JP2003271268A - Electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electronic equipment which can reduce current consumption at power saving operation time in regard to the electronic equipment operable in normal operation time as well as in power saving operation time. <P>SOLUTION: The electronic equipment having a built-in clock function is provided with a first oscillating circuit in which a first clock is generated at normal operation time and the operation is stopped at power saving operation time; a second oscillating circuit which is driven by a first driving voltage, and generates a second clock of lower frequency than the first clock at least at the power saving operation time; a processing circuit which is driven by a second driving voltage which is higher than the first driving voltage, operated by the first clock generated in the first oscillating circuit at normal operation time, and operated by the second clock generated in the second oscillating circuit at power saving operation time; and a level adjustment circuit which adjusts the level of the second clock generated in the second oscillating circuit to a level corresponding to the first driving voltage, and supplies it to the processing circuit. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device, and more particularly to an electronic device that can be operated during normal operation and power saving operation.

[0002]

2. Description of the Related Art FIG. 4 shows a block diagram of a conventional example.

The conventional electronic device 1 is a multi-display for a vehicle, which displays selected information when the accessory switch of the automobile is on, and performs a normal operation of timing the time, and the accessory switch is turned on. When it is turned off, the power saving operation time is performed to measure the time to hold the time. The electronic device 1 includes a power supply circuit 11, a smoothing capacitor 12, a watchdog timer 13, a microcomputer 14, a first oscillator circuit 15, a second oscillator circuit 16,
Display changeover switch 17, display driver 18, display device 1
It is composed of 9.

The power supply circuit 11 includes a power supply terminal Tvin 1
A power supply voltage Vcc of 2V is supplied. The power supply circuit 11 is 3
It is composed of a terminal regulator and the like, and generates a drive voltage V0 of 5V from a power supply voltage Vcc of 12V. The 5V drive voltage V0 generated by the power supply circuit 11 is smoothed by the smoothing capacitor 12, and the watchdog timer 1
3, the microcomputer 14, and the second oscillator circuit 16.

The watchdog timer 13 includes a power supply circuit 1
It is driven by the drive voltage V0 of 5V from 1 to monitor the operation of the microcomputer 14. The microcomputer 14 applies a drive voltage to the first oscillation circuit 15 during normal operation. The first oscillating circuit 15 oscillates by the drive voltage from the microcomputer 14, and the first clock CL1 having a frequency of about 8 MHz.
To generate. The first clock CL1 is supplied to the microcomputer 14 as a main clock. During normal operation, the microcomputer 14 receives the first clock CL from the first oscillator circuit 15.
The process is executed based on 1.

The second oscillator circuit 15 has a frequency of about 4.19 MHz due to the drive voltage V0 generated by the power supply circuit 11.
It oscillates at and frequency is about 32.8kH by dividing it.
The second clock CL2 of z is generated. The second clock CL2 generated by the second oscillation circuit 15 is the microcomputer 1
4 is supplied as a sub clock. The microcomputer 14
During the power saving operation, the time counting operation is performed based on the second clock CL2 from the second oscillation circuit 15. The second oscillator circuit 15 oscillates at a frequency of about 4.19 MHz and divides the frequency to generate a second clock CL2 having a frequency of about 32.8 kHz. Ensures temperature accuracy.

Data such as atmospheric pressure and temperature are supplied to the microcomputer 14 from the input port Pin. Further, the microcomputer 14 is supplied with an accessory switch status signal from the input port Pacc. Further, a display changeover switch 17 is connected to the microcomputer 14.

FIG. 5 shows an operation flowchart of the microcomputer 14.

When the accessory switch status signal from the input port Pacc is a signal indicating ON in step S1, the microcomputer 14 determines the first oscillating circuit 15 in step S2.
Are operated, and the normal operation state is set in step S3. In the normal operation state, the processing operation can be performed with the first clock CL1 of 8 MHz.

When the accessory switch status signal from the input port Pacc is a signal indicating OFF in step S1, the microcomputer 14 sets the operation clock in step S4 to the second clock CL generated by the second oscillation circuit 16.
Set to 2. Next, the microcomputer 14 performs the first operation in step S5.
The operation of the oscillation circuit 15 is stopped, and the power saving operation state is set in step S6.

The operation of the microcomputer 14 in the normal operation state will be described.

In the normal operation, the data selected by the display changeover switch 17 is subjected to predetermined processing and supplied to the display driver 18. The display driver 18 controls the display device 19 according to the data supplied from the microcomputer 14, and displays according to the data from the microcomputer 14. For example, when the time display is selected by operating the display changeover switch 17, the microcomputer 14 displays the time data measured by the time measuring function inside the microcomputer 14 in the display driver 1
8 and the time is displayed on the display device 19.

Further, when the temperature display is selected by operating the display changeover switch 17, the microcomputer 14 supplies to the display driver 18 the temperature data obtained by filtering the temperature data supplied from the input port Pin. The temperature is displayed on the display device 19.

At this time, the power supply circuit 11 outputs an output voltage of 5
V ± 10%, current consumption was about 0.5 mA. The watchdog timer 13 had a current consumption of about 0.1 mA. The microcomputer 14 has a drive voltage of 5 V and a current consumption of about 0.06 mA during power saving operation. The second oscillator circuit 16 had a current consumption of about 800 μA. Furthermore, the leakage current of the capacitors including the smoothing capacitor 12 was about 0.04 mA.

Therefore, when the conventional electronic device 1 is operated in a power saving mode, that is, when the battery is driven, the total current consumption is 1.
It was 5 mA.

[0016]

However, an automobile is equipped with electric equipment, and a current called dark current is consumed by the power supply voltage from the battery even when the power supply is cut off. In recent years, the number of electrical devices mounted on automobiles has increased, and this has increased dark current. The increase in the dark current causes a great consumption of the battery, causing a problem such as battery exhaustion. For this reason, further reduction of the current consumption is required for the vehicle-mounted electronic device 1 as described above.

The present invention has been made in view of the above points, and an object of the present invention is to provide an electronic device capable of reducing current consumption during power saving operation.

[0018]

According to a first aspect of the present invention, in an electronic device having a built-in clock function, a first clock is generated during a normal operation, and the first oscillation is stopped during a power saving operation. A second oscillator circuit that is driven by the first drive voltage and that generates a second clock having a frequency lower than the first clock at least during power saving operation; and a second oscillator circuit that is greater than the first drive voltage Driven by drive voltage,
A processing circuit which operates by a first clock generated by a first oscillation circuit during normal operation and operates by a second clock generated by a second oscillation circuit during power saving operation;
And a level adjusting circuit for adjusting the level of the second clock generated by the second oscillating circuit to a level according to the first drive voltage and supplying the level to the processing circuit.

According to the first aspect of the present invention, the drive voltage of the second oscillation circuit driven during the power saving operation is reduced, and the second
By adjusting the level of the clock of and supplying it to the processing circuit, compared to the increase in current consumption due to level adjustment,
It is possible to sufficiently reduce the current consumption. Therefore, it is possible to further reduce the current consumption.

According to a second aspect of the present invention, a power supply circuit for generating a third drive voltage higher than the first drive voltage from the power supply voltage and a third drive voltage for decreasing the third drive voltage to generate the first drive voltage. A voltage drop circuit, and the power supply circuit is designed to ensure that the first drive voltage generated by the voltage drop circuit is the minimum drive voltage of the processing circuit.

According to the second aspect of the present invention, the power supply circuit is designed to ensure that the first drive voltage generated by the voltage drop circuit guarantees the minimum drive voltage of the processing circuit. It is possible to reduce the voltage to the vicinity of the minimum drive voltage and further reduce current consumption.

[0022]

1 is a block diagram of an embodiment of the present invention.

The electronic device 100 of this embodiment is different from the conventional electronic device 1 in the specifications of the power supply circuit 111.

The power supply circuit 111 of this embodiment is composed of an IC chip capable of outputting an output voltage of 5 V with an error of ± 2% with a current consumption of 0.1 mA. As a result, the current consumption of the power supply circuit 111 can be reduced to 0.1 mA, and the output voltage of the power supply circuit 11 can be guaranteed to be 4.8V to 5.2V.

Further, in this embodiment, the voltage generated by the power supply circuit 111 is stepped down to 4.8V by the step-down diode 13 to drive the watchdog timer 13 and the microcomputer 14. The voltage generated by the power supply circuit 111 is smoothed by the smoothing capacitor 12 and supplied to the step-down diode 112. The step-down diode 112 is composed of, for example, a Schottky diode, is connected in the forward direction with respect to the output voltage of the power supply circuit 11, and is connected to the power supply circuit 1.
The output voltage of 11 is decreased by 0.2V. Power supply circuit 111
When the output voltage of 5 is 5V, it is stepped down to 4.8V.

The voltage stepped down by the step-down diode 13 is applied to the watchdog timer 13, the microcomputer 14, the step-down diode 113, and the level adjusting circuit 114.

The microcomputer 14 has a minimum drive voltage of 4.5V. At this time, the output voltage of the power supply circuit 11 is 4.8V.
Since it is guaranteed at ~ 5.2V, step-down diode 1
Even if the voltage is reduced by 0.2V at 8, 4.6V to 5V is guaranteed,
It does not fall below the minimum drive voltage of 4.5V. Therefore, the microcomputer 14 can be operated reliably. Further, by driving the microcomputer 14 at 4.8V, the current consumption of the microcomputer 14 can be reduced as compared with the conventional case of driving at 5V.

The watchdog timer 13 also has 4.8.
Since it is driven by V, the current consumption can be reduced as compared with the case of driving by 5V as in the conventional case.

The first oscillation circuit 16 is the microcomputer 1
Since the first clock CL1 generated by the first oscillator circuit 16 is driven by the voltage from the microcomputer 14,
Since it is output at a level suitable for, no level adjustment is required.

Further, in the electronic device 100 of this embodiment, the driving voltage of the second oscillation circuit 16 is 4.8 V and the voltage drop circuit 11 is used.
It is further lowered by 3 to drive. Down circuit 113
Has a configuration in which diodes D11 and D12 are connected in series and connected in the forward direction toward the second oscillation circuit 16. At this time, the drop circuit 113 causes the diode D11,
A forward voltage Vf × 2 of D12 is dropped, and a driving voltage of 3.9 V is applied to the second oscillation circuit 16.
At this time, the second drive circuit 16 has a minimum drive voltage
Since it is 3.5V, it can be sufficiently driven at 3.9V.

In this way, the driving voltage of the second oscillator circuit 16 is reduced to 3.7 V, whereby the second oscillator circuit 1
The current consumption in 6 can be reduced.

At this time, the second oscillator circuit 16 has a voltage of 3.9V.
Since the microcomputer 14 is driven at 4.8 V and is driven at 4.8 V, the level of the second clock CL2 output from the second oscillation circuit 16 does not reach the level specified by the microcomputer 14. Therefore, in this embodiment, the second oscillator circuit 1
A level adjusting circuit 114 for adjusting the level of the second clock CL2 generated in 6 is added.

FIG. 2 shows a block diagram of the level adjusting circuit 114.

The level adjusting circuit 114 is composed of two inverters 121 and 122 driven by the output voltage of the step-down diode 112. The second clock CL2 is supplied from the second oscillator circuit 16 to the inverter 121. The inverter 121 uses the second clock CL2.
Is inverted, and the level is amplified so as to reach the specified level of the microcomputer 14. The second clock CL2 inverted by the inverter 121 is supplied to the inverter 122. The inverter 122 inverts the second clock CL2 from the inverter 121 and restores the original state.

The second clock CL2, which is set to the prescribed level of the microcomputer 14 by the level adjusting circuit 114, is the microcomputer 1
4 is supplied as a sub clock. Level adjustment circuit 1
14 is driven at the same voltage of 4.8 V as that of the microcomputer 14, but is sufficiently smaller than the current consumption reduced by driving the drive voltage of the second oscillation circuit 16 at 3.7 V. Even if the circuit 114 is added, the current consumption does not increase.

Next, the current consumption reduced by the configuration of this embodiment will be described.

FIG. 3 is a diagram for explaining the effect of reducing the current consumption according to one embodiment of the present invention.

First, the current consumption during the power saving operation of the conventional electronic device 1 is set to about 1.52 mA.

Here, the power supply circuit 1 with a current consumption of 0.1 mA
By adopting No. 11, the current consumption of the electronic device 100 can be reduced to 1.29 mA. Further, the consumption current can be reduced to 0.92 mA by reducing the drive voltage by the power source step-down diode 12.

Here, by adding the level adjusting circuit 114, the current consumption increases to 0.98 mA. But,
The step-down diode 112 can reduce the drive voltage of each electronic component. Therefore, the consumption current is 0.9m
It can be reduced to A.

As described above, the power consumption of the electronic device 100 of the present embodiment, that is, the power consumption when the accessory switch is turned off can be 0.9 mA, which is a small current consumption of 1 mA or less. Therefore, when the vehicle is mounted on the vehicle, it is possible to easily reduce the consumption of the battery and prevent the battery from running down.

In the present embodiment, the multi-display has been described as an example of the electronic device 100, but the electronic device to which the present invention is applied is not limited to this.
It is applicable to general electronic devices that can operate in normal operation and power saving operation.

[0043]

As described above, according to the first aspect of the present invention, the drive voltage of the second oscillator circuit driven during the power saving operation is reduced and the level of the second clock is adjusted to thereby perform the processing circuit. By supplying the current to the device, the current consumption can be sufficiently reduced as compared with the increase in the current consumption due to the level adjustment, so that the current consumption can be further reduced.

According to a second aspect of the present invention, the first drive voltage is processed by setting the power supply circuit so that the first drive voltage generated by the voltage drop circuit guarantees the minimum drive voltage of the processing circuit. Since the voltage can be lowered to around the minimum drive voltage of the circuit, it is possible to further reduce current consumption.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a level adjustment circuit 114.

FIG. 3 is a diagram for explaining an effect of reducing current consumption according to an embodiment of the present invention.

FIG. 4 is a block diagram of a conventional example.

5 is an operation flowchart of the microcomputer 14. FIG.

[Explanation of symbols]

12: smoothing capacitor, 13: watchdog timer, 14: microcomputer 15: first oscillation circuit, 16: second oscillation circuit, 17:
Display changeover switch 18: display driver, 19: display device 100: electronic device, 111: power supply circuit, 112, step-down diode 113: step-down circuit, 114: level adjustment circuit 121, 122: inverter

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 5/00 550 G06F 1/00 332Z 5/18 1/04 310A F term (reference) 5B011 DA06 DB03 DB05 DB05 LL02 LL08 LL13 5B079 AA05 AA07 BA02 BA13 BA20 BC01 DD02 5C080 DD26 EE01 FF03 GG02 JJ02 JJ03 JJ05 JJ07 KK20 5C082 AA21 BA16 BA26 DA76 DA81 DA86

Claims (2)

[Claims] 1. An electronic device capable of operating in a normal operation and a power saving operation, the first oscillation circuit generating a first clock during the normal operation and stopping the operation during the power saving operation, A second oscillating circuit which is driven by a first driving voltage and generates a second clock having a frequency lower than the first clock at least during the power saving operation; and a second driving circuit which is higher than the first driving voltage. It is driven by a voltage, operates at the first clock generated by the first oscillation circuit during the normal operation, and operates at the second clock generated by the second oscillation circuit during the power saving operation. A processing circuit; and adjusting the level of the second clock generated by the second oscillator circuit to a level according to the first drive voltage,
An electronic device comprising a level adjusting circuit supplied to the processing circuit. 2. A power supply circuit that generates a third drive voltage that is higher than the first drive voltage from a power supply voltage, and a voltage drop circuit that drops the third drive voltage to generate the first drive voltage. 2. The electronic device according to claim 1, wherein the power supply circuit has a specification that the first drive voltage generated by the voltage drop circuit guarantees a minimum drive voltage of the processing circuit. .