JP2010062599A - Hysteresis comparator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hysteresis comparator capable of drastically reducing its circuit scale. <P>SOLUTION: The hysteresis comparator is provided with: a ferroelectric capacitor Cs; an input terminal T1 for receiving input voltage Vin and outputting the input voltage Vin to the ferroelectric capacitor Cs; a reference capacitor Co connected to the ferroelectric capacitor Cs in series; and a switching circuit SW1 for outputting output voltage Vout, wherein a control terminal Tg is connected to a connection point between the ferroelectric capacitor Cs and the reference capacitor Co. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hysteresis comparator.

In recent years, various hysteresis comparators have been proposed. For example, in Patent Document 1, as shown in FIG. 13, a differential amplifier circuit including six MOSFETs (M1) to (M6) and a current source (I1), a MOSFET (M7), and a current source ( And a hysteresis comparator constituted by an output amplifier circuit constituted by I2). A technique for providing a hysteresis comparator having a reduced circuit scale by changing the gate length and gate width of the MOSFETs (M3) and (M4) according to the level of the output voltage is disclosed.
JP 2008-5547 A

  However, as shown in Patent Document 1, a conventional hysteresis comparator employs a configuration mainly including a transistor in which a plurality of transistors are combined. Therefore, there is a certain limit in reducing the circuit scale. For example, in Patent Document 1, although the circuit scale is reduced, at least seven transistors are required as shown in FIG.

  An object of the present invention is to provide a hysteresis comparator capable of greatly reducing the circuit scale.

  (1) A hysteresis comparator according to one aspect of the present invention is characterized by using a ferroelectric capacitor.

  According to this configuration, since the hysteresis comparator is configured using the ferroelectric capacitor having the hysteresis function, the hysteresis comparator can be realized without providing a plurality of transistors in order to provide the hysteresis function. As a result, it is possible to provide a hysteresis comparator whose circuit scale is significantly reduced as compared with a conventional hysteresis comparator mainly composed of transistors.

  (2) a first input terminal to which a first input voltage is input and output to the ferroelectric capacitor; a reference capacitor connected in series to the ferroelectric capacitor; the ferroelectric capacitor and the reference capacitor; And a switching circuit that outputs an output voltage.

  The ferroelectric capacitor reverses its polarization when the voltage input from the outside rises and exceeds the positive threshold. At this time, the charge of the reference capacitor induced by the spontaneous polarization of the ferroelectric capacitor is also inverted, and the charge induced in the reference capacitor is discharged and an instantaneous discharge current (voltage) having a peak on the positive side is generated. And the voltage at the control terminal is increased, and the switching circuit is turned on, for example.

  On the other hand, when the voltage input from the outside falls below the negative threshold value of the ferroelectric capacitor, the charge induced in the reference capacitor is reversed and the peak having a negative peak is obtained in the same manner as described above. A discharge current (voltage) is output, the voltage at the control terminal decreases, and the switching circuit is turned off, for example.

  Here, the hysteresis comparator is mainly composed of three circuit elements such as a ferroelectric capacitor, a reference capacitor, and a switching circuit. Therefore, the number of circuit elements can be greatly reduced as compared with a conventional hysteresis comparator mainly including transistors. Thereby, it is possible to provide a hysteresis comparator whose circuit scale is significantly reduced.

  In addition, since a switching circuit is provided, current backflow, such as current flowing from the switching circuit to the ferroelectric capacitor side through the control terminal, is prevented, and the operation of the circuit can be stabilized. Therefore, impedance matching of the circuit can be easily performed.

(3) a resistor connected between the reference capacitor and ground;
A second input terminal connected to the resistor and the reference capacitor and receiving a second input voltage is preferably provided.

  According to this configuration, a comparator that compares two inputs can be provided.

  (4) An input-side diode having the anode connected to the first input terminal and a cathode connected to the ferroelectric capacitor, and a voltage applied to the ferroelectric capacitor are set to be negative of the ferroelectric capacitor. It is preferable to include an offset voltage unit that outputs an offset voltage for lowering the threshold voltage on the side, and an offset diode in which the offset voltage is input to the cathode and the anode is connected to the cathode of the input side diode.

  When the first input voltage is positive, the input-side diode is turned on, and the first input voltage is input to the ferroelectric capacitor. On the other hand, when the first input voltage becomes negative, the offset diode is turned on, the offset voltage is applied to the ferroelectric capacitor, and a voltage lower than the negative threshold value of the ferroelectric capacitor is applied. As a result, an instantaneous discharge current having a peak on the negative side is output from the ferroelectric capacitor, the voltage at the control terminal is lowered, and the switching circuit is turned off.

  Therefore, the switching circuit that has been turned on can be quickly turned off, and a monostable hysteresis comparator can be provided.

  (5) The ferroelectric capacitor and the reference capacitor are configured by one circuit element, and the circuit element is formed on a substrate, a lower electrode formed on an upper layer of the substrate, and an upper layer of the lower electrode. The first dielectric layer, the intermediate electrode formed on the first dielectric layer, the second dielectric layer formed on the intermediate electrode, and the second dielectric layer An upper electrode formed on an upper layer of the first dielectric layer, wherein the first dielectric layer is composed of a paraelectric material when the second dielectric layer is composed of a ferroelectric material; When the body layer is made of a paraelectric material, it is preferably made of a ferroelectric material.

  According to this configuration, the ferroelectric capacitor and the reference capacitor can be configured by one circuit element, and the circuit scale can be further reduced.

  (6) It is preferable that the capacitance of the reference capacitor is larger than the capacitance of the ferroelectric capacitor.

  According to this configuration, a hysteresis comparator is provided in which the voltage applied to both ends of the ferroelectric capacitor is larger than the voltage applied to both ends of the reference capacitor, and can accurately react to changes in the input voltage. can do.

  (7) It is preferable that the ferroelectric capacitor is made of a fat free ferroelectric.

  According to this configuration, even when the number of times of switching of the hysteresis comparator increases, polarization fatigue is reduced, and a highly durable hysteresis comparator can be provided.

  (8) The reference capacitor is preferably composed of a relaxor dielectric.

  According to this configuration, the capacitance of the reference capacitor can be easily made larger than the capacitance of the ferroelectric capacitor.

  According to the present invention, it is possible to provide a hysteresis comparator whose circuit scale is significantly reduced.

(Embodiment 1)
The hysteresis comparator according to Embodiment 1 of the present invention will be described below. FIG. 1 is a circuit diagram showing the overall configuration of a hysteresis comparator according to Embodiment 1 of the present invention. As shown in FIG. 1, the hysteresis comparator includes an input terminal T1, a ferroelectric capacitor Cs, a reference capacitor Co, a switching circuit SW1, and an output terminal Tout.

The input terminal T1 receives the input voltage Vin and outputs it to the ferroelectric capacitor Cs. The ferroelectric capacitor Cs is connected between the input terminal T1 and the reference capacitor Co. In the present embodiment, as the ferroelectric capacitor Cs, for example, lead zirconate titanate (Pb (Zr, Ti) O ₃ ), barium titanate (BaTiO ₃ ), lead lanthanum zirconate titanate ((Pb, La ) (Zr, Ti) O ₃ ), lead titanate (PbTiO ₃ ), potassium niobate (KNbO ₃ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), ammonium sulfate NH ₃ LiSO ₄ , Ferroelectric materials such as K ₂ ZnCl ₄ and (N (CH ₃ ) ₄ ) ₂ ZnCl ₄ may be used. In addition, as the ferroelectric capacitor Cs,
An antiferroelectric material or a ferrielectric material may be employed. Examples of the antiferroelectric material and ferrielectric material include PbZrO ₃ and Pb (Nb, Zr, Sn, Ti) O ₃ that are lead zirconate-based materials, and RbLiSO ₄ that is an ammonium sulfate-based material.

  There are many substances that exhibit ferroelectricity at low temperatures, but the above substances have a phase transition point to a paraelectric material at room temperature or higher, so that they can be used as ferroelectrics, antiferroelectrics, and ferrielectrics at room temperature Can be used.

In addition, since the above ferroelectrics are fatigued (deteriorated) due to repeated polarization inversion, there is a problem in the durability of the device when the switching frequency of the hysteresis comparator is increased. This problem can be solved by employing a fatig-free ferroelectric. Examples of the fat-free ferroelectric include bismuth-based ferroelectrics such as BaBi ₂ Ta ₂ O ₉ , SrBi ₂ Ta ₂ O ₉ , (Bi, La) ₄ Ti ₃ O _{12, and the} like.

  FIG. 2 is a diagram showing hysteresis characteristics of the ferroelectric capacitor Cs. In the graph shown in the center, the vertical axis indicates the polarization of the ferroelectric capacitor Cs, and the horizontal axis indicates the voltage applied to both ends of the ferroelectric capacitor Cs.

  As shown in FIG. 2, when the voltage is increased from the point P1, the polarization value increases accordingly, and when the voltage exceeds the positive threshold, the polarization is reversed from negative to positive. When the voltage is further increased and the voltage reaches the point P2, the polarization value is saturated and does not increase even if the voltage is further increased. When the voltage is lowered from the point P2, the polarization value decreases accordingly. When the voltage is further decreased and the voltage falls below the negative threshold, the polarization is reversed from positive to negative. Thus, it can be seen that the ferroelectric capacitor Cs has a hysteresis because the voltage when the polarization is inverted from negative to positive is higher than the voltage when the polarization is inverted from positive to negative.

  The reference capacitor Co is connected in series with the ferroelectric capacitor Cs. Specifically, the reference capacitor Co has one end connected to the ferroelectric capacitor Cs and the other end connected to the ground. As the reference capacitor Co, it is preferable to use, for example, a relaxor dielectric as will be described later.

  In the present embodiment, the capacitance CCo of the reference capacitor Co is larger than the capacitance CCs of the ferroelectric capacitor Cs. That is, CCo> CCs. Therefore, a hysteresis comparator is provided in which the voltage Vcs applied to both ends of the ferroelectric capacitor Cs is larger than the voltage Vco applied to both ends of the reference capacitor, and can accurately react to changes in the input voltage. be able to.

  The switching circuit SW1 includes a transistor Q1 and a resistor R1. The transistor Q1 is composed of, for example, an npn bipolar transistor, the base as the control terminal Tg is connected to the connection point between the ferroelectric capacitor Cs and the reference capacitor Co, the emitter is connected to the ground via the resistor R1, The collector is connected to the voltage source Vdd.

  The output terminal Tout is connected to the emitter of the transistor Q1 and outputs the output voltage Vout.

  FIG. 3 is a waveform diagram showing the operation of the hysteresis comparator shown in FIG. 3A shows the input voltage Vin, FIG. 3B shows the current output from the ferroelectric capacitor Cs, and FIG. 3C shows the output voltage Vout.

  As shown in FIG. 3A, an input voltage Vin that is a sine wave is input to the input terminal T1. When the input voltage Vin exceeds the positive threshold value Vth1, the voltage Vcs exceeds the positive threshold value of the ferroelectric capacitor Cs, and the polarization is reversed. At this time, the charge of the reference capacitor Cs induced by the spontaneous polarization of the ferroelectric capacitor Cs is also inverted, and the charge induced in the reference capacitor Cs is discharged to output an instantaneous discharge current having a peak on the positive side. (FIG. 3B) As a result, the gate voltage Vg applied to the control terminal Tg is raised, and the transistor Q1 is turned on. As shown in FIG. 3C, a high level output is output from the output terminal Tout. The voltage Vout is output.

  When the input voltage Vin falls below the negative threshold Vth2, the voltage Vcs falls below the negative threshold of the ferroelectric capacitor Cs, and the induced charge of the reference capacitor is inverted and has a peak on the negative side in the same manner as described above. An instantaneous discharge current is output (FIG. 3B). As a result, the voltage Vg of the control terminal Tg decreases, and the transistor Q1 is turned off. Then, as shown in FIG. 3C, a low-level output voltage Vout is output from the output terminal Tout.

  Thus, the hysteresis comparator according to the first embodiment is mainly composed of three circuit elements such as the ferroelectric capacitor Cs, the reference capacitor Co, and the switching circuit SW1. Therefore, the number of circuit elements can be greatly reduced as compared with a conventional hysteresis comparator mainly including transistors. Thereby, it is possible to provide a hysteresis comparator whose circuit scale is significantly reduced.

  In addition, since the switching circuit SW1 is provided, a reverse current flow such as a current flowing from the switching circuit SW1 to the ferroelectric capacitor Cs via the control terminal Tg is prevented, and the operation of the circuit can be stabilized. .

  That is, when another circuit element is connected to the output terminal Tout, a current from this circuit element is prevented from flowing into the ferroelectric capacitor Cs, and a hysteresis comparator that realizes stable operation can be provided. At the same time, signal input / output is separated, and impedance matching to the output side of the circuit can be easily performed.

  In the above description, an npn bipolar transistor is used as the transistor Q1, but the present invention is not limited to this, and a pnp bipolar transistor may be employed. In this case, the switching circuit SW1 turns off when the input voltage Vin exceeds the positive threshold value Vth1, and turns on when the input voltage Vin falls below the negative threshold value Vth2.

  The transistor Q1 may be a field effect transistor instead of the bipolar transistor. In this case, the gate of a field effect transistor such as a MOSFET may be used as the control terminal Tg. When a field effect transistor is employed, an n-channel field effect transistor or a p-channel field effect transistor may be employed. These modifications can also be applied to the following embodiments.

(Embodiment 2)
The hysteresis comparator according to the second embodiment of the present invention includes two input terminals T1 and T2. FIG. 4 is a circuit diagram showing the overall configuration of the hysteresis comparator according to the second embodiment of the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The input terminal T2 is connected to a connection point between the reference capacitor Co and the resistor R2 connected between the reference capacitor Co and the ground.

  The input voltage Vin1 is input to the input terminal T1, and the input voltage Vin2 is input to the input terminal T2. In the present embodiment, when the input voltage Vin1−the input voltage Vin2 exceeds the positive threshold value Vth1, that is, when Vin1−Vin2 ≧ Vth1, the switching circuit SW1 is turned on and the hysteresis comparator When the voltage Vin1−the input voltage Vin2 falls below the negative threshold Vth2, that is, when Vin1−Vin2 <Vth2, the switching circuit SW1 is turned off.

  Thus, according to the hysteresis comparator according to the second embodiment, in addition to the effects of the first embodiment, a two-input hysteresis comparator can be provided.

(Embodiment 3)
The hysteresis comparator according to the third embodiment is characterized in that the hysteresis comparator of the first embodiment is a monostable type. FIG. 5 is a circuit diagram showing the overall configuration of the hysteresis comparator according to the third embodiment of the present invention. In the present embodiment, the same components as those in the first and second embodiments are denoted by the same reference numerals, and the description thereof is omitted.

  The hysteresis comparator shown in FIG. 5 further includes a diode D1 as an input side diode, a diode D2 as an offset diode, and an offset voltage unit 10 with respect to the hysteresis comparator shown in FIG.

  The diode D1 has an anode connected to the input terminal T1 and a cathode connected to the ferroelectric capacitor Cs. The diode D2 has an anode connected to the cathode of the diode D1 and a cathode connected to the offset voltage unit 10.

  The offset voltage unit 10 includes a constant voltage circuit that outputs an offset voltage Vofs having a constant voltage value. Here, as the value of the offset voltage Vofs, a value that makes the voltage at the connection point J1 between the diode D1 and the diode D2 equal to or lower than the negative threshold value Vth2 is adopted.

  FIG. 6 is a waveform diagram showing the operation of the hysteresis comparator according to the third embodiment of the present invention. 6A shows a waveform diagram of the input voltage Vin, and FIG. 6B shows a waveform diagram of the output voltage Vout.

  When the input voltage Vin is positive, the diode D1 is on and the diode D2 is off. Therefore, the offset voltage Vofs is not applied to the connection point J1, but only the input voltage Vin is applied. Therefore, when the input voltage Vin exceeds the positive threshold value Vth1, the switching circuit SW1 is turned on, and a high-level output voltage Vout is output from the output terminal Tout as shown in FIG. 6B.

  On the other hand, when the input voltage Vin is negative, the diode D1 is off and the diode D2 is on. Therefore, the offset voltage Vofs is applied to the connection point J1, and the voltage at the connection point J1 is lowered to the negative threshold value Vth2 or less. As a result, the switching circuit SW1 is turned off, and a low-level output voltage Vout is output from the output terminal Tout as shown in FIG. 6B.

  That is, in the first embodiment, as shown in FIG. 3, the output voltage Vout does not become low level unless the input voltage Vin is lower than the threshold value Vth2. On the other hand, in this embodiment, when the input voltage Vin becomes negative as shown in FIG. 6, the output voltage Vout becomes low level. Therefore, after the output voltage Vout becomes high level, it immediately becomes low level and performs monostable operation.

  Thus, according to the third embodiment, in addition to the effects of the first embodiment, a monostable hysteresis comparator can be provided.

(Embodiment 4)
The hysteresis comparator according to the fourth embodiment is characterized in that the ferroelectric capacitor Cs and the reference capacitor Co are constituted by one circuit element Dev1. FIG. 7A shows a structural diagram of the ferroelectric capacitor Cs when the ferroelectric capacitor Cs is constituted by one circuit element, and FIG. 7B shows a circuit element according to the fourth embodiment of the present invention. The structure diagram of Dev1 is shown.

  The ferroelectric capacitor Cs is formed on the substrate 101, the lower electrode 102 formed on the upper layer of the substrate 101, the ferroelectric layer 103 formed on the upper layer of the lower electrode 102, and the upper layer of the ferroelectric layer 103. The upper electrode 104 is provided.

  In the first to third embodiments, the lower electrode 102 of the ferroelectric capacitor having the structure shown in FIG. 7A is connected to, for example, the reference capacitor Co side, and the upper electrode 104 is connected to, for example, the input terminal T1 side. The hysteresis comparator was configured by connecting to.

  As shown in FIG. 7B, the circuit element Dev1 used in the fourth embodiment includes a substrate 201, a lower electrode 202 formed on the upper layer of the substrate 201, and a paraelectric formed on the upper layer of the lower electrode 202. Body layer 203, intermediate electrode 204 formed on the upper layer of paraelectric layer 203, ferroelectric layer 205 formed on the upper layer of intermediate electrode 204, and upper electrode formed on the upper layer of ferroelectric layer 205 206.

  1, 4 and 5, the lower electrode 202 is connected to, for example, the ground side, the upper electrode 206 is connected to, for example, the input terminal T1, and the intermediate electrode 204 is connected to the control terminal Tg. . As a result, the ferroelectric capacitor Cs and the reference capacitor Co can be configured by one circuit element Dev1, and the circuit scale can be further reduced.

  In FIG. 7B, the paraelectric layer 203 is formed on the lower layer side than the ferroelectric layer 205. However, the present invention is not limited to this, and the paraelectric layer 203 and the ferroelectric layer 205 are interchanged. Thus, the paraelectric layer 203 may be formed on the upper layer side of the ferroelectric layer 205.

In the structure of FIG. 7B, the capacitance CCo of the paraelectric layer 203 needs to be larger than the capacitance CCs of the ferroelectric layer 205. The capacitances of the paraelectric layer 203 and the ferroelectric layer 205 are expressed by C = ε ₀ · ε _r · S / d.

Where ε ₀ is the vacuum dielectric constant, ε _r is the relative dielectric constant, S is the electrode area, and d is the layer thickness. In the laminated structure, the electrode areas of the ferroelectric layer 205 and the paraelectric layer 203 are the same. Therefore, increasing the thickness d of the ferroelectric layer 205, adopting a ferroelectric having a low relative permittivity ε _r as the ferroelectric 205, reducing the thickness d of the paraelectric layer 203, CCo and CCs can be controlled by any one of employing a dielectric having a high relative dielectric constant ε _r as the paraelectric layer 203 or by a combination of these.

  Therefore, for example, by using a dielectric having a high relative dielectric constant for the paraelectric layer 203, the relationship of CCo> CCs can be easily realized. Here, as a dielectric having a high relative dielectric constant, for example, a relaxor dielectric having a relative dielectric constant of 100 times or more that of a normal ferroelectric is known. Therefore, if, for example, a relaxor dielectric is used as the paraelectric layer 203, the relationship of CCo> CCs can be easily realized.

Examples of relaxor dielectrics include Ba (Zr, Ti) O ₃ and (Sr, Bi) TaO ₉ which are non-lead materials, Pb (Mg, Nb) O ₃ and Pb (Zn, Nb) which are lead materials. ) O ₃ , Pb (Co, Nb) O ₃ , Pb (Mg, Ta) O ₃ , Pb (Ni, Ta) O ₃ , Pb (Co, Ta) O ₃ , Pb (Sc, Nb) O ₃ , Pb (Sc, Ta) O ₃ , Pb (Fe, Nb) O ₃ , Pb (Fe, Ta) O ₃ , Pb (Cd, W) O ₃ , Pb (Mn, W) O ₃ , Pb (Fe, W) O ₃ etc. are mentioned.

(Experimental example)
Next, an experiment performed on the hysteresis comparator according to the present invention will be described. In this experiment, the hysteresis comparator shown in FIG. 1 was used. Further, the ferroelectric capacitor Cs with a ferroelectric layer of lead zirconate titanate was used. FIG. 8 is a diagram showing the crystal structure of lead zirconate titanate. 8A shows a unit lattice of lead zirconate titanate, FIG. 8B shows a crystal lattice of lead zirconate titanate, and FIG. 8C schematically shows a thin film structure of lead zirconate titanate. FIG.

  As shown in FIG. 8 (a), in the unit cell of lead zirconate titanate, oxygen ions are arranged at the eight vertices of the cube, and lead ions are arranged at the six vertices of the regular octahedron inside the cube. And has a structure in which titanium ions are arranged at the center of the regular octahedron. Here, the titanium ions are displaced in the c-axis direction, and due to this displacement, the zirconate titanate is spontaneously polarized in the c-axis direction. When an electric field E is applied to zirconate titanate from the outside, the polarization of zirconate titanate is reversed.

FIG. 9 shows a structural diagram of the ferroelectric capacitor Cs used in this experiment. As shown in FIG. 9, the ferroelectric capacitor Cs includes an Nb-doped SrTiO ₃ electrode substrate as a lower electrode, a Pb (Zr, Ti) O ₃ ferroelectric layer as a ferroelectric layer, and Au as an upper electrode. And an electrode.

  FIG. 10 shows the result of the X-ray diffraction structure analysis of the ferroelectric capacitor Cs shown in FIG. The vertical axis in FIG. 10 indicates the X-ray intensity, and the horizontal axis indicates the X-ray incident angle (θ). As shown in FIG. 10, a peak of lead zirconate titanate (PZT) is observed around 2θ = 20 degrees, and it can be seen that a c-axis preferentially oriented thin film capable of spontaneous polarization is obtained.

FIG. 11 is a graph showing measurement results of polarization-voltage characteristics of the ferroelectric capacitor Cs using the lead zirconate titanate used in this experiment. In the graph of FIG. 11, the vertical axis represents polarization (μC / cm ² ), and the horizontal axis represents voltage (V). As shown in FIG. 11, it can be seen that the ferroelectric capacitor Cs has hysteresis.

  FIG. 12 is a graph showing experimental results of the hysteresis comparator. 12A shows a waveform diagram of the input voltage Vin, FIG. 12B shows a waveform diagram of the voltage output from the ferroelectric capacitor Cs, and FIG. 12C shows the output voltage Vout.

  As shown in FIG. 12A, when the input voltage Vin exceeds the positive threshold value Vth1, as shown in FIG. 12B, an impulse voltage having a peak on the positive side from the ferroelectric capacitor Cs, That is, an instantaneous discharge voltage is output. Accordingly, it can be seen that the output voltage Vout is at a high level as shown in FIG.

  As shown in FIG. 12A, when the input voltage Vin falls below the negative threshold Vth2, as shown in FIG. 12B, the instantaneous discharge voltage having a peak on the negative side from the ferroelectric capacitor Cs. Is output. Along with this, as shown in FIG. 13C, it can be seen that the output voltage Vout is at a low level.

It is a circuit diagram which shows the whole structure of the hysteresis comparator by Embodiment 1 of this invention. It is the figure which showed the hysteresis characteristic of the ferroelectric capacitor shown in FIG. It is a wave form diagram which shows the operation | movement of a hysteresis comparator shown in FIG. It is a circuit diagram which shows the whole structure of the hysteresis comparator by Embodiment 2 of this invention. It is a circuit diagram which shows the whole structure of the hysteresis comparator by Embodiment 3 of this invention. It is a wave form diagram which shows the operation | movement of the hysteresis comparator by Embodiment 3 of this invention. FIG. 7A shows a structural diagram of the ferroelectric capacitor Cs when the ferroelectric capacitor Cs is constituted by one circuit element, and FIG. 7B shows a circuit element according to the fourth embodiment of the present invention. FIG. It is the figure which showed the crystal structure of lead zirconate titanate. The structure figure of the ferroelectric capacitor used for this experiment is shown. The result of the X-ray diffraction structure analysis of the ferroelectric capacitor shown in FIG. 9 is shown. It is the graph which showed the measurement result of the polarization-voltage characteristic of the ferroelectric capacitor Cs using the lead zirconate titanate used for this experiment. It is a graph which shows the experimental result of a hysteresis comparator. It is a circuit diagram which shows the conventional hysteresis comparator.

Explanation of symbols

10 Offset Voltage Co Reference Capacitor Cs Ferroelectric Capacitor Dev1 Circuit Element Q1 Transistor R1, R2 Resistor SW1 Switching Circuit T1, T2 Input Terminal Tg Control Terminal Tout Output Terminal Vin, Vin1, Vin2 Input Voltage Vofs Offset Voltage Vout Output Voltage Vth1, Vth2 threshold

Claims (8)

  A hysteresis comparator using a ferroelectric capacitor. A first input terminal that receives a first input voltage and outputs the first input voltage to the ferroelectric capacitor;
A reference capacitor connected in series to the ferroelectric capacitor;
2. The hysteresis comparator according to claim 1, further comprising a switching circuit having a control terminal connected to a connection point between the ferroelectric capacitor and the reference capacitor and outputting an output voltage. A resistor connected between the reference capacitor and ground;
The hysteresis comparator according to claim 2, further comprising a second input terminal connected between the resistor and the reference capacitor and receiving a second input voltage. An input-side diode having an anode connected to the first input terminal and a cathode connected to the ferroelectric capacitor;
An offset voltage unit for outputting an offset voltage for making a voltage applied to the ferroelectric capacitor lower than a negative threshold value of the ferroelectric capacitor;
The hysteresis comparator according to claim 2, further comprising an offset diode having the offset voltage input to a cathode and an anode connected to a cathode of the input side diode. The ferroelectric capacitor and the reference capacitor are composed of one circuit element,
The circuit element is:
A substrate,
A lower electrode formed in an upper layer of the substrate;
A first dielectric layer formed on an upper layer of the lower electrode;
An intermediate electrode formed in an upper layer of the first dielectric layer;
A second dielectric layer formed on the intermediate electrode;
An upper electrode formed on an upper layer of the second dielectric layer,
When the second dielectric layer is composed of a ferroelectric, the first dielectric layer is composed of a paraelectric, and when the second dielectric layer is composed of a paraelectric, The hysteresis comparator according to claim 2, wherein the hysteresis comparator is made of a ferroelectric material.   6. The hysteresis comparator according to claim 2, wherein a capacitance of the reference capacitor is larger than a capacitance of the ferroelectric capacitor.   The hysteresis comparator according to claim 1, wherein the ferroelectric capacitor is made of a fat free ferroelectric substance. The hysteresis comparator according to claim 1, wherein the reference capacitor is made of a relaxor dielectric.

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