JP2008171092A - Microcomputer power supply voltage monitoring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microcomputer power supply voltage monitoring device capable of quickly and surely detecting the hit of a power supply voltage in a microcomputer. <P>SOLUTION: A power source monitoring circuit 11 having D/A 14 and 15 for generating an analog signal whose signal level is the lower threshold voltage Vref-L and upper threshold voltage Vref-H of a proper voltage Vref and a comparators 16 and 17 as comparator circuits for comparing the signal levels Vref-L and Vref-H of the generated analog signal with the signal level Vin of a power supply voltage is arranged in a microcomputer 10. Thus, it is possible to quickly detect the hit of a power supply voltage, and to continuously monitor the fluctuation of a power voltage, and to surely detect the hit of the power supply voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a microcomputer power supply voltage monitoring device.

Conventionally, there has been proposed a microcomputer power supply voltage monitoring system that determines whether or not a power supply voltage supplied to a microcomputer is appropriate (see, for example, Patent Document 1). Patent Document 1 discloses that a microcomputer power supply voltage is A / D converted using A / D conversion inside the microcomputer, and the A / D converted binary code X and a binary code indicating an appropriate power supply voltage value of the microcomputer are disclosed. A power supply monitoring method is described in which a power supply monitor comparing Y is performed to determine whether or not the power supply voltage is within an appropriate power supply voltage. Patent Document 1 describes a power supply monitoring method for monitoring whether a power supply voltage is within an appropriate power supply voltage (range) in an overvoltage / undervoltage monitor circuit provided in a power supply unit outside a microcomputer.
JP 2005-208939 A

  However, in the power supply monitoring method using A / D conversion inside the microcomputer, the analog signal is intermittently sampled at a predetermined sampling period and converted into a digital signal to monitor the fluctuation of the power supply voltage. When a power supply voltage fluctuation (instantaneous interruption) occurs in a short time span, the instantaneous interruption cannot be detected.

  In addition, the power supply monitoring method using the overvoltage / undervoltage monitor circuit outside the microcomputer can detect the instantaneous interruption as described above because the power supply is monitored by hardware, but it is necessary to transmit the detection result of the instantaneous interruption to the microcomputer. Therefore, a delay due to the transmission occurs. When an instantaneous power supply voltage interruption is detected, the microcomputer saves data such as calculation results to a non-volatile storage medium (for example, EEPROM or flash ROM) until the power supply is completely shut down. Although the processing for preventing the data is performed in a short time, the above-described delay may cause the data to be saved immediately after the occurrence of the instantaneous interruption, and the data may be lost.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a microcomputer power supply voltage monitoring device capable of detecting a power supply voltage instantaneous interruption quickly and reliably in a microcomputer.

In order to achieve the above object, the microcomputer power supply voltage monitoring apparatus according to claim 1 determines whether or not the power supply voltage supplied to the microcomputer used in the vehicle is an appropriate voltage that guarantees the operation of the microcomputer. And
Inside the microcomputer,
An analog signal generation circuit for generating an analog signal indicating a signal level of an appropriate voltage;
A comparison circuit that inputs an analog signal of the power supply voltage and compares the signal level of the input power supply voltage with the signal level of the analog signal generated by the analog signal generation circuit;
It is characterized by determining whether or not the power supply voltage is an appropriate voltage from the comparison result of the comparison circuit.

  As described above, according to the present invention, the analog signal generation circuit that generates the analog signal indicating the signal level of the appropriate voltage and the comparison circuit that compares the signal level of the analog signal and the signal level of the power supply voltage are arranged inside the microcomputer. Therefore, the instantaneous interruption of the power supply voltage can be detected quickly. Further, since the fluctuation of the power supply voltage can be continuously monitored by the analog signal generation circuit and the comparison circuit, it is possible to reliably detect an instantaneous interruption of the power supply voltage.

  According to a second aspect of the present invention, it is preferable that the analog signal generation circuit includes a signal level variable means for changing the signal level of the appropriate voltage in response to an instruction from the microcomputer. This is because a separate analog signal generation circuit is not provided according to the signal level of the power supply voltage.

  Embodiments of a microcomputer power supply voltage monitoring apparatus according to the present invention will be described below with reference to the drawings. In the present embodiment, the case where the present invention is applied to a microcomputer constituting a millimeter wave sensor mounted and used in a vehicle will be described.

  FIG. 1 shows the overall configuration of the millimeter wave sensor 1. The millimeter wave sensor 1 operates by receiving power supply from a power supply unit 2 provided outside. The millimeter wave sensor 1 shown in FIG. 1 mainly includes a microcomputer 10, an antenna 20, and a peripheral processing circuit 30. The antenna 20 includes a transmission antenna AS and a reception antenna AR. The transmission antenna AS receives a supply of a transmission signal fs from a transmitter (not shown) that transmits millimeter wave radar waves included in the peripheral processing circuit 30, and transmits the radar waves to the periphery of the vehicle.

  The transmitter includes a voltage-controlled oscillator that generates a millimeter-wave band high-frequency signal, and a distributor that distributes the output of the voltage-controlled oscillator to the transmission signal fs and the local signal L0. When the radar wave from the transmitting antenna AS is reflected by an object such as a preceding vehicle, the reflected radar wave (reflected radar wave) is received by the receiving antenna AR. The reception antenna AR generates a reception signal fr corresponding to the reflected radar wave and supplies it to a receiver (not shown) provided in the peripheral processing circuit 30.

  The receiver 6 mixes the reception signal fr from the reception antenna AR and the local signal L0, generates a beat signal corresponding to the frequency difference between these signals, and the beat signal generated by the mixer MX. And an amplifier AMP for amplification (none of them are shown). The beat signal amplified by the amplifier AMP is A / D converted into digital data, and the digital data of the beat signal is given to the microcomputer 10.

  As shown in FIG. 1, the microcomputer 10 is mainly configured by a power supply monitoring circuit 11, a calculation unit 12, an EEPROM 13, and a RAM (not shown). The calculation unit 12 performs a fast Fourier transform (FFT) process as a frequency analysis process on the digital data of the beat signal from the peripheral processing circuit 30 to calculate a distance and a relative speed with respect to the object. The calculation result data is written in the RAM.

  The EEPROM 13 is for saving data written in the RAM when the power supply monitoring circuit 11 detects an instantaneous interruption of the power supply voltage supplied from the power supply unit 2. In the present embodiment, an EEPROM is used for saving data, but the present invention is not limited to an EEPROM, and any non-volatile storage medium such as a flash ROM may be used.

  Next, the power supply monitoring circuit 11 that is a characteristic part of the present embodiment will be described. As shown in FIG. 2, the power supply monitoring circuit 11 takes the logical sum of the outputs from the D / A conversion circuits (hereinafter referred to as D / A) 14 and 15, the comparators 16 and 17, and the comparators 16 and 17. An OR circuit 18 that outputs to the arithmetic unit 12 is included.

  The D / A 14 and 15 convert the digital signal received from the microcomputer 10 into an analog signal. In the D / A 14, in accordance with the digital signal received from the microcomputer 10, an analog signal whose signal level is the lower threshold voltage Vref-L (for example, 1.5 [V]) of the appropriate voltage Vref that guarantees the operation of the microcomputer 10 Convert to

  The D / A 15 converts the signal level into an analog signal whose signal level is the upper threshold voltage Vref-H (for example, 2.5 [V]) of the appropriate voltage Vref according to the digital signal received from the microcomputer 10. In this way, the power supply monitoring circuit 11 generates analog signals whose signal levels are the lower threshold voltage Vref-L and the upper threshold voltage Vref-H, which are appropriate voltages Vref.

  The comparator 16 inputs the power supply voltage supplied from the power supply unit 2 to the microcomputer 10 and compares the signal level Vin of the power supply voltage with the signal level (Vref−L) of the analog signal from the D / A 14. The output of the comparator 16 becomes “1” (High) level when Vin <Vref−L, and becomes “0” (Low) level when Vin ≧ Vref−L.

The comparator 17 receives the power supply voltage supplied from the power supply unit 2 to the microcomputer 10 and compares the signal level Vin of the power supply voltage with the signal level (Vref−H) of the analog signal from the D / A 15. The output of the comparator 17 becomes “1” (High) level when Vin> Vref−H, and becomes “0” (Low) level when Vin ≦ Vref−L.
.

  As a result, the power supply monitoring circuit 11 continuously monitors the power supply voltage even when the power supply voltage is momentarily interrupted (when Vin <Vref−L) as shown in FIG. Therefore, the instantaneous interruption can be reliably detected and output to the calculation unit 12. Further, in the calculation unit 12, when the detection result of the instantaneous interruption is input from the power supply monitoring circuit 11, it is possible to quickly save the data to the EEPROM 13, and thus the data calculated by the calculation unit 12 can be lost. Low.

  As described above, in the millimeter wave sensor 1 according to the present embodiment, D that generates an analog signal having signal levels of the lower threshold voltage Vref-L and the upper threshold voltage Vref-H that are appropriate for the voltage Vref inside the microcomputer 10. / A14, 15 and a power supply monitoring circuit 11 having comparators 16, 17 as comparison circuits for comparing the generated analog signal signal levels Vref-L and Vref-H with the power supply voltage signal level Vin are arranged. As a result, the instantaneous interruption of the power supply voltage can be detected quickly and the fluctuation of the power supply voltage is continuously monitored by the D / A 14 and 15 and the comparators 16 and 17, so that the instantaneous interruption of the power supply voltage is reliably detected. It becomes possible to do.

  Further, in the conventional technique, the power supply unit is provided with the power supply monitoring means. However, by providing the power supply monitoring circuit 11 inside the microcomputer 10 as in the present embodiment, an extra mounting space is not required.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  For example, since the D / A 14 and 15 of the present embodiment convert a digital signal received from the microcomputer 10 into an analog signal, in the microcomputer 10, the lower threshold voltage Vref-L and the upper threshold value of the appropriate voltage Vref. You may comprise so that the signal level of voltage Vref-H can be changed. This eliminates the need for a separate D / A converter according to the signal level of the power supply voltage supplied from the power supply unit 2.

1 is a circuit block diagram showing a configuration of a millimeter wave sensor 1. FIG. 2 is a circuit block diagram showing a configuration of a power supply monitoring circuit 11. FIG. It is a figure for demonstrating the case where the signal level Vin of a power supply voltage instantaneously exceeds the upper threshold voltage Vref-H, and the case where it falls below the lower threshold voltage Vref-L.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Millimeter wave sensor 2 Power supply part 10 Microcomputer 11 Power supply monitoring circuit 12 Arithmetic part 13 EEPROM
14, 15 D / A conversion circuit 16, 17 Comparator 18 OR circuit

Claims (2)

A microcomputer power supply voltage monitoring device for determining whether or not a power supply voltage supplied to a microcomputer used in a vehicle is an appropriate voltage that guarantees the operation of the microcomputer,
Inside the microcomputer,
An analog signal generation circuit for generating an analog signal indicating the signal level of the appropriate voltage;
A comparison circuit that inputs an analog signal of the power supply voltage and compares the signal level of the input power supply voltage with the signal level of the analog signal generated by the analog signal generation circuit;
A microcomputer power supply voltage monitoring device that determines whether or not the power supply voltage is the appropriate voltage from a comparison result of the comparison circuit.   2. The microcomputer power supply voltage monitoring apparatus according to claim 1, wherein the analog signal generation circuit includes a signal level changing means for changing a signal level of the appropriate voltage in response to an instruction from the microcomputer.

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