Charge Pump Timing Circuit for Low-Spur Phase Locking
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Solution Overview
Problem
Conventional charge pumps in phase locking systems suffer from nonlinearity due to dead zones and reference spur issues, leading to undesired noise and performance degradation.
Innovation Solution
A phase/frequency detector and charge pump design that includes a core circuit and timing circuit to generate control signals for the charge pump, enabling or disabling current branches based on phase differences between reference and input clock signals, reducing current flow and noise during phase locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an offset current is added to provide a constant current to avoid the dead zone, then the linearity of the charge pump is improved when phase-locked, but a reference spur is generated due to periodic current flow
Solution Approach 1:
The patent applies periodic action by enabling the offset current only during specific phases of the reference clock cycle rather than continuously. The offset current is activated during the first half-cycle and disabled during the second half-cycle, creating a periodic modulation that maintains linearity while avoiding continuous periodic current flow that causes reference spurs.
Solution Approach 2:
The patent implements dynamics by making the offset current configurable and phase-adjustable. The offset current's magnitude and timing can be dynamically adjusted based on operating conditions, allowing the system to optimize between linearity and reference spur suppression by controlling when and how the offset current is applied.
2Reliability
If conventional charge pump current sources are used to maintain phase-lock, then phase synchronization is achieved, but undesired noise is generated from residual current flow
Solution Approach 1:
The patent extracts and removes residual current flow from the system by implementing a current cancellation mechanism. The offset current is specifically designed to cancel out the residual current from the main charge pump current sources, eliminating the noise-generating current flow while maintaining the phase-lock function.
Solution Approach 2:
The patent converts the harmful residual current flow into a beneficial cancellation effect. By intentionally introducing an offset current that mirrors and opposes the residual current, the system transforms the noise problem into a solution where the offset current serves to nullify the harmful current flow.
3Reliability
If multiple current sources are used in the charge pump to maintain phase-lock, then phase synchronization is achieved, but the chip area increases
Solution Approach 1:
The patent implements multi-functionality by designing the offset current source to serve multiple purposes simultaneously. The same offset current circuit is used for both canceling residual current (reducing noise) and providing linearity correction, eliminating the need for separate dedicated circuits for each function and thereby reducing overall chip area.
Data Source
AI summary
A phase/frequency detector for controlling a charge pump includes: a core circuit arranged to output a first phase signal and a second phase signal according to a phase/frequency difference between a reference clock signal and an input clock signal; and a timing circuit coupled to the core circuit and arranged to generate a first control signal and a second control signal for controlling the charge pump according to the first phase signal and the second phase signal, wherein only one of the first control signal and the second control signal is indicative of an enabled operation when the reference clock signal and the input clock signal are substantially identical in phase.