Referenceless clock and data recovery circuits

1. A circuit, comprising:

recovered clock generation circuitry configured to generate a recovered clock signal from a received signal using an oscillator, the recovered clock signal being for use in generating a recovered data signal from the received signal;

frequency error detection circuitry configured to generate one or more outputs representing a relationship between a number of transitions of the recovered data signal and a number of transitions of the received signal;

phase error detection circuitry configured to generate one or more outputs representing a relationship between transitions of the recovered clock signal and corresponding transitions of the received signal; and

selection circuitry configured to provide at least one of the one or more outputs of the frequency error detection circuitry to the recovered clock generation circuitry for use in driving the oscillator if a difference between the number of transitions of the recovered data signal and the number of transitions of the received signal is above a threshold, the selection circuitry also being configured to provide at least one of the one or more outputs of the phase error detection circuitry to the recovered clock generation circuitry for use in driving the oscillator if the difference between the number of transitions of the recovered data signal and the number of transitions of the received signal is below the threshold.

2. The circuit of claim 1 , wherein the oscillator comprises a voltage-controlled oscillator, wherein the recovered clock generation circuitry includes a charge pump and a capacitor that are configured to generate a control voltage for the voltage-controlled oscillator, and wherein the recovered clock generation circuitry is configured to use the one or more outputs of the frequency error detection circuitry or the one or more outputs of the phase error detection circuitry to drive the charge pump.

3. The circuit of claim 1 , wherein the frequency error detection circuitry includes a first counter configured to count the transitions of the received signal, a second counter configured to count the transitions of the recovered data signal, difference circuitry for determining the difference between the number of transitions of the recovered data signal and the number of transitions of the received signal, and comparison circuitry for comparing the difference between the number of transitions of the recovered data signal and the number of transitions of the received signal to the threshold.

4. The circuit of claim 3 , wherein the first counter is configured to count the transitions of the received signal by counting a number of rising edges of the received signal, a number of falling edges of the received signal, or a number of rising and falling edges of the received signal, and wherein the second counter is configured to count the transitions of the recovered data signal by counting a number of rising edges of the recovered data signal, a number of falling edges of the recovered data signal, or a number of rising and falling edges of the recovered data signal.

5. The circuit of claim 3 , wherein the frequency error detection circuitry is configured to operate in a first mode in which the first counter is configured to count a number of rising or falling edges of the received signal, and the second counter is configured to count a number of rising or falling edges of the recovered data signal, and wherein the frequency error detection circuitry is configured to operate in a second mode in which the first counter is configured to count a number of rising and falling edges of the received signal, and the second counter is configured to count a number of rising and falling edges of the recovered data signal.

6. The circuit of claim 3 , wherein the difference circuitry includes negation circuitry configured to invert the output of one of the first and second counters to generate an inverted counter output, and addition circuitry to add the inverted counter output to the output of the other of the first and second counters.

7. The circuit of claim 3 , wherein the frequency error detection circuitry includes synchronization circuitry configured to synchronize operation of the difference circuitry and the comparison circuitry.

8. The circuit of claim 1 , wherein the phase error detection circuitry is configured to generate the recovered data signal by using the recovered clock signal to sample the received signal.

9. The circuit of claim 1 , wherein the received signal conforms to a serial data protocol, and wherein the serial data protocol corresponds to one of a DisplayPort standard, a High-Definition Multimedia Interface (HDMI) standard, a Serial ATA standard, a Peripheral Component Interconnect Express (PCI-E) standard, or a Universal Serial Bus (USB) standard.

10. The circuit of claim 1 , wherein the frequency error detection circuitry is configured to enter a low power mode when the difference between the number of transitions of the recovered data signal and the number of transitions of the received signal is below the threshold.

11. The circuit of claim 10 , wherein the frequency error detection circuitry is configured not to detect the transitions of the recovered data signal or the received signal during at least part of the low power mode.

12. The circuit of claim 10 , wherein the frequency error detection circuitry is configured to detect only rising edges or only falling edges during at least part of the low power mode.

13. A circuit, comprising:

recovered clock generation circuitry configured to generate a recovered clock signal from a received signal using an oscillator, the recovered clock signal being for use in generating a recovered data signal from the received signal;

frequency error detection circuitry including one or more counters configured to count transitions of the received signal and transitions of the recovered data signal, and comparison circuitry for comparing a difference between a number of transitions of the recovered data signal and a number of transitions of the received signal to a threshold;

phase error detection circuitry configured to generate one or more outputs representing a relationship between transitions of the recovered clock signal and corresponding transitions of the received signal; and

selection circuitry configured to provide one or more outputs of the frequency error detection circuitry to the recovered clock generation circuitry for use in driving the oscillator if the difference between the number of transitions of the recovered data signal and the number of transitions of the received signal is above the threshold, the selection circuitry also being configured to provide at least one of the one or more outputs of the phase error detection circuitry to the recovered clock generation circuitry for use in driving the oscillator if the difference between the number of transitions of the recovered data signal and the number of transitions of the received signal is below the threshold.

14. The circuit of claim 13 , wherein the oscillator comprises a voltage-controlled oscillator, wherein the recovered clock generation circuitry includes a charge pump and a capacitor that are configured to generate a control voltage for the voltage-controlled oscillator, and wherein the recovered clock generation circuitry is configured to use the one or more outputs of the frequency error detection circuitry or the one or more outputs of the phase error detection circuitry to drive the charge pump.

15. The circuit of claim 13 , wherein the one or more counters includes a first counter configured to count the transitions of the received signal, and a second counter configured to count the transitions of the recovered data signal, and wherein the frequency error detection circuitry includes difference circuitry for determining the difference between the number of transitions of the recovered data signal and the number of transitions of the received signal.

16. The circuit of claim 15 , wherein the difference circuitry includes negation circuitry configured to invert the output of one of the first and second counters to generate an inverted counter output, and addition circuitry to add the inverted counter output to the output of the other of the first and second counters.

17. The circuit of claim 15 , wherein the frequency error detection circuitry includes synchronization circuitry configured to synchronize operation of the difference circuitry and the comparison circuitry.

18. The circuit of claim 13 , wherein the one or more counters are configured to count the transitions of the received signal by counting a number of rising edges of the received signal, a number of falling edges of the received signal, or a number of rising and falling edges of the received signal, and wherein the one or more counters are configured to count the transitions of the recovered data signal by counting a number of rising edges of the recovered data signal, a number of falling edges of the recovered data signal, or a number of rising and falling edges of the recovered data signal.

19. The circuit of claim 13 , wherein the one or more counters are configured to operate in a first mode to count a number of rising or falling edges of the received signal, and a number of rising or falling edges of the recovered data signal, and wherein the one or more counters are configured to operate in a second mode to count a number of rising and falling edges of the received signal, and a number of rising and falling edges of the recovered data signal.

20. The circuit of claim 13 , wherein the phase error detection circuitry is configured to generate the recovered data signal by using the recovered clock signal to sample the received signal.

21. The circuit of claim 13 , wherein the received signal conforms to a serial data protocol, and wherein the serial data protocol corresponds to one of a DisplayPort standard, a High-Definition Multimedia Interface (HDMI) standard, a Serial ATA standard, a Peripheral Component Interconnect Express (PCI-E) standard, or a Universal Serial Bus (USB) standard.

22. The circuit of claim 13 , wherein the frequency error detection circuitry is configured to enter a low power mode when the difference between the number of transitions of the recovered data signal and the number of transitions of the received signal is below the threshold.

23. The circuit of claim 22 , wherein the frequency error detection circuitry is configured not to detect the transitions of the recovered data signal or the received signal during at least part of the low power mode.

24. The circuit of claim 22 , wherein the frequency error detection circuitry is configured to detect only rising edges or only falling edges during at least part of the low power mode.