Dual-Charge-Pump PLL Circuit for Long-Term Jitter Suppression
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Solution Overview
Problem
Classic PLL circuits face challenges in suppressing long-term jitter without increasing circuit scale, as they struggle to manage noise from resistance elements while maintaining capacitance values within specifications.
Innovation Solution
The PLL circuit design includes a phase comparator, first and second charge pumps, a filter that removes high-frequency components, an integrator for current integration, and a voltage-current conversion circuit, allowing for independent adjustment of capacitance and resistance values without mutual influence, thereby reducing noise and jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitance value of the capacitative element Cint is increased to suppress long term jitter, then the long term jitter is reduced, but the circuit scale increases
Solution Approach 1:
The patent divides the control current generation into two separate charge pumps (first charge pump 121 and second charge pump 131) with distinct functions. The first charge pump generates control current based on phase difference, while the second charge pump generates control current based on frequency difference. This segmentation allows independent optimization of each charge pump's parameters, enabling long term jitter suppression without proportionally increasing overall circuit scale.
Solution Approach 2:
The patent transitions from a single-dimensional phase-based control to a two-dimensional control space by adding frequency difference detection. The second charge pump responds to frequency differences (including long term drift), adding a new dimension of control that addresses long term jitter without requiring proportional increases in capacitance values.
2Object-generated harmful factors
If the resistance value of the resistance element Rpr is reduced to decrease noise, then the noise is reduced, but the long term jitter suppression capability deteriorates
Solution Approach 1:
The patent segments the control current generation into two independent paths. The first charge pump path can use lower resistance values for noise reduction, while the second charge pump path compensates for long term jitter through frequency difference detection. This segmentation decouples the trade-off between noise and long term jitter suppression.
Solution Approach 2:
The second charge pump acts as an intermediary that compensates for the limitations of the first charge pump. By detecting frequency differences and generating appropriate control current, it mediates between the noise reduction achieved by lowering Rpr and the need for long term jitter suppression.
3Reliability
If the capacitance value of the capacitative element Cint is increased to suppress long term jitter, then the long term jitter is reduced, but the circuit area increases
Solution Approach 1:
The patent segments the jitter suppression function between two charge pumps with different operational characteristics. The first charge pump handles short-term phase synchronization, while the second charge pump handles long-term frequency stabilization. This segmentation allows use of smaller capacitance values overall while maintaining long term jitter suppression capability.
Solution Approach 2:
The patent changes the operational parameters of the charge pumps - specifically, the second charge pump operates based on frequency difference rather than phase difference. This parameter change enables effective long term jitter suppression with optimized (smaller) capacitance values, reducing the required circuit area.
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 configuration effectively suppresses output noise and long-term jitter within specified ranges without increasing the circuit scale, improving stability and performance.
Implementation Method 1
a filter that outputs a first current obtained by removing a high frequency component of the output current of the first charge pump
Implementation Method 2
an integrator that outputs an integrated result obtained by integrating the output current of the second charge pump
Implementation Method 3
a voltage-current conversion circuit that outputs a second current according to an integrated result of the integrator
Data Source
AI summary
A PLL circuit includes: a phase comparator for detecting a phase difference between a reference signal and a feedback signal; a first charge pump for outputting a current Ipr according to a detection result of the phase comparator; a second charge pump for outputting a current Iint according to the detection result of the phase comparator; a filter for outputting a current Iprop from which a high frequency component of the Ipr is removed; an integrator for integrating the Iint; a voltage-current conversion circuit for outputting a current Ivi according to an integrated result of the integrator; and an oscillator that generates an oscillating signal of a frequency according to a current Iro, a sum of the Iprop and the Ivi, and feeds it back to the phase comparator.