Analog signal input device

Abstract

This analog signal input device (1) comprises: a first pulse transformer (3) which insulates an analog signal (W1) input from the outside; a first switch element (5) which is connected to a primary si

Description

TECHNICAL FIELD 5

[0001] The present disclosure relates to an analog signal input device. BACKGROUND ART

[0002] Analog signal input devices are used in control monitor equipment for 10 industrial applications, and so on in many cases. These analog signal input devices each capture an analog signal outputted from equipment, such as a temperature sensor, into an AD converter with a high degree of accuracy, for example. At this time, isolation is needed in order for the AD converter to perform AD conversion on the analog signal. It is assumed that analog signal input devices are used typically in a 15 severe installation environment, and, in analog signal input devices, a measure of providing isolation is adopted between an input unit and an internal circuit in order to avoid troubles resulting from a ground loop via ground or the like.

[0003] Accordingly, a method of adopting an isolating method using a transformer 20 element as an isolating means when receiving an analog signal into analog signal input devices has been proposed. An analog signal input device which adopts an isolating method is disclosed in Patent Literature 1. CITATION LIST PATENT LITERATURE 25

[0004] Patent Literature 1: JP 2013-145509 A SUMMARY OF INVENTION TECHNICAL PROBLEM

[0005] 30 The analog signal input device disclosed in Patent Literature 1 includes a waveform shaping circuit on a secondary side of a pulse transformer. This waveform shaping circuit demagnetizes the magnetic core of the pulse transformer. However, because when outputting an analog signal to an AD converter, the waveform shaping circuit is in a state where the waveform shaping circuit is electrically connected at all 5 times, distortion easily occurs in the waveform of the analog signal outputted from the waveform shaping circuit. When distortion occurs in the waveform of the analog signal, as mentioned above, there is a possibility that the accuracy in sensing the analog signal by the AD converter is reduced.

[0006] 10 The present disclosure is made in order to solve the above-mentioned problem, and it is therefore an object of the present disclosure to provide an analog signal input device that can suppress distortion in an analog signal. SOLUTION TO PROBLEM

[0007] 15 An analog signal input device according to the present disclosure, to input an analog signal which is inputted from an outside to an AD converter via isolation, including: a pulse transformer to isolate the analog signal, thereby providing the isolation; a first switch element having one end to receive input of the analog signal, and another end being connected to a primary side of the pulse transformer; a reset 20 circuit connected in parallel to the pulse transformer on a secondary side of the pulse transformer, and having a resistance element and a second switch element which are connected in series to each other; and a control circuit to output a drive signal for performing on / off control on the first switch element to the first switch element, and to output a reset signal for performing on / off control on the second switch element to the 25 second switch element, in which the control circuit turns on the second switch element when turning off the first switch element, thereby passing a reset current occurring on the secondary side of the pulse transformer through the resistance element, and the second switch element conducts at a timing other than a timing at which the analog signal is captured by the AD converter. 30 ADVANTAGEOUS EFFECTS OF INVENTION

[0008] According to the present disclosure, distortion in the analog signal can be suppressed. As a result, the analog signal input device according to the present disclosure can sense the analog signal with a high degree of accuracy. 5 BRIEF DESCRIPTION OF DRAWINGS

[0009] Fig. 1 is a circuit configuration diagram showing the configuration of an analog signal input device according to Embodiment 1; Fig. 2 is a timing chart showing the operating waveform of each unit in the 10 analog signal input device according to Embodiment 1; Fig. 3A is a circuit configuration diagram showing a driving state of a first pulse transformer, and Fig. 3B is a timing chart showing the operating waveform of each unit in the driving state of the first pulse transformer; Fig. 4A is a circuit configuration diagram showing a reset state of the first pulse 15 transformer, and Fig. 4B is a timing chart showing the operating waveform of each unit in the reset state of the first pulse transformer; Fig. 5 is a circuit configuration diagram showing the configuration of an analog signal input device according to Embodiment 2; Fig. 6 is a circuit configuration diagram showing a conventional analog signal 20 input device; and Fig. 7 is a circuit configuration diagram showing a conventional reset circuit. DESCRIPTION OF EMBODIMENTS

[0010] Hereinafter, in order to explain the present disclosure in greater detail, 25 embodiments of the present disclosure will be explained with reference to the accompanying drawings.

[0011] Embodiment 1. An analog signal input device 1 according to Embodiment 1 will be explained 30 using Figs. 1 to 4, 6, and 7.

[0012] First, an overview of the operation of an analog signal input device which uses a transformer isolation method will be explained by taking, as an example, the technology disclosed in Patent Literature 1. 5

[0013] An analog signal outputted from a sensor element is transmitted, via a switch element and a pulse transformer, finally to an AD converter. It is assumed that the sensor element is a temperature sensor, for example. At this time, in a case where the analog signal outputted from the sensor element is a signal having a very low frequency 10 (substantially, a direct current signal), isolated transmission via the transformer cannot be performed or it is necessary to enlarge the pulse transformer extremely if the analog signal remains having a low frequency. Accordingly, in the technology disclosed in Patent Literature 1, an analog signal is formed (modulated) to have the shape of a transient pulse waveform, and thus isolated transmission of the analog signal is 15 performed using a small-sized pulse transformer.

[0014] Fig. 1 is a circuit configuration diagram showing the configuration of the analog signal input device 1 according to Embodiment 1. This analog signal input device 1 has input terminals la and lb. To these input terminals la and lb are 20 connected one or more sensor elements 2 via cables or the like.

[0015] The analog signal input device 1 includes a first pulse transformer 3, a second pulse transformer 4, a first switch element 5, a reset circuit 6, an amplifier element 7, a multiplexer 8, buffer elements 9a and 9b, an AD converter 10, and a control circuit 11. 25 This analog signal input device 1 adopts the transformer isolation method.

[0016] The analog signal input device 1 configured in this way captures an analog signal (sensor element signal) W1 outputted from a sensor element 2 into the AD converter 10 via isolation with a high degree of accuracy. Further, the analog signal 30 input device 1 has the number of circuits corresponding to the number of input channels (the number of analog channels). Fig. 1 shows an example in which the number of input channels is eight (Chi to Ch8).

[0017] The first pulse transformer 3 isolates the analog signal W1 inputted from the 5 sensor element 2. The first pulse transformer 3 constitutes a pulse transformer.

[0018] The second pulse transformer 4 controls the first switch element 5 which will be mentioned later.

[0019] 10 The first switch element 5 is connected to a primary side (isolation side) of the first pulse transformer 3. This first switch element 5 applies the analog signal W1 to the first pulse transformer 3. Further, to the first switch element 5 can be inputted a drive signal W2 from the second pulse transformer 4. The drive signal W2 is a signal for performing on-off (opening or closing) control on the first switch element 5. 15

[0020] The reset circuit 6 is connected in parallel to the first pulse transformer 3 on a secondary side (internal circuit side) of the first pulse transformer 3. This reset circuit 6 demagnetizes a magnetic core which constitutes the first pulse transformer 3. In other words, the reset circuit 6 resets a magnetization current W6 (refer to Fig. 3) which 20 flows through the first pulse transformer 3.

[0021] Further, the reset circuit 6 has a resistance element 61 and a second switch element 62 which are connected in series to each other. Concretely, the resistance element 61 and the second switch element 62 are connected in series to a signal line 25 extending from the first pulse transformer 3. To the second switch element 62 can be inputted a reset signal W4. The reset signal W4 is a signal for performing on-off (opening or closing) control on the second switch element 62.

[0022] The amplifier element 7 is connected to a subsequent stage of the reset circuit 6. 30 This amplifier element 7 amplifies the analog signal W1 outputted from the first pulse 10 15 20 25 30 transformer 3.

[0023] The multiplexer 8 selects one channel out of the multiple input channels. This multiplexer 8 is controlled by the control circuit 11 which will be mentioned later.

[0024] The AD converter 10 is connected to a subsequent stage of the multiplexer 8. This AD converter 10 converts the analog signal W1 outputted from the multiplexer 8 into a digital signal. The AD converter 10 also outputs the digital signal after the conversion to the control circuit 11. In Fig. 1, the analog signal W1 outputted from the multiplexer 8 is shown as an AD conversion input signal W3.

[0025] The control circuit 11 has a processing unit 111, a timing control unit 112, and a Ch selection unit 113.

[0026] The processing unit 111 processes the digital signal outputted from the AD converter 10. The processing unit 111 also outputs a result of the processing to the timing control unit 112 and the Ch selection unit 113.

[0027] The timing control unit 112 outputs a sample signal W8, the drive signal W2, and the reset signal W4 on the basis of the digital signal processed by the processing unit 111.

[0028] The sample signal W8 is a signal for enabling the AD converter 10 to sample the AD conversion input signal W3 This sample signal W8 is outputted to the AD converter 10 by the timing control unit 112. The drive signal W2 is outputted, via the buffer element 9a, the multiplexer 8, and the second pulse transformer 4, to the first pulse transformer 3 by the timing control unit 112. The reset signal W4 is outputted, via the buffer element 9b and the multiplexer 8, to the reset circuit 6 by the timing control unit 112.

[0029] Here, in order to make it possible for the control circuit 11 to perform the on / off control on the first switch element 5, it is necessary to isolate the drive signal W2. To this end, the analog signal input device 1 includes the second pulse transformer 4. As shown in Fig. 1, the primary sides of the first and second pulse transformers 3 and 4 5 in the analog signal input device 1 are constituted by only the first switch element 5 which employs a transistor.

[0030] In contrast with this, Fig. 6 is a circuit configuration diagram showing a conventional analog signal input device IB. The conventional analog signal input 10 device IB shown in this Fig. 6 adopts a photocoupler isolation method. The conventional analog signal input device IB includes an amplifier element 7, a multiplexer 8, buffer elements 9a and 9b, an AD converter 10, a control circuit 11, a photocoupler 12, and an isolated power supply circuit 13. On a primary side of the analog signal input device IB are arranged the AD converter 10 and the isolated power 15 supply circuit 13.

[0031] Therefore, it is seen from a comparison between the circuit configuration of the analog signal input device 1 using the transformer isolation method and the circuit configuration of the analog signal input device IB using the photocoupler isolation 20 method, as shown in Figs. 1 and 6, that the analog signal input device 1 is more advantageous compared with the analog signal input device IB in the number of parts and the manufacturing cost.

[0032] Further, the control circuit 11 controls the second switch element 62 in such a 25 way that the reset circuit 6 functions immediately after the first pulse transformer 3 is driven and only at the time that the demagnetization of the magnetic core of the first pulse transformer 3 is needed.

[0033] Next, the operation of the analog signal input device 1 will be explained using 30 Fig. 2.

[0034] Fig. 2 is a timing chart showing the operating waveform of each unit of the analog signal input device 1 according to Embodiment 1. The vertical axis of Fig. 2 shows the analog signal W1 inputted to the input terminals la and lb, the drive signal 5 W2 outputted from the timing control unit 112, the AD conversion input signal W3 inputted to the AD converter 10, and the reset signal W4 outputted from the timing control unit 112. Further, the horizontal axis of Fig. 2 shows the passage of time.

[0035] The analog signal W1 is the output signal from the sensor element 2, and varies 10 gradually with the passage of time.

[0036] The drive signal W2 turns on or off the first switch element 5 via the buffer element 9a, the multiplexer 8, and the second pulse transformer 4. More specifically, the time period during which the drive signal W2 has a high potential is the one during 15 which the first pulse transformer 3 is driven. During the time period, a voltage corresponding to the amplitude of the analog signal W1 is transmitted to the secondary side of the first pulse transformer 3. Further, the time period during which the drive signal W2 has a low potential is the one during which the first pulse transformer 3 is reset. 20

[0037] The waveform of the AD conversion input signal W3 is observed on the secondary side of the first pulse transformer 3. The AD conversion input signal W3 has a value corresponding to the amplitude of the analog signal W1 during the time period when the drive signal W2 has a high potential. At this time, the amplitude of 25 the AD conversion input signal W3 is sampled by the AD converter 10. Further, a backswing occurs in the AD conversion input signal W3 at the time that the reset signal W4 has a high potential. This backswing results from a reset current W7 (refer to Fig. 4) which occurs as a residual part of the magnetization current W6 (refer to Fig. 3) of the first pulse transformer 3. The reset circuit 6 is disposed in order to prevent the 30 backswing from having an excessive amplitude and vibrating for a long time.

[0038] The reset signal W4 turns on or off the second switch element 62 of the reset circuit 6 via the buffer element 9b and the multiplexer 8. More specifically, the time period during which the reset signal W4 has a high potential is the one during which the 5 magnetic core of the first pulse transformer 3 is demagnetized (reset). The backswing is attenuated and shrunk promptly by the power consumption by the resistance element 61 of the reset circuit 6 within the time period when the magnetic core of the first pulse transformer 3 is demagnetized.

[0039] 10 Next, the operation of the first pulse transformer 3 will be explained in detail using Figs. 3 and 4.

[0040] Fig. 3A is a circuit configuration diagram showing a driving state of the first pulse transformer 3. Fig. 3B is a timing chart showing the operating waveform of each 15 unit in the driving state (driving period) of the first pulse transformer 3. The vertical axis of Fig. 3B shows the analog signal Wl, the drive signal W2, the AD conversion input signal W3, the sample signal W8, and the magnetization current W6. The horizontal axis of Fig. 3B shows the passage of time.

[0041] 20 As shown in Fig. 3, to the first pulse transformer 3 is inputted the analog signal Wl with a constant value. Further, during the driving period of the first pulse transformer 3, the first switch element 5 is in an on state in which the first switch element conducts the drive signal W2. On the other hand, the second switch element 62 is in an off state in which the second switch element blocks the reset signal W4. 25

[0042] When the drive signal W2 passes through the first switch element 5, the magnetization current W6 flows through the primary side of the first pulse transformer 3. Within the driving period of the first pulse transformer 3 (the conduction period of the first switch element 5), the magnetization current W6 increases linearly according to 30 the Faraday's law (electromagnetic induction), and the integral of the magnetization current W6 reaches Idr.

[0043] Further, within the driving period of the first pulse transformer 3, the AD conversion input signal W3 corresponding to the analog signal Wl occurs on the 5 secondary side of the first pulse transformer 3. This AD conversion input signal W3 has a constant electric potential Vin. In addition, the sample period using the sample signal W8 falls within the conduction period of the AD conversion input signal W3.

[0044] Fig. 4A is a circuit configuration diagram showing a reset state of the first pulse 10 transformer 3. Fig. 4B is a timing chart showing the operating waveform of each unit in the reset state (reset period) of the first pulse transformer 3. The vertical axis of Fig. 4B shows the analog signal Wl, the reset signal W4, the AD conversion input signal W3, and the reset current W7. The horizontal axis of Fig. 4B shows the passage of time.

[0045] 15 In order to prevent the saturation or the biased magnetization of the magnetic core which constitutes the first pulse transformer 3, it is necessary to demagnetize the magnetic core during the reset period using the reset signal W4.

[0046] As shown in Fig. 4, to the first pulse transformer 3 is inputted the analog signal 20 Wl with a constant value. Further, during the reset period of the first pulse transformer 3, the first switch element 5 is in an off state in which the first switch element blocks the drive signal W2. On the other hand, the second switch element 62 is in an on state in which the second switch element conducts the reset signal W4.

[0047] 25 When the reset signal W4 passes through the second switch element 62, the reset current W7 flows through the secondary side of the first pulse transformer 3. Within the conduction period of the second switch element 62 in the reset period of the first pulse transformer 3, the integral of the reset current W7 reaches Irst. At this time, the reset current W7 flows through the resistance element 61 of the reset circuit 6, and 30 this results in power consumption occurring in the reset current W7. Therefore, the backswing of the AD conversion input signal W3 is converged promptly.

[0048] More specifically, the reset circuit 6 has the resistance element 61 and the second switch element 62, and the reset current W7 flows through the resistance 5 element 61 only during the reset period. Therefore, the first pulse transformer 3 is not affected by the power consumption by the resistance element 61 during the driving period of the first pulse transformer 3. As a result, when the AD converter 10 samples the AD conversion input signal W3, the AD converter 10 can suppress distortion in the waveform of the AD conversion input signal W3, and can sense the AD conversion 10 input signal W3 with a high degree of accuracy.

[0049] In the analog signal input device 1, because the reset circuit 6 is disposed on the secondary side of the first pulse transformer 3, it is not necessary to dispose an isolating element for the reset circuit 6 which controls the second switch element 62. 15

[0050] Here, Fig. 7 is a circuit configuration diagram showing a conventional reset circuit 6B. In this conventional reset circuit 6B, to a signal line extending from a first switch element 5 are connected in series a resistance element 61 and a rectifier element 64 such as a diode. In contrast with this, because the reset circuit 6 does not have such 20 an element as the rectifier element 64 which the conventional reset circuit 6B includes, the reset circuit 6 can exhibit the above-mentioned reset function even if the analog signal W1 has a minute amplitude smaller than the forward drop voltage of a diode.

[0051] As mentioned above, the analog signal input device I according to 25 Embodiment 1 includes: the first pulse transformer 3 to isolate the analog signal W1 which is inputted from the outside; the first switch element 5 connected to the primary side of the first pulse transformer 3; the reset circuit 6 connected in parallel to the pulse transformer 3 on the secondary side of the pulse transformer 3, and having the resistance element 61 and the second switch element 62 which are connected in series to 30 each other; and the control circuit 11 to output the drive signal W2 for performing on / off control on the first switch element 5 to the first switch element 5, and to output the reset signal W4 for performing on / off control on the second switch element 62 to the second switch element 62, and the control circuit 11 turns on the second switch element 62 when turning off the first switch element 5. Therefore, the analog signal input 5 device 1 can suppress distortion in the analog signal W1 (AD conversion input signal W3). As a result, the analog signal input device 1 can sense the analog signal W1 with a high degree of accuracy.

[0052] Embodiment 2. 10 An analog signal input device 1A according to Embodiment 2 will be explained using Fig. 5. Fig. 5 is a circuit configuration diagram showing the configuration of the analog signal input device 1A according to Embodiment 2. Components having the same functions as those of the components explained in the above-mentioned embodiment are denoted by the same reference signs, and an explanation of the 15 components will be omitted.

[0053] The analog signal input device 1A according to Embodiment 2 includes a reset circuit 6A, instead of the reset circuit 6 of the analog signal input device 1 according to Embodiment 1. 20

[0054] The reset circuit 6A is disposed on a secondary side of a first pulse transformer 3. This reset circuit 6A demagnetizes a magnetic core which constitutes the first pulse transformer 3. Further, the reset circuit 6A has a resistance element 61, a second switch element 62, and an inverting buffer element 63. The resistance element 61, the 25 second switch element 62, and the inverting buffer element 63 are connected in series to a signal line extending from the first pulse transformer 3.

[0055] A drive signal W2 outputted from a timing control unit 112 of a control circuit 11 is inputted, via a buffer element 9a, a multiplexer 8, and a second pulse transformer 4, 30 to the first switch element 5. The drive signal W2 is further inputted, via the buffer element 9a, the multiplexer 8, and the inverting buffer element 63, to the second switch element 62.

[0056] More specifically, a reset signal W4 for performing on / off control on the 5 second switch element 62 is generated by inverting the polarity of the drive signal W2 using the inverting buffer element 63. Therefore, the timing control unit 112 does not have to include a circuit for generating the reset signal W4 and a circuit for adjusting the output timing of the reset signal W4. As a result, in the analog signal input device 1 A, the circuit configuration of the control circuit 11 can be simplified. 10

[0057] As mentioned above, in the analog signal input device 1A according to Embodiment 2, the reset circuit 6A has the inverting buffer element 63 to generate the reset signal W4 by inverting the polarity of the drive signal W2. Therefore, in the analog signal input device 1A, the circuit configuration of the control circuit 11 can be 15 simplified.

[0058] It is to be understood that any combination of the above-mentioned embodiments can be made, various changes can be made in any component according to each of the above-mentioned embodiments, or any component according to each of 20 the above-mentioned embodiments can be omitted within the scope of the present disclosure. INDUSTRIAL APPLICABILITY

[0059] The analog signal input device according to the present disclosure can suppress 25 distortion in an analog signal by, when turning off a first switch element to which a drive signal is inputted, turning on a second switch element to which a reset signal is inputted, and is suitable for use in analog signal input devices and so on. REFERENCE SIGNS LIST

[0060] 30 1, 1A, IB analog signal input device, la, lb input terminal, 2 sensor element, 3 CM first pulse transformer, 4 second pulse transformer, 5 first switch element, 6, 6A, 6B reset circuit, 61 resistance element, 62 second switch element, 63 inverting buffer element, 64 rectifier element, 7 amplifier element, 8 multiplexer, 9a, 9b buffer element, 10 AD converter, 11 control circuit, 111 processing unit, 112 timing control unit, 113 Ch 5 selection unit, 12 photocoupler, 13 isolated power supply circuit, W1 analog signal, W2 drive signal, W3 AD conversion input signal, W4 reset signal, W6 magnetization current, W7 reset current, and W8 sample signal. 11 07 24

Claims

1. An analog signal input device to input an analog signal which is inputted from an outside to an AD converter via isolation, comprising:a pulse transformer to isolate the analog signal, thereby providing the isolation;a first switch element having one end to receive input of the analog signal, and another end being connected to a primary side of the pulse transformer;a reset circuit connected in parallel to the pulse transformer on a secondary side of the pulse transformer, and having a resistance element and a second switch element which are connected in series to each other; anda control circuit to output a drive signal for performing on / off control on the first switch element to the first switch element, and to output a reset signal for performing on / off control on the second switch element to the second switch element,wherein the control circuit turns on the second switch element when turning off the first switch element, thereby passing a reset current occurring on the secondary side of the pulse transformer through the resistance element, andthe second switch element conducts at a timing other than a timing at which the analog signal is captured by the AD converter.

2. The analog signal input device according to claim 1, wherein the reset circuit has an inverting buffer element to generate the reset signal by inverting polarity of the drive signal.

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