JP4797366B2 - Pyroelectric infrared detector - Google Patents

Description

  The present invention uses a pyroelectric element to detect infrared energy radiated from the human body, detect the presence or movement of the human body, and detect infrared energy and room temperature to detect infrared energy and function as a radiation thermometer. It relates to the device.

  FIG. 10 shows a basic configuration of a conventional pyroelectric infrared detection device. The pyroelectric element 1 has one end connected to the ground and the other end connected to the inverting input terminal of the operational amplifier 2. Between the output terminal and the inverting input terminal, an AC feedback circuit is configured by connecting a feedback capacitor Cf made of a capacitor. Further, a series circuit of a DC feedback circuit 3 and an input resistor Ri is further provided between the output terminal and the inverting input terminal of the operational amplifier 2, and feedback is performed by the input resistor Ri. A bias potential Vr is applied to the non-inverting input terminal of the operational amplifier 2. Such a circuit constitutes a current-voltage conversion circuit that converts a current signal generated in the pyroelectric element 1 into a voltage signal upon detection of heat rays and outputs the voltage signal. The inverting input terminal of the operational amplifier 2 is Sin, the output terminal of the operational amplifier 2 is Sout, and the output terminal of the DC feedback circuit 3 is Sfo.

  Such a pyroelectric infrared detector functions as a radiation thermometer by detecting infrared energy radiated from the human body, detecting the presence and movement of the human body, and detecting radiant energy and room temperature. is there. In general, the detection frequency when human body detection is performed is centered at 1 Hz. Therefore, in a voltage amplification unit (not shown) provided at the subsequent stage of the current-voltage conversion circuit, a frequency band around 0.1 Hz centering on 1 Hz is present. Is selectively amplified. Therefore, as shown in FIG. 11, the output terminal Sout of the operational amplifier 2 is often connected to a high-pass filter composed of a capacitor C2 and a resistor R2, and passes a frequency component of 0.1 Hz or more. Here, one end of the capacitor C2 is connected to the output terminal Sout of the operational amplifier 2, the other end of the capacitor C2 is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the bias potential Vr. A connection point Vx1 between the resistor R2 and the resistor R2 is an output of the pyroelectric infrared detector.

  FIG. 11 also shows a specific circuit of the DC feedback circuit 3 of FIG. 10. The DC feedback circuit 3 includes an operational amplifier 31 in which the output of the operational amplifier 2 is connected to a non-inverting input terminal, and an output terminal of the operational amplifier 31. A capacitor C1 connected between the inverting input terminals and a resistor R1 connected between the inverting input terminal of the operational amplifier 31 and the bias potential Vr. The output of the operational amplifier 31 is the output of the DC feedback circuit 3. It becomes.

  In the current-voltage conversion circuit having such a configuration, the current signal output from the pyroelectric element 1 is converted into a voltage signal using the impedance of the feedback capacitor Cf, and the frequency characteristic of the conversion impedance serves as a bandpass filter. . The center frequency ω 0 and the selectivity Q of this band pass filter are expressed by Equation 1.

Since the detection frequency in human body detection, which is the largest application of the pyroelectric element 1, is centered at 1 Hz, the output characteristics of the voltage signal should be determined by the impedance characteristics of the feedback capacitor Cf in the frequency band of 0.1 Hz or higher. Then, the center frequency ω0 must be 0.1 Hz or less. Therefore, the time constant of this current-voltage conversion circuit is very slow.

Further, since thermal noise due to the input resistance Ri is dominant as one of the noise components, the value of the input resistance Ri is usually set to a high resistance of 1T (tera) Ω or more in order to suppress this thermal noise. Such a high resistance generally has a characteristic that the resistance value largely fluctuates due to a temperature change. (For example, see Patent Document 1)
Japanese Patent Laid-Open No. 10-267759 (paragraph numbers [0013] and [0014], FIG. 1)

  In the current-voltage conversion circuit having a slow time constant as in the above-mentioned conventional example, the time from when the power is turned on until the circuit operation is stabilized (circuit stabilization time), or when a large external noise is applied during the circuit operation, etc. When the operating point is saturated, there is a problem that it takes a long time to return to the original normal state.

  Here, simulation results for the current-voltage conversion circuit in which the DC feedback circuit 3 is configured by an integration circuit as shown in FIG. 11 are shown in FIGS. Here, the circuit constants are a feedback capacity Cf = 10 pF, an input resistance Ri = 3 TΩ, a capacitor C1 = 10 nF, and a resistance R1 = 6 GΩ.

  FIG. 12 shows the results of transient analysis when the power is turned on and when external noise is applied. FIG. 12A shows the voltage waveform at the output terminal Sout of the operational amplifier 2, and FIG. 12B shows the relationship between the capacitor C2 and the resistor R2. A voltage waveform (output waveform of a high-pass filter) at the connection point Vx1 is shown. At time t = 0, the power supply potential 3 V and the bias potential Vr = 1.5 V of the operational amplifiers 2 and 31 are applied, and a current signal composed of a 1 Hz sine wave is applied to the inverting input terminal Sin of the operational amplifier 2 at time t = Continue to input from 0. Further, at time t = 500 seconds (state of stable operation after power-on), a negative charge of 60 pC is applied to the inverting input terminal Sin of the operational amplifier 2 assuming external noise. Here, the voltage waveform at the output terminal Sout of the operational amplifier 2 fluctuates at a very slow frequency as shown in FIG. 12A, but the voltage waveform at the connection point Vx1 as shown in FIG. 12B. The fluctuation is cut by the high-pass filter by the resistor R2 and the capacitor C2, so that a very slow frequency fluctuation is not transmitted to the subsequent circuit.

  Then, when the power is turned on, the potential of the output terminal Sout of the operational amplifier 2 is saturated to the positive side, and as shown in FIGS. For about 25 seconds (time t = 0 to 25 seconds) after the power is turned on, the circuit does not respond normally to the input signal and the circuit operation is not stable.

  Further, when external noise is applied at time t = 500 seconds, the potential of the output terminal Sout of the operational amplifier 2 is saturated to the negative side, and time t = 594 to FIG. As shown in the enlarged view of each waveform at 610 seconds, it does not respond normally to the input signal for about 100 seconds (time t = 500 to 600 seconds) after applying external noise, and does not return to normal operation.

  The present invention has been made in view of the above reasons, and its purpose is to shorten the time from when the power is turned on until the circuit operation is stabilized, and to enable quick recovery even when external noise is applied during circuit operation. An object is to provide an electric infrared detector.

According to the first aspect of the present invention, a pyroelectric element that generates a current signal when detecting heat rays, an AC feedback circuit including a first capacitor, and a series circuit of the DC feedback circuit and the first resistance element are connected between the input and output. And a current-voltage conversion circuit configured to convert the current signal into a voltage signal and output the voltage signal. An AC feedback circuit is connected between the output terminal and the inverting input terminal of the operational amplifier, and one end of the DC feedback circuit. Is connected to the output side of the operational amplifier, the first resistance element is connected between the other end of the DC feedback circuit and the inverting input terminal of the operational amplifier, the pyroelectric element is connected to the inverting input terminal of the operational amplifier, and the limiter The circuit includes a first MOS transistor having a source terminal connected to one end of the first resistance element, a gate terminal and a drain terminal connected to the other end of the first resistance element, and a gate terminal and a drain terminal connected to the first resistance element. One end of resistance element And a second MOS transistor having a source terminal connected to the other end of the first resistance element. When the first and second MOS transistors are P-type, each substrate terminal is connected to a power supply potential. When the first and second MOS transistors are N-type, each substrate terminal is connected to the ground, and a series circuit of a second resistor and a second capacitor connected between the power supply potential and the ground, Connection between the first switch element connected between the gate terminal and the drain terminal of at least one of the first and second MOS transistors, the second resistance element, and the second capacitor A second switch element connected between the midpoint and the gate terminal of at least one of the MOS transistors, and after power-on, the first switch element is turned off; The switch element is turned on, the at least one MOS transistor is turned on, and the first switch element is turned on after the at least one MOS transistor is turned off by the charging voltage of the second capacitor. When the two switch elements are turned off, at least one of the MOS transistors is made conductive for a predetermined period when the power is turned on.

According to the present invention, even in a current-voltage conversion circuit having a slow time constant, the time from when the power is turned on until the circuit operation is stabilized is short, and even if external noise is applied during circuit operation, it can be quickly restored. Can do. Further, since the leakage current from the substrate terminal of the MOS transistor to the inverting input terminal of the operational amplifier can be reduced, the shot noise component due to this leakage current can be suppressed to a negligible level, and the deterioration of the S / N ratio can be prevented. . Further, since the limiter circuit is composed of MOS transistors, it is advantageous for circuit integration and miniaturization. Further, the circuit can be further reduced in size by using the start-up circuit together with the limiter circuit.

According to a second aspect of the present invention, in the first aspect, a third resistance element is connected in series to each MOS transistor of the limiter circuit.

According to the present invention, when the PMOS transistor is turned on by the third resistance element, the resistance value between the inverting input terminal of the operational amplifier and the output of the DC feedback circuit is suppressed from abruptly decreasing. The output discontinuity can be suppressed. Therefore, malfunction due to the discontinuity of the output of the operational amplifier can be prevented.

As described above, in the present invention, since the potential difference between both ends of the first resistance element is limited by the limiter circuit, the time from when the power is turned on until the circuit operation is stabilized is short, and external noise is applied during the circuit operation. Also has the effect of being able to return quickly. Further, since the leakage current from the substrate terminal of the MOS transistor to the inverting input terminal of the operational amplifier can be reduced, the shot noise component due to this leakage current can be suppressed to a negligible level, and the deterioration of the S / N ratio can be prevented. . Further, since the limiter circuit is composed of MOS transistors, it is advantageous for circuit integration and miniaturization. Further, the circuit can be further reduced in size by using the start-up circuit together with the limiter circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
As shown in FIG. 1, the basic configuration of the pyroelectric infrared detecting device of the present invention is that the limiter circuit 4 is connected in parallel to the input resistance Ri in the conventional example shown in FIG. The same components are denoted by the same reference numerals, and description thereof is omitted.

  The limiter circuit 4 is connected in parallel to the input resistor Ri to limit the potential difference between both ends of the input resistor Ri.

  FIG. 2 shows specific circuits of the DC feedback circuit 3 and the limiter circuit 4 shown in FIG. 1. The DC feedback circuit 3 is an integration circuit similar to the conventional example shown in FIG.

  In the limiter circuit 4, the PMOS transistors Tr1 and Tr2 are connected in antiparallel to each other and connected in parallel to the input resistor Ri. The input resistor Ri has one end connected to the output terminal Sfo of the DC feedback circuit 3 and the other end connected to the inverting input terminal Sin of the operational amplifier 2. The PMOS transistor Tr1 has a source terminal connected to the output terminal of the DC feedback circuit 3. The gate terminal and the drain terminal are connected to the inverting input terminal Sin. The PMOS transistor Tr2 is connected to the output terminal Sfo of the DC feedback circuit 3 and the source terminal is connected to the inverting input terminal Sin. Connected. The substrate terminals of the PMOS transistors Tr1 and Tr2 are connected to the power supply potential Vcc. In this way, the limiter circuit 4 is constituted by the PMOS transistors Tr1 and Tr2, which is advantageous for integration.

  Next, simulation results for the current-voltage conversion circuit shown in FIG. 2 are shown in FIGS. Here, the circuit constants are a feedback capacity Cf = 10 pF, an input resistance Ri = 3 TΩ, a capacitor C1 = 10 nF, and a resistance R1 = 6 GΩ.

  FIG. 3 shows the results of transient analysis when the power is turned on and when external noise is applied. FIG. 3 (a) shows the voltage waveform at the output terminal Sout of the operational amplifier 2, and FIG. 3 (b) shows the relationship between the capacitor C2 and the resistor R2. A voltage waveform (output waveform of a high-pass filter) at the connection point Vx1 is shown. At time t = 0, the power supply potential 3 V (= Vcc) and the bias potential Vr = 1.5 V of the operational amplifiers 2 and 31 are applied, and a current signal composed of a 1 Hz sine wave is applied to the inverting input terminal Sin of the operational amplifier 2. Is continuously input from time t = 0. Further, at time t = 500 seconds (state of stable operation after power-on), a negative charge of 60 pC is applied to the inverting input terminal Sin of the operational amplifier 2 assuming external noise.

  When the power is turned on, the potential of the output terminal Sout of the operational amplifier 2 fluctuates to the positive side. FIGS. 4 (a) and 4 (b) show enlarged views of the respective waveforms at time t = 0 to 16 seconds. When the potentials at the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 try to increase to 3V immediately after the power is turned on, the source potential of the PMOS transistor Tr1 connected to the output terminal Sfo also increases. When the potentials of the terminals Sout and Sfo rise to around 2V, the gate-source voltage Vgs of the PMOS transistor Tr1 exceeds the threshold value (negative voltage), and the PMOS transistor Tr1 is turned on. When both ends of the input resistor Ri are short-circuited by the PMOS transistor Tr1, the potentials at the terminals Sout and Sfo no longer rise and fall without being saturated. Therefore, it responds normally to the input signal 1 to 2 seconds after the power is turned on at time t = 0. This operation is performed not only when the power is turned on, but also when external noise is applied such that the potential of the output terminal Sout of the operational amplifier 2 fluctuates to the positive side (for example, positive charge is applied to the inverting input terminal Sin of the operational amplifier 2). The same applies to the cases where given.

  Furthermore, when external noise that applies a negative charge to the inverting input terminal Sin of the operational amplifier 2 is applied at time t = 500 seconds, the potential of the output terminal Sout of the operational amplifier 2 varies to the negative side. Then, as shown in FIGS. 5 (a) and 5 (b), enlarged views of each waveform at time t = 498 to 505 seconds, each potential at the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 is 0V. If it is going to lower, the gate potential of the PMOS transistor Tr2 connected to the output terminal Sfo is similarly lowered. When the potentials of the terminals Sout and Sfo drop to near 1V, the gate-source voltage Vgs of the PMOS transistor Tr2 exceeds the threshold value (negative voltage), and the PMOS transistor Tr2 is turned on. When both ends of the input resistor Ri are short-circuited by the PMOS transistor Tr2, the potentials at the terminals Sout and Sfo will not drop any further and rise without saturation. Therefore, about 1 to 2 seconds (time t = 501 to 502 seconds) after application of external noise, the operation returns to a normal response to the input signal.

  Here, the presence of a current noise component at the inverting input terminal Sin of the operational amplifier 2 greatly affects the output. In particular, a leak current generated when the PN junction is reverse biased has a current shot noise component. is required. In this embodiment, as a leakage current affecting the inverting input terminal Sin of the operational amplifier 2, the inverting input terminal Sin from the substrate (N type) terminal connected to the power supply potential Vcc of the PMOS transistor Tr1 through the drain (P type) terminal. Leak current from the substrate (N-type) terminal connected to the power supply potential Vcc of the PMOS transistor Tr2 to the inverting input terminal Sin via the source (P-type) terminal. The area of this PN junction Is affected by the source areas of the PMOS transistors Tr1 and Tr2, so that the area is very small. The shot noise component of the leakage current generated at the PN junction can be suppressed to a negligible level, and the S / N ratio is deteriorated due to the leakage current. Can be prevented.

  Also, the input leakage current at the inverting input terminal Sin of the operational amplifier 2 must be reduced for the same reason as described above. In this embodiment, by using the operational amplifier 2 in which the internal circuit is composed of MOS transistors, the input leakage current is reduced. Current is suppressed.

  In this embodiment, the P-type MOS transistors Tr1 and Tr2 are used to connect each substrate terminal to the power supply potential Vcc. However, when an N-type MOS transistor is used, each substrate terminal is connected to the ground. Then, it can be used similarly.

( Reference Example 1 )
FIG. 6 shows the configuration of the pyroelectric infrared detection apparatus of the present reference example , which is different from FIG. 2 of the first embodiment only in the configuration of the limiter circuit 4. Similar components are denoted by the same reference numerals. Description is omitted.

In the limiter circuit 4 of this reference example , PMOS transistors Tr1 and Tr2 are connected in antiparallel to each other and connected in parallel to the input resistor Ri. The input resistor Ri has one end connected to the output terminal Sfo of the DC feedback circuit 3 and the other end connected to the inverting input terminal Sin of the operational amplifier 2. The PMOS transistor Tr1 has a drain terminal connected to the output terminal of the DC feedback circuit 3. The gate terminal, the source terminal, and the substrate terminal are connected to the inverting input terminal Sin. The PMOS transistor Tr2 has the gate terminal, the source terminal, and the substrate terminal connected to the output terminal Sfo of the DC feedback circuit 3, and the drain terminal. Is connected to the inverting input terminal Sin. In this way, the limiter circuit 4 is constituted by the PMOS transistors Tr1 and Tr2, which is advantageous for integration.

  When the potentials of the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 try to rise to 3V when the power is turned on or when positive external noise is applied, the PMOS transistor Tr1 connected to the output terminal Sfo Similarly, the drain potential rises. A forward diode junction is formed from the drain (P-type) terminal of the PMOS transistor Tr1 to the substrate (N-type) terminal, and a potential difference of a certain level or more in a direction in which the potential of the terminal Sfo> the potential of the terminal Sin. When this occurs, the drain (P-type) terminal and the substrate (N-type) terminal of the PMOS transistor Tr1 conduct as a diode. When both ends of the input resistor Ri are short-circuited by the PMOS transistor Tr1, the potentials at the terminals Sout and Sfo no longer rise and fall without being saturated. Therefore, it responds normally to the input signal 1 to 2 seconds after the power is turned on or external noise is applied.

  Further, when negative external noise is applied and the respective potentials at the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 are lowered to 0 V, the substrate potential of the PMOS transistor Tr2 connected to the output terminal Sfo. Goes down as well. A forward diode junction is formed from the drain (P-type) terminal of the PMOS transistor Tr2 to the substrate (N-type) terminal, and a potential difference of a certain level or more in a direction in which the potential of the terminal Sin> the potential of the terminal Sfo. When this occurs, the drain (P-type) terminal and substrate (N-type) terminal of the PMOS transistor Tr2 conduct as a diode. When both ends of the input resistor Ri are short-circuited by the PMOS transistor Tr2, the potentials at the terminals Sout and Sfo will not drop any further and rise without saturation. Therefore, about 1 to 2 seconds after application of external noise, the operation returns to a normal response to the input signal.

In this reference example , since the limiter circuit 4 is configured using the characteristics of the PN junctions of the PMOS transistors Tr1 and Tr2, compared to the case where the transistor characteristics of the PMOS transistors Tr1 and Tr2 are used, Manufacturing variation can be reduced.

( Reference Example 2 )
FIG. 7 shows the configuration of the pyroelectric infrared detection apparatus of this reference example , which is different from FIG. 2 of the first embodiment only in the configuration of the limiter circuit 4. Similar components are denoted by the same reference numerals. Description is omitted.

In the limiter circuit 4 of this reference example , the PMOS transistor Tr1 is connected in parallel to the input resistor Ri. One end of the input resistor Ri is connected to the output terminal Sfo of the DC feedback circuit 3, and the other end is connected to the inverting input terminal Sin of the operational amplifier 2. The PMOS transistor Tr1 has a source terminal and a substrate terminal connected to the DC feedback circuit 3. The drain terminal and the gate terminal are connected to the inverting input terminal Sin. In this way, the limiter circuit 4 is constituted by the PMOS transistor Tr1, which is advantageous for integration.

  When the potentials of the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 try to rise to 3V when the power is turned on or when positive external noise is applied, the PMOS transistor Tr1 connected to the output terminal Sfo Similarly, the source potential rises. When the potentials of the terminals Sout and Sfo rise to around 2V, the gate-source voltage Vgs of the PMOS transistor Tr1 exceeds the threshold value (negative voltage), and the PMOS transistor Tr1 is turned on. When both ends of the input resistor Ri are short-circuited by the PMOS transistor Tr1, the potentials at the terminals Sout and Sfo no longer rise and fall without being saturated. Therefore, it responds normally to the input signal 1 to 2 seconds after the power is turned on or external noise is applied.

  Further, when negative external noise is applied and the respective potentials at the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 are lowered to 0 V, the substrate potential of the PMOS transistor Tr1 connected to the output terminal Sfo. Goes down as well. A forward diode junction is formed from the drain (P-type) terminal of the PMOS transistor Tr1 to the substrate (N-type) terminal, and a potential difference of a certain level or more in a direction in which the potential of the terminal Sin> the potential of the terminal Sfo. When this occurs, the drain (P-type) terminal and the substrate (N-type) terminal of the PMOS transistor Tr1 conduct as a diode. When both ends of the input resistor Ri are short-circuited by the PMOS transistor Tr1, the potentials of the terminals Sout and Sfo will not drop any further and rise without saturation. Therefore, about 1 to 2 seconds after application of external noise, the operation returns to a normal response to the input signal.

In this reference example , the PMOS transistor Tr1 is turned on as a transistor when the power is turned on or when positive external noise is applied, and is turned on as a diode when negative external noise is applied to prevent output saturation. It is possible to take measures against external noise in both directions, and to reduce the size. Further, the leakage current from the substrate terminal of the MOS transistor to the inverting input terminal of the operational amplifier can be reduced, and the shot noise component due to this leakage current can be suppressed to a negligible level, and the S / N ratio can be prevented from deteriorating.

( Embodiment 2 )
FIG. 8 shows the configuration of the pyroelectric infrared detector of this embodiment. In the limiter circuit 4 (see FIG. 6) of Reference Example 1 , resistors R11 and R12 are connected in series to PMOS transistors Tr1 and Tr2. Similar components are denoted by the same reference numerals, and description thereof is omitted.

  First, let us consider an operation in the case where fluctuations of a very slow frequency compared with 1 Hz are input to the inverting input terminal Sin of the operational amplifier 2 when the resistors R11 and R12 are not provided. In this case, the potentials at the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 also fluctuate in response to this fluctuation, but when the fluctuation amplitude is large, the limiter circuit 4 operates and the PMOS transistor Since Tr1 or Tr2 is turned on and the resistance value between the inverting input terminal Sin of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 rapidly decreases, a discontinuity occurs in the output waveform of the output terminal Sout.

  Here, considering the application of human body detection, since the movement of the human body is mainly in the vicinity of 1 Hz, the voltage amplification unit (not shown) provided in the subsequent stage performs amplification around 1 Hz. Therefore, the fluctuation of the frequency that is very slow compared with 1 Hz is not amplified by the voltage amplification unit at the subsequent stage, so that it does not cause a false alarm. However, when a discontinuity occurs in the output waveform of the output terminal Sout, the fluctuation of the discontinuous portion includes a high-frequency component. Therefore, the frequency component in the vicinity of 1 Hz of the high-frequency component is amplified by the voltage amplification unit at the subsequent stage, resulting in malfunction. Connected.

  Therefore, in this embodiment, when the PMOS transistors Tr1 and Tr2 are turned on by the resistors R11 and R12 connected in series to the PMOS transistors Tr1 and Tr2, the inverting input terminal Sin of the operational amplifier 2 and the output terminal of the DC feedback circuit 3, respectively. The resistance value between Sfo is prevented from abruptly decreasing, and the discontinuity of the output waveform at the output terminal Sout is suppressed. Therefore, malfunction due to discontinuity of the output waveform of the output terminal Sout can be prevented.

In this embodiment, the limiter circuit 4 of Reference Example 1 has been described as an example. However, the same effect can be obtained even if resistors are connected in series to the PMOS transistors of the limiter circuit 4 of Embodiment 1 and Reference Example 2. it can.

( Embodiment 3 )
FIG. 9 shows the configuration of the pyroelectric infrared detection device of the present embodiment, which is different from FIG. 2 of the first embodiment only in the configuration of the limiter circuit 4. The same components are denoted by the same reference numerals. Description is omitted.

  In the limiter circuit 4 of the present embodiment, the PMOS transistor Tr1 is connected in parallel to the input resistor Ri. The input resistor Ri has one end connected to the output terminal Sfo of the DC feedback circuit 3 and the other end connected to the inverting input terminal Sin of the operational amplifier 2. The PMOS transistor Tr1 has a drain terminal connected to the output terminal of the DC feedback circuit 3. The source terminal and the substrate terminal are connected to the inverting input terminal Sin. One end of the series circuit of the switch elements SWA and SWB is connected to the drain terminal of the PMOS transistor Tr1, and the other end of the series circuit of the switch elements SWA and SWB is connected to a connection point between each end of the resistor R3 and the capacitor C3. Is done. The other end of the resistor R3 is connected to the power supply potential Vcc, and the other end of the capacitor C3 is connected to the ground. The gate terminal of the PMOS transistor Tr1 is connected to the connection point of the switch elements SWA and SWB.

  Immediately after the power is turned on, the switch element SWA is turned off and the switch element SWB is turned on. Immediately after the switch element SWB is turned on, the capacitor C3 is not charged, and the gate signal of the PMOS transistor Tr1 is at the L level. Therefore, the gate-source voltage Vgs of the PMOS transistor Tr1 is the threshold value ( The PMOS transistor Tr1 is turned on exceeding the negative voltage), the capacitor Cf of the DC feedback circuit 3 is rapidly charged, and the potential of the output terminal Sout rapidly reaches the operating point. Thereafter, as the capacitor C3 is charged to the potential Vcc via the resistor R3, the gate potential of the PMOS transistor Tr1 also rises, and the PMOS transistor Tr1 is turned off after a predetermined time determined by the time constant of the resistor R3 and the capacitor C3. To do.

  Thereafter, the switch element SWA is turned on and the switch element SWB is turned off, and the drain terminal and the gate terminal of the PMOS transistor Tr1 are connected via the switch element SWA. When positive external noise is applied, if the potentials at the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 are increased to 3 V, the drain potential of the PMOS transistor Tr1 connected to the output terminal Sfo is also the same. Therefore, the drain (P-type) terminal of the PMOS transistor Tr1 and the substrate (N-type) terminal become conductive as a diode. When both ends of the input resistor Ri are short-circuited by the PMOS transistor Tr1, the potentials at the terminals Sout and Sfo no longer rise and fall without being saturated. Therefore, about 1 to 2 seconds after application of external noise, the operation returns to a normal response to the input signal.

  Further, when negative external noise is applied and each potential of the output terminal Sout of the operational amplifier 2 and the output terminal Sfo of the DC feedback circuit 3 is lowered to 0 V, the output terminal Sfo is connected to the output terminal Sfo via the switch element SWA. Similarly, the gate potential of the PMOS transistor Tr1 also decreases. When the potentials of the terminals Sout and Sfo drop to near 1V, the gate-source voltage Vgs of the PMOS transistor Tr1 exceeds the threshold value (negative voltage), and the PMOS transistor Tr1 is turned on. When both ends of the input resistor Ri are short-circuited by the PMOS transistor Tr1, the potentials of the terminals Sout and Sfo will not drop any further and rise without saturation. Therefore, about 1 to 2 seconds after application of external noise, the operation returns to a normal response to the input signal.

  Thus, by providing the startup circuit that rapidly charges the capacitor Cf when the power is turned on, the time from when the power is turned on until the circuit operation is stabilized can be further shortened, and the limiter circuit 4 is used together with the startup circuit. Thus, the circuit can be reduced in size.

In Embodiment 1 and Reference Examples 1 and 2 , the same effect as described above can be obtained by providing a startup circuit for rapidly charging the capacitor Cf by turning on the MOS transistor included in the limiter circuit 4 for a predetermined period when the power is turned on. be able to.

In the first to third embodiments and the reference examples 1 and 2 , the transistors Tr1 and Tr2 use PMOS. However, NMOS may be used. Further, the limiter circuit 4 may be constituted by a diode instead of a transistor.

It is a schematic circuit diagram which shows the pyroelectric infrared detection apparatus of this invention. It is a specific circuit diagram which shows the pyroelectric infrared detection apparatus of Embodiment 1 of this invention. It is a waveform diagram same as the above, (a) shows the output waveform of the operational amplifier, (b) shows the output waveform of the high-pass filter. It is an enlarged view at the time of power-on in the waveform diagram same as the above, (a) shows the output waveform of the operational amplifier, (b) shows the output waveform of the high pass filter. It is an enlarged view at the time of external noise application in the same waveform diagram, (a) shows the output waveform of the operational amplifier, (b) shows the output waveform of the high-pass filter. It is a specific circuit diagram which shows the pyroelectric infrared detection apparatus of the reference example 1 of this invention. It is a specific circuit diagram which shows the pyroelectric infrared detection apparatus of the reference example 2 of this invention. It is a specific circuit diagram which shows the pyroelectric infrared detection apparatus of Embodiment 2 of this invention. It is a specific circuit diagram which shows the pyroelectric infrared detection apparatus of Embodiment 3 of this invention. It is a schematic circuit diagram which shows the conventional pyroelectric infrared detection apparatus. It is a specific circuit diagram same as the above. It is a waveform diagram same as the above, (a) shows the output waveform of the operational amplifier, (b) shows the output waveform of the high-pass filter. It is an enlarged view at the time of power-on in the waveform diagram same as the above, (a) shows the output waveform of the operational amplifier, (b) shows the output waveform of the high pass filter. It is an enlarged view at the time of external noise application in the same waveform diagram, (a) shows the output waveform of the operational amplifier, (b) shows the output waveform of the high-pass filter.

Reference Signs List 1 pyroelectric element 2 operational amplifier 3 DC feedback circuit 4 limiter circuit Cf feedback capacitance Ri input resistance Vr bias potential

Claims (2)

It is composed of a pyroelectric element that generates a current signal when sensing heat rays, an AC feedback circuit composed of a first capacitor, and an operational amplifier in which a series circuit of a DC feedback circuit and a first resistance element is connected between the input and output. A current-voltage conversion circuit that converts the current signal into a voltage signal and outputs the voltage signal;
The AC feedback circuit is connected between the output terminal and the inverting input terminal of the operational amplifier, one end of the DC feedback circuit is connected to the output side of the operational amplifier, and the first resistance element is connected to the other end of the DC feedback circuit and the inverse of the operational amplifier. Connect between the input terminals, connect the pyroelectric element to the inverting input terminal of the operational amplifier,
The limiter circuit includes a first MOS transistor having a source terminal connected to one end of the first resistance element, a gate terminal and a drain terminal connected to the other end of the first resistance element, and a gate terminal and a drain terminal connected to the first resistance element. And a second MOS transistor having a source terminal connected to the other end of the first resistor element, and each substrate terminal when the first and second MOS transistors are P-type. Is connected to the power supply potential, and when the first and second MOS transistors are N-type, each substrate terminal is connected to the ground ,
A series circuit of a second resistor and a second capacitor connected between the power supply potential and the ground, and a gate terminal and a drain terminal of at least one of the first and second MOS transistors A second switching element connected between a first switching element connected between the first switching element, a connection middle point of the second resistance element and the second capacitor, and a gate terminal of the at least one of the MOS transistors. Having a switch element, after turning on the power, the first switch element is turned off, the second switch element is turned on, the at least one MOS transistor is turned on, and the charge voltage of the second capacitor After at least one of the MOS transistors is turned off, the first switch element is turned on and the second switch element is turned off. Serial at least one of the MOS transistors, a pyroelectric infrared detection device, characterized in that for a predetermined period conductive when power is turned on. 2. The pyroelectric infrared detector according to claim 1, wherein a third resistance element is connected in series to each MOS transistor of the limiter circuit.

Images