JPH04133114A - Oscillation stop detector - Google Patents

Abstract

PURPOSE:To prevent the malfunction of a device caused by oscillation instability due to the voltage drop of a long battery service life device, and an oscillation circuit by detecting a state immediately before a stop of the oscillation circuit. CONSTITUTION:An oscillation circuit output 103 of an output of an oscillation circuit 101 is inputted to an amplitude detecting circuit 102. The amplitude detecting circuit 102 detects its dropped amplitude. Immediately before an oscillation stop, the oscillation circuit output 103 being the output of the circuit 101 lowers remarkably its amplitude. When a voltage applied to the oscillation circuit 101 drops, and amplitude of the oscillation circuit output 103 becomes smaller, the charging capacity of a transistor 303 to a capacitor 304 drops. An amplitude detecting circuit output 104 comes to a low level, when the amplitude of the oscillation circuit 103 becomes larger, and comes to a high level, when the amplitude becomes smaller. In such a way, a state immediately before a stop of the oscillation circuit 101 can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device that detects in advance the stoppage of an oscillation circuit that generates a frequency that serves as the source oscillation of a control clock or the like of a device.

[Prior Art] A conventional circuit for detecting the stoppage of an oscillation circuit detects the stoppage of oscillation after the oscillation actually stops.

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology detects a state in which a system, such as a microcomputer, is just before oscillation stops and is still operating normally, and saves system data at that point. The problem is that it cannot be applied to cases where protection is required.

Therefore, the present invention is intended to solve these problems.
The purpose is to provide a device that can detect just before the oscillation circuit stops.

[Means for Solving the Problems] The oscillation stop detection device of the present invention comprises: (L) (a) an oscillation circuit that generates a frequency that serves as a source oscillation such as a control clock of the device; and (b) an output of the oscillation circuit. an amplitude detection circuit that detects a decrease in the amplitude of the input signal, and the amplitude detection circuit is characterized in that: (a) one end is connected to a first power supply and the other end is connected to a first N-channel a first resistor connected to the drain of the MOS transistor; (b) a second resistor having one end connected to the first power supply and the other end connected to the drain of the second N-channel MO3) transistor; (C) a first capacitor having one end connected to a first power supply and the other end connected to the drain of the first N-channel MOS transistor; (d) a first capacitor having a drain connected to one end of the first resistor; , the first N-channel MOS transistor whose source is connected to a second power supply and whose gate is connected to the drain of the second N-channel MOS transistor; (e) whose gate and drain are connected to the second resistor; said second N whose source is connected to one end of said N
channel MOS transistor; (f) a second capacitor having one end connected to the output of the oscillation circuit and the other end connected to the drain of the second N-channel MOS transistor; It is characterized by using the drain of the channel MOS transistor as the output.

[Example] A block diagram of the present invention is shown in FIG. 101 is an oscillation circuit, an example of which is shown in FIG. This is a general crystal oscillation circuit consisting of an oscillation inverter 201, a drain resistor 202, and a feedback resistor 203. The output of the oscillation inverter 201 is the oscillation circuit output 103, which is connected to one end of the drain resistor 202. drain resistance 2
The other end of 02 is connected to one end of feedback resistor 203, and serves as the drain terminal of 205. One end of a crystal oscillator 206 is connected to the drain terminal 205. The other end of the crystal oscillator 206 is connected to the input of the oscillation inverter 201 and the gate terminal 204 to which one end of the feedback resistor 203 is connected.

An oscillation circuit output 103, which is an output of the oscillation circuit 101, is input to an amplitude detection circuit 102 as shown in FIG.

The amplitude detection circuit 102 is a circuit that detects a decrease in the amplitude of the oscillation circuit output 102.

Normally, the oscillation circuit 101 stops oscillating below a certain voltage when the power supply voltage supplied to the circuit decreases.

Immediately before the oscillation stops, the amplitude of the oscillation circuit output 103, which is the output of the oscillation circuit 101, decreases significantly with respect to the power supply voltage. The amplitude detection circuit 102 is a circuit that detects the reduced amplitude. Figure 3 shows the details.

The oscillation circuit output 103 is input to one end of a second capacitor 309. The MOS gate input 308, which is the other end of the second capacitor 309, is connected to the gate of the first N-channel MOS transistor 303 and the second N-channel MOS transistor 307.
Connected to the gate and drain of the channel MOS transistor.

Also, a second N-channel MOS transistor 307
The gate and drain of are connected to one end of a second resistor 306, and the other end of the second resistor 306 is connected to the first power supply 301.

With this configuration, if the resistance value of the second resistor 306 is sufficiently larger than the resistance value of the second N-channel MOS transistor, the potential of the MOS gate input 308 is set such that the source of the second N-channel MOS transistor 3o7 is connected to the second N-channel MOS transistor 3o7. Because it is connected to the power supply 302, the second N-channel MO
S)-becomes close to the threshold voltage value of transistor 307.

Further, the drain of the first N-channel MOS transistor 303 is connected to one end of the first resistor 305 and one end of the first capacitor 304, and serves as an output of the amplitude detection circuit 104. The source of the first N-channel MOS transistor 303 is connected to the second power supply 302. first resistor 305 and first capacitor 304
The other end is connected to a first power source 301. first N
Although the channel MOS transistor 303 and the second N-channel MOS transistor 307 may have different threshold values, they are assumed to be the same for the sake of simplicity. In that case, the second N-channel MOS transistor 307 is
Since its gate, MOS gate input 308, is approximately close to the threshold voltage value of the second N-channel MOS transistor 307, it is always in a conductive state when the oscillation circuit output 103 is stopped. At this time, the resistance value of the first resistor 305 is determined so that the potential of the amplitude detection circuit output 104 becomes a high level.

This state is a static state (the state in which the oscillation circuit 101 is stopped), and the amplitude detection circuit output 104 is at a "high level". In this state, a vibration signal is input to the oscillation circuit output 103, and the MOS gate input 308 generates the same oscillation frequency as the oscillation frequency in the oscillation circuit 101 near the threshold voltage value of the first N-channel MOS transistor 303. If the oscillation circuit 101 is stably oscillating and the amplitude of its output, the oscillation circuit output 103, is large enough, the amplitude of the MOS gate input 308 is also large, and the potential is the same as that of the first power source. When the voltage swings to the side, the resistance value of the first N-channel MOS transistor 303 becomes low, charging the first capacitor 304, and lowering the potential of the detection circuit output 104 to the second voltage B502 side.MOS gate input 30
8 swings to the second power supply side, the resistance value of the first N-channel MOS transistor 303 becomes high, the first capacitor 304 is discharged, and the amplitude detection circuit output 1
The potential of 04 approaches the first power supply side. In other words, the amplitude detection circuit output 104 oscillates, but in order to bring the average level closer to the second power supply side and make it a "low level", the first resistor 305, the first capacitor 304, and the first This is possible by adjusting the characteristic values of the N-channel MOS transistor 303.

In addition, the power supply voltage applied to the oscillation circuit 101 decreases,
When the amplitude of the oscillation circuit output 103 becomes smaller, the charging ability of the first N-channel MOS transistor 303 for the first capacitor 304 decreases, and the amplitude detection circuit output 1
The potential of 04 approaches the second power supply side and becomes a "high level."

As explained above, the amplitude detection circuit output 104 becomes "low level" when the amplitude of the oscillation circuit output 103 is large.
If the amplitude is small, it will be a "2 high level". That is, when the oscillation circuit 101 is about to stop and its output amplitude becomes small,
The amplitude detection circuit output 104 changes from a "low level" to a "high level", making it possible to detect just before the oscillation circuit 101 stops.

4 and 5 show examples of application of the oscillation stop detection device of the present invention. The amplitude detection circuit output 104 in FIG.
In this example, the oscillation circuit control output 403 is input to the oscillation circuit 401 according to the input. However, the oscillation circuit 401 in this example is different from the oscillation circuit 101 and has a configuration as shown in FIG. The difference from the example shown in FIG. 2 is that a sub-oscillation inverter 501 is added in parallel to the oscillation inverter 201. As a result, when the amplitude of the oscillation circuit output 103 decreases and the amplitude detection circuit output 104 becomes a "high level", the control circuit 402 determines and sets the oscillation circuit control output 403 to a "high level".

As a result, the sub oscillation inverter 501 becomes operational,
Increase the amplitude of the oscillation circuit output 103. That is, the oscillation stop voltage can be further reduced. This has great significance when realizing a long-life battery-powered device. Typically, the oscillation stop voltage is lower than the average operating voltage of the device. Furthermore, the length of life of the device depends on the power consumption at the average operating voltage. Therefore, in order to develop a long-life device, the oscillation stop voltage is usually brought close to the average operating voltage of the oscillation circuit, and the power consumption of the oscillation circuit is designed to be low. However, if such a design is adopted, the stop voltage of the oscillation circuit will increase, and the device will stop operating at a short period of time, reducing the effectiveness of the low power consumption design of the oscillation circuit.

Therefore, if the above-described circuit is used, the life of the device can be further extended.

[Effects of the Invention] As described above, according to the present invention, it is possible to detect the state immediately before the oscillation circuit stops, and it is possible to detect the state immediately before the oscillation circuit stops, and to prevent oscillation from occurring due to a drop in the voltage of the oscillation circuit or the long battery life device as described above. This has the great effect of realizing a device that prevents device malfunctions caused by stability.

[Brief explanation of drawings] FIG. 1 is a block diagram of the present invention. 2 and 3 are specific circuit example diagrams of FIG. 1. FIG. 4 is a block diagram of an application example of the present invention. FIG. 5 is a diagram showing a specific example of the circuit shown in FIG. 101...Oscillation circuit 102...amplitude detection circuit 103...Oscillation circuit output 104... Amplitude detection circuit output 201...Oscillation inverter drain resistance feedback resistance gate terminal drain terminal crystal oscillator first power supply second power supply The first N-channel N-cho OS transistor first capacitor first resistance second resistance Second N-channel MOS transistor MOS gate input second capacitor oscillation circuit control circuit Oscillation circuit control output Sub oscillation inverter Figure 3 Figure 5

Claims (2)

[Claims] (1) Consisting of (a) an oscillation circuit that generates a frequency that serves as the source oscillation of a device control clock, and (b) an amplitude detection circuit that receives the output of the oscillation circuit as an input and detects a decrease in its amplitude. An oscillation stop detection device characterized by: (2) The amplitude detection circuit according to claim 1 comprises: (a) a first resistor whose one end is connected to the first power supply and whose other end is connected to the drain of the first N-channel MOS transistor; (b) ) a second resistor having one end connected to the first power supply and the other end connected to the drain of the second N-channel MOS transistor; (c) a second resistor having one end connected to the first power supply and the other end connected to the second N-channel MOS transistor; a first capacitor connected to the drain of one N-channel MOS transistor; (d) a drain connected to one end of the first resistor, a source connected to a second power supply, and a gate connected to the second connected to the drain of the N-channel MOS transistor,
(e) the second N-channel MOS transistor whose gate and drain are connected to one end of the second resistor and whose source is connected to a second power supply;
channel MOS transistor; (f) a second capacitor having one end connected to the output of the oscillation circuit and the other end connected to the drain of the second N-channel MOS transistor; 2. The oscillation stop detection device according to claim 1, wherein the drain of the channel MOS transistor is used as an output.