Multi-Phase Clock Generation for Duty-Cycle-Error-Free DDR Timing
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Solution Overview
Problem
High-speed data transmission in electronic devices is affected by duty cycle errors in clock signals, leading to jitter and inaccurate timing, which becomes more significant at higher frequencies, potentially causing clock signal failures and data transmission errors.
Innovation Solution
A clock synchronization circuit generates reference signals based on the rising edges of an external clock signal, with a 180° phase difference and half the frequency, to produce four-phase clock signals that are immune to duty cycle errors, ensuring accurate falling edge information and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed data transmission is implemented using DDR schemes, then data processing speed is improved, but duty cycle errors in clock signals cause jitter and timing inaccuracies that worsen at higher frequencies
Solution Approach 1:
A delay-locked loop (DLL) is introduced as an intermediary device between the external clock signal and the internal circuitry. The DLL receives the external clock signal, generates multiple phase-shifted versions through delay elements, and uses a phase detector to lock onto the correct phase. This intermediary structure filters out duty cycle errors from the original clock signal while preserving the timing information needed for high-speed DDR data transmission, thereby maintaining both speed and timing accuracy
Solution Approach 2:
The invention changes the phase parameter of the clock signal by generating multiple phase-shifted versions (0°, 90°, 180°, 270°) of the external clock signal. By selecting and locking onto a specific phase that is immune to duty cycle errors, the system maintains accurate timing at high frequencies. The phase detector dynamically adjusts the selected phase based on feedback, ensuring optimal timing accuracy regardless of the original clock signal's duty cycle variations
2Productivity
If clock signal frequency is increased to match improved data processing speed, then productivity is improved, but clock signal failures and data transmission errors increase due to duty cycle errors
Solution Approach 1:
The invention implements a feedback mechanism where the output of the delay elements is fed back to a phase detector that compares the phase-shifted signals with the original external clock signal. The phase detector generates feedback control signals that adjust the delay elements to lock onto the correct phase. This closed-loop feedback system ensures that even at high frequencies, the system can dynamically compensate for duty cycle errors and maintain accurate timing, preventing data transmission errors
Solution Approach 2:
The clock signal generation is segmented into multiple independent phase-shifted signals (0°, 90°, 180°, 270°) generated by separate delay elements. Each phase signal can be independently controlled and selected by the phase detector. This segmentation allows the system to divide the single clock signal into multiple usable phases, enabling high-speed DDR transmission while selecting the phase least affected by duty cycle errors, thus improving reliability at high frequencies
Data Source
AI summary
An apparatus and method for multi-phase clock generation are disclosed. One embodiment of the apparatus includes a module generating first and second intermediate signals delayed from first edges of a clock signal having a first frequency. Each of the first and second intermediate signals has a second frequency that is half of the first frequency. The first and second intermediate signals have a phase difference of 180° from each other. The apparatus also includes a first delay line delaying the first intermediate signal by a first delay amount; a second delay line delaying the first intermediate signal by a second delay amount; a third delay line delaying the second intermediate signal by a third delay amount; and a fourth delay line delaying the second intermediate signal by a fourth delay amount. The apparatus also includes a closed feedback loop for detecting and adjusting the second and fourth delay amount.