Charge Pump Switching Topology for PLL Leakage Isolation
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Solution Overview
Problem
Conventional charge pumps in phase-locked loops (PLLs) experience leakage currents when disconnected from the phase detector, leading to inaccurate output frequencies of the voltage control oscillator (VCO), especially when the phase difference between input signals is small.
Innovation Solution
A charge pump design incorporating a first and second transistor, along with selectors, where the gate electrodes of the transistors are coupled, and selectors are used to selectively connect the transistors to supply voltages, ensuring no current flows when disconnected, thereby maintaining a constant control voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the charge pump is disconnected from the phase detector to maintain constant control voltage, then the control voltage stability is improved, but leakage current enters the filter and degrades the output frequency accuracy
Solution Approach 1:
The patent extracts the harmful leakage current path from the system by adding selection switches that disconnect the charge pump transistors from the filter when the charge pump is idle. This removes the source of leakage current that would otherwise enter the filter and degrade frequency accuracy, while maintaining control voltage stability through proper disconnection.
Solution Approach 2:
The patent introduces selection switches as intermediary components between the charge pump transistors and the filter. These switches act as mediators that can connect or disconnect the transistor leakage current paths from the filter, allowing the system to maintain both control voltage stability and output frequency accuracy by controlling when the charge pump is active.
2Speed
If the charge pump transistors remain connected to maintain readiness, then the response speed is improved, but leakage current continuously flows and changes the control voltage
Solution Approach 1:
The patent implements preliminary action by pre-configuring the selection switches to be in the disconnected state by default, and only connecting the charge pump transistors to the filter when needed. This allows the system to maintain reliability by preventing leakage current flow during idle periods, while still achieving fast response when the charge pump is activated through the pre-configured switch network.
3Device complexity
If conventional charge pump design is used, then the device complexity is low, but leakage current cannot be prevented and frequency accuracy deteriorates
Solution Approach 1:
The patent merges the charge pump transistors with selection switch networks in an integrated manner, combining the functionality of the charge pump with the switching mechanism. This integration allows the system to maintain low overall device complexity while effectively preventing leakage current through the combined transistor-switch structure, thereby preserving frequency accuracy.
Data Source
AI summary
A charge pump includes a first transistor, a second transistor, a first, a second and a third selectors. The first transistor includes a gate electrode, a first electrode, and a second electrode which serves as an output port of the charge pump. The second transistor includes a gate electrode, a first electrode and a second electrode, where the gate electrode of the first transistor is coupled to the gate electrode of the second transistor, and the gate electrode of the second transistor is coupled to the second electrode of the second transistor. The first selector is utilized for selectively connecting the first transistor to a first supply voltage. The second selector is utilized for selectively connecting the first transistor to a second supply voltage. The third selector is utilized for selectively connecting the second transistor to the second supply voltage.