THROUGH TRANSFER SENSOR

Abstract

Throughput sensor, comprehensive: a sensor unit configured to detect a change in gas flow rate; an analog-to-digital converter (ADC) of the switched-capacitor type, configured to convert an analog signal output by the sensor unit into a digital signal; and an interruption detection circuit configured to detect an interruption in a wiring connection between the A / D converter and the sensor unit, wherein The interrupt detection circuit comprises a first capacitor, one of whose connecting sections is connected to an input node of the A / D converter, and a detection unit configured to detect the interruption of the wiring, and The detection unit detects an interruption in the wiring based on a potential derived from the ratio of the electrostatic capacitance of input capacitors connected to input units of the A / D converter to the electrostatic capacitance of the first capacitor.

Description

Technical area

[0001] The present invention relates to a flow rate sensor, and more particularly, to a technique effective for detecting a break in a flow rate sensor that measures a flow rate of air supplied to an internal combustion engine and the like. State of the art

[0002] The use of flow sensors is widely used to control the amount of air flowing into internal combustion engines that use fossil fuels, such as automotive internal combustion engines. This is particularly true because the requirement to increase fuel efficiency in motor vehicles requires that the air-to-gasoline mixture ratio be maintained at an optimal level to achieve efficient combustion.

[0003] There are various performance indicators required for automotive internal combustion engines, and even globally, the required performance varies from region to region. In the case of Japan, for example, urban driving is characterized by special conditions such as frequent stop-and-go traffic caused by traffic lights and frequent traffic jams. Since efficient combustion is necessary even at low engine power, a flow sensor is required to accurately detect even the smallest changes in air flow.

[0004] For example, a known detection method for a flow sensor is a method that uses a resistance bridge circuit. It detects that a resistance value used in the resistance bridge circuit has changed due to airflow, and the change is converted into an air flow rate.

[0005] An analog signal detected by the resistor bridge circuit is converted into a digital signal by an analog-to-digital converter (A / D converter). There are various types of A / D converters, but they can be roughly divided into sample-and-hold type, which uses a switched capacitor, and continuous type, which uses a resistor. The switched capacitor type is widely used because this type of converter allows for increased accuracy, consumes less power, and exhibits less characteristic variation due to ambient temperature fluctuations.

[0006] However, in the switched capacitor type A / D converter, when an input unit of the A / D converter and an output unit of the bridge circuit are separated, the input unit of the A / D converter is floating, and it is difficult to detect a difference from a state in which the bridge circuit is normally connected.

[0007] As a result, the adjustment and control of the air-fuel mixture of the internal combustion engine does not function normally, fuel consumption deteriorates and there is a risk of an increase in environmentally harmful gas emissions.

[0008] As a technique for considering a disconnection between the bridge circuit and the A / D converter, for example, a technique is known that detects a disconnection between the bridge circuit and the A / D converter by providing a disconnection detection circuit at the input unit of the A / D converter (see PTL 1). List of reference literaturePatent literature

[0009] PTL 1: JP 2012-8014 A Summary of the inventionTechnical problem

[0010] The above open-circuit detection technique according to PTL 1 includes the open-circuit detection circuit. The open-circuit detection circuit detects an open-circuit based on the fact that a small current continues to flow from a DC power source to the input unit of the A / D converter, and that no current flows from the power source when an open-circuit occurs.

[0011] However, since the detection current continues to flow in this open-circuit detection technique, deterioration of the conversion accuracy of the A / D converter due to fluctuations in a current value of the detected current or fluctuations in a resistance value used in the bridge circuit is not sufficiently taken into account.

[0012] As a result, in the flow sensor, which is provided with an A / D converter that converts the small signal into the digital signal at low flow rate, the conversion accuracy may be deteriorated, thereby increasing the risk of engine malfunction, deterioration of fuel efficiency, and the like.

[0013] An object of the invention is to provide a technique capable of detecting a wiring break without reducing the detection accuracy of a gas flow rate.

[0014] The above and other objects and novel features of the invention will be apparent from the description and the accompanying drawings. Solution to the problem

[0015] The following is a brief description of typical aspects of the invention disclosed in the present application.

[0016] That is, a typical flow sensor comprises a sensor unit, an A / D converter, and an interruption detection circuit. The sensor unit detects a change in gas flow. The A / D converter is a switched-capacitor type A / D converter and converts an analog signal output from the sensor unit into a digital signal.

[0017] The open circuit detection circuit includes a first capacitor and a detection unit. A connecting portion of the first capacitor is connected to an input node of the A / D converter, and the detection unit detects the open circuit of a wiring. This detection unit detects the open circuit of the wiring using a potential based on the ratio of each electrostatic capacitance of input capacitors connected to input units of the A / D converter to the electrostatic capacitance of the first capacitor.

[0018] A connecting portion of the disconnection detection circuit is connected to the input node of the A / D converter, and the disconnection detection circuit includes a second capacitor (holding capacitance 144) that holds an electric charge of a potential in the first capacitor. The detection unit detects the disconnection of the wiring based on a potential change of the second capacitor. Beneficial effect

[0019] The effect achieved by the typical aspects of the invention disclosed in the present application is as follows. (1) The interruption of the wiring can be detected without reducing the detection accuracy of the gas flow rate. (2) According to the above point (1), the reliability of the flow sensor can be increased. Short description of the drawings [ Fig. 1] Fig. 1 is an illustrative diagram showing a configuration example of a flow sensor according to an embodiment. [ Fig. 2] Fig. 2 is an illustrative diagram showing a configuration example of a power generation unit used in the flow sensor of Fig. 1 is provided. [ Fig. 3] Fig. 3 is an illustrative diagram showing a configuration example of an analog switch used in the flow sensor of Fig. 1 is provided. [ Fig. 4] Fig. Figure 4 is a timing diagram schematically showing the timing of signals from units in a detection unit used in the flow sensor of Fig. 1 is provided. [ Fig. 5] Fig. 5 is an illustrative diagram showing a relationship between a capacitance ratio of an N-side input capacitance to a detection capacitance and a voltage ratio of a potential change to a reference potential in the flow sensor of Fig. 1 shows. [ Fig. 6] Fig. Figure 6 is an illustrative diagram showing the dependence of the detection capacity in the flow sensor on Fig. 1 shows. [ Fig. 7] Fig. Figure 7 is an illustrative diagram showing an example of signal waveforms caused by an electrostatic capacitance sum of the detection capacitance and a holding capacitance in the flow sensor of Fig. 1 can be generated. [ Fig. 8] Fig. Fig. 8 is an illustrative diagram showing an example of an operating window in the circuit operation of an open circuit detection circuit in the flow rate sensor of Fig. 1 shows. [ Fig. 9] Fig. 9 is an illustrative diagram showing another example of an operating window in the circuit operation of the interruption detection circuit in the flow rate sensor of Fig. 1 shows. [ Fig. 10] Fig. 10 is an illustrative diagram showing a configuration example of a control system for the flow sensor of Fig. 1 shows. [ Fig. 11] Fig. 11 is an illustrative diagram showing a configuration example of a flow rate sensor according to a second embodiment. [ Fig. 12] Fig. Fig. 12 is a timing chart schematically showing a clock and an internal waveform in the detection unit used in the flow sensor in Fig. 11 is provided. Description of embodiments

[0020] In all drawings for describing the embodiments, like elements are denoted by like reference numerals throughout, and repeated descriptions thereof will be omitted. (First embodiment)

[0021] An embodiment is described in detail below. (Configuration example and operation of the flow sensor)

[0022] Fig. 1 is an illustrative diagram showing a configuration example of a flow rate sensor 10 according to the present embodiment.

[0023] The flow rate sensor 10 is a sensor that measures a flow rate of air or the like and is used for an internal combustion engine such as an internal combustion engine in a motor vehicle or the like.

[0024] As in Fig. As shown in Figure 1, the flow sensor 10 includes a resistance bridge 100 and a control circuit 110. The resistance bridge 100 and the control circuit 110 are formed, for example, on a semiconductor chip.

[0025] The resistance bridge 100, which is a sensor unit, has four resistors 102 to 105 and detects a change in gas flow rate. Resistor 102 and resistor 103 are connected in series. Accordingly, resistor 104 and resistor 105 are also connected in series.

[0026] One connecting portion of the resistor 102 and one connecting portion of the resistor 104 are connected to each other, and the other connecting portion of the resistor 103 and the other connecting portion of the resistor 105 are also connected to each other.

[0027] A first potential 101 is supplied to a node to which one connecting portion of resistor 102 and one connecting portion of resistor 104 are connected. A second potential 106 is supplied to a node to which the other connecting portion of resistor 103 and the other connecting portion of resistor 105 are connected.

[0028] The first potential 101 and the second potential 106 are supplied from outside the flow sensor 10. Alternatively, the first potential 101 and the second potential 106 may be supplied from a power supply circuit (not shown) provided in the control circuit 110, a power generation unit 200 described below, or the like. In any case, it is desirable that the first potential 101 and the second potential 106 be power sources stabilized using electrostatic capacitance or the like.

[0029] The resistor bridge 100 has an output unit ELEMOP and an output unit ELEMOM. A connecting portion between the resistor 102 and the resistor 103, which are connected in series, is the output unit ELEMOP, and a connecting portion between the resistor 104 and the resistor 105, which are connected in series, is the output unit ELEMOM.

[0030] The output unit ELEMOP of the resistance bridge 100 is connected to an input unit VINP provided in the control circuit 110 via a bonding wire 164. The output unit ELEMOM of the resistance bridge 100 is connected to an input unit VINM provided in the control circuit 110 via a bonding wire 165. Hereinafter, "open" means that the above bonding wire 164 or the bonding wire 165 is open.

[0031] The control circuit 110 includes an input processing unit 111, a differential A / D converter 122, an interrupt detection circuit 130, a clock generation circuit 170, a logic unit 180, and the current generation unit 200.

[0032] The input processing unit 111 includes analog switches 112 to 115 and 118 to 121, a P-side input capacitance 116, and an N-side input capacitance 117. A connecting portion of the analog switch 112, which is a first switch, and a connecting portion of the analog switch 114, which is a third switch, are connected to the input unit VINP. A connecting portion of the analog switch 113, which is a second switch, and a connecting portion of the analog switch 115, which is a fourth switch, are each connected to the input unit VINM.

[0033] The other connecting portions of the analog switches 112, 113 are connected to a connecting portion of the P-side input capacitance 116. A connecting portion between the analog switches 112, 113 and the P-side input capacitance 116 is a node CPI.

[0034] The other connection sections of the analog switches 114, 115 are connected to a connection section of the N-side input capacitance 117. A connection section between the analog switches 114, 115 and the N-side input capacitance 117 is a node CMI.

[0035] A connecting portion of the analog switch 118 and a connecting portion of the analog switch 119 are each connected to the other connecting portion of the P-side input capacitance 116, which is an input capacitor. A connecting portion of the analog switch 120 and a connecting portion of the analog switch 121 are each connected to the other connecting portion of the N-side input capacitance 117, which is an input capacitor.

[0036] The other connecting portion of the analog switch 120 is connected to the other connecting portion of the analog switch 119. A current supply unit of the differential A / D converter 122 is connected to a connecting portion of the analog switch 119 and the analog switch 120. This current supply unit is supplied with a reference potential VB from the connecting portion of the analog switch 119 and the analog switch 120.

[0037] The other connecting portion of the analog switch 118 is connected to a P-side input unit ADINP of the differential A / D converter 122, and the other connecting portion of the analog switch 121 is connected to an N-side input unit ADINM of the differential A / D converter 122.

[0038] An output signal ADOUT is output from an output unit of the differential A / D converter 122. The output signal ADOUT is input to the logic unit 180. The logic unit 180 performs correction operations on the output signal ADOUT, such as temperature correction, pulsation correction, and humidity correction, and transmits flow information to a higher-level system, such as an electronic control unit (ECU) responsible for controlling an internal combustion engine.

[0039] A control terminal of the differential A / D converter 122 is connected so that a control signal ADCTRL output from the logic unit 180 is input to the control terminal. The differential A / D converter 122 is, for example, a sample-and-hold type input differential A / D converter.

[0040] Clock generation circuit 170 generates and outputs clock signals of clocks P1, P1B, P2, and P2B. Clock P1B is an inverted clock of clock P1, and clock P2B is an inverted clock of clock P2. Clocks P1 and P1B are first control clocks, and clocks P2 and P2B are second control clocks.

[0041] The switching on and off operations of the analog switches 112, 115, 118, 121, which are Fig. 1 shown in white are controlled by the clock P1 and the clock P1B generated by the clock generation circuit 170.

[0042] The switching on and off operations of the analog switches 113, 114, 119, 120, which are Fig. 1, shown in black, are controlled by the clock P2 and the clock P2B generated by the clock generation circuit 170. The clocks P1, P2 are also used as control clocks for the differential A / D converter 122 to control an A / D conversion operation.

[0043] Here, phase 1 is the time when clock P1 is HIGH, and phase 2 is the time when clock P2 is HIGH. In phase 2, the input unit VINP of the control circuit 110, the P-side input capacitor 116, and the P-side input unit ADINP of the differential A / D converter 122 are connected in series.

[0044] Here, the input unit VINM of the control circuit 110, the N-side input capacitance 117 and the N-side input unit ADINM of the differential A / D converter 122 are connected in series, so that a signal detection operation is performed by the differential A / D converter 122.

[0045] In contrast, in phase 1, the input unit VINP of the control circuit 110, the N-side input capacitance 117, and the current injection unit of the differential A / D converter 122 are connected in series. The input unit VINM of the control circuit 110, the P-side input capacitance 116, and the current injection unit of the differential A / D converter 122 are connected in series, so that signal sampling is performed at the P-side input capacitance 116 and the N-side input capacitance 117.

[0046] During the transition from phase 1 (or phase 2) to phase 2 (phase 1), a potential connected to node CPI changes from a P-side to an N-side, and a potential connected to node CMI changes from the N-side to the P-side. This establishes a state during an input of the differential A / D converter 122 in which a common mode of an output of the resistance bridge 100 is eliminated. This can increase the dynamic range of the differential A / D converter 122, enabling high-accuracy A / D conversion.

[0047] The disconnection detection circuit 130 includes a disconnection detection unit 131, a disconnection detection unit 132, and a determination unit 133. The disconnection detection unit 131 detects a disconnection of the bonding wire 164, which is a wiring. The disconnection detection unit 132 detects a disconnection of the bonding wire 165, which is a wiring.

[0048] The determination unit 133, which is a disconnection determination unit, determines whether the bonding wires 164, 165 are disconnected or not based on a determination signal DIAGM output from the disconnection detection unit 131 and a determination signal DIAGP output from the disconnection detection unit 132. If it is determined that the bonding wire 164 or the bonding wire 165 is disconnected, a disconnection detection signal DIAGOUT is output to the logic unit 180.

[0049] The interruption detection unit 131 includes analog switches 140, 142, 143, a detection capacitor 141, a holding capacitor 144, and a comparator 145.

[0050] A connecting portion of the analog switch 140, which is a fifth switch, is connected to the input unit VINM of the control circuit 110. A connecting portion of the detection capacitor 141, a connecting portion of the analog switch 142, and a connecting portion of the analog switch 143 are each connected to the other connecting portion of the analog switch 140. A connecting portion of the analog switch 140, the detection capacitor 141, and the analog switches 142, 143 is a node VM.

[0051] The other connection portion of the analog switch 142, which is a sixth switch, is connected to the other connection portion of the detection capacitor 141, which is a first capacitor. The analog switch 142 is connected to the detection capacitor 141 such that a detection reference potential V1, which is a first detection reference voltage, is applied to a connection portion of the detection capacitor 141 and the analog switch 142.

[0052] A connecting portion of the holding capacitor 144 and an input unit of the comparator 145 are connected to the other connecting portion of the analog switch 143, which is a seventh switch. A connecting portion of the analog switch 143, the holding capacitor 144, and the comparator 145 is a detection node VDETM.

[0053] The other connection portion of the holding capacitor 144, which is a second capacitor, is connected so that a detection reference potential V2 is applied to the other connection portion of the holding capacitor 144, and the other input unit of the comparator 145 is connected so that a detection reference potential V3 is applied to the other input unit of the comparator 145. The detection reference potential V2, which is a second detection reference potential, is a potential different from the detection reference potential V1.

[0054] The power generation unit 200 generates the detection reference potential V3 and the reference potential VB. The detection reference potential V3 and the reference potential VB can be supplied from outside the flow sensor 10.

[0055] Accordingly, the detection reference potentials V1, V2 can be supplied from outside the flow sensor 10. Alternatively, the power generation unit 200 can generate the detection reference potentials V1, V2, or a new power generation unit can be provided in the flow sensor 10 to generate the detection reference potentials V1, V2.

[0056] The comparison signal DIAGM is output as a comparison result from one output unit of the comparator 145. The comparison signal DIAGM is connected so that the comparison signal DIAGM is input to the other input unit of the determination unit 133.

[0057] Here, a configuration of the interruption detection unit 132 is the same as that of the interruption detection unit 131, and differs only in that one connection portion of the analog switch 140 of the interruption detection unit 132 is connected to the input unit VINM of the control circuit 110, and the comparison signal DIAGP, which is the comparison result, is input from the output unit of the comparator 145 to the other input unit of the determination unit 133.

[0058] The operation of the interruption detection unit 131 is described below.

[0059] Since the configurations of the interruption detection unit 131 and the interruption detection unit 132 are the same, only the interruption detection unit 131 will be described.

[0060] The analog switch 142 operates in the clock P2 generated by the clock generation circuit 170, and the analog switches 140, 143 operate in the clock P1 generated by the clock generation circuit 170.

[0061] The comparator 145, which is a detection unit, compares the potential magnitude ratio between the detection node VDETM, which is a potential based on the detection capacitance 141 and the holding capacitance 144, and the detection reference potential V3, and outputs the comparison signal DIAGM from the output unit as the comparison result of the potential magnitude ratio.

[0062] The analog switch 142 is responsible for discharging the detection capacitor 141 in Phase 2 above. The interrupt detection unit 131 is connected to the input unit VINM of the control circuit 110 during Phase 1, and during this time, the interrupt detection operation is performed on the bond wire 165. In Phase 2, the interrupt detection unit 131 is disconnected from the input unit VINM.

[0063] The differential A / D converter 122 is connected to the input unit VINM of the control circuit 110 in phase 2 and disconnected therefrom in phase 1. Therefore, the interruption detection unit 131 is disconnected from an input node of the differential A / D converter 122 during the operation of detecting the signal of the differential A / D converter 122.

[0064] This allows the noise generated during the detection of the signal of the differential A / D converter 122 by the interruption detection circuit 130 to be isolated, enabling A / D conversion to be performed with high accuracy.

[0065] A potential of the detection node VDETP is determined by a ratio of an electrostatic capacitance value CIN of the P-side input capacitance 116, an electrostatic capacitance value C1 of the detection capacitance 141, and an electrostatic capacitance value C2 of the holding capacitance 144, and is given by VDETM = (VB - V1) × CIN / (CIN + C1 + C2).

[0066] The electrostatic capacitance value C2 is intended only for holding. As long as the potential of the detection node VDETM can be held, a parasitic capacitance of the wiring, a gate capacitance of an input transistor provided in the comparator 145, and the like can be utilized, and the electrostatic capacitance value C2 can be a very small electrostatic capacitance.

[0067] In this case, no specific capacitance element is specified in the circuit layout of the semiconductor chip on which the flow sensor 10 is formed. However, a charge-holding function provided by the electrostatic capacitance value C2 is desirable in that the circuit area can be reduced.

[0068] Since the electrostatic capacitance value C1 is dominant compared to the electrostatic capacitance value C2, the above equation is shortened by VDETM = (VB - V1) × CIN / (CIN + C1).

[0069] The fact that the potential of the detection node VDETM is determined here by the ratio of the electrostatic capacitance is advantageous in the following respect.

[0070] Since manufacturing variations in a capacitance in an integrated circuit are small, potential changes in the detection node VDETM can be reduced. Furthermore, maintaining a capacitance ratio is also expected to have a fluctuation-cancelling effect.

[0071] When the potential change at the detection node VDETM becomes small, the probability of the detection reference potential V3 being adjusted increases, thereby simplifying the circuit design. By setting the detection reference potential V1 to a potential lower than a ground potential (GND), which is a reference potential, the potential change (DVDET) of the detection node VDETM can be increased. This makes it possible to simplify the design of the comparator 145 and the potential adjustment of the detection reference potential V3.

[0072] A potential of the detection reference potential V1 can be lower or higher than the reference potential VB. For example, if a step-up current source is already provided on the semiconductor chip forming the flow sensor 10, the detection reference potential V1 is preferably set higher than the reference potential VB.

[0073] This is because it is common practice to use a step-up current source that is higher than the operating current supply of an analog circuit, rather than a negative current source that is lower than the GND potential. The detection reference potential V2 can, in principle, be the GND potential, but can be any potential suitable for circuit operation.

[0074] The determination unit 133 is, for example, an OR circuit and receives an OR operation (logical sum) of the determination signal DIAGM output from the interruption detection unit 131 and the determination signal DIAGP output from the interruption detection unit 132.

[0075] When a break in the bonding wire 164 on the VINP side of an input unit or a break in the bonding wire 165 on the VINM side of an input unit occurs, the control circuit 110 cannot operate normally.

[0076] Therefore, in a sensor signal SENOUT output from the logic unit 180, which is an output of the flow sensor 10, interruption information is included when the bonding wire 164 or the bonding wire 165 is interrupted, in order to inform a higher-level system such as a Fig. 10 to notify the controller 353 shown.

[0077] In view of the power consumption, it is undesirable to operate the differential A / D converter 122 in a state where the control circuit 110 cannot operate normally, therefore, it is preferable to provide immediate feedback when the disconnection of the bonding wire 164 or the disconnection of the bonding wire 165 is detected to stop the operation of the differential A / D converter 122.

[0078] In this case, the logic unit 180 outputs the control signal ADCTRL to the control terminal of the differential A / D converter 122 when the interruption detection signal DIAGOUT is output from the determination unit 133. The differential A / D converter 122 stops operating when the control signal ADCTRL is input. (Power generation unit configuration example)

[0079] Fig. Fig. 2 is an illustrative diagram showing a configuration example of the power generation unit 200 used in the flow rate sensor 10 of Fig. 1 is provided.

[0080] The power generation unit 200 includes a plurality of resistors 202 and stabilizing capacitors 204, 205 and generates the detection reference potential V3 and the reference potential VB mentioned above.

[0081] The plurality of resistors 202 generates the detection reference potential V3 and the reference potential VB through a so-called resistor chain connected in series between an analog reference potential 201 and a reference potential 203.

[0082] Fluctuations in the reference potential VB affect the potentials of the detection node VDETP and the detection node VDETM. When the potentials of the detection nodes VDETP, VDETM are compared with the detection reference potential V3 by the comparator 145 in Fig. 1, it is therefore desirable that the reference potential VB and the detection reference potential V3 fluctuate to the same extent.

[0083] In order for the reference potential VB and the detection reference potential V3 to fluctuate to the same extent, it is necessary, as in Fig. 2, it is desirable to generate the reference potential VB and the detection reference potential V3 from the same resistor chain.

[0084] In the resistor chain, the stabilizing capacitor 204 and the stabilizing capacitor 205 are each connected to nodes that output the detection reference potential V3 and the reference potential VB. This stabilizes the potentials of the detection reference potential V3 and the reference potential VB.

[0085] However, since the stabilizing capacitances 204, 205 increase the chip area and ultimately lead to an increase in chip costs, it is desirable to keep the capacitance value of the stabilizing capacitances 204, 205 to a required minimum value. (Configuration example of an analog switch)

[0086] Fig. 3 is an illustrative diagram showing a configuration example of the analog switch 112 used in the flow sensor 10 of Fig. 1 is provided.

[0087] As in Fig. 3, the analog switch 112 comprises a transistor 301 made of a P-channel metal oxide semiconductor (MOS) and a transistor 302 made of an N-channel MOS Fig. 3 shows the configuration example of the analog switch 112, and the other analog switches have the same configuration as the analog switch 112 in Fig. 3.

[0088] The clock P1B is input to a gate of the transistor 301, and the clock P1 is input to a gate of the transistor 302. By using a structure in which the transistor 301 and the transistor 302 are connected in parallel, it is possible to transfer a potential from the GND potential to a power supply voltage without loss. (Signal timing example of the detection unit)

[0089] Fig. Fig. 4 is a timing diagram schematically showing the timing of the signals of units in the interruption detection unit 131 used in the flow sensor 10 of Fig. 1 is provided.

[0090] In Fig. 4 shows, from top to bottom, the signal timing of the clock P1, the clock P1B, the clock P2, the clock P2B, the node VM, the input unit VINM of the control circuit 110 and the detection node VDETM.

[0091] Fig. 4 represents a state between the output unit ELEMOM and the input unit VINM in Fig. 1, which changes from conductive to non-conductive, that is, Fig. Figure 4 shows changes in the potential state of the node VM and the detection node VDETM before the interruption of the bond wire 165 (“connected” in Fig. 4) and after the interruption of the bonding wire 165 (“interrupted” in Fig. 4).

[0092] In a period t0, which is one period of a cycle of the clocks P1 and P2 in Fig. 4, a period t1 in which clock P1 is in the HIGH state and a period t2 in which clock P2 is in the HIGH state are each provided with overlap periods t3 and t4 so that rising and falling edges do not overlap. This can reduce the influence of a clock conduction induced during the operation of the analog switch.

[0093] If the node VM is not interrupted, the node VM is at the level of a potential VSIG, which is an output level of the resistance bridge 100, during the period t1 with P1 = HIGH and the overlap period t3. During the subsequent period t2 with the clock P2 = HIGH and the overlap period t4, the node VM is at a level of the detection reference potential V1. This is due to a voltage being short-circuited by the analog switch 142 through the detection capacitance 141.

[0094] In the example of Fig. Figure 4 shows a case with a detection reference potential V1 = GND. When the bond wire 165 is interrupted, the behavior changes during period t1 and period t3 such that the input unit VINM reaches a level of the reference potential VB - potential change DVDET.

[0095] This is due to the fact that |VB - V1| in Fig. 1 is changed to a potential |VB - V1| * CIN / (CIN + C1), which is obtained by dividing |VB - V1| by a potential of the node CMI and the potential of the detection capacitance 141.

[0096] Since the potential change DVDET is a change with respect to the reference potential VB of the detection node VDET, DVDET = VB - V1 * CIN / (CIN + C1) =VB * C1 / (CIN + C1) when the detection reference potential V1 = 0.

[0097] A potential of the input unit VINM is a potential applied to the N-side input unit ADINM of the differential A / D converter 122. Therefore, a state of the signal level VSIG output from the resistance bridge 100 is maintained when the bonding wire 165 is not broken.

[0098] When the break of the bonding wire 165 occurs, the break detection unit 131 is connected to the input unit VINM of the control circuit 110 during the period t1 and the period t3, so that the input unit VINM and the node VM have the same potential |VB - V1| * CIN / (CIN + C1).

[0099] A break detection potential in the detection node VDETM does not change at the time the break occurred, but only in the first period t1 after the break. If the potential of the detection node VDETM drops below the detection reference potential V3 at this time, the break detection unit 131 determines that the bonding wire 165 is broken. (Setting the detection capacity)

[0100] Fig. 5 is an illustrative diagram showing a relationship between a capacitance ratio of the N-side input capacitance 117 to the detection capacitance 141 and a voltage ratio of the potential change DVDET to the reference potential VB in the flow sensor 10 of Fig. 1 shows.

[0101] Fig. Figure 5 shows the relationship between C1 / CIN (capacitance ratio of the electrostatic capacitance value C1 of the detection capacitance 141 to the electrostatic capacitance value CIN of the N-side input capacitance 117) and DVDET / VB (voltage ratio of the potential change DVDET to the reference potential VB), for example, when the detection reference potential V1 = 0. The greater the signal strength of the potential change DVDET of the detection node, the easier the open-circuit detection, and the closer DVDET / VB is to 1, the better.

[0102] For this purpose, it is necessary to increase the electrostatic capacitance value C1 of the detection capacitance 141. However, increasing the electrostatic capacitance value of the detection capacitance 141 increases the circuit area. Considering this, when designing the electrostatic capacitance value C1 of the detection capacitance 141, it is more effective and preferable if C1 / CIN = approximately 0.5 to 1.0.

[0103] Fig. Fig. 6 is an illustrative diagram showing the dependence of the detection capacity 141 in the flow sensor 10 on Fig. 1 shows.

[0104] Fig. 6 shows the dependence of the detection capacitance 141 on the voltage ratio of the potential change DVDET to the reference potential VB at a detection reference potential V1 = 0, when the electrostatic capacitance value CIN of the N-side input capacitance 117 is approximately 1 pF to 4 pF.

[0105] If, as in Fig. As shown in Figure 6, the electrostatic capacitance value of the N-side input capacitance 117 is small, a relatively large signal strength of the potential change DVDET can be obtained even if the electrostatic capacitance value C1 of the detection capacitance 141 is 2 pF or less. However, if the electrostatic capacitance value of the N-side input capacitance 117 is large, the potential change DVDET cannot be achieved with the same signal strength unless the electrostatic capacitance value C1 of the detection capacitance 141 is set larger.

[0106] To improve the noise performance of the differential A / D converter 122, it is necessary to increase the electrostatic capacitance values ​​of the input capacitances 116, 117. However, this means that in this case, the electrostatic capacitance value of the detection capacitance 141 must be increased simultaneously.

[0107] The permissible size of the electrostatic capacitance values ​​of the detection capacitance 141 and the holding capacitance 144 is described below.

[0108] Fig. Fig. 7 is an illustrative diagram showing examples of signal waveforms generated by an electrostatic capacitance sum of the detection capacitance 141 and the holding capacitance 144 in the flow sensor 10 of Fig. 1 can be generated.

[0109] Fig. 7(a) shows the relationship between the signal transmission delay time caused by the sum of the capacitances of the sampling capacitance 141 and the holding capacitance 144, and schematically illustrates how the delay in the circuit operation of the A / D converter 122 increases with increasing electrostatic capacitance sum of the detection capacitance 141 and the holding capacitance 144.

[0110] Out of Fig. 5 and Fig. 6 shows that the signal strength of the potential change DVDET increases with increasing electrostatic capacitance value of the detection capacitance 141. However, if the electrostatic capacitance value of the detection capacitance 141 is too large, not only does the chip area increase as mentioned above, but also the signal delay becomes long and exceeds an allowable delay time DelayLim.

[0111] Here, the allowable delay time DelayLim is determined by the operating frequency of the sampling-hold differential A / D converter 122. When the differential A / D converter 122 uses an oversampling method, the accuracy increases with increasing operating frequency. At the same time, however, the allowable delay time DelayLim decreases, and the allowable value of the sum of the capacitances of the detection capacitance 141 and the hold capacitance 144 becomes small.

[0112] Since the value of the allowable delay time DelayLim can be regarded as the time required until the potential of the input node of the differential A / D converter 122 becomes static, it is necessary to determine a sampling frequency of the differential A / D converter 122 according to the allowable delay time DelayLim when the signal strength required for interruption detection is determined in this way.

[0113] As described above, when determining the electrostatic capacitance values ​​of the detection capacitance 141 and the holding capacitance 144, the operating frequency of the differential A / D converter 122 must be taken into account, and therefore the electrostatic capacitance value of the detection capacitance 141 can be determined based on the sampling frequency of the differential A / D converter 122.

[0114] Fig. 7(b) illustrates the relationship between the electrostatic capacitance sum of the detection capacitance 141 and the holding capacitance 144 and an input impedance of the differential A / D converter 122.

[0115] The differential A / D converter 122 connected to the resistance bridge 100 converts an analog resistance value into a digital value, which is why the operation can be performed with higher accuracy as the input impedance increases. On the other hand, as the sum of the electrostatic capacitance of the detection capacitance 141 and the electrostatic capacitance of the holding capacitance 144 increases, the input impedance becomes small, and the performance of the flow sensor 10 deteriorates.

[0116] The sum of the capacitances of the detection capacitance 141 and the holding capacitance 144 must be set so that the input impedance is greater than a permissible impedance value ImpedanceLim, which is determined by the size of the resistance value of the resistance bridge 100.

[0117] As described above, the electrostatic capacitance values ​​of the detection capacitance 141 and the holding capacitance 144 must be appropriately set to a value that satisfies both the allowable delay time DelayLim for the circuit operation delay of the differential A / D converter 122 and the allowable impedance value ImpedanceLim for the input impedance. In this way, the electrostatic capacitance values ​​of the detection capacitance 141 and the holding capacitance 144 are determined. (Operating range of the interruption detection circuit)

[0118] Fig. Fig. 8 is an illustrative diagram showing an example of an operating window in the circuit operation of the interruption detection circuit 130 used in the flow rate sensor 10 of Fig. 1 is provided.

[0119] Fig. Figure 8 schematically shows a relationship between voltages when the detection reference potential V1 in Fig. 1 is smaller than the reference potential VB.

[0120] Due to manufacturing-related variations in resistance value and the like, the common mode voltage of the resistance bridge 100 fluctuates within a certain range as indicated by the common mode voltage fluctuation amount DVCOM in Fig. 8. When a maximum value SIGMAX of the signal from the resistance bridge 100 is output from this lower limit, the potential of the detection node VDET decreases to a potential NormalLim.

[0121] Since the potential of the detection node VDET also drops to the potential NormalLim when no interruption occurs, the detection reference potential V3 at the input of the comparator 145 must be lower than the potential NormalLim.

[0122] On the other hand, since the potential change DVDET is designed according to the ratio of the electrostatic capacitance value of the input capacitance 116 (or the input capacitance 117) to the electrostatic capacitance value of the detection capacitance 141, the potential change DVDET can only be reduced to a potential VdetLim upon interruption.

[0123] This means that a DIAGWIN working window lies between the NormalLim potential and the VdetLim potential. The detection reference potential V3 must be adjusted within this DIAGWIN working window, taking into account fluctuations of the comparator 145 and changes in the ambient temperature.

[0124] In this case, considering that fluctuation of the potential VdetLim is small, the detection reference potential V3 is preferably set to satisfy V3 ​​< (NormalLim - VdetLim) / 2.

[0125] Fig. Fig. 9 is an illustrative diagram showing another example of a window in the circuit operation of the interruption detection circuit 130 included in the flow rate sensor 10 in Fig. 1 is provided.

[0126] Fig. 9 shows an operating window in the interruption detection circuit 130 when the detection reference potential V1 is set larger than the reference potential VB.

[0127] In Fig. 9, the detection reference potential V3 is as in Fig. 8 preferably set so that V3 > (VdetLim - NormalLim) / 2 is satisfied.

[0128] Fig. 10 is an illustrative diagram showing a configuration example of a control system 350 for the flow sensor 10 of Fig. 1 shows.

[0129] The tax system in Fig. 10, for example, is an engine control system for controlling an internal combustion engine. The engine controlled by this engine control system is an internal combustion engine, i.e., a machine used, for example, in a motor vehicle or a generator.

[0130] As in Fig. 10, the control system 350 includes an air flow control module 351, a control module 352, and the controller 353. The air flow control module 351 is a module that adjusts an amount of air supplied to the internal combustion engine and includes the flow sensor 10 and a flow controller 355.

[0131] The flow controller 355 regulates the amount of air supplied to the internal combustion engine based on a result in the sensor signal SENOUT output from the flow sensor 10. The control module 352 includes various controls for controlling the internal combustion engine, such as a throttle valve control and an injector control.

[0132] The throttle valve controller controls a throttle valve opening, that is, a fuel quantity supplied to the internal combustion engine, and the like. The fuel injector controller controls the operation of an injector that injects fuel into an intake port or the like of the internal combustion engine.

[0133] The controller 353 controls the overall control system 350. That is, the overall control system 350 is controlled based on an input and output signal FLOWCTRL input to and output from the air flow control module 351 and an input and output signal MODULECTRL input to and output from the control module 352.

[0134] Here, an example has been described in which the flow sensor 10 is used for an internal combustion engine of an automobile or the like. However, a sensor using a resistance bridge as the detection principle is applicable to various other sensors, such as a sensor for measuring pressure and strain.

[0135] As mentioned above, the breakage of a bonding wire 164, 165 can be detected with low noise by performing the detection of the potential of the input node of the differential A / D converter 122 only when the sampling of the input node of the differential A / D converter 122 is performed.

[0136] This allows for the implementation of a highly reliable flow sensor 10. The reliability of the internal combustion engine control system can be increased by equipping the control system 350 with the flow sensor 10. (Second Embodiment) (Configuration Example and Operation of the Flow Sensor)

[0137] Fig. 11 is an illustrative diagram showing a configuration example of a flow rate sensor 10 according to a second embodiment.

[0138] The flow sensor 10 in Fig. 11 differs from the flow sensor 10 in Fig. 1 according to the first embodiment in the operation of the analog switches 140, 142, 143 of the interruption detection units 131, 132 and the clock types generated by the clock generation circuit 170. Since the configuration of the flow rate sensor 10 is the same as that of the flow rate sensor 10 of Fig. 1, their description is omitted.

[0139] In addition to the clocks P1, P1B, P2, P2B generated by the clock generation circuit 170, which are shown in Fig. 1, the clock generation circuit 170 generates the clocks PD1, PD1B, PD2, and PD2B. The clock PD1B is an inverted signal of the clock PD1, and the clock PD2B is an inverted signal of the clock PD2.

[0140] Analog switch 142 operates based on clocks PD2 and PD2B. Analog switches 140 and 143 each operate based on clocks PD1 and PD1B. Clocks PD1, PD1B, PD2, and PD2B are clocks that are different from clocks P1, P1B, P2, and P2B.

[0141] Since the clocks PD1, PD1B, PD2, PD2B are different from the clocks P1, P2, which are operating clocks of the differential A / D converter 122, as mentioned above, a difference from the first embodiment is that the interruption detection circuit 130 and the differential A / D converter 122 are operated on the basis of different control clocks. (Signal timing example of the detection unit)

[0142] Fig. Fig. 12 is a timing chart schematically showing a clock and an internal waveform in the interruption detection unit 131 used in the flow rate sensor 10 of Fig. 11 is provided.

[0143] Fig. 12 shows, from top to bottom, the signal timing of the clock P1, the clock P2, the clock PD1, the clock PD2, the node VM of the interrupt detection unit 131, the input unit VINM of the control circuit 110, and the detection node VDETM, respectively.

[0144] The clocks P1, P2 are the control clocks of the differential A / D converter 122 as described in the first embodiment and are therefore the same as those in Fig. 4.

[0145] In period t1, a high period of clock P1D is the same as that of clock P1, but a low period of clock P1D differs from that of clock P1 in that one cycle of clock P1D is as long as several cycles of clock P1. Similarly, in period t2, a high period of clock P2D is the same as that of clock P2, but a low period of clock P2D differs from that of clock P2 in that one cycle of clock P2D is as long as several cycles of clock P2.

[0146] In this way, the operating frequency of the interrupt detection circuit 130 can be reduced to approximately 1 / 4 compared to the first embodiment. This makes it possible to reduce the noise from the interrupt detection circuit 130 that is superimposed on the differential A / D converter 122.

[0147] In addition, by reducing the operating frequency, the power consumption associated with the operation of the interruption detection circuit 130 can be reduced.

[0148] As described above, a flow sensor 10 may be provided which enables more accurate interruption detection with low power consumption.

[0149] Fig.12 shows an example in which the operating frequency of the interrupt detection circuit 130 is reduced to approximately 1 / 4 compared to the operating frequency of the differential A / D converter 122. However, the operating frequency is not limited to 1 / 4 as long as the operating frequency of the interrupt detection circuit 130 is lower than the sampling frequency of the differential A / D converter 122.

[0150] The operating frequency of the differential A / D converter 122 is often as high as several hundred kHz due to the oversampling method. In contrast, the interrupt detection frequency can be several hundred Hz, and the operating frequency of the interrupt detection circuit 130 can be reduced to about 1 / 1000 of that of the differential A / D converter 122.

[0151] It is desirable to appropriately determine the extent to which the operating frequency of the interruption detection circuit 130 is reduced based on the required response sensitivity, etc., of the flow rate sensor 10.

[0152] Although the present invention has been described in detail with reference to the embodiments, the invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention.

[0153] The present invention is not limited to the above embodiments, but includes various modifications. For example, the above embodiments may be described in detail to facilitate understanding of the invention and are not necessarily limited to those having all of the described configurations.

[0154] A portion of the configuration of one embodiment may be replaced by a configuration of another embodiment, and the configuration of another embodiment may be added to the configuration of one embodiment. A portion of the configuration of each embodiment may be added to, deleted from, or replaced by another configuration. List of reference symbols 10 flow sensor 100 resistance bridge 102 Resistance 103 Resistance 104 Resistance 105 Resistance 110 Control circuit 111 Input processing unit 112 analog switches 113 analog switches 114 analog switches 116 P-side input capacity 117 N-side input capacity 118 analog switches 119 analog switches 120 analog switches 121 analog switches 122 differential A / D converters 130 Interruption detection circuit 131 Interruption detection unit 132 Interruption detection unit 133 Determination unit 140 analog switches 141 detection capacity 142 analog switches 143 analog switches 144 holding capacity 145 Comparator 164 bonding wire 165 bonding wire 170 Clock generation unit 180 logic unit 200 power generation units 202 Resistance 204 Stabilization capacity 205 Stabilization capacity 301 transistors 302 transistors 350 tax system 351 Air flow control module 352 control module 353 controllers 355 flow controller

Claims

[1] Flow sensor comprising: a sensor unit configured to detect a change in a gas flow rate; a switched capacitor type A / D converter configured to convert an analog signal output from the sensor unit into a digital signal; and a break detection circuit configured to detect a break in a wiring connecting the A / D converter to the sensor unit, wherein the interruption detection circuit comprises a first capacitor, one connection portion of which is connected to an input node of the A / D converter, and a detection unit configured to detect the interruption of the wiring, and the detection unit detects a break in the wiring using a potential based on a ratio of the electrostatic capacitance of input capacitors connected to input units of the A / D converter to an electrostatic capacitance of the first capacitor. [2] Flow sensor according to claim 1, wherein the interruption detection circuit further comprises a second capacitor having a connecting portion connected to an input node of the A / D converter and configured to hold an electric charge of a potential in the first capacitor, and the detection unit detects an interruption in the wiring based on a change in the potential of the second capacitor. [3] The flow sensor according to claim 2, wherein the second capacitor stores an electric charge by a potential based on a ratio of the input capacitor to the first capacitor. [4] The flow sensor according to claim 2, wherein the second capacitor stores electric charges when the A / D converter detects the analog signal and is disconnected from the wiring during a period in which the input capacitor performs sampling of the signal. [5] Flow sensor according to claim 2, wherein a first detection reference potential is supplied to another connection portion of the first capacitor, and a second detection reference potential different from the first detection reference potential is supplied to another connection portion of the second capacitor. [6] The flow rate sensor according to claim 2, wherein the detection unit comprises a comparator that compares the potential based on the ratio of the electrostatic capacitance of the input capacitor to the electrostatic capacitance of the first capacitor with a preset reference potential, and detects that the wiring is broken when the potential based on the ratio of the electrostatic capacitance of the input capacitor to the electrostatic capacitance of the first capacitor is lower than the reference potential. [7] The flow sensor of claim 6, wherein the second capacitor is a gate capacitance of an input transistor from which the comparator is configured. [8] The flow sensor according to claim 6, wherein the second capacitor is a parasitic capacitance of a wiring connected to an input unit of the comparator. [9] The flow rate sensor according to claim 1, wherein an electrostatic capacitance value of the first capacitor is set to satisfy an allowable delay time of the circuit operation and an allowable input impedance of the A / D converter based on an operating frequency of the A / D converter. [10] The flow sensor according to claim 1, wherein an electrostatic capacitance value of the first capacitor is smaller than an electrostatic capacitance value of the input capacitor connected to the A / D converter. [11] The flow rate sensor according to claim 1, wherein an operating frequency of the A / D converter is set based on a delay of the circuit operation of the A / D converter, which is determined based on the input capacitor connected to the A / D converter and an electrostatic capacitance of the first capacitor. [12] Flow sensor comprising: a sensor unit configured to detect a change in a gas flow rate; a clock generation circuit configured to generate a first control clock and a second control clock; a switched capacitor type differential A / D converter configured to operate based on the first control clock and convert an analog differential signal output from the sensor unit into a digital signal; a break detection circuit configured to detect a break in a wiring connecting the A / D converter to the sensor unit; a first input capacitor connected between an output unit of the sensor unit and an input unit of the A / D converter; a first switch configured to switch a connection between the one input unit of the A / D converter and the first input capacitor based on the first control clock generated by the clock generation circuit; a second switch configured to switch a connection between another input unit of the A / D converter and the first input capacitor based on the second control clock; a second input capacitor connected between another output unit of the sensor unit and another input unit of the A / D converter; a third switch configured to switch a connection between an input unit of the A / D converter and the second input capacitor based on the second control clock; and a fourth switch configured to switch a connection between another input unit of the A / D converter and the second input capacitor based on the first control clock, wherein the disconnection detection circuit comprises: a first disconnection detection unit configured to detect a disconnection of a wiring connected to the sensor unit, a second disconnection detection unit configured to detect a disconnection of another wiring connected to the sensor unit, and a disconnection determination unit configured to determine whether the wiring is disconnected or not based on the detection results of the first disconnection detection unit and the second disconnection detection unit, the first interruption detection unit comprises: a first capacitor connected between the one wiring and a first reference voltage, a fifth switch configured to switch a connection between the wiring and the first capacitor based on the second control clock, a sixth switch configured to reset the first capacitor based on the first control clock, a seventh switch configured to switch a connection between the first capacitor and the first input capacitor based on the second control clock, and a first detection unit configured to detect the interruption of the wiring, the second interruption detection unit comprises: a second capacitor connected between the other wiring and the first reference voltage, an eighth switch configured to switch a connection between the other wiring and the second capacitor based on the second control clock, a ninth switch configured to discharge the second capacitor based on the first control clock, a tenth switch configured to switch a connection between the second capacitor and the second input capacitor based on the second control clock, and a second detection unit configured to detect the interruption of the wiring, the connection of the second switch, the third switch, the fifth switch, the seventh switch, the eighth switch, and the tenth switch is switched such that during a sampling operation of the A / D converter, the potentials of the input nodes of the A / D converter are each applied to one of the first interruption detection unit and the second interruption detection unit, and the first detection unit and the second detection unit detect the interruption of the wiring based on the potential of the input node of the A / D converter during the sampling operation of the A / D converter. [13] The flow rate sensor according to claim 12, wherein the disconnection detection unit determines that the wiring is disconnected when the first disconnection detection unit or the second disconnection detection unit detects the disconnection, and outputs a disconnection detection signal. [14] The flow rate sensor according to claim 12, wherein the second control clock generated by the clock generating circuit is a clock whose frequency is different from that of the first control clock. [15] The flow rate sensor according to claim 12, wherein the second control clock generated by the clock generating circuit has a period longer than a period of the first control clock.

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