Circuit device, sensor device, and determination device

Abstract

This circuit device comprises: a power supply terminal connected to a power supply potential; a reference potential terminal connected to a reference potential; a signal terminal connected to a signal line; a first MOSFET electrically connected between the signal terminal and the power supply terminal and having a first control electrode; and a second MOSFET electrically connected between the signal terminal and the reference potential terminal and having a second control electrode. The first MOSFET and the second MOSFET are composed of MOSFETs of the same channel type. The first control electrode is connected to the signal terminal and the second control electrode is connected to the reference potential terminal, or the first control electrode is connected to the power supply terminal and the second control electrode is connected to the signal terminal.

Description

Circuit device, sensor device and determination device

[0001] The present invention relates to a circuit device, a sensor device including the circuit device, and a determination device including the sensor device.

[0002] Conventionally, an ESD element may be disposed in a circuit as a countermeasure against static electricity. For example, an input / output protection circuit described in Patent Document 1 uses an NMOS transistor and a PMOS transistor connected in parallel and disposed between a signal line and a power supply potential or between a signal line and a ground potential.

[0003] Japanese Patent Application Publication No. 11-121750

[0004] When connecting circuit blocks with different reference DC voltages, a capacitance element may be connected in series to the signal line to cut the DC component between the circuit blocks. Each circuit block connects a resistor between the reference DC voltage source and the signal line to determine the DC voltage on the signal line. In this case, each circuit has high-pass filter characteristics. In such a high-pass filter, a large capacitance element of several μF is required to process signals with low frequencies, for example, on the order of a few Hz. However, it is extremely difficult to install a large-capacity element inside an IC. Therefore, it is possible to increase the resistance value of the parallel resistor.

[0005] Furthermore, in circuits connected to sensors having capacitance, such as piezoelectric sensors, pyroelectric sensors, or capacitive sensors, a resistor is connected between a reference DC voltage source and the signal line to determine the DC voltage on the signal line. If the impedance of the resistor is Zr and the impedance of the capacitance is Zc, the output voltage Vout of the sensor signal is given by "Vout = Vin × (Zr / (Zr + Zc))." The value of Zc increases as the frequency decreases. For example, in order to prevent attenuation of a sensor signal with a low frequency of around a few Hz, it is possible to increase the resistance value of the resistor and the value of Zr.

[0006] In the above circuit, the potential difference between the signal line and the reference DC voltage source, i.e., the DC voltage of the signal line, is determined by the resistance value of the resistor. Therefore, for example, if an ESD element such as that disclosed in Patent Document 1 is connected to the signal line for electrostatic protection, the resistance value of the resistor is large, so even a small leakage current in the ESD element will cause a very large fluctuation in the DC voltage of the signal line.

[0007] An object of the present invention is to provide a circuit device, a sensor device, and a determination device that suppress the above-mentioned fluctuations in DC voltage.

[0008] A circuit device according to one embodiment of the present invention comprises: a power supply terminal connected to a power supply potential; a reference potential terminal connected to a reference potential; a signal terminal connected to a signal line; a first MOSFET electrically connected between the signal terminal and the power supply terminal and having a first control electrode; and a second MOSFET electrically connected between the signal terminal and the reference potential terminal and having a second control electrode, wherein the first MOSFET and the second MOSFET are configured as same-channel MOSFETs, and the first control electrode is connected to the signal terminal and the second control electrode is connected to the reference potential terminal, or the first control electrode is connected to the power supply terminal and the second control electrode is connected to the signal terminal.

[0009] The circuit device according to the present invention can suppress fluctuations in DC voltage.

[0010] FIG. 1 is a circuit diagram showing a circuit device 1 and a sensor device S1 according to a first embodiment. FIG. 2 is a diagram showing the configuration of a piezoelectric sensor 2. FIG. 3 is an equivalent circuit diagram of the piezoelectric sensor 2. FIG. 4 is a circuit diagram showing details of a P-channel MOSFET 100 and a P-channel MOSFET 101. FIG. 5 is a circuit diagram showing details of a P-channel MOSFET 110 and a P-channel MOSFET 110. FIG. 6A is a circuit diagram showing the configuration of a first embodiment. FIG. 6B is a circuit diagram showing the configuration of a comparative example. FIG. 7 is an experimental result showing the magnitude of leakage current G1 in the comparative example and the magnitude of leakage current G2 in the first embodiment. FIG. 8 is an experimental result showing the amount of DC voltage fluctuation G3 in the comparative example and the amount of DC voltage fluctuation G4 in the first embodiment. FIG. 9 is an experimental result showing a signal value G5 in the comparative example and a signal value G6 in the first embodiment. FIG. 10 is a circuit diagram showing a first circuit 10a of a circuit device 1a according to a first modification of the circuit device 1a. Fig. 11 is a circuit diagram showing a circuit device 1b according to a second modification of the circuit device 1. Fig. 12 is a circuit diagram showing a circuit device 1c according to a third modification of the circuit device 1.

[0011] [First Embodiment] Hereinafter, a circuit device 1 and a sensor device S1 according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a circuit diagram showing a circuit device 1 and a sensor device S1 according to the first embodiment.

[0012] The sensor device S1 is a device provided in an electronic device such as a smartphone, etc. As shown in FIG.

[0013] The piezoelectric sensor 2 is attached to, for example, a touch panel display of an electronic device such as a smartphone. The piezoelectric sensor 2 detects a user's operation on the touch panel display. As shown in FIG. 1 , the piezoelectric sensor 2 is connected to ground GP3. The piezoelectric sensor 2 is connected in series between ground GP3 and a signal terminal SP1 of the circuit device 1. The potential of ground GP3 does not necessarily have to be 0 V, and may be a potential other than 0 V. The piezoelectric sensor 2 is an example of an external component arranged outside the circuit device 1. As an example, the piezoelectric sensor 2 generates an electric charge according to a change in the user's pressure on the touch panel display.

[0014] 2 is a diagram showing the configuration of the piezoelectric sensor 2. As shown in FIG. 2, the piezoelectric sensor 2 includes a piezoelectric film 200, a first electrode 201, and a second electrode 202.

[0015] The piezoelectric film 200 has a sheet shape. The piezoelectric film 200 has a first film principal surface SF1 and a second film principal surface SF2. The first film principal surface SF1 faces the second film principal surface SF2.

[0016] The piezoelectric film 200 is polarized according to the amount of deformation of the piezoelectric film 200. For example, the piezoelectric film 200 is a film formed from a chiral polymer. An example of a chiral polymer is polylactic acid (PLA), particularly poly-L-lactic acid (PLLA). PLLA, a chiral polymer, has a helical main chain structure. The piezoelectric film 200 has a piezoelectric constant of d14. The piezoelectric film 200 exhibits piezoelectricity in which the molecules are oriented in an orientation direction when uniaxially stretched. This orientation direction forms, for example, a 45-degree angle with respect to a predetermined direction (hereinafter referred to as the X-axis direction). This 45-degree angle includes angles ranging from 45 degrees to 10 degrees. The potential difference between the first film principal surface SF1 and the second film principal surface SF2 when polarized depends on the time differential value of the amount of deformation of the piezoelectric film 200 due to expansion or contraction. The direction of polarization when the piezoelectric film 200 is stretched in the X-axis direction is opposite to the direction of polarization when the piezoelectric film 200 is stretched in the Y-axis direction, which is perpendicular to the X-axis direction. The piezoelectric film 200 functions as an AC signal source that generates an AC signal.

[0017] 3 is an equivalent circuit diagram of the piezoelectric sensor 2. The piezoelectric sensor 2 has an AC signal source 20 composed of a piezoelectric film 200, a first electrode 201, and a second electrode 202, and a capacitance element 21. In FIG. 3, the capacitance element 21 is connected in series between the AC signal source 20 and the circuit device 1.

[0018] The sensor device S1 may include a pyroelectric sensor or a capacitive sensor instead of the piezoelectric sensor 2. Similar to the piezoelectric sensor 2, the pyroelectric sensor or the capacitive sensor is equivalently configured as a series-connected circuit of a capacitive element and an AC voltage source.

[0019] The circuit device 1 is, for example, an integrated circuit (IC). As shown in Fig. 1, the circuit device 1 is connected to a piezoelectric sensor 2. The circuit device 1 includes a first circuit 10, a second circuit 11, an AD converter 12, a digital filter 13, and an MPU (micro processing unit) 14.

[0020] 1 , the first circuit 10 is electrically connected to the piezoelectric sensor 2. The first circuit 10 receives a signal from the piezoelectric sensor 2. The first circuit 10 includes a signal terminal SP1, a signal line SL1, a ground terminal GP1 connected to the ground, a DC terminal RP1 connected to a DC voltage source, a power supply terminal PP1 connected to a power supply potential, a P-channel MOSFET 100 (corresponding to the first MOSFET of the present invention), a P-channel MOSFET 101 (corresponding to the second MOSFET of the present invention), a resistor 102, an amplifier 103, and an output terminal OP1.

[0021] The signal terminal SP1 is connected to the signal line SL1. The signal terminal SP1 is electrically connected to the piezoelectric sensor 2. In this way, the piezoelectric sensor 2 is electrically connected to the circuit device 1.

[0022] 1, the resistor 102 is connected between the signal line SL1 and the DC terminal RP1. The resistor 102 is a resistor for determining the DC voltage of the signal line SL1.

[0023] Here, if the impedance of the resistor 102 is Zr and the impedance of the capacitive element 21 is Zc, the output voltage Vout of the signal on the signal line SL1 is Vout = Vin × (Zr / (Zr+Zc)) . To increase the gain of the signal, Zr / (Zr+Zc) should be increased. The lower the frequency of the signal, the higher the value of Zc. However, the frequency of the signal output by the piezoelectric sensor 2 is very low, about 1 Hz, to correspond to the user's pressing operation. Therefore, to increase the gain, Zr must be increased. By increasing the resistance value R of the resistor 102 corresponding to Zr, the first circuit 10 can output an output voltage Vout at an appropriate level in response to the user's pressing operation.

[0024] Furthermore, the resistor 102 and the capacitance element 21 form a high-pass filter. This high-pass filter passes signals with a frequency equal to or higher than a cutoff frequency determined by the resistance value R of the resistor 102 and the capacitance C of the capacitance element 21. The frequency of the signal output by the piezoelectric sensor 2 is very low, about 1 Hz. By setting the resistance value R of the resistor 102 sufficiently high, the cutoff frequency becomes sufficiently lower than 1 Hz. Therefore, the first circuit 10 can pass signals of about 1 Hz.

[0025] Next, FIG. 4 is a circuit diagram showing the details of the P-channel MOSFET 100 and the P-channel MOSFET 101. As shown in FIGS. 1 and 4 , the P-channel MOSFET 100 is electrically connected between the signal terminal SP1 and the power supply terminal PP1. The P-channel MOSFET 100 has a first control electrode CE1, which serves as its gate. The first control electrode CE1 is connected to the power supply terminal PP1. The source of the P-channel MOSFET 100 is also connected to the power supply terminal PP1. The drain of the P-channel MOSFET 100 is connected to the signal terminal SP1. When static electricity that has entered the signal terminal SP1 has negative polarity, the gate potential relative to the source potential becomes lower than a predetermined threshold, turning on the P-channel MOSFET 100. As a result, a current flows from the power supply terminal PP1 to the signal line SL1 via the P-channel MOSFET 100, and the P-channel MOSFET 100 functions as an EDS element that protects various components of the circuit device 1.

[0026] The P-channel MOSFET 101 is electrically connected between the signal terminal SP1 and the ground terminal GP1. The P-channel MOSFET 101 has a second control electrode CE2 which serves as its gate. The second control electrode CE2 is connected to the signal terminal SP1. The source of the P-channel MOSFET 101 is also connected to the signal terminal SP1. The drain of the P-channel MOSFET 101 is connected to the ground terminal GP1.

[0027] The first circuit 10 includes the P-channel MOSFET 100 and the P-channel MOSFET 101. When leakage currents from the P-channel MOSFETs 100 and 101 flow through the resistor 102, a potential difference occurs between the signal line SL1 and the DC terminal RP1. The leakage currents of the two MOSFETs of the same channel type do not vary significantly. Furthermore, the temperature dependence of the leakage currents of the two MOSFETs of the same channel type also does not vary significantly. In other words, the magnitude of the leakage current flowing from the DC terminal RP1 to the signal line SL1 (the leakage current of the P-channel MOSFET 100) is approximately the same as the magnitude of the leakage current flowing from the signal line SL1 to the ground terminal GP1 (the leakage current of the P-channel MOSFET 101). Therefore, the leakage currents of the P-channel MOSFET 100 and the P-channel MOSFET 101 tend to cancel each other out, resulting in a smaller net leakage current. Therefore, even if the resistance value R of the resistor 102 is very large, the effect of the leakage current of the P-channel MOSFETs 100 and 101 on the DC voltage of the signal line SL1 is extremely small. Therefore, the first circuit 10 can suppress fluctuations in the DC voltage. As a result, adverse effects such as temperature drift of the DC voltage of the signal line SL1 and a reduction in the dynamic range of the circuit device 1 due to the temperature drift can be suppressed.

[0028] In particular, if the relationship between the voltage VDD of the power supply terminal PP1, the voltage Vstd of the DC terminal RP1, and the voltage VSS of the ground terminal GP1 is set to "VDD-Vstd=Vstd-VSS," and the P-channel MOSFETs 100 and 101 are the same size, the difference between the magnitude of the leakage current flowing into the signal line SL1 and the magnitude of the leakage current flowing out of the signal line SL1 will be almost zero. Therefore, the fluctuation in the DC voltage of the signal line SL1 can be reduced to almost zero.

[0029] The input of the amplifier 103 is connected to the signal line SL1, and the output of the amplifier 103 is connected to the output terminal OP1. The signal amplified by the amplifier 103 is output to the outside of the circuit device 1 via the output terminal OP1.

[0030] The first circuit 10 may further include an ESD element on the output side of the amplifier 103. If the output impedance of the amplifier 103 is low, the voltage fluctuation due to the leakage current is small, so the ESD element on the output side of the amplifier 103 may be composed of MOSFETs of different channel types. If the output impedance of the amplifier 103 is high, it is preferable to use MOSFETs of the same channel type.

[0031] Next, a capacitor 3 is electrically connected to the output terminal OP1 of the first circuit 10. The capacitor 3 is connected in series between the first circuit 10 and the second circuit 11. The capacitor 3 separates the DC components of the first circuit 10 and the second circuit 11. As shown in FIG. 2 , the capacitor 3 is arranged outside the circuit device 1. As the capacitance of a capacitor increases, the size of the capacitor increases. It is difficult to arrange a capacitor with a large capacitance inside the circuit device 1, which is an IC. For this reason, in this embodiment, a large capacitance is achieved by arranging the capacitor 3 outside the circuit device 1.

[0032] 1, the second circuit 11 is connected between the capacitor 3 and the AD converter 12. The second circuit 11 includes an input terminal SP2, a P-channel MOSFET 110 (corresponding to the first MOSFET of the present invention), a P-channel MOSFET 111 (corresponding to the second MOSFET of the present invention), a resistor 112, a ground terminal GP2 connected to ground, a DC terminal RP2 connected to a DC voltage source, a power supply terminal PP2 connected to a power supply potential, and a signal line SL2.

[0033] The input terminal SP2 is a signal terminal that receives a signal that has passed through the capacitor 3. The input terminal SP2 is electrically connected to the capacitor 3, as shown in FIG.

[0034] The resistor 112 is connected between the signal line SL2 and the DC terminal RP2. The resistor 112 and the capacitor 3 form a high-pass filter. This high-pass filter passes signals with a frequency equal to or higher than a cutoff frequency determined by the resistance value R of the resistor 112 and the capacitance C of the capacitor 3. The frequency of the signal output by the piezoelectric sensor 2 is very low, about 1 Hz. If the resistance value R of the resistor 112 is high, the cutoff frequency will be sufficiently lower than 1 Hz. Therefore, the second circuit 11 can pass signals of about 1 Hz.

[0035] 5 is a circuit diagram showing the P-channel MOSFET 110 and the P-channel MOSFET 110 in detail. As shown in FIGS. 1 and 5, the P-channel MOSFET 110 is electrically connected between the input terminal SP2 and the power supply terminal PP2. The P-channel MOSFET 110 has a first control electrode CE3 which is its gate. The first control electrode CE3 is connected to the power supply terminal PP2. The drain of the P-channel MOSFET 110 is also connected to the power supply terminal PP2. The source of the P-channel MOSFET 110 is connected to the signal line SL2. The other configurations of the P-channel MOSFET 110 are the same as those of the P-channel MOSFET 100, and therefore description thereof will be omitted.

[0036] The P-channel MOSFET 111 is electrically connected between the input terminal SP2 and the ground terminal GP2. The P-channel MOSFET 111 has a second control electrode CE4 which is its gate. The second control electrode CE4 is connected to the input terminal SP2. The drain of the P-channel MOSFET 111 is also connected to the input terminal SP2. The source of the P-channel MOSFET 111 is connected to the ground terminal GP2. The other configurations of the P-channel MOSFET 111 are the same as those of the P-channel MOSFET 101, and therefore description thereof will be omitted.

[0037] Similar to the first circuit 10, the second circuit 11 includes the P-channel MOSFET 110 and the P-channel MOSFET 111. The leakage currents of the P-channel MOSFETs 110 and 111 flow through the resistor 112, generating a potential difference between the signal line SL2 and the DC terminal RP2. The leakage currents of the two MOSFETs of the same channel type do not vary significantly. Furthermore, the temperature dependence of the leakage currents of the two MOSFETs of the same channel type also does not vary significantly. In other words, the magnitude of the leakage current flowing from the DC terminal RP2 to the signal line SL2 (the leakage current of the P-channel MOSFET 110) is approximately the same as the magnitude of the leakage current flowing from the signal line SL2 to the ground terminal GP2 (the leakage current of the P-channel MOSFET 111). Therefore, the leakage currents of the P-channel MOSFET 110 and the P-channel MOSFET 111 tend to cancel each other out. Therefore, even if the resistance value R of the resistor 112 is very large, the influence of the leakage current of the P-channel MOSFETs 110 and 111 on the DC voltage of the signal line SL2 is extremely small. Therefore, the second circuit 11 can suppress fluctuations in the DC voltage.

[0038] 1, the AD converter 12 is connected between the second circuit 11 and the digital filter 13. The AD converter 12 converts the analog signal input from the second circuit 11 into a digital signal.

[0039] The digital filter 13 is connected between the AD converter 12 and the MPU 14. The digital filter 13 digitally filters the signal output by the AD converter 12 to remove signal components outside a predetermined frequency band.

[0040] The MPU 14 (an example of an arithmetic circuit) inputs the signal filtered by the digital filter 13. Based on the input signal, the MPU 14 determines the amount of deformation of an electronic device, such as a smartphone, equipped with the circuit device 1. The amount of deformation of the electronic device is an example of a physical quantity applied to the electronic device and corresponds to the magnitude of the force of a pressing operation on the electronic device. For example, when the MPU 14 detects a signal value equal to or greater than a predetermined threshold value (stored in a storage device, not shown), the MPU 14 determines that a predetermined amount of deformation or greater has occurred in the electronic device and that a pressing operation has been performed by the user. Note that if the sensor device S1 includes a pyroelectric sensor instead of the piezoelectric sensor 2, the physical quantity applied to the electronic device is heat. Note that if the sensor device S1 includes a capacitive sensor instead of the piezoelectric sensor 2, the physical quantity is charge. Of course, the physical quantity may be something other than the amount of deformation, heat, or charge of the electronic device.

[0041] The circuit device 1 does not necessarily have to include the MPU 14 as an arithmetic circuit.

[0042] Example 1 Below, Example 1 of the sensor device S1 will be described in comparison with a comparative example. Fig. 6A is a circuit diagram showing the configuration of Example 1. As shown in Fig. 6A, the circuit of Example 1 corresponds to the circuit shown in Fig. 1 and configured with the second circuit 11 and capacitor 3. The frequency of the signal processed by the circuit of Example 1 is 1 Hz. In Example 1, the capacitance of capacitor 3 is 0.22 µF, the resistance value R of resistor 112 is 40 MΩ, the potential of the power supply terminal PP2 is 1.5 V, the potential of the ground terminal GP2 is 0 V, and the potential of the DC terminal RP2 is 0.5 V.

[0043] 6B is a circuit diagram showing the configuration of the comparative example. As shown in FIG. 6B, the comparative example includes a second circuit 11X that is different from the second circuit 11. The second circuit 11X includes an N-channel MOSFET 111X instead of the P-channel MOSFET 111. In other words, the comparative example includes two MOSFETs with different channel types. The other configurations of the comparative example are the same as those of Example 1, and therefore description thereof will be omitted.

[0044] An experiment was conducted to measure the change in the magnitude of the leakage current in the signal line SL2 with a change in temperature for each of Example 1 and the comparative example. In this experiment, the magnitude of the leakage current in the signal line SL2 for each of Example 1 and the comparative example was measured. In the evaluation of this experiment, a qualitative evaluation was conducted to determine whether the leakage current increased or decreased with a change in temperature, rather than a quantitative evaluation based on the value of the leakage current.

[0045] 7 shows experimental results showing the magnitude of leakage current G1 in the comparative example and the magnitude of leakage current G2 in Example 1. The horizontal axis in FIG. 7 represents temperature (° C.), and the vertical axis in FIG. 7 represents leakage current value (pA).

[0046] Furthermore, an experiment was also conducted to measure the fluctuation in the DC voltage of the signal line SL2 accompanying changes in temperature for Example 1 and the Comparative Example. In this experiment, the amount of fluctuation in the DC component of the signal line SL2 of the second circuit 11 in Example 1 was measured. In this experiment, the amount of fluctuation in the DC component of the signal line SL2 of the second circuit 11X in the Comparative Example was measured. In the evaluation of this experiment, a qualitative evaluation was conducted to determine whether the amount of fluctuation in the DC component increased or decreased due to changes in temperature, rather than a quantitative evaluation based on the value of the amount of fluctuation in the DC component.

[0047] 8 shows experimental results showing the amount of change G3 in the DC voltage in the comparative example and the amount of change G4 in the DC voltage in Example 1. The horizontal axis in FIG. 8 represents temperature (°C), and the vertical axis in FIG. 8 represents the amount of change (mV) in the DC voltage of signal line SL2.

[0048] 7, in the comparative example, the magnitude G1 of the leakage current increases as the temperature increases, and as a result, as shown in FIG. 8, in the comparative example, the fluctuation amount G3 of the DC voltage of the signal line SL2 increases as the temperature increases.

[0049] On the other hand, in Example 1, even when the temperature becomes high, the magnitude of the leakage current G2 is unlikely to increase, as shown in Fig. 7. As a result, as shown in Fig. 8, the fluctuation amount G4 of the DC voltage of the signal line SL2 is much smaller than the fluctuation amount G3 in the comparative example.

[0050] Next, an experiment was conducted in which Example 1 and the Comparative Example were each placed in a space at a temperature of 80° C. for a sufficient period of time, and then placed in a space at a temperature of 20° C. In this experiment, the signal value (the value obtained by digitizing and integrating the DC voltage fluctuation of the signal line SL2) was measured from the time Example 1 and the Comparative Example were placed in a space at a temperature of 20° C. until a predetermined time had elapsed.

[0051] Fig. 9 shows experimental results showing a signal value G5 of the comparative example and a signal value G6 of Example 1. The horizontal axis in Fig. 9 represents time (sec). The vertical axis in Fig. 9 represents the output value of the digital filter 13. In the experiment in Fig. 9, the user did not press the sensor.

[0052] In the experiment shown in FIG. 9 , the temperature decreases (changes) over time. The digital output value of the AD converter 12 in the comparative example fluctuates due to DC voltage fluctuations caused by leakage current due to temperature changes. The digital filter 13 in the comparative example cannot sufficiently suppress the fluctuations in the digital output value of the AD converter 12. Therefore, the signal value G5 in the comparative example fluctuates significantly. Therefore, as shown in FIG. 9 , the signal value G5 increases over time even though the user is not pressing the sensor. After the signal value G5 increases, the temperature of the circuit device 1 drops to approximately 20°C, which is the ambient temperature of the circuit device 1, thereby reducing the rate of change in the leakage current. Therefore, the signal value G5 decreases over time due to the effect of the digital filter 13. As a result, as shown in FIG. 9 , the signal value G5 may exceed the threshold value Th for determining a pressure. Therefore, the comparative example may erroneously determine that a user has pressed the sensor even though the user has not pressed the sensor.

[0053] Furthermore, in the comparative example, a large leakage current occurs due to a change in temperature, and the magnitude of the signal when a small strain occurs in the piezoelectric sensor 2 is very small compared to the magnitude of the leakage current. As a result, the leakage current becomes noise, and the comparative example may not be able to detect the signal from the piezoelectric sensor 2. As a result, the comparative example may have difficulty detecting a user's operation on the piezoelectric sensor 2.

[0054] On the other hand, in the circuit device 1 of Example 1, the temperature dependency of the leakage current of the P-channel MOSFETs 100 and 101 is small. In Example 1, the amount of fluctuation in the signal value G6 due to changes in temperature is very small. Therefore, as shown in FIG. 9 , the amount of change in the signal value G6 due to changes in temperature is very small. As a result, the possibility that the signal value G6 will exceed the threshold value Th is low. Therefore, in Example 1, there is a low possibility that the sensor will erroneously determine that a pressing operation has been performed when the user has not performed a pressing operation on the sensor.

[0055] Furthermore, in Example 1, since the temperature dependency of the leakage current is small, even when a small strain occurs in the piezoelectric sensor 2, the magnitude of the signal from the piezoelectric sensor 2 does not become extremely small compared to the magnitude of the leakage current. Therefore, the leakage current becomes noise, and it is unlikely that the circuit device 1 will be unable to detect the signal from the piezoelectric sensor 2. Therefore, since the circuit device 1 can easily detect changes in the output of the piezoelectric sensor 2, it is possible to provide a sensor device S1 with good sensitivity even in an environment where the temperature is prone to change.

[0056] The piezoelectric elements constituting the piezoelectric film 200 of this embodiment may be made of PVDF (polyvinylidene fluoride) or polylactic acid. However, PVDF has pyroelectric properties. Piezoelectric sensors using piezoelectric elements with pyroelectric properties experience temperature drift. This temperature drift fluctuates the output of the piezoelectric sensor, potentially hindering accurate sensing by the piezoelectric sensor. However, polylactic acid piezoelectric elements do not have pyroelectric properties. Therefore, piezoelectric sensors equipped with such polylactic acid piezoelectric elements are less susceptible to temperature drift.

[0057] On the other hand, a piezoelectric sensor with electrodes formed on both main surfaces of a piezoelectric element such as polylactic acid forms a series capacitance element using this structure. Because the frequency of the signal output by the piezoelectric sensor is very low, at around 1 Hz, the impedance of the series capacitance element has a large effect, resulting in a low sensor signal output. One way to reduce the effect of this impedance is to connect a parallel resistor to increase the resistance value R. However, increasing the resistance value R in a circuit like the comparative example significantly affects the temperature dependency of the leakage current, making it impossible to stabilize the output of the piezoelectric sensor.

[0058] On the other hand, the temperature dependency of the leakage current is small in the circuit device 1 according to Example 1. Therefore, the circuit device 1 according to Example 1 can increase the output of the sensor signal and achieve accurate sensing even when using a piezoelectric sensor having a structure in which electrodes are formed on both main surfaces of a piezoelectric element such as polylactic acid.

[0059] [First Modification of Circuit Device 1] Hereinafter, a circuit device 1a according to a first modification of the circuit device 1 will be described with reference to the drawings. Fig. 10 is a circuit diagram showing a first circuit 10a of the circuit device 1a according to the first modification of the circuit device 1a.

[0060] 10 , the circuit device 1a differs from the circuit device 1 in that it includes a first circuit 10a that is different from the first circuit 10. The first circuit 10a differs from the first circuit 10 in that it includes N-channel MOSFETs 100a and 101a instead of P-channel MOSFETs 100 and 101.

[0061] The N-channel MOSFET 100a (corresponding to the first MOSFET of the present invention) has a first control electrode CE1a different from the first control electrode CE1. The first control electrode CE1a, which is the gate, is connected to a signal terminal SP1. The N-channel MOSFET 101a (corresponding to the second MOSFET of the present invention) has a second control electrode CE2a different from the second control electrode CE2. The second control electrode CE2a, which is the gate, is connected to a DC terminal RP1.

[0062] The leakage currents of the N-channel MOSFETs 100a and 101a of the same channel type do not differ significantly. Furthermore, the temperature dependence of the leakage currents of the two MOSFETs of the same channel type also does not differ significantly. In other words, similar to the circuit device 1, the magnitude of the leakage current flowing from the DC terminal RP1 to the signal line SL1 (the leakage current of the N-channel MOSFET 100a) is approximately the same as the magnitude of the leakage current flowing from the signal line SL1 to the ground terminal GP1 (the leakage current of the N-channel MOSFET 101a). Therefore, for the same reasons as in the circuit device 1, the leakage current of the N-channel MOSFETs 100a and 101a has an extremely small effect on the DC voltage of the signal line SL1.

[0063] The second circuit (not shown) in the circuit device 1 a may include two N-channel MOSFETs instead of the P-channel MOSFETs 110 and 111 .

[0064] [Modification 2 of Circuit Device 1] Hereinafter, a circuit device 1b according to Modification 2 of the circuit device 1 will be described with reference to the drawings. Fig. 11 is a circuit diagram showing a circuit device 1b according to Modification 2 of the circuit device 1.

[0065] 11 , the circuit device 1b differs from the circuit device 1 in that it includes a first circuit 10b that is different from the first circuit 10. The first circuit 10b differs from the first circuit 10 in that it further includes a capacitor 104.

[0066] The capacitor 104 is electrically connected between the signal terminal SP1 and the P-channel MOSFET 100. The capacitor 104 is electrically connected between the signal terminal SP1 and the P-channel MOSFET 101. The capacitor 104 is connected in series to the signal line SL1. In this modification, the capacitor 104 and the resistor 102 effectively form a high-pass filter.

[0067] The circuit device 1b has the same effects as the circuit device 1.

[0068] The circuit device 1 b may include two N-channel MOSFETs instead of the P-channel MOSFET 100 and the P-channel MOSFET 101 .

[0069] [Modification 3 of Circuit Device 1] Hereinafter, a circuit device 1c according to Modification 3 of the circuit device 1 will be described with reference to the drawings. Fig. 12 is a circuit diagram showing the circuit device 1c according to Modification 3 of the circuit device 1.

[0070] As shown in FIG. 12, the circuit device 1c differs from the circuit device 1 in that it includes a first circuit 10c that is different from the first circuit 10, and a second circuit 11c that is different from the second circuit 11.

[0071] The first circuit 10c differs from the first circuit 10 in that it further includes a protection circuit 105c. As shown in FIG. 12 , the protection circuit 105c is electrically connected between the power supply terminal PP1 and the ground terminal GP1. The protection circuit 105c is connected in parallel with the P-channel MOSFETs 100 and 101. The protection circuit 105c is a Zener diode for ESD protection, a MOSFET (a P-channel MOSFET, an N-channel MOSFET), or the like.

[0072] If static electricity that has entered the signal line SL1 of the first circuit 10c has positive polarity, the potential of the signal line SL1 may become equal to or higher than the potential of the power supply terminal PP1. In this case, current flows from the signal line SL1 to the power supply terminal PP1. At this time, the current flowing from the signal line SL1 to the power supply terminal PP1 passes through the first circuit 10c, first through the protection circuit 105c and then through the ground terminal GP1, and is discharged to ground via the ground terminal GP1. In addition, the current is shunted from the signal line SL1 to the ground terminal GP1 via the P-channel MOSFET 101. This protects various components of the circuit device 1c.

[0073] Furthermore, if static electricity that has entered the signal line SL1 of the first circuit 10c has negative polarity, the potential of the signal line SL1 may become equal to or lower than the potential of the ground terminal GP1. In this case, a discharge current flows from the ground terminal GP1 to the signal terminal SP1 via the P-channel MOSFET 101. This protects various components of the circuit device 1c.

[0074] The second circuit 11c differs from the second circuit 11 in that it further includes a protection circuit 115c. As shown in FIG. 8, the protection circuit 115c is electrically connected between the power supply terminal PP2 and the ground terminal GP1. The protection circuit 115c is connected in parallel to the P-channel MOSFETs 110 and 111. The second circuit 11c including the protection circuit 115c protects various components of the circuit device 1c for the same reasons as the first circuit 10c.

[0075] The circuit device 1c has the same effects as the circuit device 1.

[0076] [Other Embodiments] The description of the present embodiment should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above-described embodiments. Furthermore, the scope of the present invention includes the scope equivalent to the claims.

[0077] The circuit device according to the present invention is not limited to the circuit devices 1, 1a to 1c, and can be modified within the scope of the gist thereof. The configurations of the circuit devices 1, 1a to 1c may be combined in any manner.

[0078] The present invention has the following structure:

[0079] (1) A circuit device comprising: a power supply terminal connected to a power supply potential; a reference potential terminal connected to a reference potential; a signal terminal connected to a signal line; a first MOSFET electrically connected between the signal terminal and the power supply terminal and having a first control electrode; and a second MOSFET electrically connected between the signal terminal and the reference potential terminal and having a second control electrode, wherein the first MOSFET and the second MOSFET are configured as same-channel MOSFETs, and the first control electrode is connected to the signal terminal and the second control electrode is connected to the reference potential terminal, or the first control electrode is connected to the power supply terminal and the second control electrode is connected to the signal terminal.

[0080] (2) The circuit device according to (1), further comprising: a capacitor electrically connected between the signal terminal and the first MOSFET and the second MOSFET.

[0081] (3) The circuit device according to (1) or (2), further comprising: a protection circuit electrically connected between the power supply terminal and the reference potential terminal.

[0082] (4) The circuit device according to any one of (1) to (3), wherein the signal terminal is electrically connected to an external component disposed outside the circuit device.

[0083] (5) A sensor device comprising: the circuit device according to any one of (1) to (4); and an external component disposed outside the circuit device and electrically connected to the circuit device, wherein the external component is a sensor connected to the signal terminal, and the sensor is a piezoelectric sensor, a pyroelectric sensor, or a capacitive sensor.

[0084] (6) The sensor device according to (5), wherein the sensor is connected between the signal terminal and a reference voltage source and is configured as a series-connected circuit of an AC signal source and a capacitive element.

[0085] (7) A determination device comprising: the sensor device according to (5) or (6); and an arithmetic circuit that determines a physical quantity applied to the sensor device based on an output signal of the sensor.

[0086] (8) The circuit device according to any one of (1) to (4), wherein the circuit device includes a first circuit having an output terminal and a second circuit having an input terminal as the signal terminal, the second circuit includes the first MOSFET and the second MOSFET, and the output terminal and the input terminal are electrically connected to a capacitor disposed outside the circuit device.

[0087] 1, 1a to 1c: Circuit device 2: Piezoelectric sensor 3: Capacitor 10, 10a to 10c: First circuit 11, 11X, 11c: Second circuit 12: AD converter 13: Digital filter 14: MPU 20: AC signal source 21: Capacitor 102, 112: Resistor 103: Amplifier 104: Capacitor 105c, 115c: Protection circuit 200: Piezoelectric film 201: First electrode 202: Second electrode CE1, CE1a, CE3: First control electrode CE2, CE2a, CE4: Second control electrode G1, G2: Leakage current magnitude G3, G4: Fluctuation amount G5, G6: Signal value GP1, GP2: Ground terminal GP3: Ground 100, 101, 110, 111: P-channel MOSFET 100a, 101a, 111X: N-channel MOSFET OP1: Output terminal PP1, PP2: Power supply terminal RP1, RP2: DC terminal S1: Sensor device SF1: First film main surface SF2: Second film main surface SL1, SL2: Signal line SP1: Signal terminal SP2: Input terminal Th: Threshold value

Claims

1. A circuit device comprising: a power supply terminal connected to a power supply potential; a reference potential terminal connected to a reference potential; a signal terminal connected to a signal line; a first MOSFET electrically connected between the signal terminal and the power supply terminal and having a first control electrode; and a second MOSFET electrically connected between the signal terminal and the reference potential terminal and having a second control electrode, wherein the first MOSFET and the second MOSFET are configured as same-channel type MOSFETs, and the first control electrode is connected to the signal terminal and the second control electrode is connected to the reference potential terminal, or the first control electrode is connected to the power supply terminal and the second control electrode is connected to the signal terminal.

2. The circuit device according to claim 1, further comprising a capacitor electrically connected between the signal terminal and the first MOSFET and between the signal terminal and the second MOSFET.

3. The circuit device according to claim 1 or 2, further comprising a protection circuit electrically connected between the power supply terminal and the reference potential terminal.

4. The circuit device according to claim 1, wherein the signal terminal is electrically connected to an external component disposed outside the circuit device.

5. A sensor device comprising: a circuit device according to any one of claims 1 to 4; and an external component arranged outside the circuit device and electrically connected to the circuit device, wherein the external component is a sensor connected to the signal terminal, and the sensor is a piezoelectric sensor, a pyroelectric sensor, or a capacitive sensor.

6. The sensor device according to claim 5, wherein the sensor is connected between the signal terminal and a reference voltage source and is configured as a series-connected circuit of an AC signal source and a capacitive element.

7. A determination device comprising: a sensor device according to claim 5 or 6; and an arithmetic circuit that determines a physical quantity applied to the sensor device based on an output signal of the sensor.

8. The circuit device according to any one of claims 1 to 4, wherein the circuit device includes a first circuit having an output terminal and a second circuit having an input terminal as the signal terminal, the second circuit includes the first MOSFET and the second MOSFET, and the output terminal and the input terminal are electrically connected to a capacitor disposed outside the circuit device.

Images