Sensor output circuit and sensor device

Abstract

Sensor output circuit (1) with an output terminal (9) that outputs a pulse signal, comprising: a first MOS transistor (8) which is driven by a constant current; a first current mirror circuit which includes the first MOS transistor (8) as a component a second MOS transistor (7) which is provided between the first MOS transistor (8) and the output terminal (9); and a second current mirror circuit, which includes the second MOS transistor (7) and a third MOS transistor (19) as components, wherein a source terminal of the second MOS transistor (7) is connected to a drain terminal of the first MOS transistor (8), and a drain terminal of the second MOS transistor (7) is connected to the output terminal (9), where a breakdown voltage between a drain and a source of the second MOS transistor (7) is higher than a breakdown voltage between a drain and a source of the first MOS transistor (8), wherein there is a circuit between the source side of the current mirror circuit and a constant current source (20) which controls a current on a source side, and wherein a circuit for controlling a current of the second current mirror circuit exists between a source side of the second current mirror circuit and a second constant current source (16).

Description

Technical field

[0001] The present invention relates to a sensor output circuit that outputs a pulse waveform to an output signal line (an output circuit of a sensor device), and in particular to a sensor output circuit that can reduce radio wave radiation from the output signal line. State of the art

[0002] As an example of a method for reducing noise in an output circuit that outputs a pulse waveform to an output signal line, a technique is described in patent literature 1. In patent literature 1, the noise is reduced by converting the output current into a constant current and the output current into a differential signal. Patent literature 2 describes a high-performance charge pump circuit consisting of two switching mirror circuits, two current sources, two switches, and an inverter. In the switching mirror, the switch coupled to the reference transistor configured as a diode is indirectly mirrored to the output.

[0003] Patent literature 3 discloses a supply control via a current flowing to a DMOS transistor acting as a high breakdown voltage switching transistor. The control is achieved using a constant current circuit 2, which supplies a constant current corresponding to the signal level of a binary input signal Sin with the amplitude of a first source voltage VCC1 on a low-voltage side.

[0004] Further circuits of this type are described in patent literature 4 and 5. List of literature Patent literature Patent Literature 1: JP H07-249 975 A Patent literature 2: US 2006 / 0 226 917 A1 Patent literature 3: JP 2006-129 331 A Patent literature 4: US 2015 / 0 056 935 A1 Patent Literature 5: JP 2007-135 097 A Summary of the invention; Technical task

[0005] In patent literature 1, noise is reduced by converting an output current into a constant current and then into a differential signal. Since patent literature 1 intends signal transmission within an LSI (Limited Signal Interference) circuit, it is also possible to use a differential signal. The differential signal has an excellent effect on both noise reduction and noise radiation. However, the output signal line is several meters or more, as in a sensor output circuit, making it difficult to use a differential signal in an output circuit under strict cost constraints, and signal transmission is achieved via a single-wire signal. For this reason, it is necessary to limit the output current with higher precision in the sensor output circuit to suppress radio wave radiation.This means that considerations for limiting the output current with high accuracy are lacking in the related field described above.

[0006] The invention was made in view of the above-mentioned circumstances, and one object of the invention is to provide a sensor output circuit that reduces radio wave radiation even during signal transmission with the single-line signal. Solution to the task

[0007] To solve the above problem, a sensor output circuit according to claim 1 is provided according to a first aspect of the invention. Further aspects of the invention are the subject of the dependent claims, the drawings, and the description of exemplary embodiments. Advantageous effects of the invention

[0008] According to the present invention, it is possible to provide a sensor output circuit that reduces radio wave radiation even during signal transmission with a single-line signal. Brief description of the drawings Fig. Figure 1 is a diagram illustrating a configuration of a sensor output circuit according to a first embodiment. Fig. Figure 2 is a graphical representation illustrating the features of a MOS transistor 8. Fig. Figure 3 is a graphical representation illustrating the voltage-current characteristic of an output terminal 9. Fig. Figure 4 is a diagram illustrating the operating waveform of output terminal 9. Fig. Figure 5 is a diagram illustrating a configuration of a sensor output circuit according to a third embodiment. Fig. Figure 6 is a diagram illustrating a current waveform at the output terminal 9 in the third embodiment. Fig. Figure 7 is a diagram illustrating a configuration of a sensor output circuit according to a fourth embodiment. Fig. Figure 8 is a diagram illustrating a configuration of a sensor output circuit according to a fifth embodiment. Fig. Figure 9 is a diagram illustrating a voltage waveform at output terminal 9 in the fifth embodiment. Description of embodiments

[0009] The following describes embodiments of the invention with reference to the accompanying drawings. These embodiments can also be combined with one another, provided there is no incompatibility. First embodiment

[0010] First, a sensor output circuit according to a first embodiment of the invention is described with reference to the Fig. 1 to 4 described. Further illustrated. Fig. 1 the configuration of the sensor output circuit of the first embodiment, Fig. Figure 2 illustrates the characteristics of a MOS transistor 8, Fig. Figure 3 illustrates the voltage-current characteristic of an output terminal 9 and Fig. Figure 4 represents an operating waveform of the output terminal 9.

[0011] A sensor output circuit 1 of this embodiment includes a pulse signal Vin, which changes according to a physical quantity to be measured; MOS transistors 3 and 5, which perform on / off operations according to the pulse signal Vin; a constant current source 2, which generates a constant current; a MOS transistor 4, which generates a gate voltage of a MOS transistor 7; MOS transistors 6 and 8, which form a current mirror circuit; and MOS transistor 7, which operates such that it maintains a drain voltage of the MOS transistor 8 at a constant voltage, as well as the output terminal 9, which is driven by the series-connected MOS transistors 7 and 8. Furthermore, an output signal from the sensor output circuit 1 is transmitted via an output signal line 10 to a control circuit 11. The control circuit 11 includes a pull-up resistor 12, a capacitor 14 and an input gate circuit 13.

[0012] Here, the characteristics of the MOS transistor 8 are fundamentally controlled by a constant current, as in Fig. Figure 2 shows that the drain current increases as the drain terminal voltage increases. Specifically, as the process becomes more refined, the rate of increase in drain current also increases. In recent years, even in circuits primarily configured by an analog circuit, such as a sensor output circuit, miniaturization of the sensor signal processing unit integrated on the same chip has been driven forward. This characteristic of increasing drain current causes radio wave emission to increase, as described below.

[0013] Therefore, in this embodiment, the MOS transistor 7 is positioned between the output terminal and the MOS transistor 8 such that the drain voltage of the MOS transistor 8 remains constant. The gate voltage of the MOS transistor 7 is determined by the current value of the constant current source 2 and the MOS transistors 4 and 6, which are connected as diodes, and is kept essentially constant. The source voltage of the MOS transistor 7 (the drain voltage of the MOS transistor 8) is kept lower than the gate voltage of the MOS transistor 7 by a threshold value of the MOS transistor 7. This allows, as described in Fig. Figure 3 illustrates that the increase in current at output terminal 9 can be reduced to 1 / 10 or less due to the increase in voltage at output terminal 9.

[0014] Next, the functionality of sensor output circuit 1 will be described with reference to Fig. As described in section 4, when the pulse signal Vin is at a high level, MOS transistor 3 is switched off and MOS transistor 5 is switched on. As a result, the gate voltages of MOS transistors 7 and 8 become 0 V, so that MOS transistors 7 and 8 are switched off and the voltage of the output terminal 9 is pulled up to a high level by the pull-up resistor 12. When the pulse signal Vin is at a low level, MOS transistor 3 is switched on and MOS transistor 5 is switched off, so that the current from the constant current source 2 flows through MOS transistors 4 and 6. As a result, a current proportional to the drain current of MOS transistor 6, which is the source side of the current mirror circuit configured by MOS transistors 6 and 8, flows to the drain of MOS transistor 8 and is driven with a constant current. As shown in Fig. As shown in Figure 2, the drain current tends to increase with increasing drain voltage. Since the MOS transistor 7 operates in the saturation region in this embodiment, it operates such that the drain voltage of the MOS transistor 8 is constant and a constant current flows through the output terminal 9, as shown in Figure 2. Fig. Figure 3 is shown. Since this current flows through the pull-up resistor 12, the voltage at the output terminal becomes a low level.

[0015] If the MOS transistor 7 is not present, a large whisker-like current is generated at this point, flowing to the output terminal 9, as shown in Fig. 4 is shown; however, if the MOS transistor 7 is provided, no whisker-like current is generated. The one in Fig. 4 illustrated whisker-like current is generated when the voltage and current characteristics of the in Fig. The output circuit 9 shown in Figure 3 exhibits a gradient. By adding the MOS transistor 7 as in this embodiment, this characteristic can be improved so that a whisker-like current can be suppressed. Since the Fig. Since the whisker-like current illustrated in Figure 4 has many high-frequency components, radio waves are emitted when this current flows through the output signal line 10. According to this embodiment, however, the whisker-like current can be eliminated, thus reducing the emission of radio waves from the output signal line 10.

[0016] Additionally, in this embodiment, the breakdown voltage of the output terminal 9 can be improved by adding the MOS transistor 7. In the sensor output circuit 1, it is necessary to prevent damage to the sensor output circuit 1 even if static electricity or overvoltage is applied to the output terminal 9, and therefore it is necessary to improve the breakdown voltage of the output terminal 9.

[0017] The reason why the breakdown voltage of output terminal 9 is improved in this embodiment is described below. First, in a case where the pulse signal Vin is at a high level and the MOS transistors 7 and 8 are switched off, the breakdown voltage of output terminal 9 is the sum of the source-to-drain breakdown voltages of the MOS transistors 7 and 8. This means that by adding the MOS transistor 7, the breakdown voltage of output terminal 9 can be improved by an amount equal to the source-to-drain breakdown voltage of the MOS transistor 7.

[0018] Next, in a case where the pulse signal Vin is at a low level and the MOS transistors 7 and 8 are switched on, the breakdown voltage of the output terminal 9 is determined by the product of the current flowing through the output terminal 9 and the voltage across the output terminal 9. In this embodiment, where the current at the output terminal 9 can be kept constant regardless of the voltage across the output terminal 9, breakdown can therefore be prevented up to a higher voltage. This means that a higher breakdown voltage can be obtained.

[0019] Next, the application of a high breakdown voltage MOS transistor for the first embodiment is described.

[0020] The high breakdown voltage MOS transistor suitable for use in precision manufacturing has a worse drain voltage dependence of the drain current than the one in Fig. The features of the MOS transistor shown in Figure 2 are detailed. Therefore, it makes sense to change only MOS transistor 7 to a MOS transistor with a high breakdown voltage. Since the breakdown voltage of the output terminal 9 is initially determined by the sum of the breakdown voltages of MOS transistor 7 and MOS transistor 8, a higher breakdown voltage can be achieved by replacing at least MOS transistor 7 with a MOS transistor with a high breakdown voltage.

[0021] Next, a control method is described for the first embodiment. The circuit configuration of this embodiment can be considered a current mirror circuit configured by the MOS transistors 4, 6, 7, and 8. The current on the source side of this current mirror circuit is controlled by the MOS transistors 3 and 5. By controlling the current on the source side of the current mirror circuit in this way, the amplitude of the voltage used to drive the gate of the MOS transistor 7 can be reduced. The signal to drive the gate of the MOS transistor 7 passes through the capacitance between the gate and the drain of the MOS transistor 7 to the output terminal 9 and causes radio wave radiation from the output signal line 10.This means that by controlling the current on the source side of the current mirror circuit, configured by MOS transistors 4, 6, 7, and 8 using MOS transistors 3 and 5, the current between the gate and drain of MOS transistor 7 is controlled. Radio waves reaching output terminal 9 and radiated from output signal line 10 can be reduced. Second embodiment

[0022] A second embodiment of the invention is described. A description of the aspects that are identical to the first embodiment is not provided.

[0023] In this embodiment, MOS transistor 8 is a low-defibrillation-voltage MOS transistor, and MOS transistor 7 is a high-defibrillation-voltage MOS transistor. Since the drain-voltage dependence of the drain current of MOS transistor 8 can be reduced, and the drain voltage of MOS transistor 8 can be kept constant by MOS transistor 7, the dependence of the output terminal current 9 on the output terminal voltage 9 is favorable.

[0024] This is because the drain voltage dependence of the drain current of the MOS transistor is better for a low-defibrillation voltage MOS than for a high-defibrillation voltage MOS, and the effect of MOS transistor 7, which keeps the drain voltage of MOS transistor 8 constant, is the same for both high-defibrillation and low-defibrillation MOS transistors. Furthermore, in terms of chip size, the size of the high-defibrillation voltage MOS transistor that allows the same drain current to flow is larger than the size required for the low-defibrillation voltage MOS transistor. Therefore, it is possible to reduce the chip size by using MOS transistor 7 as the high-defibrillation voltage MOS transistor and MOS transistor 8 as the low-defibrillation voltage MOS transistor.In other words, the breakdown voltage of the output terminal 9 can be improved by increasing the breakdown voltage between drain and source of the MOS transistor 7 compared to the breakdown voltage between drain and source of the MOS transistor 8, the dependence of the voltage of the output terminal 9 on the current of the output terminal 9 can be improved, and the chip size can be reduced. Third embodiment

[0025] Next, a sensor output circuit according to a third embodiment of the invention is described with reference to the Fig. 5 and Fig. Section 6 is described. Further details are provided in Fig. 5 illustrates the configuration of the sensor output circuit of the third embodiment and in Fig. Figure 6 shows the current waveform of the output terminal 9.

[0026] A sensor output circuit 1 of this embodiment is in principle the same as the sensor output circuit 1 of the first embodiment, except that a capacitor 15 has been added. The addition of the capacitor 15 makes the change in the gate voltage of the MOS transistors 7 and 8 smoother. This is because the capacitor 15 is charged by the constant current source 2, and the rate of change of the current flowing through the MOS transistors 4 and 6 is reduced by the capacitance value of the capacitor 15 and the current of the constant current source 2. This results, as shown in Fig. Figure 6 shows that the current change at output terminal 9 is gradual. If the current change at output terminal 9 is made gradual, then the harmonic component of the signal in Fig. The current waveform shown in 9 can be reduced so that the radio wave emission from the output signal line 10 can be reduced. Fourth embodiment

[0027] Next, a sensor output circuit according to a fourth embodiment of the invention is described with reference to Fig. 7 described. Further details are provided in Fig. Figure 7 illustrates the configuration of the sensor output circuit of the fourth embodiment.

[0028] A sensor output circuit 1 of this embodiment is essentially the same as the sensor output circuit 1 of the first embodiment, except that the driver circuits for the MOS transistor 7 and the MOS transistor 8 are provided separately. The driver circuit for the MOS transistor 7 includes the MOS transistors 17 and 18, which perform on / off operations in response to the pulse signal Vin, a constant current source 16, which generates a constant current, and a MOS transistor 19, which generates a gate voltage for the MOS transistor 7. The driver circuit for the MOS transistor 8 includes the MOS transistors 21 and 22, which perform on / off operations in response to the pulse signal Vin, a constant current source 20, which generates a constant current, and a MOS transistor 23, which forms a current mirror circuit with the MOS transistor 8.

[0029] The configuration of the fourth embodiment allows the gate voltage of the MOS transistor 7 to be lower than that of the first embodiment. Therefore, the low level of the output terminal 9 can be set to a lower voltage. Fifth embodiment

[0030] Next, a sensor output circuit according to a fifth embodiment of the invention is described with reference to the Fig. 8 and Fig. 9 described. Further details are provided in Fig. Figure 8 illustrates the configuration of the sensor output circuit of the fifth embodiment and is described in Fig. 9 shows the voltage waveform of the output terminal 9.

[0031] A sensor output circuit 1 of this embodiment is in principle the same as the sensor output circuit 1 of the fourth embodiment, except that the driver circuit of the MOS transistor 7 is converted into a DA converter 24 and the output voltage of the DA converter 24 is controlled by the signal Din to control the gate voltage of the MOS transistor 7. In the configuration of the fifth embodiment, since the gate voltage of the MOS transistor 7 can be controlled, the low level of the output terminal 9 can also be controlled. This allows, as in Fig. Figure 9 shows a low-level signal of the output signal modified so that a low-amplitude waveform can be superimposed.

[0032] In a case where a voltage waveform, such as that found in Fig. As shown in Figure 9, when a signal is applied to a single-wire signal line, radio waves are emitted in proportion to the current of the single-wire signal for high-frequency signals, while radio waves are emitted in proportion to the voltage for low-frequency signals. The frequency component of this low-frequency radio wave radiation essentially corresponds to the frequency component of the radiation in Figure 9. Fig. 4 shown voltage waveform. To determine the harmonic components of the waveform shown in Fig. To cancel out the voltage waveform shown in 4, a waveform with a small amplitude was superimposed on the low level, as in Fig. Figure 9 illustrates this. This means that by superimposing the low level of output terminal 9 with a waveform with a small amplitude, it is possible to convert the radio wave radiation of the harmonic component of the in Fig. To reduce the voltage waveform shown in section 4. Reference symbol list 1 Sensor output circuit 2 Constant current source 3 MOS transistor 4 MOS transistor 5 MOS transistor 6 MOS transistor 7 MOS transistor 8 MOS transistor 9 Output port 10 Output signal line 11 Control circuit 12 Pull-up resistors 13 Input Gate Circuit 14 Capacitor 15 Capacitor 16 Constant current source 17 MOS transistor 18 MOS transistor 19 MOS transistor 20 Constant current source 21 MOS transistor 22 MOS transistor 23 MOS transistor 24 DA converters

Claims

[1] Sensor output circuit (1) with an output terminal (9) which outputs a pulse signal, comprising: a first MOS transistor (8) which is driven by a constant current; a first current mirror circuit which includes the first MOS transistor (8) as a component a second MOS transistor (7) which is provided between the first MOS transistor (8) and the output terminal (9); and a second current mirror circuit, which includes the second MOS transistor (7) and a third MOS transistor (19) as components, wherein a source terminal of the second MOS transistor (7) is connected to a drain terminal of the first MOS transistor (8), and a drain terminal of the second MOS transistor (7) is connected to the output terminal (9), where a breakdown voltage between a drain and a source of the second MOS transistor (7) is higher than a breakdown voltage between a drain and a source of the first MOS transistor (8), wherein there is a circuit between the source side of the current mirror circuit and a constant current source (20) which controls a current on a source side, and wherein a circuit for controlling a current of the second current mirror circuit exists between a source side of the second current mirror circuit and a second constant current source (16). [2] Sensor output circuit (1) according to claim 1, wherein a gate voltage of the second MOS transistor (7) is kept constant, so that a drain terminal voltage of the first MOS transistor (8) is kept as a constant voltage. [3] Sensor output circuit (1) according to claim 1, wherein a capacitor is arranged on a gate terminal of the first MOS transistor (8) and / or a gate terminal of the second MOS transistor (7). [4] Sensor output circuit (1) according to claim 1, wherein a DA converter (24) is connected to a gate terminal of the second MOS transistor (7). [5] Sensor output circuit (1) according to claim 4, wherein a waveform with a small amplitude is superimposed on a low level of the output terminal (9). [6] Sensor device comprising: the sensor output circuit (1) according to one of claims 1 to 5.

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