Reset circuit and reset circuit design method

Abstract

To obtain a reset circuit capable of stably operating in a high temperature environment in which leak current of a diode is not negligible.SOLUTION: A reset circuit for solving the above problem includes a resistance element, a diode, a capacitor, a power supply input terminal, a power supply feedback terminal, and an output terminal for outputting a reset signal. The power supply input terminal, the resistance element, the capacitor, and the power supply feedback terminal are sequentially connected in series. The diode is connected in parallel with the resistance element between the power supply input terminal and the capacitor. The output terminal is connected to the high-voltage side of the capacitor. Assuming that a reverse resistance value of the diode at a temperature T is RD(T), a resistance value of the resistance element is R, and a capacitance of the capacitor is C, a time constant of the reset circuit at the temperature T is given by CRRD(T) / (R+RD(T)), an output signal of the reset circuit has a rise time of the reset signal from zero volt to a reset release threshold value voltage at the temperature T is a specified time for reset operation specified by a CPU or longer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The disclosed technology relates to a reset circuit that operates stably in a high-temperature environment where the leakage current of a diode cannot be ignored. [Background technology]

[0002] For example, if there is a momentary interruption in the drive voltage of a CPU (Central Processing Unit), the internal circuits of the CPU (semiconductor elements such as logic gates and memory) will malfunction, and calculations will not proceed normally even if the drive voltage is restored to a normal value. In such a case, it is necessary to initialize the CPU. This is called a reset. In this specification, IC chips with names such as MPU (Micro Processor Unit), MCU (Micro Controller Unit), and DSP (Digital Signal Processor) are collectively referred to as CPU.

[0003] Many CPUs have a reset port and receive a reset signal through the reset port. The reset signal is generated using a dedicated reset circuit. Figure 1(a) shows a schematic diagram of a reset circuit and a CPU. CC indicates the drive voltage source (and voltage value) for the reset circuit and CPU, and 12 indicates ground.

[0004] Figure 1(b) shows a schematic diagram of the relationship between the reset circuit output and the CPU state. If the reset circuit output is “High”, the CPU starts or maintains its operating state, and if the reset circuit output becomes “Low”, the CPU transitions to the reset state. When initializing the CPU, the CPU must wait for the system clock to stabilize and initialize the internal circuits, so it takes a certain amount of time (hereafter referred to as t d Therefore, a "Low" signal is d The "Low" signal needs to be maintained for a longer period. d If it is shorter, the reset will fail.

[0005] [CR-Type Reset Circuit] Figure 2 shows one specific example of a circuit (CR-type reset circuit) that generates High and Low signals. A similar circuit is introduced in Non-Patent Document 1. The CR-type reset circuit 2 includes a resistor element 21, a capacitor 22, a diode 23, a power input terminal 24, a power feedback terminal 25, and an output terminal 26. The power input terminal 24 is connected to V CC and the power feedback terminal 25 is connected to ground 12. The resistor element 21 and the capacitor 22 are arranged in series between the power input terminal 24 and the power feedback terminal 25. The diode 23 is arranged in parallel with the resistor element 21 between the power input terminal 24 and the capacitor 22. The diode 23 is arranged with its cathode on the power input terminal 24 side and its anode on the capacitor 22 side. The output terminal 26 outputs the high-potential side voltage of the capacitor 22.

[0006] Assuming that the resistance of the resistor element 21 is R [Ω], the capacitance of the capacitor 22 is C [F], the output voltage of the output terminal 26 is V1 [V], and the capacitor charge is 0 [C] at time t = 0, when voltage V CC is supplied to the CR-type reset circuit 2, the output voltage V1 after t = 0 is expressed by the following equation.

Equation

[0007] The CPU recognizes a High signal if the reset port input is equal to or higher than a predetermined voltage, and a Low signal if it is lower than the predetermined voltage. If the predetermined voltage is V T and V1(t1) = V T , the CR-type reset circuit 2 is a circuit that outputs a Low signal for 0 < t < t1 and a High signal for t1 < t. When t becomes sufficiently large, V1 ≈ V CC . In the graph of Figure 2(b), the region where t is negative corresponds to the state where V1 ≈ V CC .

[0008] V1 ≈ V CC means that the capacitor 22 is fully charged. For reset, the V of the CR type reset circuit 2 is once set to zero. CC Then, the charge stored in the capacitor 22 flows in the forward direction through the diode 23 and is quickly discharged through the power input terminal 24. As a result, the CR type reset circuit 2 achieves a transition from a High signal to a Low signal across t = 0.

[0009] As described above, t1 needs to be t d or more. When obtaining the time t1 at which V1 becomes V from Equation (1), it becomes Equation (2). T [Equation] However, log is the natural logarithm (the same applies hereinafter in this specification). V CC and V T are values determined by the specifications of the CPU. By adjusting C and R, t1 ≥ t d is realized.

[0010] [Time Constant of CR Type Reset Circuit] The denominator of the exponent of the exponential function in Equation (1) (in the CR type reset circuit 2, the product of C and R) is called the "time constant" and has the dimension of "time". When CR [seconds] elapses, V1 rises from zero to about 63% of V CC , and when 2CR [seconds] elapses, it rises to about 86% of V CC . Thus, the time constant represents the characteristics (fast or slow rise) of the transient response of the CR circuit.

[0011] [Reset IC] Reset circuits (reset ICs) that suppress power consumption using transistors are also commercially available. Transistors have a minute current called an OFF leakage current that rapidly increases as the temperature rises, and the output of the reset IC fluctuates depending on the ambient temperature. Technologies for obtaining stable operation against ambient temperature changes have been developed (Patent Documents 1 and 2). [Prior Art Documents] [Patent Documents] ​

[0012] [Patent Document 1] JP 2004-80772 A [Patent Document 2] JP 2006-50437 A [Non-patent literature]

[0013] [Non-Patent Document 1] Masahiko Kuwano, "Constant Design and Component Selection for Microcontroller Circuits," Transistor Technology, June 2004, pp.163-164 Summary of the Invention [Problem to be solved by the invention]

[0014] There are cases where it is necessary to use a CPU in a high-temperature environment of around 200°C. For example, when drilling for shale oil, the drill must proceed along the shale layer that contains the oil, so the drill is equipped with a sensor that measures position and direction. In this case, the sensor control chip needs to operate stably in an environment of around 200°C.

[0015] Existing reset ICs are designed for use at up to 100°C, and there are no reset ICs guaranteed to operate at 200°C. In fact, reset ICs cannot withstand high temperatures, as malfunctions occur at temperatures as high as 200°C. High temperature environments cause higher failure rates and shorter life spans for electronic components. The greater the number of components, the greater the number of components that can fail. For this reason, it is desirable for electronic components to be used in high temperature environments to have as simple a circuit and circuits using as simple elements as possible. In this sense, CR-type reset circuits are more promising than reset ICs.

[0016] Using FIG. 3, we consider the operation of the CR type reset circuit at high temperatures. At room temperature, the reverse resistance of a diode can be considered to be infinite, but at high temperatures the reverse resistance decreases to a non-negligible value, causing leakage current. The reverse resistance of the diode 23 is RD [Ω], the output voltage at output terminal 26 is as follows:

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[0017] Low leakage current even at high temperatures (R D It would be ideal if diodes with a large reverse resistance were available, but diodes that maintain sufficient reverse resistance at 200°C are currently not generally available. [Means for solving the problem]

[0018] In order to solve the above problem, a reset circuit according to the disclosed technique includes a resistive element, a diode, a capacitor, a power supply input terminal, a power supply feedback terminal, and an output terminal that outputs a reset signal. The power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal are connected in series in this order: power supply input terminal, resistive element, capacitor, and power supply feedback terminal. The diode is connected in parallel with the resistive element between the power supply input terminal and the capacitor, with the cathode on the power supply input terminal side and the anode on the capacitor side. The output terminal is connected to the resistive element side of the capacitor. The high temperature at which the reset circuit operates is T, and the reverse resistance of the diode at temperature T is R D(T), the resistance of the resistor element is R, and the capacitance of the capacitor is C. The time constant of the reset circuit at temperature T is CRR. D (T) / (R+R D (T)). The output signal of the reset circuit has a time (rise time) during which the reset signal rises from zero volts to the reset release threshold voltage at temperature T, which is equal to or longer than a specified time for a reset operation specified by the CPU. Effect of the Invention

[0019] According to the disclosed technology, a reset circuit that operates at high temperatures and has a low failure rate can be realized. [Brief description of the drawings]

[0020] [Figure 1] A schematic diagram showing the reset circuit and the CPU to be reset. [Diagram 2] 1A and 1B are diagrams illustrating a configuration and an output signal of a CR type reset circuit. [Diagram 3] FIG. 13 is a diagram for explaining problems with the operation of a CR-type reset circuit at high temperatures. [Figure 4] 2A to 2C are diagrams for explaining the configuration and design method of a reset circuit according to the first embodiment. [Diagram 5] 10A and 10B are diagrams for explaining the configuration and design method of a reset circuit according to a second embodiment. [Figure 6] 13A to 13C are diagrams for explaining the configuration and design method of a reset circuit according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, embodiments of the disclosed technology will be described in detail. Note that components having the same functions are given the same reference numbers and duplicated descriptions will be omitted. EXAMPLES

[0022] The inventors of this application have demonstrated that in environments exceeding 200°C, if the semiconductor is encapsulated in glass or ceramic, the R DWe confirmed that the characteristic values ​​such as these are highly reproducible, and found that by combining them with passive elements made of materials with good temperature characteristics, an analog circuit with good high-temperature stability can be obtained. The capacitance C and resistance R of the CR reset circuit are adjustable. Therefore, by adjusting C and R, V1 can be changed from 0 to V T The time it takes for the temperature to rise to t d To obtain a longer (successful reset operation) CR type reset circuit.

[0023] Explained with reference to Fig. 4. The CR type reset circuit 4 includes a resistive element 21, a capacitor 22, a diode 23, a power supply input terminal 24, a power supply feedback terminal 25, and an output terminal 26. The connections of the elements are the same as those of the CR type reset circuit 2 described above. First, the reverse resistance R of the diode 23 at the temperature T at which the CPU is to be operated is D Measure (T).

[0024] Next, the resistance value R' of the resistor element 21 and the capacitance C' of the capacitor 22 are determined. According to equation (5), the rise time t3 of the CR type reset circuit 4 at temperature T is given by the following equation.

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[0025] The description of the first embodiment is now completed. EXAMPLES

[0026] In the first embodiment, the conditions of C' and R' are determined by focusing only on the rise time in a high temperature environment. In the second embodiment, the conditions of C' and R' are determined by also focusing on the rise time at room temperature. This will be explained using Figure 5.

[0027] The rise time t4 when the CR type reset circuit 4 of the first embodiment is operated at room temperature is given by the following equation (8).

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[0028] The description of the second embodiment is completed above.

[0029] [Modification of Example 2] R' to R D Assuming that it is set to be larger than (T), equation (7) can be transformed as follows:

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[0030] The description of the modified example of the second embodiment is completed above. EXAMPLES

[0031] In Examples 1 and 2, the rise time in a high temperature environment is t d While both the resistance value and the capacitance of the capacitor are adjusted to achieve the above, in the third embodiment, only the capacitance of the capacitor is adjusted. Specifically, at room temperature, t d For the CR reset circuit that achieves the above rise time, R is kept fixed and only C is changed.

[0032] The third embodiment will be described with reference to FIG. If the resistance value of the resistive element 21 is R and the capacitance of the capacitor 22 before the change is C0, the rise time t5 at room temperature is given by the following formula (11).

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[0033] The meaning of equation (15) will be explained below. C0, a, t d , R D (T), V CC , V T is a known or given value. The CR type reset circuit 6 with C1 calculated with b=1 has a rise time of just t d It becomes. In other words, by determining b to be 1 or more according to the desired rise time, the capacitor capacitance C1 to be changed can be obtained.

[0034] The description of the third embodiment is completed above. [Industrial Applicability]

[0035] The present invention can be used as an IC chip reset circuit that operates stably in a high-temperature environment. [Explanation of symbols]

[0036] 2,4,5,6 CR type reset circuit 21 Resistance element 22 Capacitor 23 Diode 24 Power input terminal 25 Power return terminal 26 Output terminal

Claims

1. A method for designing a reset circuit that outputs a reset signal to a CPU in a high temperature environment, comprising: the reset circuit includes a resistor element, a diode, a capacitor, a power supply input terminal, a power supply feedback terminal, and an output terminal that outputs a reset signal; the power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal are connected in series in the order of the power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal; the diode is connected in parallel with the resistance element between the power supply input terminal and the capacitor, with a cathode on the power supply input terminal side and an anode on the capacitor side; the output terminal is connected to the resistor element side of the capacitor, The reverse resistance R of the diode at the high temperature T at which the reset circuit operates Ｄ Measure (T) The specified time t for the reset operation specified by the CPU d , the drive voltage V of the reset circuit ＣＣ , reset release voltage V Ｔ Get The capacitance C of the capacitor and the resistance value R of the resistor element are determined so as to satisfy the following formula: ##EQU00016## A method for designing a reset circuit comprising:

2. 2. A method for designing a reset circuit according to claim 1, comprising the steps of: The maximum allowable rise time of the reset circuit at room temperature is t ｍａｘ As, The capacitance C of the capacitor and the resistance value R of the resistor element are further determined to satisfy the following formula: ##EQU00017## A method for designing a reset circuit comprising:

3. A method for designing a reset circuit according to claim 2, comprising: [0018] , as follows: [0019] Determine the capacitance C of the capacitor and the resistance R of the resistor element by replacing A method for designing a reset circuit comprising:

4. A method for designing a reset circuit that outputs a reset signal to a CPU in a high temperature environment, comprising: the reset circuit includes a resistor element, a diode, a capacitor, a power supply input terminal, a power supply feedback terminal, and an output terminal that outputs a reset signal; the power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal are connected in series in the order of the power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal; the diode is connected in parallel with the resistance element between the power supply input terminal and the capacitor, with a cathode on the power supply input terminal side and an anode on the capacitor side; the output terminal is connected to the resistor element side of the capacitor, The specified time t for the reset operation specified by the CPU d , the drive voltage V of the reset circuit ＣＣ , reset release voltage V Ｔ Get The capacitance of the capacitor is C ０ When the reset circuit is operated at room temperature with Ｔ The time it takes to rise to t d The value of the resistor element is set so that the value a divided by is equal to or greater than 1, The reverse resistance R of the diode at the high temperature T at which the reset circuit operates Ｄ Measure (T) The capacitance of the capacitor is C １ Set to above [0020] A reset circuit design method comprising:

5. A reset circuit that outputs a reset signal to a CPU in a high-temperature environment, the reset circuit includes a resistor element, a diode, a capacitor, a power supply input terminal, a power supply feedback terminal, and an output terminal that outputs a reset signal; the power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal are connected in series in the order of the power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal; the diode is connected in parallel with the resistance element between the power supply input terminal and the capacitor, with a cathode on the power supply input terminal side and an anode on the capacitor side; the output terminal is connected to the resistor element side of the capacitor, The reverse resistance of the diode at the high temperature T at which the reset circuit operates is R Ｄ (T), the resistance value of the resistor element is R, and the capacitance of the capacitor is C. The time constant of the reset circuit at the high temperature T is given by the following formula: ##EQU00021## The time (rise time) for the reset signal to rise from zero volts to the reset release threshold voltage at the high temperature T is equal to or longer than the specified time for the reset operation specified by the CPU. Reset circuit.

6. 6. A reset circuit according to claim 5, The time constant of the reset circuit at room temperature is given by the product of C and R, The capacitance C of the capacitor and the resistance R of the resistor are determined so that the time it takes for the reset signal to rise from zero volts to the reset release threshold voltage at room temperature is within a predetermined time. Reset circuit.

7. 7. A reset circuit according to claim 6, comprising: The time constant of the reset circuit at the high temperature T is Ｄ The capacitance C and the resistance R are determined by approximating the product of (T) Reset circuit.

8. A reset circuit that outputs a reset signal to a CPU in a high-temperature environment, the reset circuit includes a resistor element, a diode, a capacitor, a power supply input terminal, a power supply feedback terminal, and an output terminal that outputs a reset signal; the power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal are connected in series in the order of the power supply input terminal, the resistive element, the capacitor, and the power supply feedback terminal; the diode is connected in parallel with the resistance element between the power supply input terminal and the capacitor, with a cathode on the power supply input terminal side and an anode on the capacitor side; the output terminal is connected to the resistor element side of the capacitor, The reverse resistance of the diode at the high temperature T at which the reset circuit operates is R Ｄ (T), the specified time for the reset operation specified by the CPU is t d , the drive voltage of the reset circuit is V ＣＣ , reset release voltage is V Ｔ The capacitance of the capacitor is C ０ When the reset signal changes from zero volts to V Ｔ The time it takes to rise to at d When (a≧1), the capacitance of the capacitor is set to C １ The reset circuit is as above. [0022]

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