PLL Charge Pump Damping for LC Ringing and Linearity
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Solution Overview
Problem
Conventional phase lock loop circuits suffer from non-linearity issues due to parasitic inductances and capacitances forming LC resonant loops, leading to differential non-linearity and in-band noise, which are not well understood and difficult to mitigate.
Innovation Solution
The introduction of resistors in series with parasitic inductances and capacitors in parallel with circuit elements to reduce the Q factor of LC resonant loops, along with optimizing the physical layout to minimize parasitic capacitances, effectively reduces non-linearity by minimizing ringing and current flow in these loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional PLL circuits are used without additional damping components, then the circuit structure remains simple, but non-linearity and in-band noise occur due to LC resonant loops formed by parasitic inductances and capacitances
Solution Approach 1:
The patent introduces resistors as intermediary damping components connected to the power supply rails, which mediate the harmful effects of parasitic inductances and capacitances by providing a controlled discharge path for resonant currents, thereby reducing non-linearity and in-band noise without fundamentally changing the circuit topology
Solution Approach 2:
The patent extracts and addresses the harmful LC resonant loops formed by parasitic inductances and capacitances by adding separate damping resistors that specifically target these resonant paths, separating the damping function from the main signal path components
2Manufacturing precision
If the physical layout is optimized to minimize parasitic capacitances, then non-linearity is reduced, but the design and manufacturing complexity increases
Solution Approach 1:
The damping resistors serve as intermediary elements that compensate for parasitic effects without requiring radical changes to the physical layout, providing a more manufacturable solution compared to extensive layout optimization
3Manufacturing precision
If damping components are added to reduce ringing in LC resonant loops, then non-linearity is reduced, but the number of components and circuit complexity increases
Solution Approach 1:
The damping resistors are connected to existing power supply rails, utilizing existing circuit infrastructure rather than adding completely new signal paths, thereby minimizing the increase in circuit complexity while still achieving the damping effect
Solution Approach 2:
The power supply rails serve dual functions: providing power to the circuit elements and serving as connection points for the damping resistors, thereby reducing the need for additional dedicated damping circuitry
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly improves the linearity of phase frequency detectors and charge pumps, reducing in-band noise and spurs by dampening the LC resonant loops, thereby enhancing the purity of the sinusoidal output.
Implementation Method 1
The introduction of resistors in series with parasitic inductances and capacitors in parallel with circuit elements to reduce the Q factor of LC resonant loops, along with optimizing the physical layout to minimize parasitic capacitances, effectively reduces non-linearity by minimizing ringing and current flow in these loops.
Implementation Method 2
parasitic inductances and capacitances forming LC resonant loops, leading to differential non-linearity and in-band noise
Data Source
AI summary
An electric circuit, for use in a phase lock loop circuit, the electric circuit comprising: a first circuit element, being a phase frequency detector or a charge pump; at least one LC resonant loop, the first circuit element forming part of the loop; and means arranged to reduce ringing in said at least one LC resonant loop.