Internal combustion engine ignition device

Abstract

An internal combustion engine ignition device can determine ignition timing with high precision to perform ignition with high precision even where noise superimposed at the time of rise of current flowing through an ignition coil is generated. In an internal combustion engine ignition device including an output terminal for detecting an internal state such as a coil current, it is possible to prevent generation of pulse noise in the form of chattering at falling and rising edges of a voltage of the output terminal by using a hysteresis comparator, even if noise is superimposed at the time of rise of the coil current. Therefore, a voltage pulse with pulse width of high precision is transmitted to an electronic control unit without the influence of noise, and the ignition timing can be determined properly with high precision.

Claims

1. An internal combustion engine ignition device, in which an on-off control of current for energizing an ignition coil is performed by a switching element upon receiving a control signal, and an output terminal for externally outputting an ignition state of the ignition coil is provided, the internal combustion engine ignition device comprising: voltage converting means for converting the current to a voltage, the converted voltage being referred to as a sense voltage; first comparing means for comparing the sense voltage with each of two reference voltages, the two reference voltages being a first detection reference voltage for detecting the sense voltage at a time of rise and a first release reference voltage which is a voltage lower than the first detection reference voltage, to output a first output signal, the first comparing means having a hysteresis characteristic; second comparing means for comparing the sense voltage with each of two other reference voltages, the two other reference voltages being a second detection reference voltage for detecting the sense voltage at a time of rise and a second release reference voltage which is a voltage lower than the second detection reference voltage and higher than the first detection reference voltage, to output a second output signal, the second comparing means having a hysteresis characteristic; output means for receiving the first output signal output from the first comparing means and the second output signal output from the second comparing means and for outputting a third output signal; and switch means for controlling the output terminal to be on or off using the third output signal output from the output means; wherein the first comparing means is formed of an inverting input switching-type comparator.

2. The internal combustion engine ignition device according to claim 1, wherein the second comparing means is formed of a second hysteresis comparator, the second hysteresis comparator including a second comparator, a third inverter to which an output of the second comparator is input, a fourth inverter to which an output of the third inverter is input, a third analog switch which connects the second detection reference voltage to a minus terminal of the second comparator, and a fourth analog switch which connects the second release reference voltage to the minus terminal of the second comparator, and the second hysteresis comparator being configured such that the sense voltage is input to a plus terminal of the second comparator, an on-off operation of the third analog switch is caused by an output signal of the third inverter, an on-off operation of the fourth analog switch is caused by an output signal of the fourth inverter, the on-off operation of the third analog switch and the on-off operation of the fourth analog switch are in a reversed phase relationship, and the third analog switch is in an on state when the sense voltage is lower than the second release reference voltage.

3. The internal combustion engine ignition device according to claim 2, wherein the first comparing means includes two minus inputs that are switched and used for comparison, and an inverting input switching control circuit which transmits a switching signal to the inverting input switching-type comparator, receives an output signal of the second hysteresis comparator and an output signal of the inverting input switching-type comparator, and receives a signal that is in synchronization with a control signal for turning on or off the switching element for controlling the current of the ignition coil, a detection reference voltage of the inverting input switching-type comparator is the first detection reference voltage, and a release reference voltage of the inverting input switching-type comparator is at ground potential.

4. The internal combustion engine ignition device according to claim 3, wherein the inverting input switching-type comparator includes a third comparator, a fifth inverter to which an output signal of the third comparator is input, a sixth inverter to which an output signal of the fifth inverter is input, a fifth analog switch which connects the first detection reference voltage to a minus terminal of the third comparator, and a sixth analog switch which connects the first release reference voltage to the minus terminal of the third comparator, the sense voltage is input to a plus terminal of the third comparator, an on-off operation of the fifth analog switch is caused by an output signal of the inverting input switching control circuit, an on-off operation of the sixth analog switch is caused by a signal which is obtained by inverting an output signal of the inverting input switching control circuit by a seventh inverter, the on-off operation of the fifth analog switch and the on-off operation of the sixth analog switch are in a reversed phase relationship, and the fifth analog switch is in an on state when the sense voltage is at the ground potential.

5. The internal combustion engine ignition device according to claim 4, wherein the inverting input switching control circuit is a logic circuit formed of an inverter circuit, an AND circuit, and an OR circuit.

6. The internal combustion engine ignition device according to claim 3, wherein the inverting input switching control circuit is a logic circuit formed of an inverter circuit, an AND circuit, and an OR circuit.

7. The internal combustion engine ignition device according to claim 2, wherein the first comparing means includes two minus inputs that are switched and used for comparison, and an inverting input switching control circuit which transmits a switching signal to the inverting input switching-type comparator, receives an output signal of the second hysteresis comparator and an output signal of the inverting input switching-type comparator, and receives a signal that is in synchronization with a control signal for turning on or off the switching element for controlling the current of the ignition coil, a detection reference voltage of the inverting input switching-type comparator forming the first comparing means and the second release reference voltage of the second hysteresis comparator are the same, and the release reference voltage of the inverting input switching-type comparator is at ground potential.

8. The internal combustion engine ignition device according to claim 2, wherein the voltage converting means is a resistor, the output means is an exclusive OR circuit which outputs a result of exclusive OR of the first output signal output from the first comparing means and the second output signal output from the second comparing means, and the switch means is a MOSFET.

9. The internal combustion engine ignition device according to claim 1, wherein the voltage converting means is a resistor, the output means is an exclusive OR circuit which outputs a result of exclusive OR of the first output signal output from the first comparing means and the second output signal output from the second comparing means, and the switch means is a MOSFET.

10. The internal combustion engine ignition device according to claim 7, wherein the inverting input switching-type comparator includes a third comparator, a fifth inverter to which an output signal of the third comparator is input, a sixth inverter to which an output signal of the fifth inverter is input, a fifth analog switch which connects the first detection reference voltage to a minus terminal of the third comparator, and a sixth analog switch which connects the first release reference voltage to the minus terminal of the third comparator, the sense voltage is input to a plus terminal of the third comparator, an on-off operation of the fifth analog switch is caused by an output signal of the inverting input switching control circuit, an on-off operation of the sixth analog switch is caused by a signal which is obtained by inverting an output signal of the inverting input switching control circuit by a seventh inverter, the on-off operation of the fifth analog switch and the on-off operation of the sixth analog switch are in a reversed phase relationship, and the fifth analog switch is in an on state when the sense voltage is at the ground potential.

11. The internal combustion engine ignition device according to claim 7, wherein the inverting input switching control circuit is a logic circuit formed of an inverter circuit, an AND circuit, and an OR circuit.

12. An internal combustion engine ignition device, in which an on-off control of current for energizing an ignition coil is performed by a switching element upon receiving a control signal, and an output terminal for externally outputting an ignition state of the ignition coil is provided, the internal combustion engine ignition device comprising: a resistor for converting the current to a voltage, the converted voltage being referred to as a sense voltage; a first hysteresis comparator for comparing the sense voltage with each of two reference voltages, the two reference voltages being a first detection reference voltage for detecting the sense voltage at a time of rise and a first release reference voltage which is a voltage lower than the first detection reference voltage, to output a first output signal; a second hysteresis comparator for comparing the sense voltage with each of two other reference voltages, the two other reference voltages being a second detection reference voltage for detecting the sense voltage at a time of rise and a second release reference voltage which is a voltage lower than the second detection reference voltage and higher than the first detection reference voltage, to output a second output signal; an output circuit for receiving the first output signal output from the first hysteresis comparator and the second output signal output from the second hysteresis comparator and for outputting a third output signal; and a switch for controlling the output terminal to be on or off using the third output signal output from the output circuit; wherein the first hysteresis comparator is formed of an inverting input switching-type comparator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram of an internal combustion engine ignition device in a first example of this invention;

(2) FIGS. 2A and 2B show an internal circuit and input-output transmission characteristics of hysteresis comparators 15a and 16a, FIG. 2A being an internal circuit diagram of the hysteresis comparators 15a and 16a and FIG. 2B being an input-output characteristic diagram thereof;

(3) FIG. 3 is a voltage and current waveform diagram of respective parts illustrating the operation in FIG. 1;

(4) FIG. 4 is a block diagram of an internal combustion engine ignition device in a second example of this invention;

(5) FIG. 5 is an operation waveform diagram of the internal combustion engine ignition device in FIG. 4;

(6) FIG. 6 is a block diagram of an internal combustion engine ignition device in a third example of this invention;

(7) FIGS. 7A and 7B show an internal circuit and input-output operation waveforms of an inverting input switching-type comparator 19, FIG. 7A being an internal circuit diagram and FIG. 7B being a view showing representative examples of the input-output operation waveforms therefor;

(8) FIG. 8 is a voltage and current waveform diagram of respective parts illustrating the operation in FIG. 6;

(9) FIG. 9 is a block diagram of an internal combustion engine ignition device in a fourth example of this invention;

(10) FIG. 10 is an operation waveform diagram of the internal combustion engine ignition device in FIG. 9;

(11) FIG. 11 is a block diagram of an internal combustion engine ignition device of the related art;

(12) FIG. 12 is an operation waveform diagram of the internal combustion engine ignition device in FIG. 11;

(13) FIG. 13 is an internal circuit diagram of an inverting input switching control circuit 18;

(14) FIG. 14 is a block diagram of an internal combustion engine ignition device in a fifth example of this invention; and

(15) FIGS. 15A and 15B show an internal circuit and input-output transmission characteristics of a hysteresis comparators 16b, FIG. 15A being an internal circuit diagram of the hysteresis comparator 16b and FIG. 15B being an input-output characteristic diagram thereof.

DETAILED DESCRIPTION

(16) Embodiments of this invention will be described with examples below. In the description below, portions similar to those in the related art will be described briefly, and the technical content relating to this invention will be described in detail.

EXAMPLE 1

(17) FIG. 1 is a block diagram of an internal combustion engine ignition device in a first example of this invention. An internal combustion engine ignition device (igniter) 1a has a configuration in which the comparators 15 and 16 in FIG. 11 are respectively replaced by hysteresis comparators 15a and 16a. Other components are the same as those in FIG. 11.

(18) The hysteresis comparator 15a prevents pulse noise in the form of chattering in a high voltage region of a region where a sense voltage Vsns is rising, and the hysteresis comparator 16a prevents pulse noise in the form of chattering in a low voltage region of the region where the sense voltage Vsns is rising. The level on the detection side of the hysteresis comparator 15a is at a detection reference voltage VH, and the level on the release side is at a release reference voltage VHL. The level on the detection side of the hysteresis comparator 16a is at a detection reference voltage VL, and the level on the release side is at a release reference voltage VLL. The magnitude relationship is as follows: VH>VHL>VL>VLL. Note that a hysteresis comparator refers to a comparator in which a detection reference voltage and a release reference voltage lower than the detection reference voltage provide hysteresis characteristics. The sense voltage Vsns and the respective reference voltages are voltages with the ground potential as the reference.

(19) FIGS. 2A and 2B show an internal circuit and input-output transmission characteristics of the hysteresis comparators 15a and 16a, FIG. 2A being an internal circuit diagram of the hysteresis comparators 15a and 16a and FIG. 2B being an input-output characteristic diagram thereof. Note that the internal circuits of the hysteresis comparators 15a and 16a are both the same.

(20) In FIG. 2A, the hysteresis comparators 15a and 16a include a comparator 21, an inverter 22 to which an output signal (output voltage) of the comparator 21 is input, and an inverter 23 to which an output signal of the inverter 22 is input. Also included are an analog switch 24 for connecting a comparison voltage V1 which is the detection reference voltage to a minus terminal of the comparator 21 and an analog switch 25 for connecting a comparison voltage V2 which is the release reference voltage to the minus terminal of the comparator 21. The sense voltage Vsns is input to a plus terminal of the comparator 21, an on-off operation of the analog switch 24 is caused by the output signal of the inverter 22, and an on-off operation of the analog switch 25 is caused by an output signal of the inverter 23, such that the on-off operations of the analog switches 24 and 25 are in a reversed phase relationship. The analog switches 24 and 25 are both turned ON in the case where a switch switching signal is at High and turned OFF in the case where the switch switching signal is at Low, as shown in FIG. 2B. That is, in both the hysteresis comparators 15a and 16a, the analog switch 24 is in an on state in the case where an input voltage VIN in FIG. 2B is lower than the comparison voltage V2.

(21) When the input voltage VIN which is the sense voltage Vsns rises and exceeds the comparison voltage V1 in FIG. 2B, output signals VOUT of the hysteresis comparators 15a and 16a respectively switch from L level (low level) to H level (high level). On the other hand, when the input voltage VIN which is the sense voltage Vsns decreases and becomes less than the comparison voltage V2, the output signals VOUT (output voltages) which are output signals of the hysteresis comparators 15a and 16a are respectively switched from H level to L level. That is, a hysteresis operation is performed between the comparison voltage V1 and the comparison voltage V2.

(22) The operation will further be described using FIG. 1 and FIGS. 2A and 2B. In the case where the input voltage VIN which is the sense voltage Vsns is lower than the comparison voltages V1 and V2, i.e., VIN<V2<V1, the output signal of the comparator 21 is at L level, the output signal of the inverter 22 is at H level, and the output signal VOUT which is the output signal of the inverter 23 is at L level. Therefore, the analog switches 24 and 25 are respectively in states of on and off. Thus, the comparator 21 at this time performs a comparison operation with the input voltage VIN and the comparison voltage V1.

(23) The output signal VOUT is inverted from L level to H level immediately after detection of the comparison voltage V1 with the input voltage VIN, i.e., in the case where V1<VIN. This is referred to as a comparison operation on a detection side, and the comparison voltage V1 corresponds to the detection reference voltage (VH or VL).

(24) Note that the comparator 21 at this time has switched to a comparison operation of the input voltage VIN and the comparison voltage V2.

(25) Conversely, in a direction of inversion of the output signal VOUT from H level to L level, this is referred to as a comparison operation on a release side, and the comparison voltage V2 corresponds to the release reference voltage (VHL or VLL). Note that the internal configuration is not necessarily fixed as long as input-output characteristics similar to those of the hysteresis comparators 15a and 16a can be obtained.

(26) FIG. 3 is a voltage and current waveform diagram of respective parts illustrating the operation in FIG. 1. A low voltage region at the rise of the sense voltage Vsns corresponding to a coil current (the primary current Ic) is first compared with the detection reference voltage VL by the hysteresis comparator 16a, and, immediately after the output signal thereof is inverted from L level to H level, the hysteresis comparator 16a maintains the output at H level without a response when noise superimposed on the sense voltage Vsns is within a range of a hysteresis width of 1 which equals the detection reference voltage VL minus the release reference voltage VLL.

(27) Therefore, since the output signal of the hysteresis comparator 15a at this time remains at L level, an output signal of the exclusive OR circuit 17 is inverted from L level to be maintained at H level. The MOSFET 14 which is the F-output transistor is switched from an off state to an on state. As a result, the voltage Vfo of the output terminal F is maintained at L level, and pulse noise in the form of chattering is not generated at a falling edge of a voltage pulse at L level.

(28) Next, in a high voltage region at the rise of the sense voltage Vsns, the sense voltage Vsns is first compared with the detection reference voltage VH by the hysteresis comparator 15a. Immediately after the output signal thereof is inverted from L level to H level, the hysteresis comparator 15a maintains the output at H level without a response when noise superimposed on the sense voltage Vsns is in a range of a hysteresis width of 2 which equals the detection reference voltage VH minus the release reference voltage VHL. The output signal of the hysteresis comparator 16a at this time remains at H level. Therefore, an output signal of the exclusive OR circuit 17 is inverted from H level to be maintained at L level. The MOSFET 14 which is the F-output transistor is switched from the on state to be maintained in the off state. As a result, the voltage Vfo of the output terminal F is maintained at H level, and pulse noise in the form of chattering is not generated at a rising edge of the voltage pulse at L level.

(29) Thus, pulse noise in the form of chattering is not superimposed at rising and falling edges of the voltage pulse at L level which is the voltage Vfo of the output terminal F, even if noise is superimposed at the time of rise of the sense voltage Vsns. Therefore, since the ignition timing for the spark plug 4 can be determined with high precision, ignition can be performed properly with high precision.

EXAMPLE 2

(30) FIG. 4 is a block diagram of an internal combustion engine ignition device in a second example of this invention.

(31) FIG. 5 is an operation waveform diagram of the internal combustion engine ignition device in FIG. 4.

(32) An igniter 1b is configured of respective components denoted by the same reference signs as in FIG. 1, but the detection reference voltage VL which is the level on the detection side of the hysteresis comparator 16a also serves as the release reference voltage which is the level on the release side of the hysteresis comparator 15a. Other configurations are similar to those in Example 1.

(33) Thus, a hysteresis width of the hysteresis comparator 15a is 3 which equals the detection reference voltage VH minus the detection reference voltage VL, a release reference voltage for only the hysteresis comparator 15a is unnecessary, and further a noise margin greater than the hysteresis width of the hysteresis comparator 15a in FIG. 1 can be obtained.

(34) As a result, the ignition timing can be determined properly with high precision even in the case where noise superimposed in a high voltage region at the rise of the sense voltage Vsns is large.

EXAMPLE 3

(35) FIG. 6 is a block diagram of an internal combustion engine ignition device in a third example of this invention. In an igniter 1c, the hysteresis comparator 16a in FIG. 1 is replaced by an inverting input switching-type comparator 19, and an inverting input switching control circuit 18 which controls the inverting input switching-type comparator 19 is added. FIG. 13 is an internal circuit diagram of the inverting input switching control circuit 18, and Table 1 is a truth table for the inverting input switching control circuit 18.

(36) TABLE-US-00001 TABLE 1 ON/OFF 15a OUTPUT 19 OUTPUT OUTPUT SIGNAL SIGNAL SIGNAL SIGNAL VCTL H level L level L level H level H level L level H level L level H level H level L level L level H level H level H level H level L level H level ON/OFF SIGNAL: ON/OFF signal shown in FIGS. 6 and 9 15a OUTPUT SIGNAL: Output signal of the hysteresis comparator 15a shown in FIGS. 6 and 9 19 OUTPUT SIGNAL: Output signal of the inverting input switching-type comparator 19 shown in FIGS. 6 and 9 OUTPUT SIGNAL VCTL: Output signal of the inverting input switching control circuit 18 shown in FIGS. 6 and 9

(37) An input signal of the inverting input switching control circuit 18 is an ON/OFF signal (in synchronization with a sense IGBT being turned on or off) synchronized with output signals of the hysteresis comparator 15a and the inverting input switching-type comparator 19 and the output voltage Vg of the switching control circuit 11. An output signal VCTL is obtained with a combinational logic formed of inverters 31, 32, and 36, AND circuits 33, 34, and 37, and OR circuits 35 and 38.

(38) In an initial state immediately after the power is turned on, an OFF signal which is the ON/OFF signal at L level is input to the inverting input switching control circuit 18. In this initial state, the output signal VCTL of the inverting input switching control circuit 18 is at H level regardless of the output signal of the hysteresis comparator 15a and the output signal of the inverting input switching-type comparator 19. The output signal VCTL becomes a control signal for selecting one of the reference voltage VL for inverting input and a ground potential reference voltage (VLL which equals GND) of the inverting input switching-type comparator 19. The configuration and operation of the hysteresis comparator 15a is similar to the case of Example 1.

(39) FIGS. 7A and 7B show an internal circuit and input-output operation waveforms of the inverting input switching-type comparator 19, FIG. 7A being an internal circuit diagram and FIG. 7B being a view showing representative examples of the input-output operation waveforms therefor. The difference from the hysteresis comparators 15a and 16a in FIG. 2A is that an on-off control of the respective analog switches 24 and 25 with the output signals of the inverters 22 and 23 is changed to an on-off control of the respective analog switches 24 and 25 with the output signal VCTL and an output signal of an inverter 26. The analog switches 24 and 25 are both turned ON in the case where the switch switching signal is at High and turned OFF in the case where the switch switching signal is at Low, as shown in FIG. 7B.

(40) Thus, the comparison voltage V1 is selected and used for comparison with the input voltage VIN (corresponding to the sense voltage Vsns) during a period in which VCTL as the output signal of the inverting input switching control circuit 18 and an input signal of the inverting input switching-type comparator 19 is at H level, and the comparison voltage V2 is selected and used for comparison with the input voltage VIN during a period in which the output signal VCTL is at L level. Note that, in the initial state immediately after the power is turned on, the output signal VCTL of the inverting input switching control circuit 18 is at H level as described above, and the comparison voltage V1 is selected in this configuration.

(41) FIG. 8 is a voltage and current waveform diagram of respective parts illustrating the operation in FIG. 6. In a low voltage region at the rise of the sense voltage Vsns corresponding to the primary current Ic, the sense voltage Vsns is first compared with the detection reference voltage VL by the inverting input switching-type comparator 19, and an output voltage thereof is inverted from L level to H level. Since the output signal of the hysteresis comparator 15a remains at L level, the output signal VCTL of the inverting input switching control circuit 18 is inverted from H level to L level, and a minus input of the comparator 21 within the inverting input switching-type comparator 19 is switched from the detection reference voltage VL to GND level. When noise superimposed on the sense voltage Vsns is within a range of a hysteresis width of 4 which equals the detection reference voltage VL minus GND, the inverting input switching-type comparator 19 maintains the output at H level without a response.

(42) Therefore, an output signal of the exclusive OR circuit 17 at this time is inverted from L level to be maintained at H level. The MOSFET 14 which is the F-output transistor is switched from an off state to be maintained in an on state. As a result, the voltage Vfo of the output terminal F is maintained at L level, and pulse noise in the form of chattering is not generated at a falling edge of a voltage pulse at L level.

(43) Next, in a high voltage region at the rise of the sense voltage Vsns, the sense voltage Vsns is first compared with the detection reference voltage VH by the hysteresis comparator 15a, and the output voltage thereof is inverted from L level to H level. Since the output signal of the inverting input switching-type comparator 19 remains at H level, the output signal VCTL of the inverting input switching control circuit 18 is inverted from L level to H level, and the minus input of the comparator 21 within the inverting input switching-type comparator 19 is switched from GND to the the detection reference voltage VL. When noise superimposed on the sense voltage Vsns is within a range of a hysteresis width of 2, the hysteresis comparator 15a maintains the output at H level without a response. The output voltage of the exclusive OR circuit 17 at this time is inverted from H level to be maintained at L level. The MOSFET 14 which is the F-output transistor is switched from the on state to be maintained in the off state. As a result, the voltage Vfo of the output terminal F is maintained at H level, and pulse noise in the form of chattering is not generated at a rising edge of the voltage pulse at L level.

(44) Herein, by providing the hysteresis width for the inverting input switching-type comparator 19 to be 4 only during a period in which the output signal VCTL of the inverting input switching control circuit 18 is at L level, a noise margin greater than in the hysteresis comparator 16a in FIG. 1 can be obtained.

(45) As a result, the ignition timing can be determined properly with high precision even in the case where noise superimposed in a low voltage region at the rise of the sense voltage Vsns is large.

EXAMPLE 4

(46) FIG. 9 is a block diagram of an internal combustion engine ignition device in a fourth example of this invention.

(47) FIG. 10 is an operation waveform diagram of the internal combustion engine ignition device in FIG. 9.

(48) An igniter 1d is configured of respective components denoted by the same reference signs as in FIG. 6, but the detection reference voltage VL which is the level on the high-potential side of an inverting input of the inverting input switching-type comparator 19 also serves as the release reference voltage which is the level on the release side of the hysteresis comparator 15a. Thus, the hysteresis width of the hysteresis comparator 15a is 3, a release reference voltage for only the hysteresis comparator 15a is unnecessary, and further a noise margin greater than the hysteresis width of the hysteresis comparator 15a in FIG. 6 can be obtained.

(49) As a result, the ignition timing can be determined properly with high precision even in the case where noise superimposed in a high voltage region at the rise of the sense voltage Vsns is large.

EXAMPLE 5

(50) FIG. 14 is a block diagram of an internal combustion engine ignition device in a fifth example of this invention.

(51) FIGS. 15A and 15B show an internal circuit and input-output transmission characteristics of a hysteresis comparator 16b, FIG. 15A being an internal circuit diagram of the hysteresis comparator 16b and FIG. 15B being an input-output characteristic diagram thereof.

(52) The difference of an igniter 1e in FIG. 14 from the igniter 1a in FIG. 1 is that the hysteresis comparator 16a is replaced by the hysteresis comparator 16b, the exclusive OR circuit 17 is replaced by a NOR circuit 17a, the sense voltage Vsns is input to a minus terminal of the hysteresis comparator 16b, and the detection reference voltage VL and the release reference voltage VLL are input to two plus terminals.

(53) The operation waveforms of the respective parts are the same as in FIG. 3.

(54) In FIG. 14, the internal circuit of the hysteresis comparator 15a is the same as in FIG. 2A, and the sense voltage Vsns is input to a plus terminal of the hysteresis comparator 15a. The detection reference voltage VH corresponding to the comparison voltage V1 and the release reference voltage VHL corresponding to the comparison voltage V2 are input to two minus terminals of the hysteresis comparator 15a.

(55) The sense voltage Vsns is input to the minus terminal of the hysteresis comparator 16b. The detection reference voltage VL corresponding to the comparison voltage V1 and the release reference voltage VLL corresponding to the comparison voltage V2 are input to the two plus terminals of the hysteresis comparator 16b.

(56) In FIG. 15A, the hysteresis comparator 16b includes the comparator 21, the inverter 22 to which an output signal of the comparator 21 is input, the inverter 23 to which an output signal of the inverter 22 is input, the analog switch 24 which connects the comparison voltage V1 as the detection reference voltage VL to a plus terminal of the comparator 21, and the analog switch 25 which connects the comparison voltage V2 as the release reference voltage VLL to the plus terminal of the comparator 21. The sense voltage Vsns is input to a minus terminal of the comparator 21, an on-off operation of the analog switch 25 is caused by the output signal of the inverter 22, and an on-off operation of the analog switch 24 is caused by an output signal of the inverter 23, such that the on-off operations of the analog switches 24 and 25 are in a reversed phase relationship. The analog switches 24 and 25 are both turned ON in the case where a switch switching signal is at High and turned OFF in the case where the switch switching signal is at Low, as shown in FIG. 15A.

(57) When the sense voltage Vsns which is the input voltage VIN rises and exceeds the comparison voltage V1 (detection reference voltage VL or VH) in FIG. 15B, the output signal VOUT of the hysteresis comparator 15a in FIG. 14 switches from L level to H level. On the other hand, the output signal VOUT of the hysteresis comparator 16b switches from H level to L level.

(58) When the sense voltage Vsns which is the input voltage VIN decreases and becomes less than the comparison voltage V2 (release reference voltage VHL or VLL), the output signal VOUT of the hysteresis comparator 15a in FIG. 14 switches from H level to L level. On the other hand, the output signal VOUT of the hysteresis comparator 16b switches from L level to H level. That is, a hysteresis operation is performed between the comparison voltage V1 and the comparison voltage V2.

(59) By inputting the output signal VOUT of the hysteresis comparator 15a and the output signal VOUT of the hysteresis comparator 16b to the NOR circuit 17a, an output signal (voltage) waveform of the NOR circuit 17a becomes the same as an output signal (voltage) waveform of the exclusive OR circuit 17 in Example 1.

(60) As a result, pulse noise in the form of chattering is not superimposed at rising and falling edges of the voltage pulse at L level in the voltage Vfo of the output terminal F, even if noise is superimposed at the time of rise of the sense voltage Vsns. Therefore, since the ignition timing for the spark plug 4 can be determined with high precision, ignition can be performed properly with high precision.

(61) While the present invention has been particularly shown and described with reference to certain specific embodiments, it will be understood by those skilled in the art that the foregoing and other changes in form and details can be made therein without departing from the spirit and scope of the present invention.