DE-112018005419-B4 - 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).

Inventors

• Masahiro Matsumoto
• Hiroshi Nakano
• Akira Kotabe

Assignees

• HITACHI ASTEMO, LTD.

Dates

Publication Date

20260513

Application Date

20181108

Priority Date

20171130

Claims (6)

1. Sensor output circuit (1) with an output terminal (9) that outputs a pulse signal, comprising: a first MOS transistor (8) driven by a constant current; a first current mirror circuit that includes the first MOS transistor (8) as a component; a second MOS transistor (7) provided between the first MOS transistor (8) and the output terminal (9); and a second current mirror circuit comprising the second MOS transistor (7) and a third MOS transistor (19) as components, whereby 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), whereby 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), whereby there is a circuit between the source side of the current mirror circuit and a constant current source (20) that controls a current on a source side, and whereby there is a circuit for controlling a current of the second current mirror circuit between a source side of the second current mirror circuit and a second constant current source (16).
2. Sensor output circuit (1) according 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 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 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 Claim 4 , where 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 the Claims 1 until 5 .

Description

Technical field 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 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. 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. Further circuits of this type are described in patent literature 4 and 5. List of references Patent literature Patent literature 1: JP H07-249 975 APatent literature 2: US 2006/0 226 917 A1Patent literature 3: JP 2006-129 331 APatent literature 4: US 2015/0 056 935 A1Patent literature 5: JP 2007-135 097 A Summary of the invention Technical task 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 effects 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-line 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. 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 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 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 1 is a diagram illustrating a configuration of a sensor output circuit according to a first embodiment.2 is a graphical representation illustrating the characteristics of a MOS transistor 8.3 is a graphical representation illustrating the voltage-current characteristic of an output terminal 9.4 is a diagram illustrating the operating waveform of output terminal 9.5 is a diagram illustrating a configuration of a sensor output circuit according to a third embodiment.6 is a diagram illustrating a current waveform at output terminal 9 in the third embodiment.7 is a diagram illustrating a configuration of a sensor output circuit according to a fourth embodiment.8 is a diagram illustrating a configuration of a sensor output circuit according to a fifth embodiment.9 is a diagram illustrating a voltage waveform at output terminal 9 in the fifth embodiment. Description of embodiments 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 First, a sensor output circuit according to a first embodiment of the invention is described with reference to the 1 to 4 described. Further illustrated 1 the configuration of the sensor output circuit of the first embodiment, 2 illustrates the characteristics of a MOS transistor 8, 3 illustrates the voltage-current characteristic of an output terminal 9 and 4 represents an operating waveform of output terminal 9. 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