Adaptive PLL Sampling Switch Timing for Charge Pump Leakage Ripple
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Phase lock loop circuits face challenges in mitigating charge pump leakage current, which causes voltage ripple and noise, especially in low voltage designs, without using thick-oxide transistors or large loop capacitors, leading to increased integrated circuit cost and area penalties.
Innovation Solution
Adaptive control of the loop filter sampling interval is implemented by using a sampling switch controller to close the sampling switch before phase comparison and open it after completion, minimizing the duration the loop filter is connected to potential leakage paths, thus mitigating charge pump leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the loop filter is continuously connected to the charge pump output to maintain stable control voltage, then loop stability is improved, but charge pump leakage current causes voltage ripple and noise
Solution Approach 1:
The patent applies periodic sampling action by closing the sampling switch only during the phase comparison interval rather than continuously. This periodic connection allows the loop filter to be refreshed with accurate charge pump output voltage samples at regular intervals, maintaining stability while preventing continuous leakage current from causing voltage ripple and noise.
Solution Approach 2:
The patent uses preliminary action by pre-charging the sampling switch before phase comparison and opening it after completion. This timing ensures the sampling switch is ready to capture the charge pump output voltage at the precise moment when phase comparison occurs, and disconnects before leakage can accumulate and cause ripple.
2Object-generated harmful factors
If thick-oxide transistors are used in the charge pump to reduce leakage current, then voltage ripple is reduced, but integrated circuit cost and area increase
Solution Approach 1:
Instead of using thick-oxide transistors to reduce leakage, the patent employs periodic sampling action that limits the duration of charge pump connection to the loop filter. By sampling only during the brief phase comparison interval and disconnecting otherwise, the system achieves low voltage ripple without requiring area-intensive thick-oxide transistors.
Solution Approach 2:
The patent introduces a sampling switch as an intermediary between the charge pump and loop filter. This switch mediates the connection, allowing charge transfer only during phase comparison while blocking leakage current during idle periods, thereby achieving low ripple without modifying the charge pump transistor structure.
3Stability of the object's composition
If large loop capacitors are used to reduce voltage ripple, then control voltage stability is improved, but integrated circuit area and cost increase
Solution Approach 1:
The patent achieves control voltage stability through periodic sampling rather than using large capacitors. By refreshing the loop filter with accurate voltage samples during each phase comparison interval and disconnecting to prevent leakage accumulation, the system maintains stability with minimal capacitor size.
Solution Approach 2:
The patent extracts the harmful leakage current effect by removing the continuous connection between charge pump and loop filter. By taking out the leakage path through timed switching, the system achieves voltage stability without requiring large capacitors to compensate for continuous charge loss.
Data Source
AI summary
Techniques for adaptively control of a loop filter sampling interval to mitigate the effects of charge pump leakage current in an apparatus including a phase lock loop circuit are provided. In one aspect, the apparatus includes a voltage controlled oscillator (VCO), a phase frequency detector (PFD) providing a phase comparison operation, a loop filter providing a control voltage to lock the VCO to a desired operating frequency, and a charge pump configured to provide an output signal to the loop filter in response to at least one of an UP pulse and a DOWN pulse. The apparatus further includes a sampling switch, coupled between an input of the loop filter, an output of the charge pump, and characterized by a sampling interval. A sampling switch controller is configured to adaptively control the width of the sampling interval in order to mitigate the effects of leakage current from the charge pump by closing the sampling switch in advance of the phase comparison operation and opening the sampling switch when the phase comparison operation is completed.