WO2025028142A1 - Circuit device, sensor device, and determination device - Google Patents

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 DETECTION DEVICE

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

　Conventionally, ESD elements have been placed in circuits 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 between a signal line and a power supply potential or between a signal line and a ground potential as an ESD element.

Japanese Patent Application Publication No. 11-121750

When connecting circuit blocks with different reference DC voltages, a capacitive 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 capacitive element of about several μF must be used to process signals with low frequencies, for example, of about several Hz. However, it is extremely difficult to provide a large-capacity element inside an IC. Therefore, it is possible to consider increasing the resistance value of the parallel resistor.

In addition, circuits connected to sensors with capacitance, such as piezoelectric sensors, pyroelectric sensors, or capacitive sensors, also connect a resistor between a reference DC voltage source and the signal line to determine the DC voltage in the signal line. If the impedance of the resistor is Zr and the impedance of the capacitance is Zc, then the output voltage Vout of the sensor signal is Vout = Vin x (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 about a few Hz, it is possible to increase the resistance value of the resistor and the value of Zr.

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 that even if a small leakage current occurs in the ESD element, the fluctuation in the DC voltage of the signal line will be very large.

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

A circuit device according to an 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, the first MOSFET having a first control electrode;
a second MOSFET electrically connected between the signal terminal and the reference potential terminal and having a second control electrode;
Equipped with
the first MOSFET and the second MOSFET are configured as same-channel type MOSFETs,
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.

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

FIG. 1 is a circuit diagram showing a circuit device 1 and a sensor device S1 according to the first embodiment. FIG. 2 is a diagram showing the configuration of the piezoelectric sensor 2. As shown in FIG. FIG. 3 is an equivalent circuit diagram of the piezoelectric sensor 2. As shown in FIG. FIG. 4 is a circuit diagram showing the details of the P-channel MOSFET 100 and the P-channel MOSFET 101. FIG. 5 is a circuit diagram showing the P-channel MOSFET 110 and the details of the P-channel MOSFET 110. As shown in FIG. Fig. 6A is a circuit diagram showing a configuration of Example 1. Fig. 6B is a circuit diagram showing a configuration of a comparative example. FIG. 7 shows the experimental results showing the magnitude G1 of the leakage current in the comparative example and the magnitude G2 of the leakage current in the first embodiment. FIG. 8 shows experimental results illustrating the amount of fluctuation G3 of the DC voltage in the comparative example and the amount of fluctuation G4 of the DC voltage in the first embodiment. FIG. 9 shows the experimental results showing a signal value G5 of the comparative example and a signal value G6 of 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 modified example of the circuit device 1. As shown in FIG. FIG. 12 is a circuit diagram showing a circuit device 1c according to a third modified example of the circuit device 1. As shown in FIG.

[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.

The sensor device S1 is a device provided in an electronic device such as a smartphone. As shown in FIG. 1, the sensor device S1 includes a circuit device 1, a piezoelectric sensor 2, and a capacitor 3.

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 0V, and may be a potential other than 0V. The piezoelectric sensor 2 is an example of an external component disposed outside the circuit device 1. As an example, the piezoelectric sensor 2 generates an electric charge according to the amount of change in the user's pressure on the touch panel display.

FIG. 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.

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.

Piezoelectric film 200 is polarized according to the deformation amount of piezoelectric film 200. For example, piezoelectric film 200 is a film formed from a chiral polymer. Chiral polymer is, for example, polylactic acid (PLA), particularly L-type polylactic acid (PLLA). PLLA, which is made of a chiral polymer, has a main chain with a helical structure. Piezoelectric film 200 has a piezoelectric constant of d14. Piezoelectric film 200 has piezoelectricity in which the molecules are oriented in the orientation direction when uniaxially stretched. The orientation direction forms an angle of 45 degrees with respect to a predetermined direction (hereinafter, X-axis direction), for example. This 45 degrees includes angles including about 45 degrees ±10 degrees. The potential difference between first film principal surface SF1 and second film principal surface SF2 when polarized depends on the time differential value of the deformation amount of 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 perpendicular to the X-axis direction. The piezoelectric film 200 functions as an AC signal source that generates an AC signal.

FIG. 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.

The sensor device S1 may be equipped with a pyroelectric sensor or a capacitive sensor instead of the piezoelectric sensor 2. The pyroelectric sensor or capacitive sensor is equivalently configured as a series-connected circuit of a capacitive element and an AC voltage source, similar to the piezoelectric sensor 2.

The circuit device 1 is, for example, an IC (Integrated Circuit). 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.

[Configuration of first circuit 10]
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.

The signal terminal SP1 is connected to the signal line SL1. The signal terminal SP1 is electrically connected to the piezoelectric sensor 2. As a result, the piezoelectric sensor 2 is electrically connected to the circuit device 1.

As shown in FIG. 1, resistor 102 is connected between signal line SL1 and DC terminal RP1. Resistor 102 is a resistor that determines the DC voltage of signal line SL1.

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

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 the 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, at approximately 1 Hz. By making 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 approximately 1 Hz.

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 FIG. 1 and FIG. 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 is a 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 the static electricity that has entered the signal terminal SP1 has a negative polarity, the gate potential relative to the source potential becomes lower than a predetermined threshold value, and the P-channel MOSFET 100 is turned on. As a result, a current flows from the power supply terminal PP1 to the signal line SL1 via the P-channel MOSFET 100, and functions as an EDS element that protects various components of the circuit device 1.

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 is a 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.

The first circuit 10 includes the P-channel MOSFET 100 and the P-channel MOSFET 101, and the leakage currents of the P-channel MOSFETs 100 and 101 flow through the resistor 102, generating a potential difference between the signal line SL1 and the DC terminal RP1. Here, the leakage currents of the two MOSFETs of the same channel type do not change significantly. In addition, the temperature dependency characteristics of the leakage currents of the two MOSFETs of the same channel type do not change significantly. In other words, the magnitude of the leakage current (leakage current of the P-channel MOSFET 100) flowing from the DC terminal RP1 to the signal line SL1 is approximately the same as the magnitude of the leakage current (leakage current of the P-channel MOSFET 101) flowing from the signal line SL1 to the ground terminal GP1. Therefore, the leakage current of the P-channel MOSFET 100 and the leakage current of the P-channel MOSFET 101 tend to cancel each other out, and the net leakage current becomes smaller. For this reason, even if the resistance value R of resistor 102 is very large, the effect of the leakage current of P-channel MOSFETs 100 and 101 on the DC voltage of 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 signal line SL1 and a decrease in the dynamic range of the circuit device 1 due to the temperature drift can be suppressed.

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 nearly zero. This makes it possible to reduce the fluctuation in the DC voltage of the signal line SL1 to nearly zero.

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

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.

Next, the 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. The capacitor 3 is arranged outside the circuit device 1 as shown in FIG. 2. The size of a capacitor increases as the capacitance 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.

[Configuration of second circuit 11]
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 the 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.

The input terminal SP2 is a signal terminal that inputs a signal that has passed through the capacitor 3. As shown in FIG. 1, the input terminal SP2 is electrically connected to the capacitor 3.

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

FIG. 5 is a circuit diagram showing the P-channel MOSFET 110 and the details of the P-channel MOSFET 110. 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 the 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, so a description thereof will be omitted.

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 rest of the configuration of the P-channel MOSFET 111 is the same as the configuration of the P-channel MOSFET 101, so a description thereof will be omitted.

The second circuit 11, like the first circuit 10, includes the P-channel MOSFET 110 and the P-channel MOSFET 111, and 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. Here, the leakage currents of the two MOSFETs of the same channel type do not change significantly. In addition, the temperature dependency characteristics of the leakage currents of the two MOSFETs of the same channel type do not change significantly. In other words, the magnitude of the leakage current (leakage current of the P-channel MOSFET 110) flowing from the DC terminal RP2 to the signal line SL2 is approximately the same as the magnitude of the leakage current (leakage current of the P-channel MOSFET 111) flowing from the signal line SL2 to the ground terminal GP2. Therefore, the leakage current of the P-channel MOSFET 110 and the leakage current of the P-channel MOSFET 111 tend to cancel each other out. Therefore, even if the resistance value R of resistor 112 is very large, the effect of the leakage current of P-channel MOSFETs 110 and 111 on the DC voltage of signal line SL2 is extremely small. Therefore, the second circuit 11 can suppress fluctuations in the DC voltage.

[Configuration of AD converter 12, digital filter 13, and MPU 14]
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.

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 specified frequency band.

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 the electronic device, such as a smartphone, that includes 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 the pressing operation on the electronic device. For example, when the MPU 14 detects a signal value that is equal to or greater than a predetermined threshold value that is set in advance (stored in a storage device, not shown), it determines that the electronic device has been deformed by a predetermined amount or more, and determines 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 a heat quantity. Note that, if the sensor device S1 includes a capacitive sensor instead of the piezoelectric sensor 2, the physical quantity is a charge quantity. Of course, the physical quantity may be something other than the amount of deformation, heat quantity, or charge quantity of the electronic device.

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

[Example 1]
A first embodiment of the sensor device S1 will be described below in comparison with a comparative example. Fig. 6A is a circuit diagram showing the configuration of the first embodiment. As shown in Fig. 6A, the circuit of the first embodiment corresponds to the circuit shown in Fig. 1 and configured with the second circuit 11 and the capacitor 3. The frequency of the signal processed by the circuit of the first embodiment is 1 Hz. In the first embodiment, the capacitance of the capacitor 3 is 0.22 μF, the resistance value R of the 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.

FIG. 6(B) is a circuit diagram showing the configuration of the comparative example. As shown in FIG. 6(B), the comparative example has a second circuit 11X that is different from the second circuit 11. The second circuit 11X has an N-channel MOSFET 111X instead of a P-channel MOSFET 111. In other words, the comparative example has two MOSFETs with different channel types. The other configuration of the comparative example is the same as the configuration of Example 1, so a description thereof will be omitted.

An experiment was conducted to measure the change in the magnitude of the leakage current in the signal line SL2 associated with changes in temperature for Example 1 and the Comparative Example. In this experiment, the magnitude of the leakage current in the signal line SL2 for Example 1 and the Comparative Example was measured. The evaluation of this experiment was not a quantitative evaluation based on the value of the leakage current, but a qualitative evaluation of whether the leakage current increased or decreased due to changes in temperature.

Figure 7 shows the 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 Figure 7 is temperature (°C). The vertical axis in Figure 7 is leakage current value (pA).

Furthermore, an experiment was also conducted to measure the fluctuation in the DC voltage of 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 signal line SL2 of second circuit 11 in Example 1 was measured. In this experiment, the amount of fluctuation in the DC component of signal line SL2 of second circuit 11X in the Comparative Example was measured. In the evaluation of this experiment, a qualitative evaluation was conducted to see 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.

Figure 8 shows the experimental results showing the amount of DC voltage fluctuation G3 in the comparative example and the amount of DC voltage fluctuation G4 in Example 1. The horizontal axis in Figure 8 is temperature (°C). The vertical axis in Figure 8 is the amount of DC voltage fluctuation (mV) of signal line SL2.

As shown in FIG. 7, in the comparative example, the magnitude G1 of the leakage current increases as the temperature increases. 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.

On the other hand, in Example 1, as shown in Figure 7, the magnitude G2 of the leakage current is unlikely to increase even when the temperature is high. As a result, as shown in Figure 8, the fluctuation amount G4 of the DC voltage of signal line SL2 is very small compared to the fluctuation amount G3 in the comparative example.

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

FIG. 9 shows the experimental results showing signal value G5 of the comparative example and signal value G6 of Example 1. The horizontal axis in FIG. 9 is time (sec). The vertical axis in FIG. 9 is the output value of the digital filter 13. In the experiment in FIG. 9, the user did not perform a pressing operation on the sensor.

In the experiment of FIG. 9, the temperature decreases (changes) over time. The digital output value of the AD converter 12 of the comparative example changes due to the influence of DC voltage fluctuation caused by leakage current due to temperature change. The digital filter 13 of the comparative example cannot sufficiently suppress the fluctuation of the digital output value in the AD converter 12. Therefore, the signal value G5 of the comparative example changes greatly. Therefore, as shown in FIG. 9, the signal value G5 increases over time even though the user does not press the sensor. After the signal value G5 increases, the temperature of the circuit device 1 drops to around 20° C., which is the temperature around the circuit device 1, so the rate of change in the leakage current becomes smaller. 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 be equal to or greater than the threshold value Th for determining pressing. Therefore, in the comparative example, it may be erroneously determined that the user has pressed the sensor even though the user has not pressed the sensor.

In addition, in the comparative example, a large leakage current occurs due to a change in temperature, so the magnitude of the signal when a small distortion occurs in the piezoelectric sensor 2 is very small compared to the magnitude of the leakage current. For this reason, the leakage current becomes noise, and in the comparative example, the signal of the piezoelectric sensor 2 may not be detected. As a result, in the comparative example, it may be difficult to detect a user's operation on the piezoelectric sensor 2.

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. For this reason, 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 signal value G6 is unlikely to be equal to or greater than the threshold value Th. For this reason, Example 1 is unlikely to erroneously determine that a pressing operation has been performed when the user has not performed a pressing operation on the sensor.

In addition, in Example 1, since the temperature dependency of the leakage current is small, even when a small distortion 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. For this reason, 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.

The piezoelectric elements constituting the piezoelectric film 200 of this embodiment may be PVDF (polyvinylidene fluoride) or polylactic acid. However, PVDF has pyroelectricity. A piezoelectric sensor using a piezoelectric element having this pyroelectricity will experience temperature drift. This temperature drift will fluctuate the output of the piezoelectric sensor, and may hinder accurate sensing by the piezoelectric sensor. Here, a piezoelectric element made of polylactic acid does not have pyroelectricity. Therefore, a piezoelectric sensor equipped with a piezoelectric element made of this polylactic acid is less likely to experience temperature drift.

On the other hand, a piezoelectric sensor in which electrodes are formed on both main surfaces of a piezoelectric element such as polylactic acid forms a series capacitance element with this structure. Because the frequency of the signal output by a piezoelectric sensor is very low at around 1 Hz, the effect of the impedance of the series capacitance element becomes large, and the output of the sensor signal becomes low. One way to suppress the effect of this impedance is to connect a resistor in parallel to increase the resistance value R. However, if the resistance value R is increased, a circuit like the comparative example will be significantly affected by the temperature dependency of the leakage current, and the output of the piezoelectric sensor cannot be stabilized.

On the other hand, in the circuit device 1 according to the first embodiment, the temperature dependency of the leakage current is small. Therefore, in the circuit device 1 according to the first embodiment, even if the piezoelectric sensor has a structure in which electrodes are formed on both main surfaces of a piezoelectric element such as polylactic acid, it is possible to increase the output of the sensor signal and achieve accurate sensing.

[Modification 1 of Circuit Device 1]
Hereinafter, a description will be given with reference to the drawings of a circuit device 1a according to the first modification of the circuit device 1. 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.

As shown in FIG. 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.

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. 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.

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

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

[Modification 2 of Circuit Device 1]
Hereinafter, a circuit device 1b according to the second modified example 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 the second modified example of the circuit device 1.

As shown in FIG. 11, circuit device 1b differs from circuit device 1 in that it includes a first circuit 10b that is different from first circuit 10. First circuit 10b differs from first circuit 10 in that it further includes capacitor 104.

Capacitor 104 is electrically connected between signal terminal SP1 and P-channel MOSFET 100. Capacitor 104 is electrically connected between signal terminal SP1 and P-channel MOSFET 101. Capacitor 104 is connected in series to signal line SL1. In this modified example, capacitor 104 and resistor 102 effectively form a high-pass filter.

Circuit device 1b has the same effect as circuit device 1.

In addition, the circuit device 1b may include two N-channel MOSFETs instead of the P-channel MOSFET 100 and the P-channel MOSFET 101.

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

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

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 (P-channel MOSFET, N-channel MOSFET), etc.

If the static electricity that has entered the signal line SL1 of the first circuit 10c has positive polarity, there is a possibility that the potential of the signal line SL1 will be equal to or higher than the potential of the power supply terminal PP1. In this case, a current flows from the signal line SL1 to the power supply terminal PP1. At this time, the current that flows from the signal line SL1 to the power supply terminal PP1 passes through the first circuit 10c, in the order of the protection circuit 105c and 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 the various components of the circuit device 1c.

Furthermore, if the 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 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 the various components of the circuit device 1c.

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, which includes the protection circuit 115c, protects various components of the circuit device 1c for the same reasons as the first circuit 10c.

Circuit device 1c has the same effect as circuit device 1.

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

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

The present invention has the following structure:

(1)
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, the first MOSFET having a first control electrode;
a second MOSFET electrically connected between the signal terminal and the reference potential terminal and having a second control electrode;
Equipped with
the first MOSFET and the second MOSFET are configured as same-channel type MOSFETs,
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.
Circuit device.

(2)
a capacitor electrically connected between the signal terminal and the first MOSFET and the second MOSFET;
A circuit device as described in (1).

(3)
a protection circuit electrically connected between the power supply terminal and the reference potential terminal;
A circuit device according to (1) or (2).

(4)
the signal terminal is electrically connected to an external component disposed outside the circuit device;
A circuit device according to any one of (1) to (3).

(5)
A circuit device according to any one of (1) to (4);
an external component disposed outside the circuit device and electrically connected to the circuit device;
Equipped with
the external component is a sensor connected to the signal terminal,
The sensor is a piezoelectric sensor, a pyroelectric sensor, or a capacitive sensor.
Sensor device.

(6)
The sensor includes:
connected between the signal terminal and a reference voltage source;
It is composed of a series connection circuit of an AC signal source and a capacitance element.
A sensor device as described in (5).

(7)
A sensor device according to (5) or (6),
a calculation circuit for determining a physical quantity applied to the sensor device based on an output signal of the sensor;
A determination device comprising:

(8)
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;
the output terminal and the input terminal are electrically connected to a capacitor disposed outside the circuit device;
A circuit device according to any one of (1) to (4).

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 elements 102, 112: Resistor 103: Amplifier 104: Capacitors 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 terminals 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 (8)

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, the first MOSFET having a first control electrode;
a second MOSFET electrically connected between the signal terminal and the reference potential terminal and having a second control electrode;
Equipped with
the first MOSFET and the second MOSFET are configured as same-channel type MOSFETs,
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.
Circuit device. a capacitor electrically connected between the signal terminal and the first MOSFET and the second MOSFET;
The circuit device according to claim 1 . a protection circuit electrically connected between the power supply terminal and the reference potential terminal;
3. The circuit device according to claim 1 or 2. the signal terminal is electrically connected to an external component disposed outside the circuit device;
The circuit device according to any one of claims 1 to 3. A circuit device according to any one of claims 1 to 4;
an external component disposed outside the circuit device and electrically connected to the circuit device;
Equipped with
the external component is a sensor connected to the signal terminal,
The sensor is a piezoelectric sensor, a pyroelectric sensor, or a capacitive sensor.
Sensor device. The sensor includes:
connected between the signal terminal and a reference voltage source;
It is composed of a series connection circuit of an AC signal source and a capacitance element.
The sensor device according to claim 5 . The sensor device according to claim 5 or 6,
a calculation circuit for determining a physical quantity applied to the sensor device based on an output signal of the sensor;
A determination device comprising: 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;
the output terminal and the input terminal are electrically connected to a capacitor disposed outside the circuit device;
The circuit device according to any one of claims 1 to 4.

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