Dynamic aging monitor and correction for critical path duty cycle and delay degradation

1. A system, comprising:

a duty-cycle monitor, comprising:

a first oscillator having an output;

a flop having a signal input, a clock input, and an output, wherein the signal input is coupled to an input of the duty-cycle monitor, and the clock input is coupled to the output of the first oscillator;

a first counter having a count input, an enable input, and a count output, wherein the count input of the first counter is coupled to the output of the first oscillator, and the enable input of the first counter is coupled to the output of the flop; and

a second counter having a count input, an enable input, and a count output, wherein the count input of the second counter is coupled to the output of the first oscillator, and the enable input of the second counter is coupled to the output of the flop.

2. The system of claim 1 , wherein:

the first counter is enabled when the enable input of the first counter is high; and

the second counter is enabled when the enable input of the second counter is low.

3. The system of claim 1 , wherein:

the output of the flop comprises a first output and a second output, wherein the first output and the second output are complementary;

the enable input of the first counter is coupled to the first output of the flop; and

the enable input of the second counter is coupled to the second output of the flop.

4. The system of claim 3 , wherein:

the first counter is enabled when the enable input of the first counter is high; and

the second counter is enabled when the enable input of the second counter is high.

5. The system of claim 3 , wherein:

the first counter is enabled when the enable input of the first counter is low; and

the second counter is enabled when the enable input of the second counter is low.

6. The system of claim 1 , wherein the duty-cycle monitor further comprises a readout circuit coupled to the count output of the first counter and the count output of the second counter.

7. The system of claim 6 , wherein the readout circuit comprises:

a first readout latch having a data input, a clock input, and an output, wherein the data input of the first readout latch is coupled to the count output of the first counter, the clock input of the first readout latch is coupled to the output of the flop, and the output of the first readout latch is coupled to a first output of the duty-cycle monitor; and

a second readout latch having a data input, a clock input, and an output, wherein the data input of the second readout latch is coupled to the count output of the second counter, the clock input of the second readout latch is coupled to the output of the flop, and the output of the second readout latch is coupled to a second output of the duty-cycle monitor.

8. The system of claim 7 , wherein:

the output of the flop comprises a first output and a second output, wherein the first output and the second output are complementary;

the clock input of the first readout latch is coupled to the first output of the flop; and

the clock input of the second readout latch is coupled to the second output of the flop.

9. The system of claim 1 , further comprising:

a second oscillator having an output; and

a clock path coupled between the output of the second oscillator and the input of the duty-cycle monitor.

10. The system of claim 9 , wherein the clock path comprises clock buffers coupled in series.

11. The system of claim 9 , wherein a frequency of the second oscillator is within 5 percent of a frequency of the first oscillator.

12. The system of claim 9 , further comprising a duty-cycle adjuster coupled between the output of the second oscillator and the clock path.

13. The system of claim 12 , further comprising a control circuit coupled between the duty-cycle monitor and the duty-cycle adjuster.

14. The system of claim 1 , further comprising:

a second oscillator having an output;

a clock generator;

a first select circuit having a first input, a second input, and an output, wherein the first input is coupled to the output of the second oscillator, and the second input is coupled to the clock generator;

a second select circuit having an input, a first output, and a second output, wherein the first output is coupled to the input of the duty-cycle monitor, and the second output is coupled to at least one of sequential logic, a processor, and a memory; and

a clock path coupled between the output of the first select circuit and the input of the second select circuit.

15. The system of claim 14 , wherein a frequency of the second oscillator is within 5 percent of a frequency of the first oscillator.

16. The system of claim 14 , further comprising a duty-cycle adjuster coupled between the output of the first select circuit and the clock path.

17. The system of claim 16 , further comprising a control circuit coupled between the duty-cycle monitor and the duty-cycle adjuster.

18. The system of claim 14 , wherein:

in a first mode, the first select circuit is configured to select the first input and the second select circuit is configured to select the first output; and

in a second mode, the first select circuit is configured to select the second input and the second select circuit is configured to select the second output.

19. A method of duty-cycle monitoring, comprising:

receiving a clock signal and a reference signal;

inputting the clock signal to a signal input of a flop;

inputting the reference signal to a clock input of the flop;

counting a number of periods of the reference signal in which an output of the flop is high to generate a first count value; and

counting a number of periods of the reference signal in which the output of the flop is low to generate a second count value.

20. The method of claim 19 , wherein the reference signal is an oscillating signal, and a frequency of the clock signal is within 5 percent of a frequency of the reference signal.

21. The method of claim 19 , further comprising determining a duty cycle of the clock signal based on the first count value and the second count value.

22. The method of claim 21 , further comprising controlling a duty-cycle shift of a duty-cycle adjuster based on the determined duty cycle.

23. The method of claim 22 , wherein:

receiving the clock signal comprises receiving the clock signal from an output of a clock path; and

the duty-cycle adjuster is coupled to an input of the clock path.

24. The method of claim 19 , wherein:

the output of the flop comprises a first output and a second output;

the first output and the second output are complementary;

counting the number of the periods of the reference signal in which the output of the flop is high comprises counting the number of the periods of the reference signal in which the first output of the flop is high or low; and

counting the number of the periods of the reference signal in which the output of the flop is low comprises counting the number of the periods of the reference signal in which the second output of the flop is high or low.