Clock generator and methods using closed loop duty cycle correction
Closed-loop duty-cycle correctors (DCCs), clock generators, memory devices, systems, and methods for generating an output clock signal having a particular duty cycle are provided, such as clock generators configured to generate an output clock signal synchronized with a received input clock signal having a predetermined duty cycle. Embodiments of clock generators include closed-loop duty cycle correctors that receive an already-controlled and corrected output signal. For example, DLL control circuitry and DCC control circuitry may each adjust a delay of a variable delay line. The DLL control circuitry adjusts the delay such that an output clock signal is synchronized with an input clock signal. The DCC control circuitry detects a duty cycle error in the output clock signal and adjusts the delay of the variable delay line to achieve a duty cycle corrected output signal. By detecting the duty cycle error in the output signal, the clock generator may achieve improved performance that can correct accumulated duty cycle error and correct for duty cycle error introduced by the duty cycle corrector itself in some embodiments.
1. A closed-loop duty-cycle corrector comprising:
a first delay line having a first input terminal, a first output terminal, and a first control terminal, the first delay line coupled to receive a first clock signal at the first input terminal, the first delay line configured to delay the first clock signal by a first variable delay amount determined by a first control signal received at the first control terminal to produce a first output signal at the first output terminal;
a second delay line having a second input terminal, a second output terminal, and a second control terminal, the second delay line coupled to receive a second clock signal at the second input terminal, wherein the second clock signal is a complement of the first clock signal, the second delay line configured to delay the second clock signal by a second variable delay amount determined by a second control signal received at the second control terminal to produce a second output signal at the second output terminal;
a duty cycle error detector having a third input terminal, a fourth input terminal and a third output terminal, the duty cycle error detector coupled to receive the first output signal at the third input terminal and the second output signal at the fourth input terminal, the duty cycle error detector configured to generate a duty cycle error correction signal at the third output terminal based on a deviation of the first output signal from a desired duty cycle, the duty cycle error detector comprising:
a reference clock signal generator, the reference clock signal generator coupled to receive the first output signal and generate a reference clock signal delayed a predetermined portion of a clock cycle;
a phase detector, the phase detector configured to receive the second output signal and the reference clock signal, the phase detector operable to generate the duty cycle error correction signal based on a comparison between a phase of the second output signal and a phase of the reference clock signal; and
control circuitry having a fifth input terminal and a fourth output terminal, the control circuitry coupled to receive the duty cycle error correction signal at the fifth input terminal and modify at least one of the first and second variable delay amounts to compensate for the deviation from the desired duty cycle.
2. A closed loop duty cycle corrector according to claim 1 , the reference clock signal generator comprising:
a third variable delay line coupled to receive the first output signal and generate the reference clock signal based on a received third control signal;
a fourth variable delay line coupled to receive the reference clock signal and generate a feedback clock signal based on a received fourth control signal;
a second phase detector, the second phase detector operable to receive the first output signal and the feedback clock signal, and generate a phase error signal based on a comparison of a phase of the first output signal and a phase of the feedback clock signal;
a reference clock control circuit, the reference clock control circuit coupled to receive the phase error signal and generate the third and fourth control signals based on the phase error signal.
3. A closed loop duty cycle corrector according to claim 2 wherein the reference clock control circuit generates the third and fourth control signals such that the third and fourth variable delay lines have equal delay and the reference clock signal is shifted one-half a clock period from the first output signal.
4. A closed loop duty cycle corrector according to claim 1 wherein the duty cycle error detector comprises:
a duty cycle error calculator configured to determine a duty cycle error based on the first and second output signals, the duty cycle error calculator coupled to transmit the duty cycle error to the control circuitry.
5. A clock generator comprising:
a locked loop including:
a first variable delay line configured to delay a first input clock signal a first delay amount to produce a first output clock signal, the first delay amount selected to synchronize the first input clock signal with the first output clock signal;
a second variable delay line configured to delay a second input clock signal a second delay amount to produce a second output clock signal, the second delay amount selected to synchronize the second input clock signal with the second output clock signal; and
a duty cycle corrector configured to receive the first and second output clock signals, detect a duty cycle error in at least one of the output clock signals, and adjust at least one of the first and second delay amounts to compensate for the detected duty cycle error, the duty cycle corrector including:
a third variable delay line and a fourth variable delay line, the third variable delay line configured to receive the first output clock signal and delay the first output clock signal a third delay amount to generate a reference clock signal, the fourth variable delay line configured to receive the reference clock signal and delay the reference clock signal a fourth delay amount to generate a feedback clock signal;
a first phase detector coupled to receive the first output clock signal and the feedback clock signal, the first phase detector operable to compare phases of the received signals and generate a first control signal indicative of a phase difference between the signals;
first control circuitry operable to receive the first control signal and select the third and fourth delay amounts based on the phase difference;
a second phase detector coupled to receive the second output clock signal and the reference clock signal, the second phase detector configured to compare a phase of the respective received signals and generate a second control singal indicative of the phase difference; and
second control circuitry operable to receive the second control signal and modify at one or the first and second delay amounts based on the phase difference.
6. A clock generator according to claim 5 wherein the second input clock signal is a complement of the first input clock signal.
7. A clock generator according to claim 5 wherein the third and fourth delay amounts are the same.
8. A memory device comprising:
an array of memory cells;
a control circuit coupled to the array of memory cells;
a clock generator coupled to the control circuit, the clock generator comprising:
a locked loop including:
a first variable delay line configured to delay a first input clock signal a first delay amount to produce a first output clock signal;
a second variable delay line configured to delay a second input clock signal a second delay amount to produce a second output clock signal;
the first and second delay amounts selected to synchronize the first and second input clock signals with the first and second output clock signals, respectively; and
a duty cycle corrector configured to receive the first and second output clock signals, detect a duty cycle error in the output clock signals, and adjust at least one of the firsts and second delay amounts to compensate for the duty cycle error in the output signal, the duty cycle corrector comprising:
a third variable delay line and a fourth variable delay line, the third variable delay line configured to receive the first output clock signal and delay the first output clock signal a third delay amount to generate a reference clock signal, the fourth variable delay line configured to receive the reference clock signal and delay the reference clock signal a fourth delay amount to generate a feedback clock signal;
a first phase detector coupled to receive the first output clock signal and the feedback clock signal, the first phase detector operable to compare phases of the received signals and generate a first control signal indicative of a phase difference between the signals; and
first control circuitry operable to receive the first control signal and select the third and fourth delay amounts based on the phase difference;
a second phase detector coupled to receive the second output clock signal and the reference clock signal, the second phase detector configured to compare a phase of the respective received signals and generate a second control signal indicative of the phase difference; and
second control circuitry operable to receive the second control signal and modify at least one of the first and second delay amounts based on the phase difference.
9. A processor-based system comprising:
a processor;
a memory device coupled to the processor, the memory device comprising:
an array of memory cells;
a control circuit coupled to the array of memory cells;
a clock generator coupled to the control circuit, the clock generator comprising:
a locked loop including:
a first variable delay line configured to delay a first input clock signal a first delay amount to produce a first output clock signal;
a second variable delay line configured to delay a second input clock signal a second delay amount to produce a second output clock signal;
the first and second delay amounts selected to synchronize the first and second input clock signals with the first and second output clock signals, respectively; and
a duty cycle corrector configured to receive the first and second output clock signals, detect a duty cycle error in the output clock signals, and adjust at least one of the first and second delay amounts to compensate for the duty cycle error in the output signal, the duty cycle corrector comprising:
a third variable delay line and a fourth variable delay line, the third variable delay line configured to receive the first output clock signal and delay the first output clock signal a third delay amount to generate a reference clock signal, the fourth variable delay line configured to receive the reference clock signal and delay the reference clock signal a fourth delay amount to generate a feedback clock signal;
a first phase detector coupled to receive the first output clock signal and the feedback clock signal, the first phase detector operable to compare phases of the received signals and generate a first control signal indicative of a phase difference between the signals; and
first control circuitry operable to receive the first control signal and select the third and fourth delay amounts based on the phase difference;
a second phase detector coupled to receive the second output clock signal and the reference clock signal, the second phase detector configured to compare a phase of the respective received signals and generate a second control signal indicative of the phase difference; and
second control circuitry operable to receive the second control signal and modify at least one of the first and second delay amounts based on the phase difference.