Clock Domain Alignment Circuit for Reset Pulse Calibration
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Solution Overview
Problem
High-speed clock domains in digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) face alignment challenges due to start-up phase ambiguity in clock dividers, high multiplication ratios required for clock multipliers, increased process spread, and limited timing margins as clock frequency increases, leading to misalignment and power consumption issues.
Innovation Solution
A high-speed multi-channel device with a reset launch circuit that includes a variable delay unit to align reset pulses across multiple clock domains, using a reset launch clock to synchronize and retiming the launch phase, ensuring coherent reset pulse arrival and minimizing power consumption by optimizing timing margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If clock dividers are used to generate lower frequency clocks from high frequency alignment clock signals, then clock domains can be generated, but start-up phase ambiguity occurs leading to misalignment
Solution Approach 1:
The patent applies preliminary action by performing calibration of the clock dividers before normal operation. A calibration mode is activated during power-up or initialization to pre-align all clock dividers across channels, ensuring they start in the same phase state. This preliminary calibration eliminates the start-up phase ambiguity problem that would otherwise occur during normal operation.
Solution Approach 2:
The patent implements feedback through a calibration process that monitors the phase alignment of clock dividers and adjusts their reset timing accordingly. The system observes the output phases of multiple clock dividers and modifies their reset signals to achieve synchronized operation, creating a closed-loop control system that ensures proper alignment.
2Reliability
If clock multipliers are used instead of dividers to avoid alignment errors, then alignment accuracy improves, but very high multiplication ratios are required making design difficult
Solution Approach 1:
The patent inverts the conventional approach by using clock dividers instead of clock multipliers. Rather than multiplying the reference clock frequency to achieve alignment, the system divides down the high-frequency alignment clock signals and calibrates the dividers to produce properly aligned lower frequency clocks. This inversion simplifies the design while maintaining alignment accuracy.
3Reliability
If reset signals are used for low frequency clock domains, then alignment can be achieved, but the difficulty increases as clock frequency increases due to decreased timing margin
Solution Approach 1:
The patent applies preliminary action by performing calibration of the clock dividers before normal operation. A calibration mode is activated during power-up or initialization to pre-align all clock dividers across channels, ensuring they start in the same phase state. This preliminary calibration eliminates the start-up phase ambiguity problem that would otherwise occur during normal operation.
Solution Approach 2:
The patent implements feedback through a calibration process that monitors the phase alignment of clock dividers and adjusts their reset timing accordingly. The system observes the output phases of multiple clock dividers and modifies their reset signals to achieve synchronized operation, creating a closed-loop control system that ensures proper alignment.
4Measurement precision
If clocks are distributed centrally for comparison, then alignment can be measured, but power consumption increases and path matching requirements increase
Solution Approach 1:
The patent applies segmentation by performing calibration locally at each channel or group of channels rather than centrally collecting all clocks for comparison. Each channel's clock dividers are calibrated independently using local reference signals and feedback mechanisms, eliminating the need for long-distance clock distribution and reducing power consumption.
Data Source
AI summary
Described are apparatus and methods to calibrate and align multiple high-speed clock domains. A system includes at least two clock domains, a launch circuit connected to each of the at least two domains, and a calibration circuit. Each clock domain including a resettable device having a local reset retime clock. The launch circuit aligns a reset pulse with the local reset retime clock by using a launch clock from one of the domains, where the reset pulse is incoherent with respect to the domains, adjusts a delay of the launch clock to control a launch time of the reset pulse, and sends the reset pulse based on the delayed launch clock. The calibration circuit samples a local reset retime delayed clock to generate a readback signal. The launch circuit and the calibration circuit iterate through selected delays until safe arrival timing is indicated from each readout.