JPH11268659A - Controller of electric power steering unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To permit correct judgment without error with regard to abnormalities in an A/D converter which converts the output of the torque sensor into a digital signal and an amplifier. SOLUTION: The controller reads the torque signal Ts amplified by the amplifier, performs A/D conversion, and obtains the first signal. Next, the torque signal Ts which does not pass through the amplifier is read. The A/D conversion is performed and the amplification G of the amplifier is multiplied by the data obtained whereby the second signal is obtained (P1, P2, P3). Then, the difference between the first signal and the second signal is determined. When that difference is equal to or greater than a predetermined value and when an amount of time equal to or more than a predetermined amount of time which was set beforehand has passed (P4, P5, P6), there is judged an abnormality of the A/D converter and/or the amplifier and the drive control of the motor stops. Moreover, the feed to the motor drive circuit is cut off (P7, P8).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric power steering device, and more particularly to an A / D converter and a torque signal amplifier for converting an analog signal output from a torque sensor for detecting a steering torque into a digital signal. The present invention relates to a configuration of a control device of an electric power steering device capable of detecting a failure of a vehicle.

[0002]

2. Description of the Related Art An electric power steering apparatus for a vehicle detects a steering torque generated in a steering shaft by operating a steering handle, and calculates a required steering assist force by a CPU based on the detection signal. Some motors are driven according to the value of the calculated steering assist force, and the steering mechanism is driven via a speed reduction mechanism attached to a steering shaft.

In this type of electric power steering apparatus, the steering assist force is determined based on the detected steering torque. Therefore, if the torque sensor fails and an abnormal signal is output, the driver does not expect it. There was a danger of steering assist force being generated. For this reason, conventionally, it is determined whether or not the output value of the torque sensor is within the range of the normal output value, and when the output value exceeds the range of the normal output value, it is determined to be abnormal, and the operation of the control circuit is stopped. There is something.

[0004] However, the failure of the torque sensor includes a failure in which the output value of the torque sensor is fixed to a constant value while being within the range of the normal output value, and even if the torque sensor is normal, A / D arranged at the subsequent stage
In some cases, the converter may be out of order. If the output value of the torque sensor as described above exceeds the range of the normal output value, it is not possible to judge the fault accurately only by determining that the output is abnormal.

Therefore, a method has been proposed in which when the output value of the torque sensor is continuously smaller than a predetermined reference value for a predetermined period of time, it is determined that the torque sensor or the A / D converter has failed (Japanese Patent Laid-Open No. Hei 1 (1994)). -262256).

[0006]

However, the steering torque is not always fluctuating, and the fluctuation range of the steering torque is small when the vehicle is stopped or running at high speed. In such a case,
Although the A / D converter has not failed, the output value of the torque sensor is continuously smaller than a predetermined reference value for a predetermined period of time. It will be erroneously detected as a failure. Further, depending on the time width used as a reference for the failure determination and the reference value of the fluctuation range of the steering torque, it may not be possible to detect the failure despite the occurrence of the failure. Hereinafter, this point will be described.

First, when the A / D converter fails, the output value is not always fixed. It is also possible that a signal current leaks at the input terminal of the A / D converter and the signal level drifts. When the signal level drifts in the A / D converter, it is recognized as if the steering wheel was operated and the torque signal was input while the steering mechanism was in the neutral position, and the steering wheel was rotated without permission. Inconvenience that self-steering occurs.

Such a signal current leak is caused, for example, by:
In the manufacturing process of a semiconductor integrated circuit, it is conceivable that dust is attached to a circuit constituting an A / D converter and the circuit is manufactured with a defect, and the circuit is shipped without any defect being found by inspection. In such a case, a stress is applied to the defective portion during use, and a leakage current is generated or the leakage current increases.

Secondly, the torque signal input to the control device includes a torque signal used for motor control and a torque signal used for abnormality detection for detecting an abnormality of the torque sensor or the A / D converter. Are divided into two systems. And mo
The torque signal for motor control is a filter, an amplifier, and an A / D
The torque signal for abnormality detection is input to the CPU via the converter, and is input to the CPU via the filter and the A / D converter.

Therefore, the torque signal for motor control is
Even if the amplification degree of the amplifier changes due to a failure of the amplifier or its peripheral circuit, the signal processing is performed without detecting any abnormality such as the change in the amplification degree, and a motor that gives an appropriate steering assist force. The inconvenience that control cannot be performed occurs.

Third, it is conceivable that a bit for storing data in a register in the A / D converter is fixed to a specific value due to a failure, and data to be stored in the bit is lost. . If the failed bit is fixed at "1", even if the data of the bit is originally "0", the bit is erroneously recognized as "1" and is calculated by the CPU. For this reason, while the steering mechanism is in the neutral position, it is recognized as if a torque signal was input,
The disadvantage that the steering wheel rotates on its own (self-steering) occurs.

Such a bit failure of a register is caused, for example, in a process of manufacturing a semiconductor integrated circuit by manufacturing a circuit constituting a register with dust attached thereto and shipping the semiconductor integrated circuit without any defect being found by inspection. Such a case is conceivable. In addition, the bits may be destroyed due to noise, electromagnetic waves, or the like, and the register may malfunction.

An object of the present invention is to provide a control device for an electric power steering device which solves the above-mentioned problems.

[0014]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and an invention of claim 1 is an electric motor, control means for controlling the driving of the electric motor, and the electric motor. −
A motor drive circuit for driving the motor, and a control device for an electric power steering apparatus for controlling the electric motor based on a steering torque detected by a torque sensor to apply an auxiliary torque to a steering system. , An abnormality detector having a predetermined amplification factor G for amplifying a torque signal, an A / D converter for converting an analog signal into a digital signal, and an operation controller, wherein the abnormality detection means comprises: After the torque signal detected by the torque sensor is amplified by the amplifier, the first value obtained by A / D conversion by the A / D converter and the A / D signal without amplifying the detected torque signal are obtained. A value obtained by A / D conversion by the converter is multiplied by a second value obtained by multiplying the gain G of the amplifier, and a difference between the first value and the second value is equal to or greater than a predetermined value. , One time has elapsed preset predetermined time or more, and judging the abnormality of the A / D converter or amplifier.

[0015] Further, the invention according to claim 2 provides an electric motor,
Control means for controlling the driving of the electric motor; and a motor drive circuit for driving the electric motor. The electric motor is controlled based on a steering torque detected by a torque sensor.
In an electric power steering control apparatus for controlling a motor to apply an auxiliary torque to a steering system, an amplifier having a predetermined amplification factor G for amplifying a torque signal and an A / D for converting an analog signal into a digital signal are provided. A converter,
Abnormality detecting means comprising an arithmetic and control unit, wherein the abnormality detecting means amplifies the torque signal detected by the torque sensor by the amplifier and then performs A / D conversion by the A / D converter. And A / D conversion by the A / D converter without amplifying the detected torque signal.
A ratio between the converted value and a second value obtained by multiplying the amplification factor G of the amplifier is obtained, and the ratio between the first value and the second value is equal to or greater than a predetermined value, and When the predetermined time has elapsed, it is determined that the A / D converter or the amplifier is abnormal.

The control means controls a motor drive circuit so as to stop driving the electric motor when an abnormality of the A / D converter or the amplifier is detected by the abnormality detection means. And / or the circuit interrupting element may be controlled so as to interrupt power supply to the motor drive circuit.

[0017]

Embodiments of the present invention will be described below. First, a detection method when a signal current leaks at the input terminal of the A / D converter will be described.

A control device of this type of electric power steering device is generally a microprocessor (hereinafter referred to as a CPU).
). Some CPUs have an A / D converter built in.
Although some converters are provided and controlled by the CPU, there is no difference in function. In any case, the A / D converter is generally configured so that signals input from a plurality of input terminals are switched by a multiplexer and conversion processing is performed by a single A / D conversion circuit. .

FIG. 1 is a block diagram showing a basic circuit of this type of A / D converter, and shows a plurality of analog input signals AN1 to AN1.
AN4 is switched by the multiplexer 101, and any one of the analog input signals ANn is input to the sample hold circuit 102. The sample hold circuit 102 holds the input analog signal ANn.

The A / D converter 120 is a successive approximation type A / D converter.
A converter 103, a successive approximation type register 104, a D / A converter 105, and a timing control unit 1
06.

The CPU sends A /
When the D conversion start command ADS is input, the register 1
04, regardless of the contents of 04 (all bits are "1")
Is output as a reference value, and D /
After being converted into an analog signal by the A conversion circuit 105, the analog signal is input to the reference signal terminal (-) of the comparator 103. The comparator 103 is a sample hold circuit 102
Is compared with the reference value of 1/2 of the full scale converted into the analog signal.

If the analog input signal ANn is larger than the half full scale reference value, the most significant bit (MSB) of the register 104 is set to "1". Set to "0". Hereinafter, the analog input signal ANn is changed to a 1/4 full scale reference value, 1
/ 8 full-scale reference value and the like are sequentially repeated, and the least significant bit (L
Bits “1” / “0” are determined up to SB). Thus, the input analog signal ANn is converted into a digital signal. When the conversion ends, a conversion end signal ADF is output from the timing control unit 106 to the CPU, and the data bus 1
07 is output.

FIG. 2 is a block diagram showing the configuration of the torque signal processing circuit including the A / D converter 120 described above. The torque signal processing circuit 16 includes a filter 111 and an amplifier 11
3, the multiplexer 101, and the A / D converter 120 described above.

The torque signal T input from the torque sensor
s is divided into two systems, a control torque signal used for motor control and a torque signal used for abnormality detection.
The torque signal for controlling the motor
3, through the multiplexer 101 and the A / D converter 120, input from the data bus 107 to the CPU, the torque signal for abnormality detection is applied to the filter 111 and the multiplexer 10
1. C from the data bus 107 via the A / D converter 120
It is configured to be input to the PU.

Hereinafter, the detection of the leak of the signal current at the input terminal of the A / D converter 120 of the torque signal processing circuit, the detection of the change in the amplification degree of the amplifier 113, and the detection of the A / D converter 12 will be described.
The detection of missing data at 0 will be described.

[Detection of Leakage of Signal Current at Input Terminal of A / D Converter] Assuming that the torque signal input from the torque sensor is Ts and the amplification degree of the amplifier 113 is G, the A / D is passed through the multiplexer 101. The control torque signal Tc and the abnormality detection torque signal Te input to the converter 120 are as follows.

Control torque signal Tc = (Ts × G) Abnormality detecting torque signal Te = Ts Now, the abnormality detecting torque signal Te after A / D conversion is multiplied by the amplification G of the amplifier 113 to obtain A / D If the converter is normal, its value will be Te = (Ts × G) and will be equal to the control torque signal value Tc = (Ts × G).

However, if the A / D converter 120 is abnormal, that is, if the input signal leaks from the input terminal 103a of the comparator 103 in FIG. 1, the offset voltage Voff is generated in the input signal level, so that the control is performed. Torque signal T
c and the abnormality detection torque signal Te are as follows.

Control torque signal Tc = (Ts × G−Voff) Abnormality detection torque signal Te = (Ts−Voff) As before, abnormality detection torque signal Te after A / D conversion
= (Ts-Voff) multiplied by the gain G of the amplifier gives [(Ts-Voff) .times.G], which is different from the control torque signal Tc = (Ts.times.G-Voff).

Therefore, the A / D converter 1 is multiplied by the torque signal Te for abnormality detection after A / D conversion by the amplification G of the amplifier 113 and compared with the control torque signal value Tc.
It is possible to detect a leak of the signal current at the input terminal 20.

[Detection of change in amplification of torque signal amplifier] The input torque signal is Ts, and the amplification of the amplifier 113 is G
Then, the signal input to the A / D converter 120 is as follows.

Control torque signal Tc = (Ts × G) Abnormality detection torque signal Te = Ts Now, the abnormality detection torque signal Te after A / D conversion is multiplied by the amplification G of the amplifier 113, and the value becomes Te = (Ts
× G), and the control torque signal value Tc when the control torque signal amplifier 113 or its peripheral circuit is normal.
= (Ts × G).

However, the amplification G changes due to the failure of the torque signal amplifier 113 or its peripheral circuit, and the amplification G becomes Ger.
Assuming that r, the signal input to the A / D converter 120 is as follows.

Control torque signal Tc = (Ts × Gerr) Abnormality detection torque signal Te = Ts That is, when the amplification degree of the amplifier 113 becomes Gerr due to a failure of the amplifier 113 or its peripheral circuit, A / D The converted control torque signal Tc = (Ts × Gerr) is A
An amplifier 113 is added to the abnormality detection torque signal Ts after the / D conversion.
Does not coincide with the value (Ts × G) obtained by multiplying the amplification degree G by

Accordingly, by multiplying the abnormality detection torque signal Ts after the A / D conversion by the amplification G of the amplifier 113 and comparing it with the control torque signal value Tc = (Ts × Gerr), the amplifier 113 Or an abnormality in a peripheral circuit thereof can be detected.

[Detection of Data Loss in A / D Converter] Successive approximation register 104 of A / D converter 120
Will be described for an 8-bit configuration. FIG. 3 shows A /
In the figure showing the contents of the 8-bit register of the D converter, an asterisk "*" indicates that the bit is "1" or "0". In FIG. 3, the least significant bit (LSB) is
4 shows a state in which the fourth bit K is destroyed and fixed to “1”.

Here, it is verified that the missing data can be detected by applying the above-described technique for detecting the leak of the signal current at the input terminal of the A / D converter.

First, the input torque signal is set to Ts and the amplifier 11
Assuming that the amplification degree G of 3 is 2 (G = 2), the signal input to the A / D converter is as follows.

Control torque signal Tc = Ts × G = 2Ts Abnormality detection torque signal Te = Ts Further, it is assumed that the value obtained by A / D converting the torque signal Ts is a value represented as (0000100100) in binary. I do.

The control torque signal Tc = 2Ts recorded in the register 104 of the A / D converter is 2 × (00000)
100), it is expressed as (00001000) in binary, and the contents of the 8-bit register of the A / D converter are
As shown in FIG. 4, the fourth bit from the least significant bit (LSB) is "1". At this time, if the register of the A / D converter is in a state where the fourth bit K from the least significant bit (LSB) described above with reference to FIG. Overlaps with K

On the other hand, the abnormality detection torque signal Te = Ts recorded in the register 104 of the A / D converter is represented by (0000100100) in binary, and the content of the register of the A / D converter is the least significant bit ( (LSB) becomes “1”. At this time, the register 10 of the A / D converter
4, when the fourth bit from the least significant bit (LSB) described above with reference to FIG. 3 is destroyed and fixed to "1", the abnormality detection torque signal Te recorded in the register = Ts and the value "1" of the destroyed bit K is added, so that the bit contents shown in FIG.
0001100).

In the binary number shown in FIG. 5, (00001100)
Is multiplied by the amplification factor G = 2 of the amplifier 113, the binary number (000)
11000) and the register 104 of the A / D converter.
The fourth and fifth bits from the least significant bit (LSB) are set to "1", and the bit content shown in FIG. This is different from the bit contents of the control torque signal Tc = 2Ts shown in FIG.

Therefore, the contents of the register as a result of A / D conversion of the value obtained by multiplying the torque signal Ts by the amplification degree G of the amplifier, and the amplification degree G to the value obtained by A / D conversion of the abnormality detection torque signal. By comparing the result of the multiplication with the contents of the register, it is possible to detect a failure of the register such as a missing data of the register of the A / D converter.

FIG. 7 is a diagram schematically illustrating the configuration of an electric power steering apparatus suitable for applying the present invention.
The shaft 2 of the steering handle 1 is connected to a tie rod 6 of a steering wheel via a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5. The shaft 2 is provided with a torque sensor 8 for detecting the steering torque of the steering handle 1. A motor 23 for assisting the steering force is connected to the shaft 2 via the clutch 7 and the reduction gear 4. I have.

The control device for controlling the power steering device is integrated in the control unit 10. Electric power is supplied from the battery 13 via the ignition key 12. The control unit 10 calculates a steering assist command value based on the steering torque detected by the torque sensor 8 and the vehicle speed detected by the vehicle speed sensor 9, and based on the calculated steering assist command value, the motor 23. Control the current supplied to the

The clutch 7 is also controlled by the control unit 10. The clutch 7 is engaged in a normal operation state, and is disconnected when the control unit 10 determines that the power steering device has failed and when the power is off.

FIG. 8 is a block diagram of the control unit 10. As shown in FIG. 11 is a CPU, 12 is an ignition key, 13 is a battery, 14 is a key-on detection circuit for detecting the on / off state of the ignition key, 15 is a constant voltage circuit for supplying a constant voltage to a control system, and 16 is a lead voltage circuit. FIG. 2 shows the torque signal processing circuit described with reference to FIG.

Reference numeral 18 denotes a fuel relay, which is a transistor TR.
1 and has a normally open contact 18a. 21 is a field effect transistor FET1 to FET4
Are connected by an H bridge, 22 is a gate drive circuit for driving the gates of FET1 to FET4, and 23 is a motor for supplying a steering assist force to the steering system.
A motor current detecting circuit 24 detects a motor current based on a potential difference appearing across the resistor R2. The detected motor current value is input to the CPU 11, and feedback control of the motor current is performed.

The CPU 11 is supplied with a constant voltage Vcc from a constant voltage circuit 15, and the input port of the CPU 11 receives the signal output processed by the torque signal processing circuit 16 and the vehicle speed signal from the vehicle speed sensor 9. , Ignition key
Key-on detection circuit 14 for detecting the on / off state of 12
, A detection signal from the motor current detection circuit 24, and the like.

The output port of the CPU 11 is connected to the base of the transistor TR1 for driving the relay 18 and a gate drive circuit 22.

Next, an outline of the operation of the above configuration will be described. When the ignition key 12 is turned on and the state is detected by the key-on detection circuit 16, a detection signal is input to the CPU 11. CPU 11 is a transistor T
Since R1 is set to the conducting state and the ferrule 18 is excited, the normally open contact 18a of the relay is closed.
The motor drive circuit 21 is supplied with power from the battery 13 and is set in an operable state.

Thereafter, normal motor drive control is performed.
That is, the CPU 11 processes the torque signal Ts detected by the torque sensor 8 by the torque signal processing circuit 16 and the vehicle speed data obtained from the vehicle speed signal Vs detected by the vehicle speed sensor 9. The steering assist amount is determined on the basis of the above, and a PWM signal having a predetermined time width corresponding to the determined steering assist amount and a motor rotation direction signal are output to the gate drive circuit 22. The gate drive circuit 22 controls the FET1 to FET4 of the motor drive circuit 21 on / off to control the motor.
The steering wheel 23 is rotated to perform steering assist.

FIG. 9 is a flowchart for explaining the control operation executed by the CPU 11, particularly the control operation in the torque signal processing circuit 16, the motor control operation based on the result, and the fuel relay 18. FIG.

When the control operation is started, first, the amplifier 11
3 to read the torque signal Ts amplified by A / D
The first signal is obtained by the conversion (step P1). Next, the torque signal Ts not passing through the amplifier 113 is read, and the A / D
The converted data is multiplied by the gain G of the amplifier 113 to obtain a second signal (steps P2 and P3).

The difference between the first signal and the second signal is determined, and it is determined whether the difference is equal to or greater than a predetermined value (steps P4 and P5). If it is determined in step P5 that the difference between the first signal and the second signal is equal to or smaller than a predetermined value, the process returns to step P1 and proceeds to processing of the next input torque signal. Also, in the determination of step P5, the first signal and the second signal
If the difference from this signal is equal to or greater than a predetermined value, it is determined whether or not a predetermined time has elapsed (step P6).

If it is determined in step P6 that the predetermined time or more has not elapsed, the process returns to step P1 and proceeds to the processing of the next input torque signal. If it is determined in step P6 that a predetermined time or more has elapsed, it is determined that the amplifier 113 and / or the A / D converter 120 are abnormal.
The drive control of the motor is stopped, the transistor TR1 is turned off, the excitation of the ferrule 18 is released, and the normal open contact 18a is opened to cut off the power supply to the motor drive circuit 21.

In the flowchart described above, the difference between the first signal and the second signal is obtained, and when the difference is equal to or more than a predetermined value and a predetermined time has elapsed, the amplifier and / or A / A
Although it is determined that the D converter is abnormal, the first
And the ratio of the second signal to the second signal is determined.
It may be determined that the / D converter is abnormal.

[0058]

As described above, according to the control apparatus for an electric power steering apparatus of the present invention, after the detected torque signal is amplified by the amplifier having the amplification factor G, the A / A
The D-converted first value is compared with a second value obtained by multiplying a value obtained by A / D conversion without amplifying the detected torque signal by the amplification degree G of the amplifier, and the first value is compared with the second value. Difference from the value of
Alternatively, when the ratio between the first value and the second value is equal to or more than a predetermined value and a predetermined time or more elapses, it is determined that the A / D converter or the amplifier is abnormal. It is. Thus, even when the fluctuation range of the steering torque is small, such as when the vehicle is stopped or running at high speed, the abnormality of the A / D converter and the amplifier can be accurately determined without error.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of a control device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a torque signal processing circuit.

FIG. 3 is a diagram showing the contents of a register of an A / D converter (No. 1).

FIG. 4 is a diagram showing the contents of a register of an A / D converter (part 2).

FIG. 5 is a diagram showing the contents of a register of an A / D converter (part 3).

FIG. 6 is a diagram showing the contents of a register of an A / D converter (part 4).

FIG. 7 is a diagram schematically illustrating the configuration of an electric power steering apparatus.

FIG. 8 is a block diagram of a control unit.

FIG. 9 is a flowchart for explaining a control operation executed by the CPU.
Chart.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Control unit 11 CPU 12 Ignition key 13 Battery 16 Torque signal processing circuit 18 Fuel relay 18a Normally open contact 21 Motor drive circuit 22 Gate drive circuit 23 Motor 24 Motor current Detection circuit 101 Multiplexer 102 Sample hold circuit 103 Comparator 104 Register 105 D / A converter 106 Timing control unit 111 Filter 113 Amplifier 120 A / D converter

Claims (4)

[Claims] An electric motor, control means for controlling driving of the electric motor, and a motor drive circuit for driving the electric motor, wherein a steering torque detected by a torque sensor is provided. A control device for an electric power steering device for driving and controlling the electric motor to apply an auxiliary torque to a steering system based on the following: an amplifier having a predetermined gain G for amplifying a torque signal;
An A / D converter for converting an analog signal into a digital signal, and an abnormality detecting means comprising an arithmetic and control unit, wherein the abnormality detecting means amplifies the torque signal detected by the torque sensor by the amplifier. A /
A first value obtained by A / D conversion by the D converter and a second value obtained by multiplying the value obtained by A / D conversion by the A / D converter without amplifying the detected torque signal by the amplification degree G of the amplifier. And when the difference between the first value and the second value is equal to or greater than a predetermined value and a predetermined time has elapsed, the A / D converter or the amplifier A control device for an electric power steering device, characterized in that it is determined that the vehicle is abnormal. An electric motor, control means for controlling driving of the electric motor, and a motor drive circuit for driving the electric motor, wherein a steering torque detected by a torque sensor is provided. A control device for an electric power steering device for driving and controlling the electric motor to apply an auxiliary torque to a steering system based on the following: an amplifier having a predetermined gain G for amplifying a torque signal;
An A / D converter for converting an analog signal into a digital signal, and an abnormality detecting means comprising an arithmetic and control unit, wherein the abnormality detecting means amplifies the torque signal detected by the torque sensor by the amplifier. A /
A first value obtained by A / D conversion by the D converter and a second value obtained by multiplying the value obtained by A / D conversion by the A / D converter without amplifying the detected torque signal by the amplification degree G of the amplifier. And the ratio of the first value to the second value is equal to or greater than a predetermined value, and when the predetermined time has elapsed, the A / D converter or A control device for an electric power steering device, which determines that an amplifier is abnormal. 3. The control means, when the abnormality detection means detects an abnormality in the A / D converter or the amplifier,
3. The control device for an electric power steering apparatus according to claim 1, wherein the motor drive circuit is controlled so as to stop driving the electric motor. 4. The control means, when an abnormality of the A / D converter or the amplifier is detected by the abnormality detection means,
3. The control device for an electric power steering device according to claim 1, wherein the circuit cutoff element is controlled so as to cut off power supply to the motor drive circuit.