Modular Variable Current Charge Pump Circuit Design
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Solution Overview
Problem
Phase-locked loops (PLLs) experience static phase errors due to mismatched currents in charge pump circuits, leading to clock phase-alignment issues and reduced maximum frequency, which existing charge pump designs fail to adequately address.
Innovation Solution
A modular charge pump circuit with switch circuit modules and current modules, where the number of switch circuit modules receiving current from current modules is variable, allowing for adjustable output current and reduced parasitic gate-to-drain capacitance, thereby minimizing static phase errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the number of switch circuit modules is increased to increase output current, then the output current increases, but the parasitic gate-to-drain capacitance increases causing charge coupling
Solution Approach 1:
The charge pump circuit dynamically adjusts the number of active switch circuit modules based on the required output current setting. By selectively enabling or disabling modules, the circuit adapts its total parasitic capacitance to match the operating point, minimizing charge coupling effects at each current level while maintaining the required output current capability
Solution Approach 2:
The charge pump circuit is divided into multiple independent switch circuit modules, each contributing a portion of the total output current. This segmentation allows the circuit to activate only the necessary number of modules for the desired current level, thereby reducing the total parasitic gate-to-drain capacitance compared to having all modules always active
2Adaptability or versatility
If variable current sources are used to adjust charge pump current, then current settings are flexible, but voltage headroom requirement increases causing MOSFET mismatch
Solution Approach 1:
The circuit dynamically adjusts the number of parallel current paths by enabling or disabling switch circuit modules, rather than varying the current through single MOSFETs. This approach maintains constant gate-source voltages for active current sources while changing the effective current by switching whole modules, thereby preserving MOSFET matching accuracy across different current settings
Solution Approach 2:
The circuit changes the operating parameters by varying the number of active parallel current paths instead of changing the current magnitude through voltage adjustment. This parameter change approach keeps the gate-source voltages of current source MOSFETs constant, ensuring they remain in saturation and maintain precise current matching while achieving variable output current
Data Source
AI summary
A charge pump circuit includes switch circuit modules and current modules. The number of switch circuit modules that are coupled to receive current from one of the current modules is variable. The output current of the charge pump circuit increases as more of the switch circuit modules are coupled to receive current from the current modules. The net on-resistance of the switch circuit modules decreases as more of the switch circuit modules are coupled to receive current from the current modules. Charge coupling caused by the net parasitic gate-to-drain capacitance of switching transistors in the switch circuit modules is reduced at smaller output current settings of the charge pump circuit.