JP2017003567A - Drive current generator circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive current generator circuit capable of accurately generating and supplying minute current without increasing sizes of elements for feeding current to a sensor element.SOLUTION: A drive current generator circuit 10 comprises; a source current adjustment section 21(+) configured to adjust an amount of source current to be fed to a terminal S+ for feeding a drive current from a power supply to an exhaust gas sensor; and a sink current adjustment section 21(-) configured to adjust an amount of sink current to be drawn from the terminal S+ to the ground. A current control section 30 is configured to adjust the amount of drive current to be fed via the terminal S+ by fixing the amount of current through one of the source current adjustment section 21(+) and sink current adjustment section 21(-) and adjusting the amount of current through the other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a circuit that generates a drive current for energizing a sensor element.

  For example, when operating an exhaust gas sensor, the sensor is operated in a state heated to several hundred degrees C. by a heater in order to stabilize the sensor characteristics. And in order to confirm whether the exhaust gas sensor is heated appropriately, the impedance of the exhaust gas sensor is measured at any time. In addition, in order to improve the characteristics of the sensor, a constant current may be applied to the sensor.

  For this reason, the drive current supplied to the exhaust gas sensor may be a very small current in the vicinity of 0 μA, and the circuit that supplies the drive current needs to generate such a very small current value with high accuracy. In general, for example, a common connection point of two MOSFETs connected in series is connected to a driving current supply point of an exhaust gas sensor, and a source current is supplied from one side and a sink current is drawn through the other at the same time. The drive current value is adjusted in accordance with the balance.

  The following Patent Document 1 does not disclose a circuit for supplying a driving current to the sensor element, but presents it as an example of a circuit similar to the configuration of the background art described above.

JP 2008-92310 A

  However, on the premise of the above configuration, in order to allow a current to flow over a wide range from a minute value near 0 μA to a large value regardless of the terminal voltage, it is necessary to increase the element size to some extent due to the characteristics of the MOSFET. is there.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to generate a drive current that can accurately generate and supply a minute current without enlarging the size of the element that supplies the drive current to the sensor element. It is to provide a circuit.

  According to the drive current generating circuit of claim 1, the source current adjustment unit adjusts the amount of source current that flows from the power source to the energization terminal for energizing the drive element to the sensor element, and the sink current adjustment unit includes the energization Adjust the sink current flowing from the pin to ground. The current control unit is a drive that is energized via the energization terminal by adjusting the amount of current that flows through one of the source current adjustment unit and the sink current adjustment unit as a fixed value. Adjust the amount of current. With this configuration, it is possible to adjust a minute current value more easily and over a wide range without increasing the size of an element used for flowing a source current and a sink current.

  According to the drive current generation circuit of claim 2, a constant voltage supply unit that supplies a constant voltage as a bias voltage for current adjustment to the source current adjustment unit and the sink current adjustment unit, and a variable voltage supply that supplies a variable voltage A part. The variable voltage supply unit is common to the source current adjustment unit and the sink current adjustment unit. Since adjustment is performed by either the source current or the sink current, the common variable voltage supply unit can be switched to the adjustment side and used. Therefore, with this configuration, the drive current generation circuit can be made smaller.

  According to the drive current generating circuit of claim 3, the source current adjusting unit and the sink current adjusting unit are semiconductors in which one of the conduction terminals is connected to the energization terminal and the other is connected to the power supply or ground via the resistance element. An element and an operational amplifier that controls a potential of a conduction control terminal of the element. The input switching unit switches and inputs a constant voltage and a variable voltage as a bias voltage to the input terminal of the operational amplifier. With this configuration, by applying a constant voltage to the input terminal of the operational amplifier, the amount of current applied to the energization terminal through the semiconductor element becomes a fixed value, and when a variable voltage is applied, the amount of current is reduced to the voltage. It becomes the value according to. In addition, the size of the semiconductor element can be reduced.

The figure which is 1st Embodiment and shows the structure of a drive current generation circuit Functional block diagram showing the configuration of a sensor control system including an A / F sensor drive circuit Timing chart showing sweep current change pattern (Part 1) Timing chart showing sweep current change pattern (2) Timing chart showing sweep current change pattern (Part 3) The figure which is 2nd Embodiment and shows the structure of a drive current generation circuit The figure which is 3rd Embodiment and shows the structure of a drive current generation circuit Functional block diagram showing the electrical configuration of the A / F sensor drive circuit according to the fourth embodiment The figure which shows the case where a microcomputer and an exhaust gas sensor are connected to the A / F sensor drive circuit, or when a tester is connected Flowchart showing processing for obtaining correction data for A / D converter The figure which shows the relationship between an input differential voltage and A / D conversion data in case the gain of a differential amplifier circuit is "1.0" Flow chart showing processing for obtaining correction data for D / A converter The flowchart which shows the correction process which an A / F sensor drive circuit performs based on correction data. Timing chart showing the change pattern of the sweep current according to the fifth embodiment The figure which shows the structure of the drive current generation circuit The figure which is 6th Embodiment and shows the structure of a drive current generation circuit

(First embodiment)
As shown in FIG. 2, the A / F sensor drive circuit 1 of the present embodiment includes a sensor control logic 2, and the control logic 2 includes a communication interface (communication for communicating with an external microcomputer 4). I / F) 5 and a storage device 6 including a non-volatile memory such as a flash memory or EEPOM for storing data is connected. The A / F sensor driving circuit 1 is configured by a so-called ASIC (specific application IC). Further, a D / A converter (DAC) 7 and an A / D converter (ADC) 80 are connected to the control logic 2. Although details will be described in the fourth embodiment, the A / D converter 80 here includes an analog front end (AFE) and a multiplexer (MPX) arranged on the input side.

  The output terminal of the D / A converter 7 is connected to the input terminal of the drive current generation circuit 10, and the output terminal of the drive current generation circuit 10 is connected to the terminal S + of the drive circuit 1. Terminal S + corresponds to an energization terminal. The output terminal of the operational amplifier 11 is connected to its own inverting input terminal and also connected to the terminal S− of the drive circuit 1 via the resistance element 12. A series circuit of resistance elements 13 and 14 is connected between the power supply VDD and the ground, and a common connection point between them is connected to a non-inverting input terminal of the operational amplifier 11.

  An exhaust gas sensor 15 corresponding to a sensor element is connected to the terminals S + and S− outside the drive circuit 1. The terminals S + and S− and the output terminal of the operational amplifier 11 are connected to the input terminal of the A / D converter 80. Further, the microcomputer 4 transmits various control parameters for sensing by the exhaust gas sensor 15 to the communication I / F 5 of the drive circuit 1. On the other hand, the communication I / F 5 transmits data indicating the result of sensing by the exhaust gas sensor 15 and data regarding the characteristics of the exhaust gas sensor 15 to the microcomputer 4 side.

  As shown in FIG. 1, the drive current generation circuit 10 includes a voltage / current converter 21. In the voltage-current converter 21, a series circuit of a resistance element 22, a P-channel MOSFET 23, an N-channel MOSFET 24, and a resistance element 25 is connected between the power supply VDD and the ground. The common connection point of the FETs 23 and 24 is connected to the terminal S +. Output terminals of operational amplifiers 26 and 27 are connected to gates which are conduction control terminals of the FETs 23 and 24, respectively. The inverting input terminals of the operational amplifiers 26 and 27 are connected to the sources of the FETs 23 and 24, respectively. The FETs 23 and 24 correspond to semiconductor elements.

  The output terminal of the D / A converter 7 is connected to one of the input terminals of the analog switches 28 and 29 indicated by a changeover switch symbol. The analog switches 28 and 29 correspond to an input switching unit. A fixed P-side bias voltage is applied to the other input terminal of the analog switch 28 from a reference voltage (not shown). Similarly, a fixed N-side bias voltage is applied to the other input terminal of the analog switch 29. The reference voltage corresponds to a constant voltage supply unit. The output terminals of the analog switches 28 and 29 are connected to the non-inverting input terminals of the operational amplifiers 26 and 27, respectively.

  The control logic 2 performs switching control of the analog switches 28 and 29 by a switching signal POLE. The control is performed in conjunction with the input of the analog switch 28 on the D / A converter 7 side, and at the same time the input of the analog switch 29 is on the N-side fixed bias voltage side. Further, at the same time as the input of the analog switch 28 becomes the fixed bias voltage side on the P side, the input of the analog switch 29 becomes the D / A converter 7 side. The operational amplifiers 26 and 27 are configured to enable control, and the control logic 2 individually performs enable control of the operational amplifiers 26 and 27 by the enable signals EN1 and EN2.

  In the above configuration, the resistance element 22, the P-channel MOSFET 23 and the operational amplifier 26 of the voltage-current conversion unit 21 constitute a source current adjustment unit 21 (+), and the N-channel MOSFET 24, the resistance element 25 and the operational amplifier 27 are a sink current adjustment unit 21. (-) Is configured. The control logic 2, the D / A converter 7, and the analog switches 28 and 29 constitute a current control unit 30. Further, the control logic 2 and the D / A converter 7 correspond to a variable voltage supply unit.

  Next, the operation of this embodiment will be described. As described above, when the exhaust gas sensor 15 is operated, heating is performed by a heater (not shown), and the impedance of the exhaust gas sensor 15 is measured as needed to confirm the heating state. The impedance is measured by the control logic 2 detecting the terminal voltage of the resistance element 12 via the A / D converter 80. Therefore, the drive current generation circuit 10 performs control so that the source current is supplied to the exhaust gas sensor 15 via the terminal S + or the sink current is drawn from the terminal S +. These currents are minute currents in the vicinity of 0 μA.

  The drive current generation circuit 10 controls the D / A converter 7 and the analog switches 27 and 28 to adjust the voltage / current converter 21 so that the minute current flows through the terminal S +. When adjusting the source current, an N-side fixed bias voltage is applied to the non-inverting input terminal of the operational amplifier 26 as shown in FIG. The control logic 2 applies a variable bias voltage corresponding to the data CODE input to the D / A converter 7 to the non-inverting input terminal of the operational amplifier 27 for adjustment. On the other hand, when adjusting the sink current, on the contrary, a P-side fixed bias voltage is applied to the non-inverting input terminal of the operational amplifier 27, and a variable bias voltage corresponding to the data CODE is applied to the non-inverting input terminal of the operational amplifier 26. adjust. As a result of such control, the terminal S + is energized with the sum of the source current and the sink current.

  If the enable signal EN1 is made inactive and the operational amplifier 26 is disabled, only the sink current can be extracted from the terminal S +. Further, if the enable signal EN2 is made inactive and the operational amplifier 27 is disabled, only the source current can be supplied to the terminal S +.

  3 to 5, the positive side of the sensor applied current is the source current, and the negative side is the sink current. 3 to 5 show different sweep current change patterns and variations, respectively. In FIG. 3 and FIG. 4, in a steady state, driving is performed with a sink current drawn from the exhaust gas sensor 15. Thereby, depending on the type of sensor, for example, so-called “rich shift” is performed to improve sensor characteristics such as an improvement in catalyst purification rate.

  In the pattern shown in FIG. 3, all of the sweeps, that is, the “sweep (+) time” is performed with the sink current, but in the pattern shown in FIG. 4, only the “sweep (+) time” has the source current. Supply. In the pattern shown in FIG. 5, “rich shift” is not performed, and the exhaust gas sensor 15 is not energized in a steady state. The “sweep (+) time” supplies the source current, and the “sweep (−) time” extracts the sink current. The reason why the “sweep (−) time” is provided after the “sweep (+) time” is provided in this manner is that the charge charged in the internal capacitance is supplied by supplying the source current to the exhaust gas sensor 15. This is because the discharge is caused by the sink current.

  As described above, according to the present embodiment, the source current adjustment unit 21 (+) of the drive current generation circuit 10 adjusts the amount of source current that flows from the power source to the terminal S + for supplying the drive current to the exhaust gas sensor 15. The sink current adjustment unit 21 (−) adjusts the amount of sink current flowing from the terminal S + to the ground.

  Then, the current control unit 30 adjusts the amount of current flowing by one of the source current adjusting unit 21 (+) and the sink current adjusting unit 21 (−) as a fixed value and adjusting the amount of current flowing by the other. The amount of drive current energized via S + is adjusted. With this configuration, it is possible to adjust a minute current value more easily and over a wide range without increasing the size of the FETs 23 and 24 used for flowing the source current and the sink current. .

  A constant voltage supply unit that supplies a constant voltage as a bias voltage for current adjustment and a variable voltage supply unit that supplies a variable voltage are provided. The variable voltage supply unit includes a source current adjustment unit 21 (+) and a sink current. The sensor control logic 2 and the D / A converter 7 common to the adjustment unit 21 (−) are used. Therefore, the drive current generation circuit 10 can be further reduced in size.

  The source current adjusting unit 21 (+) and the sink current adjusting unit 21 (-) have a drain that is a conduction terminal connected to the terminal S +, and a source that is also a conduction terminal to the power source or the ground, respectively. FETs 23 and 24 that are connected via each other, and operational amplifiers 26 and 27 that control the gate potential of the FETs 23 and 24. The analog switches 28 and 29 switch and input a constant voltage and a variable voltage as bias voltages to the non-inverting input terminals of the operational amplifiers 26 and 27. Thus, switching between one of the source current and the sink current as a fixed value and the other as a variable value can be easily performed.

(Second Embodiment)
Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and different parts will be described. As shown in FIG. 6, the drive current generation circuit 31 of the second embodiment deletes the analog switches 28 and 29 from the drive current generation circuit 10 of the first embodiment, and the output terminal of the D / A converter 7 is connected to the operational amplifier 26. The N-side fixed bias voltage is directly applied to the non-inverting input terminal of the operational amplifier 27.

  That is, the sink current is always a fixed value, and only the source current is variable. For example, if the sink current is fixed at -1 mA and the source current is adjusted in the range of 0 to 2 mA, the current flowing through the terminal S + can be adjusted in the range of -1 mA to +1 mA. The output terminal of the D / A converter 7 is directly connected to the non-inverting input terminal of the operational amplifier 27, and the P-side fixed bias voltage is directly applied to the non-inverting input terminal of the operational amplifier 26, so that the source current is always fixed. It goes without saying that only the sink current may be varied.

(Third embodiment)
As shown in FIG. 7, the drive current generation circuit 41 of the third embodiment deletes the analog switches 28 and 29 as in the second embodiment, and the output terminal of the D / A converter 7 is not connected to the operational amplifiers 26 and 27. It is directly connected to the inverting input terminal. Further, a series circuit of a source current source 42 and a sink current source 43 is connected between the power supply VDD and the ground, and these common connection points are connected to the terminal S +. The current sources 42 and 43 are configured to enable control, and the control logic 44 in place of the control logic 2 individually enables the current sources 42 and 43 by the enable signals EN3 and EN4.

  In the above configuration, the source current adjustment unit 21 (+) of the first embodiment plus the source current source 42 constitutes the source current adjustment unit 45 (+) of the third embodiment, and the sink current adjustment unit 21 (-) plus the sink current source 43 constitutes the source current adjustment unit 45 (-). The D / A converter 7 and the control logic 44 constitute a current control unit 46 of the third embodiment.

  Next, the operation of the third embodiment will be described. In the third embodiment, the potentials of the non-inverting input terminals of the operational amplifiers 26 and 27 are adjusted to be equal by the output voltage of the D / A converter 7, so that the amount of source current that flows to the terminal S + according to the output voltages of the operational amplifiers 26 and 27. And the sink current amount have the same value.

  The control logic 44 enables one of the current sources 42 and 43 by the enable signals EN3 and EN4 and disables the operational amplifiers 26 and 27 on the same side as the first embodiment. , The same state as when a fixed bias voltage is applied to one of the operational amplifiers 26 and 27 is obtained.

  For example, the source current value flowing according to the output voltage of the D / A converter 7 is Iv (+), the sink current value is Iv (−), and the source current value flowing by the current sources 42 and 43 is Is (+), Assume that the sink current value is Is (-). Note that Is> Iv. When the current source 42 is enabled and the operational amplifier 26 is disabled, the source current value that flows is Is (+) and the sink current value is Iv (−). Therefore, the sink current that flows through the terminal S + Becomes {Is (+)-Iv (-)}.

  As described above, according to the third embodiment, the source current adjustment unit 45 (+) is provided with the source current source 42 configured to flow a constant source current to the terminal S + and configured to stop the energization operation. The sink current adjustment unit 45 (−) allows a constant sink current to flow from the terminal S +, and similarly includes a sink current source 43 configured so that the energization operation can be stopped. Then, the current control unit 46 energizes the current sources 42 and 43 on the side where the amount of current is fixed, and disables the operational amplifiers 26 and 27 on the same side. Therefore, the same effect as the first embodiment can be obtained.

(Fourth embodiment)
In the fourth embodiment, for example, initial adjustment and correction are performed for the D / A converter 7 before the drive current is adjusted in the first embodiment. As shown in FIG. 8, a sensor control logic 52 that replaces the sensor control logic 2 is arranged in the drive circuit 51. Further, the output terminal of the D / A converter 53 is connected to the non-inverting input terminal of the operational amplifier 11, and the input terminal of the D / A converter 53 is connected to the output terminal of the control logic 52.

  A D / A converter 53, an A / D converter 81, and a D / A converter 7 are connected to the control logic 52. A portion corresponding to the A / D converter 80 of the first embodiment is an A / D converter 81, an analog front end (AFE) 82, and a multiplexer (MPX) 83.

  The input terminal of the A / D converter 81 is a differential input, and each input terminal is connected to the differential output terminals ADP and ADM of the AFE 82, respectively. The AFE 82 incorporates a differential amplifier circuit (not shown). The input terminals INP and INM of the AFE 82 are connected to the output terminals of the MPX 83, respectively. The output terminal of the operational amplifier 11 and the terminals S +, S−, and AFR are connected to the input terminal of the MPX 83, respectively. The MPX 83 is controlled by the control logic 52, and selects any two of the input terminals and switches them to connect to the input terminals INP and INM of the AFE 82.

  The output terminal of the D / A converter 7 is connected to the input terminal of the voltage controlled current source 55 via the switch 54, and the output terminal of the voltage controlled current source 55 is connected to the terminal AFR via the switch 56. Yes. Here, the drive circuit 51 has three terminals S +, S−, and AFR. These are specifications that can be driven by selectively connecting two types of A / F sensors.

  FIG. 9 shows a state in which the driving circuit 51 actually drives the exhaust gas sensor 15 and the microcomputer 4 that is a target for transmitting the sensor signal output from the sensor 15 is connected to the communication I / F 5. FIG. 9 also shows a tester 61 (correction device) connected to the drive circuit 51 in order to perform correction before connecting the microcomputer 4 and the exhaust gas sensor 15. The tester 61 includes voltmeters 62 to 64 and a voltage source / ammeter 65. The tester 61 is connected to the communication I / F 5 of the drive circuit 51 instead of the microcomputer 4 and performs correction processing while communicating with the control logic 52.

The connection between the drive circuit 51 and the tester 61 is indicated by a broken line, the voltmeter 62 is connected to the terminal S +, and the voltmeter 64 is connected to the output terminal of the operational amplifier 11 via the monitor terminal. The voltmeter 63 and the voltage source / ammeter 65 are selectively connected to the terminal S− via the changeover switch 66. The target to be corrected is as follows.
-Offset value for conversion data of A / D converter-Gain of differential amplifier circuit built in AFE 82-Resistance value of resistance element 12-Offset value of conversion voltage of D / A converter

  In addition, when another A / F sensor other than the exhaust gas sensor 15 is connected to the drive circuit 51, the terminal AFR is used to supply a constant current to the A / F sensor and detect the impedance of the sensor. The

  Next, the operation of the fourth embodiment will be described. As shown in FIG. 10, when the drive circuit 51 is powered on (S1), offset correction is first performed (S2). With the terminal S- opened (S21), the tester 61 switches the MPX 83 to the output terminal side of the operational amplifier 11. Then, the control logic 52 causes the D / A converter 53 to output control data, and the operational amplifier 11 outputs a voltage of 2.5 V (S22). The tester 61 acquires the data converted by the A / D converter 81 at this time (S23).

  Since the potential difference between the input terminals INP and INM is 0V, the data value converted by the A / D converter 81 should be a value corresponding to 0V. However, in reality, an error in constants of circuit elements constituting the AFE 82, an offset of an operational amplifier, and the like cause an error in data values to be converted. Therefore, the tester 61 calculates the difference between the data value acquired in step S23 and the 0V equivalent value (ideal value) (S24), and calculates an offset correction code from the calculation result (S25).

  Next, the resistance value of the resistance element 12 (shunt resistor) is corrected (S3). A voltage source / ammeter 65 is connected to the terminal S-, and sweeping is performed within a voltage range of 1 to 4 V, for example (S31). Then, the voltage source / ammeter 65 measures the voltage at the terminal S- and the current flowing through the terminal S-, and acquires the data converted by the A / D converter 81 (S32). A resistance value of the resistance element 12 is calculated from the measured voltage value and current value (S33), and a correction code for the resistance value is calculated from the calculation result (S34).

  Next, the gain of the differential amplifier circuit built in the AFE 82 is corrected (S4). With the terminal S- opened (S41), the tester 61 causes the control logic 52 to output control data to the D / A converter 53, and causes the operational amplifier 11 to output a voltage of 1.875 V (S42). Further, a voltage of 2.5 V is applied to the terminal S- by the voltage source / ammeter 65 (S43). At this time, the terminal voltage of the resistance element 12; the input voltage of the A / D converter 81 is 0.625V. The tester 61 acquires the data converted by the A / D converter 81 at this time, and calculates the gain of the differential amplifier circuit from the resistance value of the resistance element 12 corrected using the correction code calculated in step S34 (S44). ), A gain correction code is calculated from the calculation result (S45).

Here, when the exhaust gas sensor 15 is connected to the drive circuit 51, the gain of the differential amplifier circuit is set to “1.85”. Then, the potential difference 0.625 V applied to both ends of the resistance element 12 in steps S42 and S43 is determined as follows. If the potential difference IN ± [V], the operating power supply voltage Vref, and the gain are Gain,
IN ± [V] = Vref / 2 ± Vref / 2 × 1 / (Gain) × 1/2 × 1/2
The first term on the right side is the center of the operating voltage, the last term (1/2) is a coefficient that adjusts the input voltage range to avoid clamping due to voltage variations, and the second term between them is the upper and lower limits of the input voltage Indicates.
When Vref = 5 and Gain = 1.85, the potential difference IN ± [V] is about 0.676 V, but is close to the output voltage of the D / A converter 53 and a voltage that can be easily applied from the outside. 0.625V was selected.

  When an A / F sensor other than the exhaust gas sensor 15 is connected to the drive circuit 51, the gain of the differential amplifier circuit is set to “1.0” (note that the differential amplifier circuit is a variable gain setting). Is possible). At this time, the potential difference IN ± [V] is 1.25V. The relationship between the offset correction of the A / D converter 81 when the gain is “1.0” and the gain correction of the differential amplifier circuit is as shown in FIG. When the range of the differential voltage input to the A / D converter 81 is ± 2.5V and 0V is expressed as the median value with the maximum code value MAX, the value corresponding to 0V after offset correction is “MAX / 2”. , 1.25V equivalent value (ideal value) is “MAX / 4”.

  However, if there is an error in the gain of the actual differential amplifier circuit, the A / D conversion data when a difference voltage of 1.25 V is applied produces a difference from the ideal value “MAX / 4”. Therefore, a change rate (coefficient) corresponding to the difference between the obtained A / D conversion data and the ideal value “MAX / 4” is obtained, and the change rate is used as the correction code in step S45. When the correction value is confirmed (S5), the correction value is written in the storage device 6 by the control logic 52 (S6), and the process is terminated.

  Next, a case where correction data for a D / A converter is acquired will be described. The flowchart shown in FIG. 12 shows a case where the D / A converter 7 for outputting a voltage to the drive signal generation circuit 10 is corrected as an example. When power is supplied to the drive circuit 51 (S11), offset correction is first performed on the current source side (S12). With the terminal AFR open (S121), a voltage of 2.5 V is applied to the terminal AFR by the voltage source / ammeter 65 (S122).

  Subsequently, the tester 61 turns on the switches 54 and 56 so that the control logic 52 outputs control data to the D / A converter 7 so that the current flowing from the voltage control current source 55 to the terminal AFR becomes +1 mA (S123). ). Then, the current value flowing at that time is actually measured by the voltage source / ammeter 65, the difference from the ideal value of 1 mA is calculated (S124), and the offset correction code is calculated from the calculation result (S125).

  Next, offset correction is performed on the current sink side (S13). Steps S131 to S135 are obtained by applying the processing of steps S121 to S125 on the sink side, and the current setting value in step S133 is only −1 mA, and the other processes are the same. When the correction value is confirmed (S14), the correction value is written in the storage device 6 (S15), and the process is terminated.

  As described above, the correction data is stored in the storage device 6 of the drive circuit 51. For example, when the exhaust gas sensor 15 is actually connected to the drive circuit 51 and the sensor signal output from the exhaust gas sensor 15 is A / D converted, as shown in FIG. 13, when the power is turned on (S51), The control logic 52 reads the correction data from the storage device 6 (S52), drives the exhaust gas sensor 15, and starts a sensor control operation (S53). And the data which the A / D converter 81 A / D converted the sensor signal which the exhaust gas sensor 15 outputs is correct | amended based on the said correction data (S54). Then, the corrected data is transmitted to the microcomputer 4 via the communication I / F 5.

  As described above, according to the fourth embodiment, the tester 61 uses the expected zero point data value of the A / D converter 81 as the offset correction data and the differential input to the A / D converter 81 by the D / A converter 53. The difference from the A / D conversion data value obtained when the voltage is set to 0 V is obtained, and the obtained offset correction data is stored in the storage device 6 of the drive circuit 51. In other words, the A / D converter 81 is built in the drive circuit 51, and the offset of the A / D converter 81 is corrected on the drive circuit 51 side.

  Therefore, the microcomputer 4 connected to the drive circuit 51 does not need to bear any processing for obtaining the offset correction data, and the A / D conversion data corrected by the drive circuit 51 in advance for the sensor signal of the exhaust gas sensor 15. Can be obtained.

  Further, the drive circuit 51 includes a differential amplifier circuit on the input side of the A / D converter 81. The tester 61 uses the D / A converter 53 to set the input voltage to the differential amplifier circuit as 1. The A / D conversion data value obtained when 25 V (predetermined voltage) is set to the expected data value corresponding to the gain set in the differential amplifier circuit is used as a reference for the expected zero point data value. The rate of change corresponding to the gain is obtained, and the gain correction data is stored in the storage device 6. Therefore, when the drive circuit 51 includes a differential amplifier circuit, gain correction is also performed in advance on the drive circuit 1 side, so that the processing burden on the microcomputer 4 can be reduced.

  Further, the drive circuit 51 includes a voltage control current source 55 in which a constant current amount is set according to the output voltage of the D / A converter 7, and the tester 61 inputs control data to the D / A converter 7, The difference between the output current value of the voltage controlled current source 55 measured by the voltage source / ammeter 65 and the target drive current value is obtained, and control data corresponding to the difference is obtained as drive current correction data and stored in the storage device 6. Let For example, when the exhaust gas sensor 15 is driven, the control logic 52 reads the drive current correction data and corrects the control data output to the D / A converter 7. Therefore, the microcomputer 4 does not need to correct the drive current value for driving the exhaust gas sensor 15 and the like.

  That is, the drive circuit 51 needs to correct the gain of the differential amplifier circuit and the current value output from the D / A converter 7 as described above. Therefore, mounting the A / D converter 81 in the drive circuit 51 and performing the offset correction collectively does not particularly increase the work load.

(Fifth embodiment)
In the first embodiment, FIG. 3 or FIG. 4 shows the exhaust gas sensor 15 that is driven in a steady state in which a sink current is drawn. However, depending on the type of exhaust gas sensor, there is a specification of driving with a source current supplied in a steady state as shown in FIG. Therefore, the drive current generation circuit 91 of the fifth embodiment includes a drive current source 92 connected between the power supply and the terminal S + to supply the source current, as shown in FIG.

  The drive current source 92 is provided for a different purpose from the source current source 42 of the third embodiment shown in FIG. As shown in FIG. 14, this corresponds to the case where the driving current in the steady state is required to be about 50 μA, for example, and the source current in that order is supplied to the terminal S +. In addition, the drive current source 92 is configured to be enabled, and the control logic 93 instead of the sensor control logic 2 enables the drive current source 92 by the enable signal EN3. In addition, what is necessary is just to prepare the structure for such enable control as needed.

  According to the fifth embodiment configured as described above, the drive current generating circuit 91 is provided with the drive current source 92 that supplies a steady drive current to the exhaust gas sensor by causing the source current to flow through the terminal S +. The exhaust gas sensor having such a specification can also be driven correspondingly. Further, by configuring so that the energization operation of the drive current source 92 can be stopped, it is possible to deal with a sensor that does not need to energize a steady drive current.

(Sixth embodiment)
As shown in FIG. 16, the drive current generation circuit 101 according to the sixth embodiment is driven by the exhaust gas sensor 102 that is driven in a steady state in which a source current is supplied as described in the fifth embodiment. is there. Therefore, a drive current source 103 configured to be able to adjust the amount of source current supplied to the terminal S + is provided.

  The drive current source 103 includes a resistance element 104, a P-channel MOSFET 105, and an operational amplifier 106, similarly to the source current adjustment unit 21 (+) of the voltage / current conversion unit 21. The operational amplifier 106 is enable-controlled by an enable signal EN3. The sensor control logic 107 inputs control data to the two D / A converters 7 and 109 via the controller 108 and enables the operational amplifiers 11A, 26, 27, and 106 to be enabled. The operational amplifier 11A is enable-controlled by an enable signal EN4.

  The voltage signal D / A converted by the D / A converter 109 is input to the non-inverting input terminal of the operational amplifier 106. That is, the amount of drive current that is constantly supplied to the exhaust gas sensor 102 is adjusted by the voltage signal. Further, the enable control of the drive current source 103 may be performed as necessary.

  According to the sixth embodiment configured as described above, the drive current source 103 is configured such that the amount of source current supplied to the terminal S + can be adjusted, so that the drive current required for each individual exhaust gas sensor is required. The amount can be adjusted and supplied.

The present invention is not limited to the embodiments described above or shown in the drawings, and the following modifications or expansions are possible.
In the first embodiment, D / A converters may be separately provided on the source current side and the sink current side, and voltages output via the two D / A converters may be individually controlled by the control logic.
The operational amplifiers 26 and 27 in the first embodiment do not necessarily need to be enabled.
The sensor element is not limited to the exhaust gas sensor.
The semiconductor element is not limited to a MOSFET.

  1 A / F sensor drive circuit, 2 sensor control logic, 7 D / A converter, 10 drive current generation circuit, 15 exhaust gas sensor, 21 (+) source current adjustment unit, 21 (-) sink current adjustment unit, 23 P channel MOSFET, 24 N-channel MOSFET, 26 and 27 operational amplifier, 28 and 29 analog switch, 30 current controller.

Claims (8)

An energization terminal (S +) for energizing a drive current to the sensor element (15);
A source current adjustment unit (21 (+), 45 (+)) for adjusting a source current amount flowing from the power source to the energization terminal;
A sink current adjusting section (21 (−), 45 (−)) for adjusting the amount of sink current flowing from the energization terminal to the ground;
A current control unit (30, 31, 46) for performing current adjustment control on the source current adjustment unit and the sink current adjustment unit;
The current control unit is energized via the energization terminal by adjusting the amount of current flowing through the other by setting the amount of current flowing through one of the source current adjusting unit and the sink current adjusting unit as a fixed value. A drive current generation circuit characterized by adjusting a drive current amount. The current control unit (30, 31) includes a constant voltage supply unit that supplies a constant voltage as a bias voltage for current adjustment,
A variable voltage supply unit (2, 7) for supplying a variable voltage as the bias voltage;
The drive current generation circuit according to claim 1, wherein the variable voltage supply unit (30) is common to the source current adjustment unit and the sink current adjustment unit. The source current adjustment unit and the sink current adjustment unit include a semiconductor element (23, 24) in which one of conduction terminals is connected to the energization terminal and the other is connected to the power supply or the ground via a resistance element;
Operational amplifiers (26, 27) for controlling the potential of the conduction control terminal of the semiconductor element;
The drive current generation circuit according to claim 2, further comprising an input switching unit (28, 29) for switching and inputting the constant voltage and the variable voltage at an input terminal of the operational amplifier.   4. The drive current generation circuit according to claim 3, wherein the operational amplifier is configured to be enabled by the current control unit. In the source current adjustment unit (45 (+)) and the sink current adjustment unit (45 (−)), one of conduction terminals is connected to the conduction terminal, and the other is connected to the power source or the ground via a resistance element. Connected semiconductor elements (23, 24);
Operational amplifiers (25, 26) for controlling the potential of the conduction control terminal of the semiconductor element;
A variable voltage supply unit (2, 7) for supplying a variable voltage to the input terminal of the operational amplifier;
The operational amplifier is configured to enable control,
The sink current adjusting unit is configured to flow a constant sink current from the energization terminal, and includes a sink current source (43) configured to be able to stop the energization operation.
2. The drive current generation according to claim 1, wherein the current control unit is configured to energize a current source having a fixed value for the amount of current and to disable the operational amplifier on the same side. 3. circuit.   The drive current source (92, 103) for supplying a steady drive current to the sensor element by causing a source current to flow through the energization terminal is provided. Drive current generation circuit.   The drive current generation circuit according to claim 6, wherein the drive current source is configured to be capable of adjusting a source current amount.   The drive current generation circuit according to claim 6 or 7, wherein the drive current source (92, 103) is configured to be capable of stopping an energization operation.

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