JP3564976B2 - Oscillation detection circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an oscillation detection circuit.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an apparatus for detecting an oscillation output of an oscillation circuit is disclosed in Japanese Patent Application Laid-Open No. 7-193428. This uses the inverted potential (threshold) of a CMOS inverter to which the output of the oscillating unit is input as a detection level of oscillation.
[0003]
The operation will be briefly described with reference to FIG.
[0004]
When an oscillation signal is input to the inverter 101 via the terminal X and the voltage level of the oscillation signal is smaller than the inverted potential of the inverter 101 at the start of oscillation or the like, the output of the inverter 101 becomes "1" and the P-channel MOS The transistor 102 turns off. Therefore, the capacitor 103 is not charged, and the inverter 104 outputs “1” which is a non-detection signal.
[0005]
When the voltage level of the oscillation signal exceeds the inverted potential of the inverter 101, the output of the inverter 101 becomes "0", the transistor 102 is turned on, and the capacitor 103 is charged.
[0006]
If the voltage level of the oscillation signal repeatedly exceeds the inverted potential of the inverter 101 while the oscillation continues, the capacitor 103 is gradually charged, the output of the inverter 104 is inverted, and the detection signal “0” is generated.
[0007]
[Problems to be solved by the invention]
When the oscillation signal input from the terminal X has a large amplitude, the time during which a through current flows through the inverter 101 is short.
[0008]
However, when the oscillation signal input from the terminal X has a small amplitude, the time required for the through current to flow through the inverter 101 becomes long, which causes a problem when low current consumption is required in design.
[0009]
In addition, since the threshold value of the inverter 101 is generally determined by the size of the transistor that forms the inverter 101, when changing the threshold value, the size of the transistor must be changed.
[0010]
[Means for Solving the Problems]
According to the present invention, a reference voltage is input to a first input terminal of a differential amplifier, an oscillation signal is input to a second input terminal, and the potential of a capacitive element is changed according to the output. , The oscillation detection level can be easily changed by changing the reference voltage to the first input terminal.
[0011]
Further, since the current flowing through the differential amplifier is limited by the current limiting means, the current consumption can be reduced even when the amplitude of the oscillation signal is small.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, a differential amplifier having a first input terminal for inputting a reference voltage and a second input terminal for inputting an oscillation signal, current limiting means for limiting a current flowing through the differential amplifier, A control circuit for controlling charging or discharging of the capacitive element according to the output of the differential amplifier; and a detecting circuit for detecting a desired oscillation state of the oscillation signal input to the second input terminal based on the potential of the capacitive element. And a circuit.
[0013]
【Example】
Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings.
[0014]
In FIG. 1, reference numeral 1 denotes a differential amplifier, which includes P-channel MOS transistors 2 and 3 and N-channel MOS transistors 4 and 5. The gate of the transistor 4 constitutes a first input terminal, and receives a reference voltage generated by the voltage source 6. The gate of the transistor 5 forms a second input terminal, and receives an oscillation signal from an oscillator (not shown) through a terminal X. Reference numeral 7 denotes an N-channel MOS transistor constituting a current limiting means. Reference numeral 8 denotes a control circuit comprising a P-channel MOS transistor 9 and an N-channel MOS transistor 10 connected between power supplies. 11 is a capacitor, 12 and 13 are inverters, 14 is an N-channel MOS transistor, and 15 is a P-channel MOS transistor. The inverter 12 forms a detection circuit.
[0015]
In this example, the signal input to the terminal A controls the current flowing through the differential amplifier 1 to control the ON / OFF of the differential amplifier 1 and also controls the discharge of the charge charged in the capacitor 11. Things.
[0016]
Next, the operation will be described.
[0017]
At the time of standby, a signal "1" is input to the terminal A, whereby the P-channel MOS transistor 6a in the voltage source 6 is turned off, the transistor 14 is turned on, and the electric charge stored in the capacitor 11 is discharged to discharge the capacitor 11. Is initialized. Therefore, at this time, that is, at the time of standby, the input of the inverter 12 becomes “0”, so that the output terminal Y outputs “1”. At this time, the transistor 7 is turned off by the inverted output “0” from the inverter 13, and no current flows to the differential amplifier 1. Therefore, at the time of standby, useless current does not flow through the differential amplifier 1 and low current consumption can be achieved. Further, the transistor 15 is turned on by the inverted output “0” from the inverter 13, and accordingly, the transistor 9 is turned off. Further, since the voltage source 6 is off, the transistor 10 is also off. Therefore, the operation of charging the capacitor 11 stops. Therefore, the disadvantage that the capacitor 11 is unnecessarily charged at the time of standby can be solved, and current consumption can be reduced.
[0018]
When a signal "0" is input to the terminal A and the transistor A is turned on, the transistor 14 is turned off, the initialization of the capacitor 11 is stopped, and the voltage source 6 is turned on to output the reference voltage to the gate of the transistor 4, and Turn 10 on. The transistor 7 is operated by the inverted output “1” from the inverter 13 and the transistor 15 is turned off, so that the differential amplifier 1 becomes operable.
[0019]
In this state, when an oscillation signal is input from the terminal X and the voltage level of the oscillation signal exceeds a threshold set by the reference voltage, the transistor 9 is turned on and the capacitor 11 is charged.
[0020]
Therefore, when a predetermined time elapses from the start of oscillation and the amplitude of the oscillation increases, and the voltage level of the oscillation signal repeatedly exceeds the threshold value set by the reference voltage, the capacitor 11 is gradually charged and the output of the inverter 12 is Are inverted to generate a detection output “0”. Conversely, when the voltage level of the oscillation output input via terminal X does not exceed the threshold value, transistor 9 is turned off, capacitor 11 is not charged, and inverter 12 does not output detection output "0".
[0021]
As described above, when the differential amplifier circuit is employed, the threshold value can be easily changed by changing the reference voltage input to the gate of the transistor 4. Further, the reference voltage can be adjusted by a signal from another circuit block of the IC, or the voltage may be adjusted by directly applying a voltage from outside the IC. For example, as shown in FIG. 2, a plurality of resistors 16 to 16 are connected in series between the power supplies, and one of the connection points of the resistors 16 is connected to the gate of the transistor 4 shown in FIG. In this way, the other connection points are connected to the power supply via the transistors 17 to 17, respectively, and the gate of the transistor 17 is controlled by a binary signal from another circuit block in the IC or a binary signal from outside the IC. May be adjusted digitally. Also, as shown in FIG. 3, a resistor 18 and a transistor 19 are connected between the power supplies, and the connection point is connected to the gate of the transistor 4 shown in FIG. 1, and the gate of the transistor 19 is connected to another gate in the IC. The comparison reference voltage may be adjusted in an analog manner by controlling with an analog signal from a circuit block or an analog signal from outside the IC.
[0022]
The differential amplifier is not limited to the above. For example, those shown in FIGS. 4A, 4B, and 4C may be used. In the figure, reference numeral 20 denotes an active load, reference numerals 21 and 22 denote resistors, reference numerals 23 and 24 denote P-channel MOS transistors, reference numerals 25 and 26 denote N-channel MOS transistors. I do.
[0023]
【The invention's effect】
According to the present invention, the oscillation detection level can be easily changed by changing the reference voltage to the first input terminal, and the current flowing through the differential amplifier is limited by the current limiting means, so that the amplitude of the oscillation signal is small. Even in this case, the current consumption can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the present invention.
FIG. 2 is a circuit diagram showing another example of the voltage source of FIG.
FIG. 3 is a circuit diagram showing another example of the voltage source of FIG. 1;
FIG. 4 is a circuit diagram showing a main part of the detection circuit of FIG. 1;
FIG. 5 is a circuit diagram showing a conventional oscillation detection circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Differential amplifier 7 Current limiting means 8 Control circuit 12 Detection circuit

Claims (1)

A differential amplifier having a first input terminal for inputting a reference voltage and a second input terminal for inputting an oscillation signal;
Current limiting means for limiting the current flowing through the differential amplifier;
A control circuit that controls charging or discharging of the capacitive element according to the output of the differential amplifier,
A detection circuit for detecting a desired oscillation state of an oscillation signal input to the second input terminal based on a potential of the capacitive element.

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