Duty Cycle Calibration Circuit for Low-Spur Clock Signals
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Solution Overview
Problem
Frequency doublers in digital circuits and frequency synthesizers often encounter duty cycle errors in input clock signals, leading to reference spurs and degraded performance, necessitating a solution for duty cycle calibration.
Innovation Solution
An apparatus comprising an input calibration circuit, a delay chain with adjustable delay units, and comparators to generate and align clock signals, ensuring a duty cycle of about 50% in the input clock signal, thereby calibrating the duty cycle and reducing phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If duty cycle calibration is performed using traditional methods, then reference spurs are reduced, but the calibration process becomes complex and time-consuming
Solution Approach 1:
The calibration process is segmented into distinct functional blocks: delay chain with multiple delay elements, first comparator for duty cycle detection, second comparator for phase detection, and control logic. Each block performs a specific function, making the overall complex process manageable and systematic while effectively reducing reference spurs
Solution Approach 2:
The patent implements feedback mechanisms where the comparators continuously monitor the clock signal characteristics and feed back control signals to the delay elements. This closed-loop feedback enables automatic calibration that reduces reference spurs without requiring complex manual intervention, resolving the contradiction between effectiveness and simplicity
2Reliability
If duty cycle calibration is performed accurately, then phase noise is reduced, but calibration time increases
Solution Approach 1:
The delay chain is pre-configured with multiple delay elements that can be selectively activated. The calibration process begins by enabling specific delay elements based on preliminary detection of duty cycle errors, allowing the system to reach accurate calibration faster without exhaustive searching, thus reducing calibration time while maintaining phase noise performance
Solution Approach 2:
The calibration system dynamically adjusts the delay element activation based on real-time signal characteristics. The control logic dynamically modifies which delay elements are enabled based on feedback from comparators, allowing the system to adapt quickly to different input conditions and achieve accurate calibration in minimal time
Data Source
AI summary
An apparatus for duty cycle calibration includes an input calibration circuit, a delay chain, a first comparator, and a second comparator. The input calibration circuit calibrates an input clock signal according to a first control signal so as to generate an input calibration clock signal. The delay chain includes a plurality of delay units coupled in series, and delays the input calibration clock signal so as to generate a first delay clock signal and a second delay clock signal. At least two of the delay units each have an adjustable delay time which is controlled according to a second control signal. The first comparator compares the input calibration clock signal with the first delay clock signal so as to generate the first control signal. The second comparator compares the input calibration clock signal with the second delay clock signal so as to generate the second control signal.