EDGE SELECTION TECHNIQUES FOR CORRECTING CLOCK DUTY CYCLE
Circuits and methods are provided for generating clock signals and correcting duty cycle distortion in clock signals. A circuit for generating a clock signal includes a multiplexer circuit and an edge-triggered flip-flop circuit. The multiplexer circuit selectively outputs one of a plurality of input clock signals. The edge-triggered flip-flop detects a transitioning edge of the input clock signal that is selectively output from the multiplexer circuit, and in response to the detection, samples a logic level of a received data signal, and generates a transition of an output clock signal at an output port of the edge-triggered flip-flop. The multiplexer circuit selectively outputs one of the plurality of input clock signals to a clock signal port of the edge-triggered flip-flop, based on a logic level of the output clock signal at the output port of the edge-triggered flip-flop, which is input to a select control port of the multiplexer circuit.
1 . A method for generating a clock signal, comprising:
selecting between one of a plurality of input clock signals, based on a logic level of an output clock signal;
detecting a transitioning edge of the selected one of the plurality of input clock signals;
sampling a logic level of a data signal in response to said detecting;
changing the logic level of the output clock, based on the sampled logic level of the data signal; selecting another one of the plurality of input clock signals, in response to said changing of the logic level of the output clock; and
inverting the output clock signal and using the inverted output clock signal as the data signal.
2 . The method of claim 1 , wherein a sequence of the selecting, detecting, sampling, changing and selecting steps is repeated, wherein a first input clock signal is selected when the output clock signal transitions to a first logic level and wherein a second input clock signal is selected when the output clock signal transitions to a second logic level.
3 . The method of claim 1 , wherein detecting a transitioning edge comprises detecting a rising edge of the selected one of the plurality of input clock signals.
4 . The method of claim 1 , wherein detecting a transitioning edge comprises detecting a falling edge of the selected one of the plurality of input clock signals.
5 . The method of claim 1 , wherein said detecting, sampling, and changing steps are performed by an edge-triggered flip-flop.
6 . The method of claim 5 , wherein the edge-triggered flip-flop is an asynchronously resettable edge-triggered flip-flop.
7 . The method of claim 1 , further comprising generating the data signal having a frequency equal to a frequency of the plurality of input clock signals.
8 . The method of claim 1 , wherein each of the plurality of input clock signals is generated with a corresponding one of a plurality of identical circuits.
9 . (canceled)
10 . A method for generating a clock signal, comprising:
selecting between one of a plurality of input clock signals, based on a logic level of an output clock signal;
detecting a transitioning edge of the selected one of the plurality of input clock signals;
sampling a logic level of a data signal in response to said detecting;
changing the logic level of the output clock, based on the sampled logic level of the data signal; and
selecting another one of the plurality of input clock signals, in response to said changing of the logic level of the output clock,
wherein the plurality of input clock signals are clock signals with distorted duty cycles, wherein the method further comprises correcting the duty cycles of the input clock signals by detecting transitioning edges of the input clock signals that are substantially equally spaced in time to generate an output clock signal which is substantially free of duty cycle distortion.
11 . The method of claim 10 , wherein a sequence of the selecting, detecting, sampling, changing and selecting steps is repeated, wherein a first input clock signal is selected when the output clock signal transitions to a first logic level and wherein a second input clock signal is selected when the output clock signal transitions to a second logic level.
12 . The method of claim 10 , wherein detecting a transitioning edge comprises detecting a rising edge of the selected one of the plurality of input clock signals.
13 . The method of claim 10 , wherein detecting a transitioning edge comprises detecting a falling edge of the selected one of the plurality of input clock signals.
14 . The method of claim 10 , wherein said detecting, sampling, and changing steps are performed by an edge-triggered flip-flop.
15 . The method of claim 14 , wherein the edge-triggered flip-flop is an asynchronously resettable edge-triggered flip-flop.
16 . The method of claim 10 , further comprising generating the data signal having a frequency equal to a frequency of the plurality of input clock signals.
17 . The method of claim 10 , wherein each of the plurality of input clock signals is generated with a corresponding one of a plurality of identical circuits.
18 . The method of claim 10 , further comprising inverting the output clock signal and using the inverted output clock signal as the data signal.
19 . A method for generating a clock signal, comprising:
selecting between one of a plurality of input clock signals, based on a logic level of an output clock signal;
detecting a transitioning edge of the selected one of the plurality of input clock signals;
sampling a logic level of a data signal in response to said detecting;
changing the logic level of the output clock, based on the sampled logic level of the data signal; and
selecting another one of the plurality of input clock signals, in response to said changing of the logic level of the output clock