JP2003227753A - Circuit and device for detection of infrared rays - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize an infrared detection circuit and an infrared detection device containing the circuit. <P>SOLUTION: The infrared detection circuit is constituted of a current-voltage conversion circuit 2 in which a capacitor Cf is connected across an inverting input terminal and an output terminal of an operational amplifier 21, and in which a resistance circuit element Z is connected in series with the capacitor Cf; a voltage amplifier circuit 3 composed of an inverting amplifier circuit connected to the output side of the circuit 2; a band-pass filter circuit 4 connected to the output side of the circuit 3; and an output circuit 5 connected to the output side of the circuit 4. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detection circuit and an infrared detection device.

[0002]

2. Description of the Related Art As shown in FIG. 15, a conventional infrared detecting device includes a pyroelectric element 100 for detecting infrared rays radiated from a human body and a current voltage for converting a detection current signal of the pyroelectric element 100 into a voltage signal. The conversion circuit 200 and the current-voltage conversion circuit 200 are provided with a coupling capacitor C30, and the voltage amplification circuit 300, the low-pass filter 400, the high-pass filter 500, and the amplification circuit 6 are sequentially provided on the output side thereof.
00 and the output circuit 700 are connected.

The current-voltage conversion circuit 200 includes a pyroelectric element 10
FET (field effect transistor) with 0 connected to the gate
or) and a resistor R connected in parallel to both ends of the pyroelectric element 100.
g, and a resistor Rs interposed between the source of the FET and the ground. Low pass filter 40
The 0 and high-pass filter 500 are composed of switched capacitors.

The infrared detector constructed as described above operates as follows. The detected current signal output from the pyroelectric element 100 is converted into a voltage signal by the resistor Rg, and F
It is applied to the gate of ET, which causes a drain current to flow from the source to the drain. A source voltage is generated across the resistor Rs by the drain current flowing.
The DC voltage component of this source voltage is cut by the coupling capacitor C30, and then the voltage amplification circuit 300
After being amplified by the amplification factor (1 + R20 / R10), the low-pass filter 400 and the high-pass filter 500 handle it as a voltage signal of a predetermined frequency band component in which high-frequency components and low-frequency components are cut. Then, this voltage signal is amplified by the amplifier circuit 600 with a set gain, and the output circuit 700 compares the voltage signal with a predetermined level to output as a detection signal.

[0005]

However, the coupling capacitor C30 needs to have a large capacity in order to pass the frequency component around 1.0 Hz which represents the movement of the human body and the like, so that a large capacitor. Must be used. Large capacitors are difficult to integrate, so they had to be attached externally. Such an external coupling capacitor C30 has been a major obstacle to downsizing or integration of the infrared detection device.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an infrared detecting device which can be downsized by eliminating external parts.

[0007]

The invention according to claim 1 is
A current-voltage conversion circuit in which a circuit for feeding back a DC component and a capacitor are connected in parallel between the output terminal and the inverting input terminal of the first operational amplifier connected to the pyroelectric element, and output from the current-voltage conversion circuit A first amplifier circuit for amplifying a voltage signal to be generated, and a bandpass filter circuit configured to include a switched capacitor filter, for passing a predetermined frequency band component of the voltage signal from the first amplifier circuit,
A reference clock generation circuit that outputs a reference clock signal of a predetermined frequency to the switched capacitor filter, and an output circuit that outputs a detection signal when the voltage signal output from the bandpass filter circuit is equal to or higher than a threshold level are provided. Characterize.

According to the present invention, the detected current signal output from the pyroelectric element is converted into a voltage signal by the capacitor and output from the output terminal of the first operational amplifier. The DC wave component of the output voltage signal is fed back to the inverting input terminal by the circuit for feeding back the DC component. for that reason,
The fluctuation of the DC component of the output voltage signal is suppressed and the operating point is stabilized. As a result, a coupling capacitor for cutting the variation of the operating point is not required on the output side of the current-voltage conversion circuit, and the circuit is downsized.

According to a second aspect of the invention, in the infrared detection circuit according to the first aspect, a second amplifier circuit is connected between the bandpass filter circuit and the output circuit. According to the present invention, the voltage signal output from the bandpass filter circuit is amplified to a predetermined amplitude level by the second amplifier circuit and guided to the output circuit to set the threshold level of the output circuit to a corresponding value. As a result, the detection accuracy can be improved.

According to a third aspect of the present invention, in the infrared detection circuit according to the first aspect, a high pass filter having a predetermined gain is connected between the band pass filter circuit and the output circuit. According to this invention,
The voltage signal output from the bandpass filter circuit has a low-frequency component cut by the highpass filter and is guided to the output circuit. Therefore, the fluctuation of the operating point by the bandpass filter circuit is cut. Since the high-pass filter has a predetermined gain, a voltage signal having a gain in a desired frequency band is guided to the output circuit in the subsequent stage, so that the detection accuracy of the output circuit can be further improved.

According to a fourth aspect of the present invention, in the infrared detection circuit according to any of the first to third aspects, the bandpass filter circuit has a structure in which at least three or more filters are connected in multiple stages, A high-pass filter and a low-pass filter are alternately connected.
According to the present invention, in the voltage signal output from the first amplifier circuit, the high-pass filter in the first stage cuts the fluctuation of the operating point, and the low-pass filters connected in the second and subsequent stages cut high-frequency components. It Then, the high-pass filter connected to the third and subsequent stages cuts the variation of the operating point due to the feedthrough noise generated when the switched capacitor is switched. for that reason,
A voltage signal in which fluctuations in the operating point have been cut and folding noise has been cut off is introduced to the output circuit.

According to a fifth aspect of the present invention, in the infrared detecting circuit according to the fourth aspect, the low-pass filter has a predetermined gain. According to this configuration, by connecting a plurality of low-pass filters and distributing the gains to the respective low-pass filters, a large gain as a band-pass filter circuit is suppressed while suppressing a large fluctuation of the operating point of the low-pass filters. Is obtained. As a result, it is not necessary to connect an amplifier circuit or the like to the subsequent stage of the bandpass filter circuit, and the circuit can be downsized.

According to a sixth aspect of the present invention, in the infrared detection circuit according to any one of the first to third aspects, the bandpass filter circuit includes a lowpass filter in a front stage and a highpass filter in a rear stage. To do. According to the present invention, the high-frequency component included in the voltage signal output from the first amplifier circuit is intensively cut by the low-pass filter connected in the preceding stage, so that the occurrence of aliasing noise is suppressed.

According to a seventh aspect of the invention, in the infrared detection circuit according to any of the first to sixth aspects, the current-voltage conversion circuit has a switched capacitor. According to the present invention, it is possible to equivalently make a resistance material having a high resistance by switching a small capacitor in a current-voltage conversion circuit with a clock signal, and the current-voltage conversion device is small and has excellent temperature characteristics. The circuit is obtained.

According to an eighth aspect of the present invention, in the infrared detection circuit according to any one of the first to seventh aspects, the infrared detection circuit is connected between the switched capacitor and the reference clock generation circuit and is higher than the reference clock signal. A clock signal control circuit that is connectable to an external clock generation circuit that generates an external clock signal of a frequency and that switches the reference clock signal and the external clock signal is provided. According to the present invention, it becomes possible to supply a clock signal having a frequency different from that during normal operation to the switched capacitor filter of the bandpass filter circuit. For example, by supplying a clock signal with a higher frequency than the clock signal during normal operation as the external clock signal,
The frequency characteristic of the circuit slides to the high frequency side. Therefore, the high-frequency clock signal is supplied to the switched capacitor filter, and the frequency characteristic can be inspected quickly, so that the inspection time is shortened.

According to a ninth aspect of the present invention, in the infrared detection circuit according to any one of the first to eighth aspects, the circuit for feeding back the DC component is composed of a resistance element. According to the present invention, since the circuit for feeding back the DC component is configured by the resistance element, the configuration is simple,
The operating point of the voltage signal output from the first operational amplifier can be stabilized.

According to a tenth aspect of the invention, in the infrared detection circuit according to any one of the first to eighth aspects, the circuit for feeding back the DC component is an integrating circuit. According to the present invention, since the circuit for feeding back the DC component is constituted by the integrating circuit, the signal components other than the DC are largely attenuated and fed back, and the operating point of the output voltage signal can be further stabilized. it can.

The invention according to claim 11 is defined by claims 1 to 10.
In the infrared detection circuit according to any one of the above,
Of the second operational amplifier is connected to the inverting input terminal of the second operational amplifier via a resistor for amplification, and
A low-pass filter is connected between the output terminal and the non-inverting input terminal of the second operational amplifier.

According to the present invention, the voltage signal output from the output terminal of the first operational amplifier is branched into two, one of which is input to the inverting input terminal of the second operational amplifier through the resistor for amplification. , The other is passed through a low-pass filter, high-frequency components are removed, and the result is input to the non-inverting input terminal of the second operational amplifier. Therefore, of the voltage signals output from the current-voltage conversion circuit, the voltage signal having a frequency component lower than the cutoff frequency of the low-pass filter is input to the inverting input terminal and the non-inverting input terminal of the second operational amplifier in the same phase. Therefore, the output from the first amplifier circuit is not amplified. On the other hand, a voltage signal having a frequency component higher than the cutoff frequency of the low-pass filter is not input to the non-inverting input terminal of the second operational amplifier, so that the potential of the non-inverting input terminal is not changed, and as a result, the first The amplified signal is amplified and output. Therefore, the voltage signal in the low frequency band that saturates the first amplifier circuit is not amplified by the first amplifier circuit, so that the leakage current generated at the inverting input terminal of the first operational amplifier during the predetermined period after the power is turned on. Due to the influence of 1, the saturation of the second amplifier circuit caused by the change of the operating point of the voltage signal output from the current-voltage conversion circuit is prevented.

According to a twelfth aspect of the present invention, in the infrared detection circuit according to the eleventh aspect, the low-pass filter is
A first resistor connected between the output terminal of the first operational amplifier and the non-inverting input terminal of the second operational amplifier; and a capacitor connected to the ground side of the non-inverting input terminal. It is characterized by being provided.

According to the present invention, the low-pass filter can be constructed with a simple configuration of the capacitor and the resistance section.

According to a thirteenth aspect of the present invention, in the infrared detection circuit according to the twelfth aspect, the first switch control section is provided, and the low-pass filter circuit is connected in parallel to the first resistance section. A switch circuit, the first
The switch control unit controls the first switch circuit.

According to the present invention, immediately after the power is turned on, the first
The switch circuit is turned on in accordance with an instruction from the first switch control unit, and the first resistance unit connected in parallel with the first switch circuit is short-circuited. Therefore, immediately after the power is turned on, the low-pass filter has a small time constant and an increased cutoff frequency. as a result,
In the voltage signal output from the current-voltage circuit, the low-frequency band component that saturates the first amplifier circuit is surely cut and guided to the first amplifier circuit. Saturation of the first amplifier circuit due to fluctuations is more reliably prevented.

According to a fourteenth aspect of the present invention, in the infrared detection circuit according to the twelfth or thirteenth aspect, the first resistance portion is an impurity non-diffused polysilicon resistance element.

According to the present invention, since the first resistance portion forming the low pass filter is formed of the impurity non-diffused polysilicon resistance element, the low pass filter can be integrated.
Therefore, the infrared detection circuit can be configured with zero external components.

According to a fifteenth aspect of the present invention, in the infrared detection circuit according to the fourteenth aspect, the second switch control section is provided, and the low-pass filter is a second impurity non-diffusing polysilicon resistor element connected in series. A resistor section and a second switch circuit are connected in parallel to the first resistor section, and the second switch control section turns on the second switch circuit when the atmosphere is at a low temperature. Characterize.

According to the present invention, since the second resistance portion is composed of the impurity non-diffused polysilicon resistance element,
The resistance value increases when the second resistance portion is in a low temperature state. Then, when the resistance value exceeds a certain value, the second switch control section turns on the second switch circuit, and the second resistance section is turned on. That is, the low-pass filter has a configuration in which the first and second resistance portions are connected in parallel at a low temperature, and the time constant becomes small, so that the cutoff frequency increases. Therefore, when the temperature is low, the low frequency band component that saturates the first amplifier circuit is surely cut and guided to the first amplifier circuit, and the saturation of the first amplifier circuit at low temperature is prevented.

According to a sixteenth aspect of the present invention, in the infrared detection circuit according to the fifteenth aspect, the second switch control section includes an equivalent resistance composed of a switched capacitor and a resistance of the impurity non-diffusing polysilicon resistor element. The second switch is controlled by using the divided voltage.

According to the present invention, when the atmosphere has a low temperature,
The resistance of the impurity non-diffused polysilicon resistor element is increased, and the resistance voltage division works to turn on the second switch,
Switch circuit is turned on. That is, since the change in the resistance value of the impurity non-diffused polysilicon resistor is detected using the impurity non-diffused polysilicon resistor, the change in the resistance value due to the temperature characteristic of the impurity non-diffused polysilicon resistor can be accurately detected.
In addition, since the impurity non-diffused polysilicon resistor element is used, the circuit can be integrated.

The invention as defined in claim 17 is defined in claims 11 to 1.
7. The infrared detection circuit according to any one of 6 above, wherein one reference voltage circuit for generating a reference voltage is connected to the non-inverting input terminals of the pyroelectric element and the first and second operational amplifiers. To do. According to the present invention, the reference voltage supplied to the pyroelectric element and the reference voltage supplied to the non-inverting input terminals of the first and second operational amplifiers are configured by one reference voltage circuit. It is possible to cancel the amplification of the noise component that affects the output, and reduce the noise.

The invention according to claim 18 is the same as claim 1
The infrared detection circuit described in any one of 17 is integrated into one semiconductor chip. According to the present invention, the infrared detection circuit becomes compact.

The invention according to claim 19 is the invention according to claims 1 to 18.
An infrared detection device comprising a pyroelectric element connected to the infrared detection circuit according to any one of 1. According to this invention, since the miniaturized infrared detection circuit is provided, the infrared detection device is miniaturized.

[0033]

1 is an exploded perspective view showing the structure of an infrared detecting device. The infrared detection device includes a disk-shaped base 11 having three lead wires 12 connected to the lower surface, and a disk-shaped printed wiring board 16 mounted on the upper surface of the base 11 via two crosspieces 17. A bottomed cylinder for covering the printed wiring board 16 with the pyroelectric element 1 having a square light receiving surface mounted substantially in the center of the printed wiring board 16 and having an optical filter window 14 on the upper bottom. And a dome-shaped can 13 and a large-diameter condenser lens (multi-lens) 15 mounted on the upper bottom of the can 13.

The infrared rays radiated from the human body, which have passed through the lens 15 and the optical filter window 14, are
It is incident on the pyroelectric element 1. An infrared detection circuit that performs signal processing on the detected current signal is integrated and mounted on the back surface of the printed wiring board 16.

(First Embodiment) FIG. 2 is a circuit diagram of the infrared detection circuit shown in the first embodiment. The infrared detection circuit includes a current-voltage conversion circuit 2 that converts a current signal from the pyroelectric element 1 into a voltage signal, and a voltage amplification circuit 3 (first amplification circuit) connected to the output side of the current-voltage conversion circuit 2. And a bandpass filter circuit 4 connected to the output side of the voltage amplification circuit 3 and an output circuit 5 connected to the output side of the bandpass filter circuit 4.

When the temperature of the pyroelectric element 1 rises due to the radiated heat rays, polarization charge is generated according to the temperature rise,
This polarized charge is output as a detection current signal.

The current-voltage conversion circuit 2 includes an operational amplifier 21 to which one end of the pyroelectric element 1 is connected to the inverting input terminal, and a feedback capacitor connected between the output terminal of the operational amplifier 21 and the inverting input terminal. Cf and a resistance circuit element Z connected in parallel to the feedback capacitor Cf, and a reference voltage Vr for setting the operating point of the output voltage signal between the non-inverting input terminal of the operational amplifier 21 and the ground. Is connected to the power supply unit E. Current-voltage conversion circuit 2
Is composed of the operational amplifier 21 and performs negative feedback using the resistance circuit element Z, so that the fluctuation of the operating point is suppressed. Therefore, the coupling capacitor for cutting the fluctuation of the operating point is unnecessary, and the circuit can be downsized.

Further, a capacitor Cf is connected to the current-voltage conversion circuit 2 and, from the current signal output from the pyroelectric element 1, 0.1 Hz-which is important for detection of the human body.
A current signal having a frequency component near 1.0 Hz is converted into a voltage signal by this capacitor Cf. In a conventional current-voltage conversion circuit, a resistance element is used to convert a current signal output from a pyroelectric element into a voltage signal. Since the resistance element generates thermal noise, if current-voltage conversion is performed using the resistance element, a large amount of noise will be included in the converted voltage signal. On the other hand, unlike a resistance element, a capacitor theoretically does not generate thermal noise. Therefore, in the voltage signal converted by the current-voltage conversion circuit 2, the noise component is significantly reduced.

The voltage amplification circuit 3 is an inverting amplification circuit,
The inverting input terminal has a resistor R at the output terminal of the current-voltage conversion circuit 2.
Operational amplifier 31 connected through 1 and operational amplifier 3
The resistor R interposed between the output terminal of 1 and the inverting input terminal
2 and the power supply section E for outputting the reference voltage Vr for setting the operating point of the output voltage signal is connected to the non-inverting input terminal of the operational amplifier 31.

Since the operational amplifier 21 has an extremely low output impedance, it is not necessary to consider the input impedance of the circuit connected to the output terminal of the operational amplifier 21. Therefore, an inverting amplifier circuit having a low input impedance is configured as the voltage amplifier circuit 3 and connected to the output terminal of the operational amplifier 21.

Although the inverting amplifier circuit is used as the voltage amplifier circuit 3 in the present embodiment, conversely, when the non-inverting amplifier circuit is used, it is connected to the inverting input terminal of the operational amplifier 31 in order to set the operating point. It is necessary to connect the power supply section between the gain resistance and the ground, and when the power supply section is connected in this way, current flows through the power supply section and the voltage drop caused by the internal resistance of the power supply section causes the power supply section to Becomes unstable. For this reason, a power supply unit must be connected separately from the power supply unit E connected to the pyroelectric element 1 and the current-voltage conversion circuit 2.
On the other hand, when the voltage amplifying circuit 3 is formed of an inverting amplifying circuit as in the present embodiment, the power supply section E can be directly connected to the non-inverting input terminal of the operational amplifier 31, and the non-inverting input terminal is also provided. Has a high input impedance, no current flows through the power supply unit E, and no voltage drop occurs due to the internal resistance of the power supply unit E. Therefore, the reference potential of the inverting amplifier circuit can be stabilized. Therefore, the power supply section E can be shared by the current-voltage conversion circuit 2 and the voltage amplification circuit 3, and the circuit becomes smaller accordingly. In addition, by configuring the voltage source that supplies the reference potential to the current-voltage conversion circuit 2 and the voltage amplification circuit 3 with one voltage source E, the reference potential supplied to the current-voltage conversion circuit 2 and the reference supplied to the voltage amplification circuit 3. Since the electric potential and the electric potential are exactly the same, the operating points of both circuits become exactly the same, and the fluctuation of the operating point can be sufficiently suppressed without providing a coupling capacitor between both circuits.

The bandpass filter circuit 4 is composed of a switched capacitor filter in order to miniaturize the circuit, and is important for detecting a human body.
The voltage signal in the frequency band of 0 Hz is output with a predetermined gain. The resistance part of the switched capacitor filter is composed of, for example, a capacitor and a switching element such as a MOSFET (see FIG. 4). A clock generation circuit 4a for driving the switching element is connected to the switching element. The switching element is turned on / off in response to the clock signal from the clock generation circuit 4a. This causes the capacitor to be repeatedly charged and discharged, and the capacitor equivalently functions as a resistance element. Also in the embodiments described below, the switched capacitor operates by the clock signal from the clock generation circuit 4a. When the frequency (sampling frequency) of the clock signal given to the switching element is f and the capacitance of the capacitor is C, the equivalent resistance value R of the switched capacitor is represented by R = 1 / f · C.

In this way, the bandpass filter circuit 4
, Is composed of a switched capacitor filter, if the input voltage signal contains many high frequency components,
Folding noise may occur. Here, the current-voltage conversion circuit 2 performs current-voltage conversion by the capacitor Cf, and the impedance of the capacitor Cf is 1 /
Since it is represented by (2π · f · Cf), the higher the frequency, the smaller the value. Therefore, the high frequency component of the converted voltage signal is greatly attenuated, and the high frequency component of the voltage signal input to the bandpass filter circuit 4 is reduced. As a result, aliasing noise in the bandpass filter circuit 4 is suppressed.

The output circuit 5 is composed of, for example, a comparator, compares the voltage signal output from the bandpass filter circuit 4 with a predetermined threshold level, and outputs a detection signal when the voltage level is equal to or higher than the threshold level. It has become.

The infrared detecting device operates as follows. The detected current signal output from the pyroelectric element 1 is input to the current-voltage conversion circuit 2, and the current signal having a frequency component near 0.1 to 1.0 Hz, which is important for human body detection, is the impedance component 1 of the capacitor Cf. / (2π ・ f ・ C
It is converted into a voltage signal by f). Therefore, the high frequency component is cut and the S / N ratio is improved. Next, the voltage signal converted by the current-voltage conversion circuit 2 is amplified by R2 / R1 times by the voltage amplification circuit 3, and then 0.1-1.0 by the bandpass filter circuit 4.
The component of the frequency band of Hz is extracted. Here, since the high-frequency component is cut by the current-voltage conversion circuit 2, the aliasing noise generated in the bandpass filter circuit 4 is suppressed. Next, the output circuit 5 compares the magnitude with the threshold level and outputs a detection signal.

As described above, according to the infrared detection circuit of the first embodiment, the coupling capacitor used in the conventional infrared detection circuit can be omitted, and the pyroelectric element 1 and the current-voltage conversion circuit 2 can be omitted. Since the power supply unit E connected to the voltage amplification circuit 3 can be shared, the circuit can be downsized. Further, by the current-voltage conversion circuit 2,
Since the high frequency component is cut off, the aliasing noise generated in the bandpass filter circuit 4 is suppressed.

(Second Embodiment) FIG. 3 is a circuit diagram of an infrared detection circuit according to the second embodiment. The infrared detection circuit is characterized in that an amplifier circuit 6 (second amplifier circuit) is provided between the bandpass filter circuit 4 and the output circuit 5. The amplifier circuit 6 is a non-inverting amplifier circuit, and is connected between an operational amplifier 61 having a non-inverting input terminal connected to the output terminal of the bandpass filter circuit 4, and an output terminal of the operational amplifier 61 and an inverting input terminal. Resistance R3
And a resistor R4 connected to the inverting input terminal, and a power supply unit E for setting the operating point to a predetermined level is connected between the resistor R4 and the ground.

In the detection of human body and living body,
Since the signal component in the 1.0 Hz frequency band is important,
The band pass filter circuit 4 has a peak frequency of 1.0H.
The frequency characteristic is set so as to be in the vicinity of z. Therefore, the bandpass filter circuit 4 causes 0.1H
Signal components in the frequency band near z are attenuated. Therefore, in order to detect the attenuated signal component around 0.1 Hz, the threshold level of the output circuit 5 must be set to a low level. Then, the influence of noise or the like cannot be ignored, and the possibility of false detection increases. If the voltage signal in the frequency band near 0.1 Hz is attenuated by, for example, 20 dB by the bandpass filter circuit 4 (the amplitude of the output signal is 1/10 of the input signal), the output circuit In order for 5 to accurately compare the voltage signal with the threshold level and output the detection signal, the attenuation of 20 dB of the bandpass filter circuit 4 is allowed,
The amplitude level of the voltage signal output from the voltage amplifier circuit 3 must be multiplied by 10 × threshold level. 10x
In order to secure the output voltage having the amplitude level of the threshold level, it is necessary to set the power supply voltage level of the operational amplifier 31 to at least 10 × threshold level. This power supply voltage level depends on the operational amplifier 31 used. Although it depends on the characteristics, it is usually about 15 V, and the power supply voltage level of the operational amplifier 31 has a certain limit. On the other hand, by setting the threshold level of the output circuit 5 small, the operational amplifier 31
It is possible to keep the power supply voltage level of the low level, but if the threshold level is set low, the output circuit 5 may output a detection signal even for a noise signal with a small amplitude, and the low threshold level is set. There is also a certain limit to setting. Therefore, the threshold level is usually set to about 1/2 of the power supply voltage level of the operational amplifier 31.
However, in this case, the amplitude of the voltage signal in the frequency band near 0.1 Hz is halved by the bandpass filter circuit 4.
If it is attenuated below, the output circuit 5 cannot output the detection signal.

Therefore, in the current-voltage conversion circuit according to the second embodiment, the amplifier circuit 6 is connected between the bandpass filter circuit 4 and the output circuit 5, and the amplitude of the voltage signal attenuated by the bandpass filter circuit 4 is increased. The above problem is solved by amplifying the level to a threshold level.

As described above, according to the infrared detection circuit of the second embodiment, the amplifier circuit 6 is connected between the bandpass filter circuit 4 and the output circuit 5, and the voltage output from the bandpass filter circuit 4 is connected. The detection accuracy of the output circuit 5 is improved by amplifying the attenuation of the amplitude level of the signal to a level equivalent to the threshold level.

(Third Embodiment) FIG. 4 is a circuit diagram of an infrared detection circuit showing a third embodiment. The present infrared detection circuit has a high pass filter 7 connected between a band pass filter circuit 4 and an output circuit 5. The high pass filter 7 has an inverting input terminal connected to the output side of the band pass filter circuit 4 via a capacitor C1, and a capacitor C2 connected between the output terminal of the operational amplifier 71 and the inverting input terminal. And a switched capacitor SC connected in parallel with the capacitor C2. By adopting the switched capacitor SC, the circuit is downsized as described in the first embodiment. A power supply section E is connected to each of the non-inverting input terminal of the operational amplifier 71 and the switched capacitor SC. The gain in the pass band of the high-pass filter is represented by the capacitance ratio C1 / C2, so C1 and C
A desired gain can be obtained by setting the capacitance ratio of 2.

In the second embodiment, the effectiveness of providing the amplifier circuit 6 between the bandpass filter circuit 4 and the output circuit 5 has been described. However, if the amplification factor (gain) of the amplifier circuit 6 is set to be large, the bandpass filter Since the offset component of the operating point in the output of the filter circuit 4 is amplified by this amplification factor, the operating point of the output voltage signal may vary greatly.

Therefore, by connecting the high-pass filter 7 having a gain between the band-pass filter circuit 4 and the output circuit 5 to cut off the low-frequency component of the voltage signal output from the band-pass filter circuit 4, The fluctuation of the operating point is suppressed. Further, since the voltage signal of the frequency component of 0.1 to 1.0 Hz is amplified to the threshold level and output, the detection accuracy of the output circuit 5 is improved.

As described above, according to the infrared detection circuit of the third embodiment, the fluctuation of the operating point of the voltage signal output from the high-pass filter 7 is suppressed, and at the same time, 0.1 to 1.0 can be obtained.
Since the frequency component of Hz is amplified to the threshold level and output, the detection accuracy of the output circuit 5 is improved. Further, since the switched capacitor SC is used as the resistance portion of the high pass filter 7, the circuit can be downsized and the temperature characteristic can be stabilized.

(Fourth Embodiment) FIG. 5 is a circuit diagram of an infrared detection circuit showing a fourth embodiment. This infrared detection circuit is 0.1H which is an important frequency band for human body detection.
A band-pass filter in which a high-pass filter and a low-pass filter each composed of a switched capacitor filter are alternately connected in a predetermined number of stages as a band-pass filter circuit for the purpose of more accurately extracting a signal component near z to 1.0 Hz. The circuit 41 is adopted.
That is, a total of five high-pass filters 411, low-pass filters 412, high-pass filters 413, low-pass filters 414, and high-pass filters 415 are connected in order from the output side of the voltage amplification circuit 3. These filters form filters for extracting signal components necessary for human body detection, and also have the following functions.

The first-stage high-pass filter 411 suppresses fluctuations in the operating point by cutting low-frequency components contained in the voltage signal output from the voltage amplifier circuit 3. The second-stage low-pass filter 412 has 1.0
The voltage signal in the frequency band of Hz or less is output with a predetermined gain.

The high pass filters 413 and 415 connected to the third and fifth stages cut the low frequency components of the voltage signals output from the low pass filters 412 and 414 connected to the second and fourth stages. This suppresses fluctuations in the operating point. Bandpass filter circuit 4
In order to increase the value of the resistor forming 1 and to perform integration, it is necessary to reduce the capacitance of the capacitor used in the switched capacitor filter. However, if the capacitance of the capacitor is reduced, switching operation by a pulse signal is performed. The effect of feedthrough noise that sometimes occurs cannot be ignored. That is, when the capacitance of the capacitor is reduced, the feedthrough noise increases the offset component of the operational amplifier, and as a result, the operating point of the voltage signals output from the low-pass filters 412 and 414 varies greatly. Become. Therefore, the high-pass filters 413 and 4 connected to the third and fifth stages
By reducing the low frequency component by 15, the fluctuation of the operating point is suppressed.

In the case where the bandpass filter circuit 41 is constructed by using, for example, one lowpass filter and the lowpass filter has a large gain (in this case, the bandpass filter circuit 41 includes the highpass filter 411 and the lowpass filter 412). And the high pass filter 413), the DC component may be greatly amplified, and the voltage signal output from the low pass filter 412 may be saturated. Therefore, the bandpass filter circuit 41 disperses the gains in the respective lowpass filters 412 and 414 to prevent the voltage signals output from the lowpass filters 412 and 414 from being saturated, and at the third and fifth stages. With the connected high-pass filters 413 and 415, 2
By reliably cutting the fluctuations of the operating points generated in the low-pass filters 412 and 414 of the fourth and fourth stages,
The fluctuation of the operating point is greatly suppressed. In addition, when the low-pass filters 412 and 414 are provided with dispersed gains, the switched capacitors of the low-pass filters 412 and 414 can be composed of small-capacity capacitors,
The circuit can be miniaturized.

As described above, according to the infrared detection circuit of the fourth embodiment, since the low-pass filters are connected in multiple stages to disperse the gain, the saturation of the low-pass filters is prevented and the output voltage signal is output. It can have a high gain. Therefore, the voltage signal output from the bandpass filter circuit 41 can be guided to the output circuit 5 without being amplified. As a result, there is no need to provide an amplifier circuit or the like in the subsequent stage, and the circuit can be downsized. Further, since the high-pass filters are connected before and after each low-pass, it is possible to more reliably suppress the fluctuation of the operating point caused by the feedthrough noise.

(Fifth Embodiment) FIG. 6 is a circuit diagram of an infrared detection circuit according to the fifth embodiment. In the infrared detection circuit, the bandpass filter circuit 42 is composed of a lowpass filter 421 connected to the first stage and a highpass filter 422 connected to the second stage. First
As described in the embodiment, since the current-voltage conversion circuit 2 performs the current-voltage conversion using the capacitor Cf, the aliasing noise generated in the bandpass filter circuit 4 is reduced. However, with this alone, it is difficult to completely suppress the generation of aliasing noise. Therefore, in the sixth embodiment, a low-pass filter 421 is arranged at the first stage of the band-pass filter circuit 42, the high-pass component of the voltage signal is cut by the low-pass filter 421, and the high-pass filter 422 is guided to the switched-capacitor 422. It suppresses the generation of aliasing noise due to Further, by the high-pass filter 422 connected in the latter stage,
Since the variation of the operating point is cut, the variation of the operating point is suppressed.

As described above, according to the fifth embodiment, it is possible to more reliably suppress the generation of folding noise.

(Sixth Embodiment) FIG. 7 is a circuit diagram of an infrared detection circuit according to the sixth embodiment. The present infrared detection circuit is characterized by the current-voltage conversion circuit 22. That is, the current-voltage conversion circuit 22 includes an operational amplifier 221 having the inverting input terminal to which the pyroelectric element 1 is connected, and an operational amplifier 221.
The resistor Ri and the DC feedback circuit (integrator circuit) DF are connected in parallel to the capacitor Cf connected between the output terminal and the inverting input terminal. DC feedback circuit D
F is an operational amplifier 223 having an output terminal of the operational amplifier 221 connected to its non-inverting input terminal, and a capacitor C connected between the inverting input terminal and the output terminal of the operational amplifier 223.
3 and a resistor R5 connected to the capacitor C3. Further, a power supply unit E for setting the operating point at a predetermined level is connected between the resistor R5 and the ground. According to the current-voltage conversion circuit 22, since the output from the operational amplifier 221 is fed back by using the DC feedback circuit DF, the AC component is attenuated and fed back, and the operating point of the voltage signal to be output is set. Can be more stable. As a result, the operating point can be stabilized even if the coupling capacitor is omitted.

As described above, according to the infrared detection circuit of the sixth embodiment, the DC / DC feedback circuit D is added to the current / voltage conversion circuit 22.
Since F is connected, the fluctuation of the operating point of the output voltage signal is reduced, and stable current-voltage conversion is possible.

FIG. 8 shows the pyroelectric element 1000 and the current-voltage conversion circuit 10 of the infrared detector according to the embodiment of the present invention.
01 is a circuit diagram showing a voltage amplification circuit 1002 and a voltage amplification circuit 1002. In the infrared detection circuit of FIG. 8, the pyroelectric element 1000,
Two reference voltage circuits 1003 and 1004 are used as reference voltage circuits for applying a reference voltage for setting the operating points of the current-voltage conversion circuit 1001 and the voltage amplification circuit 1002. The reference voltage circuit 1003 is connected to one end of the pyroelectric element 1000. The reference voltage circuit 1004 includes a non-inverting input terminal of the operational amplifier 1011 and the operational amplifier 1012.
It is connected to the non-inverting input terminal of.

Since the pyroelectric element 1000 is externally attached to the integrated infrared detection circuit, the pyroelectric element 100
There is a risk that noise may enter from the contact point between 0 and the current-voltage conversion circuit 1001. Therefore, if the reference voltage circuit for applying the reference voltage to the pyroelectric element 1000 and the current-voltage conversion circuit 1001 and the voltage amplification circuit 1002 is configured by one reference voltage circuit, the current due to the influence of noise mixed from the contacts Voltage conversion circuit 1001, voltage amplification circuit 1
The operation of 002 becomes unstable. Therefore, in the infrared detection device of FIG. 8, the pyroelectric element 1000 and the current-voltage conversion circuit 10
01 and the reference voltage circuit for applying the reference voltage to the voltage amplifier circuit 1002 are separate circuits. However, with this configuration, the following problems occur.

When the noise voltage constantly output by the reference voltage circuit 1003 is Vn1 and the noise voltage constantly output by the reference voltage circuit 1004 is Vn2, the operational amplifier 1012 is shown.
Noise voltage Vn1, Vn2 for the voltage signal output by
The value contributed by is shown in equation (1).

Vn1 × {(Cs + Cf10) / Cf10} × (−R300 / R200) + Vn1 × (R200 + R300) / R200 + Vn2 × (−Cs / Cf10) × (−R300 / R200) = Vn1− (R300 / R200) × (Cs / Cf10) × (Vn1-Vn2) (1) Here, Cs represents the capacitance component of the pyroelectric element. Here, since the voltage amplification circuit 3 has a gain of several tens of times, R300 / R200 has a very large value.
Further, if the capacitance component Cs becomes sufficiently large, the noise voltage will be further amplified.

On the other hand, if the reference voltage circuits 1003 and 1004 are used in common, Vn1 = Vn2, so that the second term on the right side of the equation (1) is erased and only Vn1 remains. Therefore, as in the infrared detection device of the sixth embodiment, the pyroelectric element 1 and the reference voltage circuit for applying the reference voltage to the current-voltage conversion circuit 22 and the voltage amplification circuit 3 are provided by one circuit (power supply unit E). With this configuration, the contribution of the noise voltage of the power supply unit E to the voltage signal output from the voltage amplification circuit 3 is suppressed regardless of the gain of the voltage amplification circuit 3 and the size of the capacitance component of the pyroelectric element 1. Becomes In addition, in the present invention, by removing the coupling capacitor, it is possible to configure the current-voltage conversion circuit 2 to the output circuit 5 in one chip.
The influence of external noise will be mitigated, and the influence of external noise will be reduced even if the reference voltage circuit is configured using one power supply unit E.

(Seventh Embodiment) FIG. 9 is a circuit diagram of an infrared detection circuit according to the seventh embodiment. In the infrared detection circuit, in the current-voltage conversion circuit 22 shown in the sixth embodiment, the resistors Ri and R5 are connected to the switched capacitor SC.
It is configured by. A frequency component in the vicinity of 0.1 to 1.0 Hz is important in detecting a human body and a living body, and in order to handle such a low frequency signal, a resistor Ri and a resistor R5 of the current-voltage conversion circuit are formed by a high resistance element. Must be configured. Since the high resistance element has a large temperature characteristic, the resistance value greatly changes even with a slight temperature change, which becomes a barrier in performing stable current-voltage conversion.

Therefore, in the infrared detection circuit according to the seventh embodiment, as the resistors Ri and R5 of the current-voltage conversion circuit 2, the switched capacitor SC having a high resistance and an excellent temperature characteristic is used. Has been resolved.

As described above, in the infrared detection circuit of the seventh embodiment, stable current-voltage conversion is performed by using the switched capacitor SC having high resistance as well as excellent temperature characteristics as the resistance material of the current-voltage conversion circuit 23. It will be possible.

(Eighth Embodiment) FIG. 10 is a circuit diagram of an infrared detection circuit showing an eighth embodiment. In the infrared detection circuit of the eighth embodiment, the bandpass filter circuit 4 is connected with a clock control circuit 8 and a clock generation circuit 4a via the clock control circuit 8. Clock control circuit 8
To the external clock generator 1 via the external input terminal P1.
0a is connected, and the control unit 10b is connected via the clock switching terminal P2.

The clock control circuit 8 supplies the clock signal from the clock generation circuit 4a and the clock signal from the external clock generation unit 10a to the bandpass filter circuit 4 according to the clock switching signal input from the control unit 10b. Is selectively switched and output.

The clock generation circuit 4a is for generating a clock signal having a frequency during the normal operation of the infrared detection circuit, which is supplied to the switching element of the switched capacitor of the infrared detection circuit. External clock generator 1
0a is for generating a clock signal to be supplied to the switching element of the switched capacitor at the time of shipping inspection. The frequency of this clock signal is set to, for example, 100 times the frequency of the clock signal generated by the clock generation circuit 4a.

This is 1.0 Hz in the detection of the human body.
Since the frequency component in the vicinity is important, the frequency of the clock signal generated by the clock generation circuit 4a is set so as to determine the equivalent resistance value R of the switched capacitor so as to have the frequency characteristic near 1.0 Hz. This is because the switched capacitor is operated using the clock signal. That is, since the infrared detection circuit is set to have a frequency characteristic near 1.0 Hz, the characteristic inspection requires at least 1 second, and the shipping inspection requires a long time.

On the other hand, when the switched capacitor is operated by the clock signal having the frequency 100 times generated by the external clock generator 10a, the frequency characteristic slides to around 100 Hz, so that the time required for the characteristic inspection is reduced to 1 / 100 seconds can be shortened.

Next, the operation will be described. Control unit 10b
When the clock switching signal is output from the clock control circuit 8, the clock control circuit 8 switches the connection to the external clock generator 10a,
The clock signal of the external clock generator 10a is supplied to the bandpass filter circuit 4, and the switched capacitor is operated by the external clock signal. Then, the control unit 10b
When the clock switching signal is output from the clock control circuit 8, the clock control circuit 8 switches the connection to the clock generation circuit 4a, supplies the clock signal of the clock generation circuit 4a to the bandpass filter circuit 4, and the clock generated in the clock generation circuit 4a. The switched capacitor is operated by a signal, that is, a clock signal during normal operation.

As described above, according to the infrared detection circuit of the eighth embodiment, the clock control circuit 8 is provided and the switched capacitor is operated by the high-frequency clock signal generated by the external clock generator 10a at the time of shipping inspection. The characteristic inspection time can be shortened.

(Ninth Embodiment) FIG. 11 shows a main part including a current-voltage conversion circuit 22 and a voltage amplification circuit 3 of an infrared detection circuit of a ninth embodiment. This infrared detection circuit is the same as the infrared detection circuit of the sixth embodiment except that a low-pass filter 80 is connected between the output terminal of the operational amplifier 221 and the non-inverting input terminal of the operational amplifier 31.

When the power is turned on, a minute leak current is generated in the inverting input terminal of the operational amplifier 221, but since the input impedance of the inverting input terminal is very high, the leak current causes an output from the current-voltage conversion circuit 22. The operating point of the generated voltage signal greatly varies from the operating point in the steady state. The changed operating point fluctuates, and eventually becomes an operating point in a steady state and stabilizes. This fluctuation of the operating point causes saturation of the voltage amplifier circuit 3. Since a signal component in the vicinity of 0.1 Hz to 1.0 Hz is important in human body detection, the current-voltage conversion circuit 2 converts the current signal in this band into a voltage signal using the capacitor Cf. For that purpose, the resistance Ri and the resistance R5 in FIG. 11 need to be high resistance, but generally, when trying to integrate the high resistance, manufacturing variations and temperature characteristics are often large. In that case, in order to convert the frequency band of 0.1 Hz to 1.0 Hz into a voltage signal by the capacitor Cf even in consideration of resistance value variations and temperature characteristics, in order to convert the frequency characteristics of the conversion impedance in the current-voltage conversion circuit 2, The frequency characteristic of the current-voltage conversion circuit 2 must be set so that the peak frequency becomes a value much smaller than 0.1 Hz, for example, several mHz. Therefore, since the time constant of the current-voltage conversion circuit 22 becomes very large, the period until the operating point stabilizes becomes long, and as a result, the voltage amplification circuit 3 saturates for a while (several minutes) after the power is turned on. Then, the problem that the circuit does not respond occurs. Therefore,
In the ninth embodiment, the above problem is solved by using the low pass filter 80.

The low pass filter 80 includes a resistor R6 (first
Resistance element) and a capacitor C4. Resistance R
6 is connected between the output terminal of the operational amplifier 221 and the non-inverting input terminal of the operational amplifier 31. The resistor R6 is
It is an impurity non-diffused polysilicon resistor element. Capacitor C4
Has one end connected to the non-inverting input terminal of the operational amplifier 31 and the other end grounded via the power supply unit E. The voltage signal output from the operational amplifier 221 is branched into two, one is directly input to the inverting input terminal of the operational amplifier 31 through the resistor R1, and the other is input to the inverting input terminal of the operational amplifier 31 through the low-pass filter 80. It is input to the non-inverting input terminal.

The voltage signal that has passed through the low-pass filter 80 has its frequency component higher than the cutoff frequency removed, and is input to the non-inverting input terminal of the operational amplifier 31. Therefore, the potential of the non-inverting input terminal is not changed by this high frequency component.

Among the voltage signals output from the operational amplifier 221, the voltage signal having a frequency component lower than the cutoff frequency of the low pass filter 80 has the same phase with respect to the inverting input terminal and the non-inverting input terminal of the operational amplifier 31. Since it is input, it is not amplified by the voltage amplification circuit 3. On the other hand, among the voltage signals output from the operational amplifier 221, the voltage signal higher than the cutoff frequency component of the low-pass filter 80 is input only to the inverting input terminal, and is amplified by the voltage amplifier circuit 3. Therefore, a signal having a frequency lower than the cutoff frequency that causes saturation of the voltage amplification circuit 3 is not amplified by the voltage amplification circuit 3, so that the voltage amplification circuit 3 is not saturated.

As described above, according to the infrared detection circuit of the ninth embodiment, since the low-pass filter 80 is connected to the non-inverting input terminal of the operational amplifier 31, the power is turned on for a predetermined time.
It is possible to prevent saturation of the voltage amplification circuit 3 caused by fluctuations in the operating point of the voltage signal output from the current-voltage conversion circuit 22.

(Tenth Embodiment) FIG. 12 is a circuit diagram showing a main part including a current-voltage conversion circuit 22 and a voltage amplification circuit 3 of an infrared detection circuit according to a tenth embodiment. The infrared detection circuit has a low-pass filter 81 connected between the current-voltage conversion circuit 22 and the voltage amplification circuit 3. The low pass filter 81 is connected to the resistors R8, R9, the switch S81, and the switch control circuit 90. The resistors R8 and R9 are connected between the output terminal of the operational amplifier 221 and the non-inverting amplification terminal of the operational amplifier 31. The switch S81 is connected in parallel with the resistor R8. Here, the resistance value of each of the resistors R8 and R9 is set to a value smaller than the resistance value of the resistor R6 shown in FIG. Further, as the resistors R8 and R9, impurity non-diffused polysilicon resistor elements are used.

The switch control circuit 90 controls the switch S81 so that the switch S81 is turned on for a predetermined time after the power is turned on, and the switch S81 is turned off after a predetermined time elapses. The switch control circuit 90 is composed of a circuit capable of measuring time, for example, a counter, and when the power is turned on, the switch S81 is turned on to start the counting operation. Then, when the count value of this counter reaches a preset value, the switch S81 is turned off. For the switch S81, it is preferable to use a switching element made of a semiconductor in order to integrate the circuit.

When the power is turned on, the switch control circuit 9
0 turns on the switch S81. As a result, the resistor R8 is short-circuited. Therefore, the low pass filter 81
The time constant of is determined by the capacitor C4 and the resistor R9. As a result, the time constant of the low-pass filter 81 becomes smaller than that when the switch S81 is off, and the cut-off frequency of the low-pass filter 81 becomes high.

As the resistors R8 and R9, an impurity non-diffusing polysilicon resistor element is used for the purpose of circuit integration, but this impurity non-diffusing polysilicon resistor element has a very large temperature characteristic. The low-pass filter 80 shown in FIG. 11 is set to have a small cutoff frequency so as to cope with the change in the resistance value due to the temperature characteristic.
Therefore, there is a possibility that the voltage signal in the low frequency band that causes saturation of the voltage amplification circuit 3 is sufficiently cut and cannot be guided to the voltage amplification circuit 3 in a predetermined time after the power is turned on.

Therefore, in the infrared detection circuit of the tenth embodiment, the saturation of the voltage signal is prevented by using the low-pass filter 81 which can reduce the time constant within a predetermined time after the power is turned on.

(Eleventh Embodiment) FIG. 13 is a circuit diagram showing a main part including a current-voltage conversion circuit 22 and a voltage amplification circuit 3 of an infrared detection circuit of the eleventh embodiment. This infrared detection circuit includes a current-voltage conversion circuit 22 and a voltage amplification circuit 3
A low-pass filter 82 is connected between and.
The low-pass filter 82 is different from the low-pass filter 81 of the tenth embodiment in further including a switch S82 and a resistor R10. A switch control circuit 91 for controlling the switch S82 is connected to the switch S82. The switch S82 and the resistor R10 are connected in series and are connected in parallel to the resistors R8 and R9. Impurity non-diffused polysilicon resistor elements are used for the resistors R8, R9, and R10. A semiconductor switching element is used for the switch S82.

The switch control circuit 91 controls the switch S82 so that the switch S82 is turned on when the ambient temperature becomes equal to or lower than a predetermined temperature. As a result, the resistor R10 is energized, and the time constant of the low pass filter 82 is the combined resistance value of the resistors R8, R9 and R10 and the capacitor C4.
Is determined by the capacitance of. The resistor R10 is connected in parallel to the resistors R8 and R9 which are connected in series. Therefore, the combined resistance value of the resistors R8, R9, and R10 becomes smaller than the sum of the resistance value of the resistor R8 and the resistance value of the resistor R9. Therefore, the switch S82
When is turned on, the time constant of the low-pass filter 82 becomes small.

Since the impurity non-diffused polysilicon resistor has a characteristic that its resistance value increases as the temperature becomes lower, the resistance values of the resistors R8 and R9 increase when the atmosphere becomes lower, and as a result, the low-pass filter. The time constant of 81 increases and the cutoff frequency decreases. Therefore, the voltage signal in the low frequency band that causes saturation of the voltage amplification circuit 3 may be introduced to the voltage amplification circuit 3 without being sufficiently cut.

Therefore, in the infrared detection circuit of the eleventh embodiment, the low-pass filter 82 which can reduce the time constant at low temperature is used to prevent the voltage amplifier circuit 3 from being saturated due to low temperature.

FIG. 14 shows a circuit diagram of the switch S82 and the switch control circuit 91. The switch S82 is
p (positive) type MOSFET (metal oxide semicond
a switch 821 composed of an uctor field effect transistor) and a switch 822 composed of an n (negative) type MOSFET. The switch control circuit 91 includes a control circuit 911 that controls the switch 821 and a control circuit 912 that controls the switch 822.

The control circuit 911 includes a resistor R11, a switched capacitor SC1 and a switched capacitor SC2. The resistor R11 is an impurity non-diffused polysilicon resistor element, one end of which is connected to the voltage source VCC and the other end of which is connected to the voltage dividing terminal GP. A switched capacitor SC1 and a switched capacitor SC2 are sequentially connected to the voltage dividing terminal GP. Switched capacitor SC1
Is composed of switching elements SC11, SC12 and a capacitor C5. Switched capacitor SC
2 is composed of switching elements SC12, SC13 and a capacitor C6.

One end of the capacitor C5 is grounded, and the other end is connected between the switching elements SC11 and SC12. Further, one end of the capacitor C6 is grounded, and the other end is connected between the switching elements SC12 and SC13.

Switching elements SC11 and SC13
Receives a clock signal via the terminal CA. The switching element SC12 has a terminal CA via a terminal CB.
A clock signal having a phase opposite to that of the clock signal input to is input. As a result, the switching element SC11
And SC12 are alternately turned on / off and the switching elements SC12 and SC13 are alternately turned on / off, so that the switched capacitors SC1 and SC2 are turned on and off.
Functions as a switched capacitor. The equivalent resistance of the switched capacitor is R = 1 / fC, where f is the frequency of the clock signal input to the switching element.
It is represented by. In this embodiment, C5 = C6 = 0.5p
Since the frequency of the clock signal input to F, terminals CA and CB is set to f = 100 Hz, the equivalent resistance of each of the switched capacitors SC1 and SC2 is 20 GΩ. The voltage dividing terminal GP is connected to the gate of the switch 821.

The control circuit 912 includes switched capacitors SC3 and SC4 and a resistor R12. One end of the switched capacitor SC3 is connected to the voltage source VCC,
The other end is connected to the switched capacitor SC4.
The resistor R12 is an impurity non-diffused polysilicon resistor, one end of which is connected between the switched capacitor SC4 and the voltage dividing terminal GN, and the other end of which is grounded. The switched capacitor SC3 is composed of switching elements SC31, SC32 and a capacitor C7. The switched capacitor SC4 is composed of switching elements SC32, SC33 and a capacitor C8. A clock signal is input to the switching elements SC31 and SC33 via the terminal CA. The switching element SC32 has a terminal CB.
A clock signal having a phase opposite to that of the clock signal input to the terminal CA via is input.

The equivalent resistances of the switched capacitors SC3 and SC4 are set to 20 GΩ respectively, like the switched capacitors SC1 and SC2. This control circuit 9
In No. 11, since the equivalent resistance of the switched capacitor SC1 and the equivalent resistance of the switched capacitor SC2 are connected in series, the equivalent resistance of the switched capacitor SC1 and the switched capacitor SC2 is 40 GΩ. Similarly, the equivalent resistance of the switched capacitors SC3 and SC4 is 40
It becomes GΩ. Therefore, the resistance R11 = R12 = 40G
If it is set to Ω, the potentials of the voltage dividing terminals GP and GN are ½ VCC under normal ambient temperature. When the temperature becomes low, the resistance values of the resistors R11 and R12 increase, so that the potential of the voltage dividing terminal GP decreases and the potential of the voltage dividing terminal GN increases. As a result, the switch 821 and the switch 822 are turned on, and the resistor R10 becomes conductive.

As described above, according to the infrared detection circuit of the eleventh embodiment, the switch S82 and the resistor R10 are connected in parallel to the resistors R8 and R9, and the switch control circuit 91 for turning on the switch S82 at a low temperature. Since the voltage signal in the low frequency band that causes the saturation of the voltage amplification circuit 3 is not amplified by the voltage amplification circuit 3 at low temperature, the saturation of the voltage amplification circuit 3 can be prevented.

In addition, in FIG. 2 to FIG. 6 and FIG.
As a circuit that feeds back the DC component of the current-voltage conversion circuit,
Although the resistance circuit element Z is used, the present invention is not limited to this, and an integration circuit (DC feedback circuit) may be used instead of the resistance circuit element Z. In this case, signal components other than direct current are largely attenuated and fed back, and the operating point of the output voltage signal is further stabilized.

[0102]

According to the first aspect of the present invention, since the circuit for feeding back the DC component is connected, the coupling capacitor becomes unnecessary and the circuit can be downsized.

According to the second aspect of the invention, the detection accuracy of the output circuit can be improved.

According to the third aspect of the present invention, the fluctuation of the operating point due to the bandpass filter circuit can be cut.

According to the fourth aspect of the present invention, it is possible to introduce the voltage signal in which the fluctuation of the operating point is cut and the folding noise is cut to the output circuit.

According to the invention of claim 5, the detection accuracy of the output circuit can be further improved.

According to the invention described in claim 6, it is possible to obtain a large gain as a bandpass filter while suppressing the fluctuation of the operating point. As a result, the circuit can be downsized.

According to the invention described in claim 7, it is possible to suppress the generation of folding noise.

According to the eighth aspect of the present invention, since the current-voltage conversion circuit is composed of the switched capacitor, stable current-voltage conversion can be performed.

According to the ninth aspect of the invention, it is possible to supply the switched capacitor filter with a clock signal having a frequency different from that in the normal operation.

According to the tenth aspect of the invention, the infrared detection circuit can be downsized.

According to the eleventh aspect of the invention, the infrared detecting device can be made compact.

According to the twelfth aspect of the present invention, the operating point of the voltage signal output from the first operational amplifier can be stabilized while having a simple structure.

According to the thirteenth aspect of the present invention, the signal components other than the direct current are largely attenuated and fed back, and the operating point of the output voltage signal can be further stabilized.

According to the fourteenth aspect of the present invention, it is possible to prevent the saturation of the first amplifier circuit when the power is turned on.

According to the fifteenth aspect of the present invention, the voltage signal in which the fluctuation of the operating point is small and folding noise is cut can be guided to the output circuit, and the voltage signal is generated in a predetermined period after the power is turned on. It is possible to prevent saturation of the No. 1 amplifier circuit.

According to the sixteenth aspect of the invention, the infrared detecting circuit can be constructed with the external parts as 0.

According to the seventeenth aspect of the present invention, it is possible to more reliably prevent the first amplifier circuit from being saturated for a predetermined period after the power is turned on.

According to the eighteenth aspect of the present invention, it is possible to prevent the saturation of the first amplifier circuit due to the fluctuation of the operating point during the low temperature operation.

According to the nineteenth aspect of the present invention, it is possible to reliably detect the variation in the resistance value due to the temperature characteristic, and also to make the second switch control unit compact.

According to the twentieth aspect of the invention, it is possible to further reduce the influence of the noise voltage of the reference voltage circuit on the voltage signal output from the first amplifier circuit.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an infrared detection device according to the present invention.

FIG. 2 is a circuit diagram of an infrared detection circuit according to the first embodiment.

FIG. 3 is a circuit diagram of an infrared detection circuit showing a second embodiment.

FIG. 4 is a circuit diagram of an infrared detection circuit showing a third embodiment.

FIG. 5 is a circuit diagram of an infrared detection circuit showing a fourth embodiment.

FIG. 6 is a circuit diagram of an infrared detection circuit showing a fifth embodiment.

FIG. 7 is a circuit diagram of an infrared detection circuit showing a sixth embodiment.

FIG. 8 is a diagram showing one infrared detection circuit according to the present invention.

FIG. 9 is a circuit diagram of an infrared detection circuit showing a seventh embodiment.

FIG. 10 is a circuit diagram of an infrared detection circuit showing an eighth embodiment.

FIG. 11 is a circuit diagram showing a main part including a current-voltage conversion circuit and a voltage amplification circuit of an infrared detection circuit according to a ninth embodiment.

FIG. 12 is a circuit diagram showing a main part including a current-voltage conversion circuit and a voltage amplification circuit of an infrared detection circuit of a tenth embodiment.

FIG. 13 is a circuit diagram showing a main part including a current-voltage conversion circuit and a voltage amplification circuit of the infrared detection circuit of the eleventh embodiment.

FIG. 14 is a circuit diagram of a switch control circuit.

FIG. 15 is a diagram showing a conventional infrared detection circuit.

[Explanation of Codes] Cf C1 C2 C3 capacitor Z resistance circuit element SC SC1 SC2 SC3 SC4 switched capacitor SC11 SC12 SC31 SC32 switching element E power supply unit R1 to R12 Ri resistance 1 pyroelectric element 2 22 23 current-voltage conversion circuit 3 voltage amplification circuit (First amplifier circuit) 4 41 42 Bandpass filter circuit 4a Clock generation circuit 5 Output circuit 6 Amplifier circuit (second amplifier circuit) 8 Clock control circuit 412 414 Lowpass filter 411 413 415 Highpass filter 421 Lowpass filter 422 Highpass filter 80 81 82 Low-pass filter 90 91 Switch control circuit SC11 SC12 SC13 Switching element SC31 SC32 SC33 Switching element 9 Oscillation circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuji Takada             1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works             Within the corporation F term (reference) 2G065 AA04 AB02 BA13 BC03 BC40

Claims (19)

[Claims] 1. A current-voltage conversion circuit in which a circuit for feeding back a DC component and a capacitor are connected in parallel between an output terminal and an inverting input terminal of a first operational amplifier connected to a pyroelectric element; A bandpass filter circuit that includes a first amplifier circuit that amplifies a voltage signal output from the voltage conversion circuit and a switched capacitor filter, and that passes a predetermined frequency band component of the voltage signal from the first amplifier circuit. A reference clock generation circuit that outputs a reference clock signal of a predetermined frequency to the switched capacitor filter, and an output circuit that outputs a detection signal when the voltage signal output from the bandpass filter circuit is equal to or higher than a threshold level. Infrared detection circuit characterized by the following. 2. The infrared detection circuit according to claim 1, further comprising a second amplifier circuit connected between the bandpass filter circuit and the output circuit. 3. The infrared detection circuit according to claim 1, further comprising a high-pass filter having a predetermined gain connected between the band-pass filter circuit and the output circuit. 4. The bandpass filter circuit has a structure in which at least three or more filters are connected in multiple stages,
The infrared detection circuit according to claim 1, wherein a high-pass filter and a low-pass filter are alternately connected. 5. The infrared detection circuit according to claim 4, wherein the low-pass filter has a predetermined gain. 6. The infrared detection circuit according to claim 1, wherein the band pass filter circuit has a low pass filter in a front stage and a high pass filter in a rear stage. 7. The infrared detection circuit according to claim 1, wherein the current-voltage conversion circuit has a switched capacitor that operates according to the reference clock signal. 8. The reference clock signal is connected between the switched capacitor and the reference clock generation circuit and is connectable to an external clock generation circuit that generates an external clock signal having a frequency higher than the reference clock signal. The infrared detection circuit according to claim 1, further comprising a clock signal control circuit that switches between the external clock signal and the external clock signal. 9. The infrared detection circuit according to claim 1, wherein the circuit for feeding back the DC component is composed of a resistance element. 10. The infrared detecting circuit according to claim 1, wherein the circuit for feeding back the DC component is an integrating circuit. 11. The first amplifier circuit includes a second operational amplifier, and an output terminal of the first operational amplifier is connected to an inverting input terminal of the second operational amplifier via a resistor for amplification. The infrared detection circuit according to claim 1, wherein a low-pass filter is connected between the output terminal and the non-inverting input terminal of the second operational amplifier while being connected. 12. The low-pass filter includes a first resistance unit connected between an output terminal of the first operational amplifier and a non-inverting input terminal of the second operational amplifier, and the non-inverting input terminal. The infrared detection circuit according to claim 11, further comprising a capacitor connected to the ground side of the. 13. A low-pass filter circuit comprising: a first switch control section connected in parallel to the first resistance section; and a first switch control section comprising: 13. The infrared detection circuit according to claim 12, which controls the first switch circuit. 14. The infrared detection circuit according to claim 12, wherein the first resistance portion is an impurity non-diffused polysilicon resistance element. 15. A second switch control section, wherein the low-pass filter includes a second resistance section formed of an impurity non-diffusing polysilicon resistance element connected in series and a second switch circuit, and the first resistance section. 15. The infrared detection circuit according to claim 14, wherein the second switch control unit turns on the second switch circuit when the atmosphere has a low temperature. 16. The second switch control unit uses a divided voltage between an equivalent resistance composed of a switched capacitor and a resistance of the impurity non-diffused polysilicon resistance element,
16. The infrared detection circuit according to claim 15, which controls the second switch. 17. A reference voltage circuit for generating a reference voltage is connected to the non-inverting input terminals of the pyroelectric element and the first and second operational amplifiers.
17. The infrared detection circuit according to any one of 16 to 16. 18. An infrared detecting circuit, characterized in that the infrared detecting circuit according to any one of claims 1 to 17 is integrated on one semiconductor chip. 19. An infrared detection device comprising a pyroelectric element connected to the infrared detection circuit according to any one of claims 1 to 18.