Electronic control unit

1. An electronic control unit powered from a driving power supply and connected to an analog sensor through a wire harness accommodating at least a power supply line and a signal line, comprising:

a constant voltage power supply circuit portion for generating a regulated voltage based on the power feeding from the driving power supply;

an analog signal inputting circuit portion connected to the constant voltage power supply circuit portion; and

a conversion processing circuit portion to which a detection signal from the analog sensor is supplied through the signal line,

the analog signal inputting circuit portion comprising:

a current limiting circuit portion inserted into a power supply line of the constant voltage power supply circuit portion for powering the analog sensor through the power supply line;

an integrating circuit portion inserted between an input signal line connected to the signal line and the conversion processing circuit portion;

a current limiting resistor inserted between the input signal line and the integrating circuit portion;

a signal noise absorbing circuit portion connected to the power source line, a ground line of the constant voltage power supply circuit portion, and the input signal line; and

a first bypass capacitor inserted between an output terminal of the current limiting circuit portion and the ground line,

wherein an electrostatic capacity (C 1 ) and a parasitic inductance (L 1 ) of the first bypass capacitor are set in a range expressed by Equation (1):

7×10 6 <1/[2π√( L 1× C 1)]<35×10 6   (1).

2. An electronic control unit according to claim 1 , wherein the input signal line is connected to the power supply line of the constant voltage power supply circuit portion through a pull-up resistor.

3. An electronic control unit according to claim 1 , wherein the input signal line is connected to the ground line of the constant voltage power supply circuit portion through a pull-down resistor.

4. An electronic control unit according to claim 1 , wherein the analog signal inputting circuit portion further comprises a second bypass capacitor inserted between the input signal line and the ground line, an electrostatic capacity (C 2 ) and a parasitic inductance (L 2 ) of the second bypass capacitor are set in a range expressed by Equation (2):

35×10 6 <1/[2π√( L 2× C 2)]

or

1/[2π√( L 2× C 2)]<7×10 6   (2)

and an impedance of the second bypass capacitor in a frequency band of 7 to 35 MHz has a sufficiently small value as compared to that of a composite impedance of a resistance of an integrating resistor provided in the integrating circuit portion and a resistance of the current limiting resistor.

5. An electronic control unit according to claim 4 , wherein the analog signal inputting circuit portion further comprises a third bypass capacitor inserted between the input signal line and the ground line, an electrostatic capacity (C 2 ) and a parasitic inductance (L 2 ) of the second bypass capacitor, and an electrostatic capacity (C 3 ) and a parasitic inductance (L 3 ) of the third bypass capacitor are set in a range expressed by Equation (3):

7×10 6 <1/[2π√{( L 2+ L 3)×( C 2× C 3)/( C 2+ C 3)}]<35 ×10 6   (3).

6. An electronic control unit according to claim 1 , wherein the first bypass capacitor is a chip type ceramic capacitor having an electrostatic capacity of 0.01 to 0.1 μF.

7. An electronic control unit according to claim 6 , wherein the second bypass capacitor is a chip type ceramic capacitor having an electrostatic capacity of 500 to 5,000 pF.