Programmable Charge Pump Current Mismatch Reduction
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Solution Overview
Problem
Current charge pumps in integrated circuits face challenges in providing a large variation in charging and discharging currents while minimizing current mismatch, leading to performance issues in phase-locked loops due to limitations in programmability and additional problems like voltage drop mismatches and capacitive loading.
Innovation Solution
A charge pump design incorporating a charge pump core circuit, differential amplifier, and replica bias circuit with programmable source and sink switching circuits, where the impedance of these circuits varies based on bit signals to adjust the current output and minimize current mismatch, using a combination of PMOS and NMOS transistors and transmission gates to control current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple source and sink transistors are included in the charge pump for charging and discharging the loop filter capacitor, then the charge pump can provide larger variation in charging and discharging currents, but voltage drop mismatch between the source transistors of the replica bias circuit and the source transistors of the charge pump core circuit, as well as voltage drop mismatch between the sink transistors of the replica bias circuit and the sink transistors of the charge pump core circuit, causes current mismatch to resurface
Solution Approach 1:
The patent applies dynamics by making the impedance of source and sink switching circuits variable rather than fixed. The impedance varies based on bit signals to dynamically adjust current output levels. This allows the charge pump to provide large current variation (improving programmability) while maintaining current matching accuracy through dynamic impedance adjustment that compensates for voltage drop mismatches.
Solution Approach 2:
The patent changes the impedance parameter of switching circuits based on bit signals. By varying the impedance of source and sink switching circuits, the system can adjust current output levels while maintaining proper current matching between charging and discharging paths, thus resolving the contradiction between programmability and current matching accuracy.
2Adaptability or versatility
If programmable transmission gates are used in the charge pump core circuit to connect source and sink transistors, then current variation is enabled, but capacitive loading of control signals results in additional channel charge injection and clock feed-through problems
Solution Approach 1:
The patent extracts the problematic transmission gates from the charge pump core circuit. Instead of using transmission gates to achieve current variation, the design separates the current switching function from signal transmission, eliminating the capacitive loading effects that cause channel charge injection and clock feed-through while maintaining current programmability through alternative switching mechanisms.
3Adaptability or versatility
If the impedance of source and sink switching circuits is made variable based on bit signals, then large current variation is achieved, but circuit complexity increases
Solution Approach 1:
The patent applies universality by designing switching circuits that serve multiple functions: they act as current switches, impedance adjustment elements, and current matching components simultaneously. This multi-functionality allows the charge pump to achieve large current variation through variable impedance without proportionally increasing circuit complexity, as the same circuit elements perform multiple roles in the system.
Data Source
AI summary
A charge pump includes a charge pump core circuit, a replica bias circuit, and a differential amplifier. The charge pump core circuit includes current source and sink circuits for charging and discharging an output node of the charge pump core circuit. The current source and current sink circuits are user programmable using bit signals to adjust a bandwidth and a phase margin of a phase-locked loop (PLL) that includes the charge pump. An impedance of the replica bias circuit varies based on the bit signals. The differential amplifier and the replica bias circuit form a feedback loop that reduces current mismatch between the current source and sink circuits.