing device 70 according to the present embodiment.
Then, the output signal Vout 'can be an output that does not depend on the DC signal VDC output from the low-pass filter circuit 11, as shown in the above-mentioned equation 11, and the infrared sensors 1a to 1n.
Even if the DC signal VDC in the output voltage Vout output from the differential amplifier circuit 51 varies each time, it is possible to prevent the output voltage Vout 'output from the DC bias adding circuit 71 from varying, and the infrared sensor 1a to. An accurate output signal Vout 'can be obtained every 1n.

Next, FIG. 13 shows an eighth embodiment of the present invention. The characteristics of the signal processing device 80 according to the present embodiment are as follows.
This is because an OP amplifier was used for the low-pass filter circuit.

In this embodiment, the same components as those in the above-mentioned respective embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 80 denotes a signal processing device according to this embodiment, and the signal processing device 80 is a low-pass filter circuit 8
1 and the differential amplifier circuit 51 described in the third embodiment.

Reference numeral 81 represents a low-pass filter circuit (low-pass filter circuit) as a DC component output means. The low-pass filter circuit 81 is connected between an OP amplifier 82 and an output terminal and an inverting input terminal of the OP amplifier 82. Resistor R81 and a capacitor C81 connected in parallel to the resistor R81
And an input resistor R82 connected between the non-inverting input terminal of the OP amplifier 82 and the input terminal T1.
The low pass filter circuit 81 can set the cutoff frequency by the resistance value of the resistor R81 and the electrostatic capacitance of the capacitor C81. The differential amplifier circuit 51 is connected to the output terminal of the OP amplifier 82.

The present embodiment is constructed in this way. Next, the operation of the signal processing device 80 according to the present embodiment will be described.

First, when the power source of the differential amplifier circuit 51 is turned on, the input signal Vin is input to the low-pass filter circuit 81, and the DC signal VDC having a frequency lower than a predetermined frequency in the input signal Vin is output from the OP amplifier 82. Taken from. The cutoff frequency fc is set according to the following equation by the resistance value of the resistor R81 and the electrostatic capacitance of the capacitor C81.

[0129]

(Equation 12)

Further, the OP amplifier 52 of the differential amplifier circuit 51
The divided voltage obtained by dividing the DC signal VDC by the input resistor R51 and the ground resistor R52 is input to the non-inverting input terminal of the. As a result, the difference between the input signal Vin and the divided voltage of the DC signal VDC, which can be considered as almost DC component, is the resistance R51, R52, R.
It is amplified at an amplification rate determined by the resistance values of 53 and R54.
Then, the output voltage Vout is obtained in the same manner as the equation 4, and the resistance values of the input resistors R51, R52, R53 and R54 are set to R51.
= R54 and R52 = R53, the output voltage Vout is given by the following Expression 13.

[0131]

(Equation 13)

Thus, even when the low-pass filter circuit 81 is used as in this embodiment, when the input signal Vin is input, the output voltage Vout obtained by amplifying only the AC signal VAC of the input signal Vin is taken out. be able to.

In each of the above embodiments, the low pass filter circuit 11 composed of the L type low pass filter circuit is used, but it goes without saying that the low pass filter circuit 81 shown in FIG. 13 may be used.

[0134]

As described in detail above, in the invention according to claim 1, the low-pass filter circuit outputs only the DC component in the input signal input from the pyroelectric infrared sensor, and the DC signal is output in the differential amplifier circuit. Based on the input signal input from the pyroelectric infrared sensor, only the AC signal in the input signal is output. With this, in the differential amplifier circuit, only the AC component in the input signal input from the pyroelectric infrared sensor can be output to the outside as an output signal without using the coupling capacitor according to the conventional technique.

In the invention according to claim 2, the low-pass filter circuit outputs only the direct-current component in the input signal input from the pyroelectric infrared sensor, and the differential amplifier circuit outputs this direct-current signal and the pyroelectric infrared sensor. Only the AC component is output based on the input signal that is input. Further, by adding a DC bias to the AC signal output from the differential amplifier circuit by the DC bias adding means, the DC bias adding means outputs not only the AC component signal but also the DC bias added output signal to the outside. Output. As a result, the output signal can be a signal that does not depend on the DC signal in the input signal, and fluctuations in the output signal can be suppressed.

According to the third aspect of the present invention, when a plurality of pyroelectric infrared sensors are provided, the low-pass filter circuit connected to each pyroelectric infrared sensor is included in the input signal input to each pyroelectric infrared sensor. Only the DC component is output, and the differential amplifier circuit outputs only the AC component based on each DC signal and each input signal input from each pyroelectric infrared sensor. As a result, the signal output from the differential amplifier circuit can be output to the outside as an output signal of only the AC component of the input signal input from the pyroelectric infrared sensor.

According to the fourth aspect of the present invention, when a plurality of pyroelectric infrared sensors are provided, the low-pass filter circuit connected to each pyroelectric infrared sensor is included in the input signal input to each pyroelectric infrared sensor. Only the DC component is output, and the differential amplifier circuit outputs only the AC component based on each DC signal and each input signal input from each pyroelectric infrared sensor. Further, by adding a DC bias to the AC signal output from the differential amplifier circuit by the DC bias adding means, the DC bias adding means outputs not only the AC component signal but also the DC bias added output signal to the outside. Output. As a result, the output signal can be a signal that does not depend on the DC signal in the input signal input from each pyroelectric infrared sensor, and the fluctuation of the DC component in each output signal can be suppressed, and the accurate Detection can be performed.

According to the fifth aspect of the invention, since the switching connection means is provided between the pyroelectric infrared sensor and the differential amplification circuit, and between the low-pass filter circuit and the differential amplification circuit, the switching connection means is operated. As a result, a plurality of pyroelectric infrared sensors and a low-pass filter circuit can be sequentially switched to the differential amplifier circuit. As a result, the differential amplifier circuit can output only the AC component in the input signals individually input from each pyroelectric infrared sensor as an output signal to the outside.

According to the sixth aspect of the present invention, since the DC bias adding means is composed of the inverting amplifier circuit including the OP amplifier and the reference voltage circuit, an AC signal is output from the reference voltage circuit from the output terminal of the inverting amplifier circuit. It is possible to output an output signal to which a direct current reference voltage is applied to the outside. As a result, the output signal can be a signal that does not depend on the DC signal in the input signal, and fluctuations in the output signal can be suppressed.

According to the invention of claim 7, if the low-pass filter circuit is constituted by connecting a resistor and a capacitor in series,
It is possible to cut off the AC component and output only the DC component.

According to the eighth aspect of the present invention, by connecting the switching element to both ends of the resistor forming the low-pass filter circuit, the switching element is closed at the start-up of the low-pass filter circuit, thereby interposing the resistor. Instead, a relatively large current flows into the capacitor, the charging time of the capacitor can be shortened, and the rise time of the low-pass filter circuit can be shortened.

When the low-pass filter circuit is constructed by using the OP amplifier as in the ninth aspect of the invention, the AC component can be cut off and only the DC component can be output.

According to the tenth aspect of the invention, the O of the differential amplifier circuit is
Since the inverting input terminal of the P amplifier is connected to the output side of the pyroelectric infrared sensor and the non-inverting input terminal of the OP amplifier is connected to the output side of the low pass filter circuit, the differential amplifier circuit can be configured as an inverting amplifier circuit. Even with this configuration, the differential amplifier circuit amplifies only the AC component of the input signal input from the pyroelectric infrared sensor, and outputs it as an output signal obtained by adding the DC signal to the AC signal. Can be output.

In the eleventh aspect of the invention, the differential amplifier circuit is
It is composed of an OP amplifier and a series resistance circuit connected between the output side of the low-pass filter circuit and ground, the inverting input terminal of the OP amplifier is connected to the output side of the pyroelectric infrared sensor, and the non-inverting input terminal is connected in series. Since it is connected to the voltage dividing point of the resistance circuit, the differential amplifier circuit can be configured as an inverting amplifier circuit, and of the input signals input from the pyroelectric infrared sensor, only the AC component is amplified and the DC signal is removed. It can be output to the outside as a signal.

According to the twelfth aspect of the invention, a buffer circuit is provided between the low-pass filter circuit and the differential amplifier circuit,
As in the invention of claim 13, a buffer circuit is provided between the pyroelectric infrared sensor and the differential amplifier circuit, and further, as in the invention of claim 14, between the low-pass filter circuit and the DC bias applying means. By providing the buffer circuit in the circuit, it is possible to prevent electric interference between signals between the circuits and reduce noise generation.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a signal processing device for a pyroelectric infrared sensor according to a first embodiment.

2 is a waveform diagram showing an input signal output from the pyroelectric infrared sensor in FIG. 1, a DC signal output from a low-pass filter circuit, and an output voltage output from a differential amplifier circuit, respectively.

FIG. 3 is a block diagram showing a signal processing device for a pyroelectric infrared sensor according to a second embodiment.

FIG. 4 is a circuit configuration diagram showing a signal processing device for a pyroelectric infrared sensor according to a third embodiment.

5 is a waveform diagram showing an input signal output from the pyroelectric infrared sensor in FIG. 4, a DC signal output from a low-pass filter circuit, and an output voltage output from a differential amplifier circuit.

FIG. 6 is a block diagram showing a signal processing device for a pyroelectric infrared sensor according to a fourth embodiment.

FIG. 7 is a block diagram showing a signal processing device for a pyroelectric infrared sensor according to a fifth embodiment.

FIG. 8 is a circuit configuration diagram showing a signal processing device for a pyroelectric infrared sensor according to a fifth embodiment.

9 is an input signal output from the pyroelectric infrared sensor in FIG. 8, a DC signal output from a low-pass filter circuit, an output voltage output from a differential amplifier circuit, and an output output from a DC bias addition circuit. It is a wave form diagram which shows each voltage.

FIG. 10 is a circuit configuration diagram showing a signal processing device for a pyroelectric infrared sensor according to a sixth embodiment.

FIG. 11 is a circuit configuration diagram showing a signal processing device for a pyroelectric infrared sensor according to a seventh embodiment.

12 is an input signal output from the pyroelectric infrared sensor in FIG. 11, a DC signal output from the low-pass filter circuit, an output voltage output from the differential amplifier circuit, and an output output from the DC bias adding circuit. It is a wave form diagram which shows each voltage.

FIG. 13 is a circuit configuration diagram showing a signal processing device for a pyroelectric infrared sensor according to an eighth embodiment.

FIG. 14 is a circuit diagram showing a sensing element and an impedance conversion circuit constituting a pyroelectric infrared sensor according to a conventional technique.

FIG. 15 is a circuit diagram of a conventional signal processing device for a pyroelectric infrared sensor.

FIG. 16 is a block diagram showing a signal processing device for a pyroelectric infrared sensor according to another conventional technique.

[Explanation of symbols]

1, 1a to 1n Pyroelectric infrared sensor 10, 10 ', 40, 40', 60, 60 ', 70, 8
0 signal processing device 11, 11a to 11n, 81 low-pass filter circuit 21, 51 differential amplifier circuit 31, 31a to 31n switching (switching connection means) 32, 32a to 32n first switching element 33, 33a to 33n second Switching element 41, 41A, 41B Buffer circuit 61, 71 DC bias addition circuit 63, 73 Inversion amplification circuit 64, 74 Reference voltage circuit

Claims (14)

[Claims] 1. A signal processing device for a pyroelectric infrared sensor, which outputs as an amplified signal of an input signal input from a pyroelectric infrared sensor, wherein a DC component in the input signal input from the pyroelectric infrared sensor is used. A low-pass filter circuit that outputs only the signal, and based on the DC signal output from the low-pass filter circuit and the input signal input from the pyroelectric infrared sensor, only the AC component in the input signal is amplified and output. Signal processing device for a pyroelectric infrared sensor. 2. A signal processing device for a pyroelectric infrared sensor, which outputs an amplified signal of an input signal input from the pyroelectric infrared sensor, wherein a DC component in the input signal input from the pyroelectric infrared sensor is used. A low-pass filter circuit that outputs only the signal, and based on the DC signal output from the low-pass filter circuit and the input signal input from the pyroelectric infrared sensor, only the AC component in the input signal is amplified and output. And a DC bias adding means that is connected to the next stage of the differential amplifier circuit and that adds a DC bias to the AC signal output from the differential amplifier circuit. Signal processing device for electric infrared sensor. 3. A signal processing device for a pyroelectric infrared sensor, which outputs an amplified signal of each input signal input from a plurality of pyroelectric infrared sensors, wherein the signal is input from each of the pyroelectric infrared sensors. Based on a plurality of low-pass filter circuits that output only the DC component in the input signal, individual DC signals output from each low-pass filter circuit, and individual input signals input from each of the pyroelectric infrared sensors And a single differential amplifier circuit that amplifies and outputs only the alternating current component of the input signal, and a signal processing device for a pyroelectric infrared sensor. 4. A signal processing device for a pyroelectric infrared sensor, which outputs an amplified signal of each input signal inputted from a plurality of pyroelectric infrared sensors, wherein the signal is inputted from each of the pyroelectric infrared sensors. Based on a plurality of low-pass filter circuits that output only the DC component in the input signal, individual DC signals output from each low-pass filter circuit, and individual input signals input from each of the pyroelectric infrared sensors A differential amplifier circuit that amplifies and outputs only the AC component of the input signal and a DC signal that is connected to the next stage of the differential amplifier circuit and that is the AC component signal output from the operation amplifier circuit. A signal processing device for a pyroelectric infrared sensor, comprising: a DC bias applying means for applying a bias. 5. A switching connecting means for switching and connecting between the pyroelectric infrared sensor and the differential amplifier circuit and between the low-pass filter circuit and the differential amplifier circuit, respectively. The signal processing device for a pyroelectric infrared sensor according to 1, 2, 3 or 4. 6. The DC bias applying means comprises an inverting amplifier circuit including an OP amplifier and a reference voltage circuit for applying a reference voltage as a bias, and an inverting input terminal of the inverting amplifier circuit is the differential amplifier circuit. Connect to the output side of
The signal processing device for a pyroelectric infrared sensor according to claim 2 or 4, wherein a non-inverting input terminal of the inverting amplifier circuit is connected to an output side of the reference voltage circuit and an output side of a low-pass filter circuit. 7. The low-pass filter circuit is located between the output side of the pyroelectric infrared sensor and the ground, and comprises a resistor and a capacitor connected in series.
The signal processing device for a pyroelectric infrared sensor according to 3, 4, 5 or 6. 8. A switching element is connected to both ends of a resistor forming the low-pass filter circuit.
A signal processing device for a pyroelectric infrared sensor as described above. 9. The low-pass filter circuit includes an OP amplifier, a resistor connected between an output terminal and an inverting input terminal of the OP amplifier, and a capacitor connected in parallel to the resistor. The non-inverting input terminal of the amplifier is connected to the output side of the infrared sensor.
The signal processing device for a pyroelectric infrared sensor according to 4, 5, or 6. 10. The differential amplifier circuit is composed of an OP amplifier, the inverting input terminal of the OP amplifier is connected to the output side of the pyroelectric infrared sensor, and the non-inverting input terminal is connected to the output side of the low-pass filter circuit. Claims 1, 2 which are connected
The signal processing device for a pyroelectric infrared sensor according to 3, 4, 5 or 6. 11. The differential amplifier circuit includes an OP amplifier,
It is composed of a series resistance circuit connected between the output side of the low-pass filter circuit and ground, the non-inverting input terminal of the OP amplifier is connected to the voltage dividing point of the series resistance circuit, and the inverting input terminal of the infrared sensor is connected. 7. The signal processing device for a pyroelectric infrared sensor according to claim 1, wherein the signal processing device is connected to the output side. 12. A buffer circuit is provided between the low-pass filter circuit and the differential amplifier circuit.
2. A signal processing device for a pyroelectric infrared sensor according to 2, 3, 4, 5 or 6. 13. A buffer circuit is provided between the pyroelectric infrared sensor and a differential amplifier circuit.
The signal processing device for a pyroelectric infrared sensor according to 3, 4, 5 or 6. 14. The signal processing device for a pyroelectric infrared sensor according to claim 2, wherein a buffer circuit is provided between the low-pass filter circuit and the DC bias applying means.