Oscillator, oscillating method, image sensor, and imaging apparatus

1. An oscillator comprising:

inverters that are connected in a loop shape and of which the number is an odd number greater than or equal to three; and

a delay section that delays change in a voltage that is input to one inverter of the odd number of inverters,

wherein the one inverter is a schmitt trigger inverter,

wherein the schmitt trigger inverter includes

a current source, and

a resistor in which current supplied by the current source flows,

wherein a hysteresis width of the schmitt trigger inverter depends on the current that flows in the resistor,

wherein the delay section includes a different current source and a capacitor, and

wherein an oscillatory period depends on current, which flows in the capacitor, and the hysteresis width.

2. The oscillator according to claim 1 , wherein the schmitt trigger inverter further includes a switch that changes a direction of the current, which flows in the resistor, in response to an oscillation output signal which is output by the oscillator.

3. The oscillator according to claim 2 , further comprising a current control section that controls the current source and the different current source so as to flow current corresponding to predetermined reference current.

4. The oscillator according to claim 3 , further comprising a current generation section that generates, in response to a predetermined reference voltage, the reference current corresponding to the reference voltage.

5. The oscillator according to claim 4 ,

wherein the current generation section includes

an operational amplifier of which a non-inverting input terminal is supplied with the reference voltage and of which a inverting input terminal is connected to one end of a resistor for voltage-to-current conversion, where the other end of the resistor is grounded, and

the resistor for voltage-to-current conversion, and

wherein the reference current flows in the resistor for voltage-to-current conversion.

6. The oscillator according to claim 4 ,

wherein the current control section includes an one-side transistor which constitutes a current mirror circuit and in which the reference current flows, and

wherein the current source and the different current source include other-side transistors that constitutes the current mirror circuit and in which current corresponding to the reference current flows.

7. The oscillator according to claim 4 ,

wherein each of the different inverters, which are other than the schmitt trigger inverter, is a CMOS (Complementary MOS) inverter in which drains of a pMOSFET (positive channel Metal Oxide Semiconductor Field Effect Transistor) and an nMOSFET (negative channel MOSFET) are connected to each other and gates of the pMOSFET and the nMOSFET are connected to each other,

wherein the schmitt trigger inverter includes

a different pMOSFET and a different nMOSFET, of which respective drains are connected to each other, as the switch,

a CMOS inverter of which an output terminal is connected to respective gates of the different pMOSFET and the different nMOSFET and of which an input terminal is connected to a connection point between the drains of the different pMOSFET and the different nMOSFET,

a first current source, which is connected to a source of the different pMOSFET, and a second current source, which is connected to a source of the different nMOSFET and flows current the same as that of the first current source, as the current source, and

the resistor of which one end is connected to the connection point between the drains of the different pMOSFET and the different nMOSFET and of which the other end is connected to an output terminal of a pre-stage inverter of the schmitt trigger inverter, and

wherein the delay section includes

the capacitor of which one end is grounded and the other end is connected to the output terminal of the pre-stage inverter, and

a third current source, which is connected to a source of a pMOSFET constituting the pre-stage inverter, and a fourth current source, which is connected to a source of an nMOSFET constituting the pre-stage inverter and flows current the same as that of the third current source, as the different current source.

8. The oscillator according to claim 4 , wherein the oscillatory period depends on the capacitor, the current which flows in the capacitor, and the hysteresis width.

9. The oscillator according to claim 4 , wherein the hysteresis width depends on the resistor and the current which flows in the resistor.

10. The oscillator according to claim 4 ,

wherein the capacitor is a capacitor with a variable capacitance, and

wherein the oscillatory period is adjusted by adjusting the capacitance of the capacitor.

11. The oscillator according to claim 4 ,

wherein the resistor has a variable resistance, and

wherein the oscillatory period is adjusted by adjusting the resistance.

12. An oscillating method comprising:

delaying change in a voltage input to one inverter of inverters, which are connected in a loop shape and of which the number is an odd number greater than or equal to three, by a delay section of an oscillator including the odd number of inverters and the delay section,

wherein the one inverter is a schmitt trigger inverter,

wherein the schmitt trigger inverter includes

a current source, and

a resistor in which current supplied by the current source flows, and

wherein a hysteresis width of the schmitt trigger inverter depends on the current that flows in the resistor,

wherein the delay section includes a different current source and a capacitor, and

wherein an oscillatory period depends on current, which flows in the capacitor, and the hysteresis width.

13. An image sensor operated in synchronization with a signal that is output by an oscillator including inverters, which are connected in a loop shape and of which the number is an odd number greater than or equal to three, and a delay section which delays change in a voltage which is input to one inverter of the odd number of inverters,

wherein the one inverter is a schmitt trigger inverter,

wherein the schmitt trigger inverter includes

a current source, and

a resistor in which current supplied by the current source flows,

wherein a hysteresis width of the schmitt trigger inverter depends on the current that flows in the resistor,

wherein the delay section includes a different current source and a capacitor, and

wherein an oscillatory period depends on current, which flows in the capacitor, and the hysteresis width.

14. An imaging apparatus comprising:

an oscillator that includes inverters, which are connected in a loop shape and of which the number is an odd number greater than or equal to three, and a delay section which delays change in a voltage which is input to one inverter of the odd number of inverters; and

an image sensor that is operated in synchronization with a signal that is output by the oscillator,

wherein the one inverter is a schmitt trigger inverter,

wherein the schmitt trigger inverter includes

a current source, and

a resistor in which current supplied by the current source flows,

wherein a hysteresis width of the schmitt trigger inverter depends on the current that flows in the resistor,

wherein the delay section includes a different current source and a capacitor, and

wherein an oscillatory period depends on current, which flows in the capacitor, and the hysteresis width.

15. An oscillator comprising:

a first inverter;

a second inverter;

a third inverter;

a fourth inverter;

a resistor; and

a capacitor,

wherein an output node of the first inverter is connected to a first terminal of the capacitor, and connected to an input node of the second inverter through the resistor,

wherein an output node of the second inverter is connected to an input node of the third inverter and an input node of the fourth inverter,

wherein an output node of the third inverter is connected to the input node of the second inverter and the first terminal of the capacitor,

wherein an output node of the fourth inverter is connected to the input node of the first inverter and an output node of the oscillator,

wherein the first inverter is configured to supply a first current from a first current source to the first terminal of the capacitor, and

wherein the third inverter is configured to supply a second current from a second current source to the first terminal of the capacitor.