Delay locked loop circuit
View Patent ↗The disclosure relates to phase detectors. Charge up and charge down signals that are generated by a phase detector cause i) following detection of a first edge of a reference clock signal, switching on of a switching transistor of sink current; ii) following detection of an edge of a feedback clock signal falling within less than 180 degrees from the first edge, switching on of a switching transistor of source current and switching off of the switching transistor of sink current; and iii) following detection of an edge of another reference signal at a point in time about midway between the first edge and a next similar edge of the reference clock signal has past, switching off of the switching transistor of source current while maintaining the switching transistor of sink current switched off.
1. A phase detector circuit for providing non-overlapping charge up and charge down control signals having first and second logic levels, comprising:
a first detecting circuit for driving a first control signal to the first logic level when a reference clock signal is detected and to the second logic level when a feedback clock signal is detected, the first detecting circuit providing a second control signal complementary to the first control signal;
a second detecting circuit for driving a third control signal to the first logic level when the reference clock signal is detected and to the second logic level when a phase shifted clock signal is detected;
a logic circuit for receiving the first control signal, the second control signal and the third control signal, the logic circuit driving the charge down signal and the charge up signal at the first logic level while the first control signal is at the first logic level, the second control signal is at the second logic level, and the third control signal is at the first logic level, the logic circuit driving the charge down signal and the charge up signal at the second logic level in response to the first control signal at the second logic level and the second control signal being at the first logic level, the charge up signal being driven at the first logic level in response to the third control signal at the second logic level while the second control signal is at the first logic level.
2. The phase detector circuit of claim 1 , wherein the first detecting circuit is an edge triggered detecting circuit for detecting an active edge of the reference clock signal and the feedback clock signal.
3. The phase detector circuit of claim 2 , wherein reference clock signal and the feedback clock signal have 50% duty cycles.
4. The phase detector circuit of claim 2 wherein reference clock signal and the feedback clock signal have duty cycles of less than 50%.
5. The phase detector circuit of claim 2 , wherein the second detecting circuit is an edge triggered detecting circuit for detecting an active edge of the reference clock signal and the phase shifted clock signal.
6. The phase detector circuit of claim 5 , wherein the reference clock signal, the feedback clock signal and the phase shifted clock signal have duty cycles of less than or equal to 50%.
7. The phase detector circuit of claim 1 , wherein the first detecting circuit includes
a first latch for driving the first control signal to the first logic level in response to the reference clock signal at the first logic level, and resettable to drive the first control signal to the second logic level, and
a second latch for resetting the first latch in response to the feedback clock signal at the first logic level, the second latch being resettable in response to the first control signal at the second logic level.
8. The phase detector circuit of claim 7 , wherein the first latch includes a D flip-flop having an input connected to VDD, a clock input for receiving the reference clock signal, a reset input for receiving an inverted output of the second latch, and an output for driving the first control signal.
9. The phase detector circuit of claim 8 , wherein the second latch includes a D flip-flop having an input connected to VDD, a clock input for receiving the feedback clock signal, a reset input for receiving the first control signal, and an output coupled to the reset input of the first latch.
10. The phase detector circuit of claim 9 , wherein the first detecting circuit further includes an inverter connected to the output of the second latch for providing the inverted output.
11. The phase detector circuit of claim 9 , wherein the output of the second latch provides the inverted output.
12. The phase detector circuit of claim 1 , wherein the second detecting circuit includes
a first latch for driving the third control signal to the first logic level in response to the reference clock signal at the first logic level, and resettable to drive the third control signal to the second logic level, and
a second latch for resetting the first latch in response to the phase shifted clock signal at the first logic level, the second latch being resettable in response to the third control signal at the second logic level.
13. The phase detector circuit of claim 12 , wherein the first latch includes a D flip-flop having an input connected to VDD, a clock input for receiving the reference clock signal, a reset input for receiving an inverted output of the second latch, and an output for driving the third control signal.
14. The phase detector circuit of claim 13 , wherein the second latch includes a D flip-flop having an input connected to VDD, a clock input for receiving the phase shifted clock signal, a reset input for receiving the third control signal, and an output coupled to the reset input of the first latch.
15. The phase detector circuit of claim 14 , wherein the first detecting circuit further includes an inverter connected to the output of the second latch for providing the inverted output.
16. The phase detector circuit of claim 14 , wherein the output of the second latch provides the inverted output.
17. The phase detector circuit of claim 1 , wherein the phase shifted clock signal is a 180 degree phase shifted version of the reference clock signal.
18. The phase detector circuit of claim 1 , wherein the logic circuit includes
a first NAND gate having a first input for receiving the first control signal, a second input for receiving the third control signal, and an output connected to an inverter that provides the charge down control signal, and
a second NAND gate having a first input for receiving the second control signal, a second input for receiving the third control signal, and an output for providing the charge up control signal.
19. A method for providing charge up and charge down control signals having active and inactive logic levels, comprising:
driving the charge down control signal to a first logic level in response to an active edge of a reference clock signal;
driving the charge down control signal to a second logic level in response to an active edge of a feedback clock signal;
driving the charge up control signal to the second logic level in response to the active edge of the feedback clock signal; and
driving the charge up control signal to the first logic level in response to an active edge of a phase shifted clock signal shifted 180 degrees relative to the reference clock.
20. The method of claim 19 , wherein the reference clock signal, the feedback clock signal and the phase shifted clock signal are pulsed signals.
21. The method of claim 20 , wherein the reference clock signal, the feedback clock signal and the phase shifted clock signal have duty cycles of less than or equal 50 percent.
22. The method of claim 19 , wherein the charge down control signal and the charge up control signal are driven to the second logic level at substantially the same time in response to the active edge of the feedback clock signal.