Charge Pump Dynamic Current Balancing for PLL Stability
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Solution Overview
Problem
Conventional charge pumps in phase locked loops suffer from performance deterioration due to the mismatched characteristics of PMOS and NMOS transistors, leading to unequal charging and discharging currents, which affects the stability and jitter of the phase locked loop.
Innovation Solution
A charge pump design that includes a first current source unit and a second current source unit with sub-switching current generators and a select circuit, allowing dynamic selection of currents based on the voltage level at the control node to maintain balanced charging and discharging currents, thereby compensating for the inherent differences between PMOS and NMOS transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional charge pump uses PMOS and NMOS transistors for charging and discharging, then the circuit structure is simple, but the charging and discharging currents are unequal due to transistor characteristic mismatch
Solution Approach 1:
The patent implements dynamic current adjustment by introducing a control node that responds to voltage level changes. The charge pump circuit dynamically modifies the charging and discharging currents based on real-time voltage conditions at the control node, transitioning from static fixed currents to dynamic adjustable currents that adapt to circuit state changes.
Solution Approach 2:
The patent changes the current parameters of the charge pump by detecting voltage level changes at the control node. When the voltage changes, the circuit adjusts the magnitude of charging and discharging currents accordingly, transforming fixed current parameters into variable parameters that can be modulated to achieve current balance despite transistor mismatches.
2Stability of the object's composition
If the charge pump uses fixed charging and discharging currents, then the circuit operation is stable, but the bandwidth cannot be maintained constant when division factor changes
Solution Approach 1:
The patent transforms the static fixed current operation into dynamic current modulation. The charge pump now dynamically adjusts its charging and discharging currents in response to control node voltage changes, enabling the circuit to adapt its operating characteristics while maintaining stability, thus achieving both stability and adaptability simultaneously.
Solution Approach 2:
The patent implements a feedback mechanism where voltage level changes at the control node are detected and used to regulate the charging and discharging currents. This feedback loop allows the circuit to automatically adjust current parameters to maintain constant bandwidth under varying division factor conditions, combining stable operation with adaptive performance.
Data Source
AI summary
A charge pump includes a first current source unit and a second current source unit. The first current source unit is connected between a first voltage terminal and the control node. The second current source unit is connected between the control node and a second voltage terminal. According to a phase comparing signal, the first current source unit provides a first switching current to the control node. The second current source unit includes a first sub-switching current generator, a second sub-switching current generator and a select circuit. According to a voltage level of the phase comparing signal, the first sub-switching current generator generates a first sub-switching current. According to the voltage level of the phase comparing signal, the second sub-switching current generator generates a second sub-switching current. By the select circuit, the first sub-switching current or the second sub-switching current is provided to the control node.