Frequency sensor and semiconductor device
View Patent ↗A frequency sensor includes at least one a resistor element and a capacitor. A frequency is detected according to a charging/discharging time to/from the capacitor, thereby realizing a frequency sensor with reduced power consumption and reduced circuit scale. Further, plural resistors and plural capacitors can be provided, along with switches connected to the respective resistors and capacitors. Additionally, a time constant can be adjusted after production, whereby variations in production can be reduced. Furthermore, a self-diagnosis circuit can be included for determining whether the frequency sensor itself operates normally or not. Thus, a highly-reliable frequency sensor can be realized.
1. A frequency sensor including:
a first conductivity type MOS transistor having a gate to which an input clock signal is applied, and a source connected to a first power supply voltage;
a second conductivity type MOS transistor having a gate to which the input clock signal is applied, and a source connected to a second power supply voltage;
a resistor connected between drains of said first and second MOS transistors; and
a capacitor connected between the drain of said first MOS transistor and said second power supply voltage;
an inverter having an input terminal connected to a connection node of said capacitor and said resistor; and
a third conductivity type MOS transistor having a gate connected to an output terminal of said inverter, a drain connected to the input terminal of said inverter, and a source connected to the second power supply voltage;
wherein a frequency of the input clock signal is detected by an output signal of the inverter.
2. A frequency sensor as defined in claim 1 wherein a resistor block comprising switch-attached resistors is provided instead of said resistor, each switch-attached resistor including a switch for switching each corresponding resistor between an enable state and a disable state.
3. A frequency sensor as defined in claim 1 wherein a capacitor block comprising switch-attached capacitors is provided instead of said capacitor, each switch-attached capacitor including a switch for switching each corresponding capacitor between an enable state and a disable state.
4. A frequency sensor as defined in claim 2 wherein the switch comprises a fuse.
5. A frequency sensor as defined in claim 3 wherein the switch comprises a fuse.
6. A frequency sensor as defined in claim 2 wherein ON/OFF of the switch is set according to data stored in a nonvolatile memory.
7. A frequency sensor as defined in claim 3 wherein ON/OFF of the switch is set according to data stored in a nonvolatile memory.
8. A frequency sensor as defined in claim 1 wherein the clock signal is applied as an inversion signal of the clock signal.
9. A frequency sensor as defined in claim 1 further including a self-diagnosis unit for checking whether the frequency sensor operates normally or not.
10. A frequency sensor as defined in claim 9 wherein said self-diagnosis unit comprises:
a high frequency generation circuit that generates a high frequency from the input clock signal, which is provided in said self-diagnosis unit;
a switching unit that switches a signal to be inputted to the frequency sensor between the input clock signal and a high frequency clock signal that is outputted from said high frequency generation circuit; and
a judgement circuit that detects a signal detected by the frequency sensor to judge whether the frequency sensor operates normally or not.
11. A frequency sensor as defined in claim 9 wherein said self-diagnosis unit comprises:
a low frequency generation circuit that generates a low frequency from the input clock signal, which is provided in said self-diagnosis unit;
a switching unit that switches a signal to be inputted to the frequency sensor between the input clock signal and a low frequency clock signal that is outputted from said low frequency generation circuit; and
a judgement circuit that detects a signal detected by the frequency sensor to judge whether the frequency sensor operates normally or not.
12. A semiconductor device comprising:
a frequency sensor, said frequency sensor including:
a first conductivity type MOS transistor having a gate to which an input clock signal is applied, and a source connected to a first power supply voltage;
a second conductivity type MOS transistor having a gate to which the input clock signal is applied, and a source connected to a second power supply voltage;
a resistor connected between drains of said first and second MOS transistors; and
a capacitor connected between the drain of said first MOS transistor and said second power supply voltage;
an inverter having an input terminal connected to a connection node of said capacitor and said resistor; and
a third conductivity type MOS transistor having a gate connected to an output terminal of said inverter, a drain connected to the input terminal of said inverter, and a source connected to the second power supply voltage, wherein a frequency of the input clock signal is detected by an output signal of the inverter; and
a semiconductor device body to which the input clock signal is applied, the operation of which is controlled according to a signal detected by the frequency sensor.
13. A semiconductor device as defined in claim 12 wherein said semiconductor device body is reset by the detected signal.
14. A semiconductor device as defined in claim 12 wherein said semiconductor device body stops its operation according to the detected signal.
15. A semiconductor device as defined in claim 12 wherein said semiconductor device body deletes or destroys the stored data for which confidentiality is required, according to the detected signal.