Duty cycle detector and phase difference detector

1. A duty cycle detector comprising:

a first ring oscillator including an odd number of first inverters and suitable for generating a first periodic signal using the first inverters, wherein at least one inverter among the first inverters is enabled during a time interval when a clock has a first value;

a second ring oscillator including an odd number of second inverters and suitable for generating a second periodic signal using the second inverters, wherein at least one inverter among the second inverters is enabled during a time interval when the clock has a second value; and

a frequency comparator suitable for comparing a frequency of the first periodic signal with a frequency of the second periodic signal and generating a duty cycle detection signal of the clock.

2. The duty cycle detector of claim 1 , wherein the first value is a logic high level and the second value is a logic low level, the at least one inverter among the first inverters including a third inverter, the at least one inverter among the second inverters including a fourth inverter,

wherein the first ring oscillator further includes a first low-pass filter (LPF) having a first end which is coupled to an output of the third inverter, and

wherein the second ring oscillator further includes a second LPF having a first end which is coupled to an output of the fourth inverter.

3. The duty cycle detector of claim 2 , wherein the first ring oscillator further includes a first Schmitt trigger circuit which is coupled to a second end of the first LPF, and

wherein the second ring oscillator further includes a second Schmitt trigger circuit which is coupled to a second end of the second LPF.

4. A duty cycle detector comprising:

a ring oscillator including an odd number of inverters and suitable for generating a periodic signal using the inverters, wherein at least one inverter among the inverters is enabled during a first time interval when a clock has a first value in a first mode and enabled during a second time interval when the clock has a second value in a second mode; and

a frequency comparator suitable for comparing a frequency of the periodic signal generated in the first mode with a frequency of the periodic signal generated in the second mode and generating a duty cycle detection signal of the clock.

5. The duty cycle detector of claim 4 , wherein the first value is a logic low level and the second value is a logic high level, the at least one inverter among the inverters including a first inverter, and

wherein the ring oscillator further includes a low-pass filter (LPF) having a first end which is coupled to an output of the first inverter.

6. The duty cycle detector of claim 5 , wherein the ring oscillator further includes a Schmitt trigger circuit which is coupled to a second end of the LPF.

7. A phase difference detector comprising:

a first ring oscillator including an odd number of first inverters and suitable for generating a first periodic signal using the first inverters, wherein at least one inverter among the first inverters is enabled during a first time interval when a first clock and a second clock have different logic values;

a second ring oscillator including an odd number of second inverters and suitable for generating a second periodic signal using the second inverters, wherein at least one inverter among the second inverters is enabled during a second time interval when the first clock and the second clock have a common logic value; and

a frequency comparator suitable for comparing a frequency of the first periodic signal with a frequency of the second periodic signal and generating a phase difference detection signal indicative of a phase difference between the first clock and the second clock.

8. The phase difference detector of claim 7 , wherein the at least one inverter among the first inverters including a third inverter, the at least one inverter among the second inverters including a fourth inverter,

wherein the first ring oscillator further includes a first low-pass filter (LPF) having a first end which is coupled to an output of the third inverter, and

wherein the second ring oscillator further includes a second LPF having a first end which is coupled to an output of the fourth inverter.

9. The phase difference detector of claim 8 , wherein the first ring oscillator further includes a first Schmitt trigger circuit which is coupled to a second end of the first LPF, and

wherein the second ring oscillator further includes a second Schmitt trigger circuit which is coupled to a second end of the second LPF.

10. The phase difference detector of claim 9 , wherein the first ring oscillator further includes an XOR gate receiving the first clock and the second clock and providing an output signal to the third inverter, the third inverter being enabled in response to the output signal of the XOR gate, and

wherein the second ring oscillator further includes an XNOR gate receiving the first clock and the second clock and providing an output signal to the fourth inverter, the fourth inverter being enabled in response to the output signal of the XNOR gate.

11. The phase difference detector of claim 7 , wherein the at least one inverter among the first inverters including a third inverter, the third inverter including:

first, second, and third PMOS transistors that are serially coupled between a power source voltage terminal and a first node; and

first, second, and third NMOS transistors that are serially coupled between a ground voltage terminal and the first node,

wherein the first PMOS transistor is turned on or off in response to an inverted version of the second clock, and the second PMOS transistor is turned on or off in response to the first clock, and the third PMOS transistor is turned on or off in response to an input signal of the third inverter, and

wherein the first NMOS transistor is turned on or off in response to the inverted version of the second clock, and the second NMOS transistor is turned on or off in response to the first clock, and the third NMOS transistor is turned on or off in response to the input signal of the third inverter.

12. The phase difference detector of claim 11 , wherein the at least one inverter among the second inverters includes a fourth inverter, the fourth inverter including:

fourth, fifth, and sixth PMOS transistors that are serially coupled between the power source voltage terminal and a second node; and

fourth, fifth, and sixth NMOS transistors that are serially coupled between the ground voltage terminal and the second node,

wherein the fourth PMOS transistor is turned on or off in response to the first clock, and the fifth PMOS transistor is turned on or off in response to the second clock, and the sixth PMOS transistor is turned on or off in response to an input signal o12f the fourth inverter, and

wherein the fourth NMOS transistor is turned on or off in response to the first clock, and the fifth NMOS transistor is turned on or off in response to the second clock, and the sixth NMOS transistor is turned on or off in response to the input signal of the fourth inverter.

13. A phase difference detector comprising:

a ring oscillator suitable for including an odd number of inverters and generating a periodic signal using the inverters, wherein at least one inverter among the inverters is enabled during a first time interval when a first clock and a second clock have different logic values in a first mode and enabled in a second time interval when the first clock and the second clock have a common logic value in a second mode; and

a frequency comparator suitable for comparing a frequency of the periodic signal generated in the first mode with a frequency of the periodic signal generated in the second mode and generating a phase difference detection signal between the first clock and the second clock.

14. The phase difference detector of claim 13 , wherein the ring oscillator further includes a low-pass filter (LPF) having a first end which is coupled to the at least one inverter.

15. The phase difference detector of claim 14 , wherein the ring oscillator further includes a Schmitt trigger circuit which is coupled to a second end of the LPF.

16. The phase difference detector of claim 13 , further comprising:

an XOR gate receiving the first clock and the second clock and generating a first output signal;

a XNOR gate receiving the first clock and the second clock and generating a second output signal; and

a selector receiving the first output signal, the second output signal, a first mode signal, and a second mode signal and selecting one of the first and second output signals in response to the first and second mode signals.

17. The phase difference detector of claim 16 , wherein the selector provides the selected one of the first and second output signals to the at least one inverter.