Precharge Buffer Circuit for Switching-Induced Input Current Cancellation
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Solution Overview
Problem
Precharge buffer stages in signal chains exhibit excessive residual input current due to switching operations, which is a limitation for high-performance applications, especially in multiplexed and discrete time embodiments, causing perturbations and errors in signal acquisition.
Innovation Solution
A precharge buffer stage circuit is designed with an amplifier circuit, precharge and bypass switches, and a perturbation limiter circuit, along with RC networks to balance impedance and stabilize voltage, ensuring that charge injection from the precharge switch compensates for that of the bypass switch, effectively reducing the net input current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a precharge buffer stage is used to limit perturbation of the input signal source, then the signal acquisition accuracy is improved, but the residual input current due to switching operations becomes excessive
Solution Approach 1:
The patent introduces a perturbation limiter circuit as an intermediary component between the precharge buffer stage and the input signal source. This circuit actively compensates for the charge injection from switching operations by injecting equal and opposite charge, thereby eliminating the harmful residual input current while preserving the signal acquisition accuracy benefits of the precharge buffer stage.
Solution Approach 2:
The perturbation limiter circuit employs feedback mechanisms to detect and counteract the charge injection from precharge and bypass switches. By continuously monitoring the voltage at the output node and adjusting the compensation charge in real-time, the system maintains zero net charge injection, resolving the contradiction between achieving accurate signal acquisition and minimizing harmful residual current.
2Speed
If precharge and bypass switches are operated to precharge the signal chain input capacitance, then the dynamic performance is improved, but charge injection perturbations increase
Solution Approach 1:
The patent converts the harmful charge injection effect into a beneficial compensation mechanism. The perturbation limiter circuit deliberately injects charge that is equal in magnitude but opposite in polarity to the charge injected by the precharge and bypass switches. This transforms the harmful perturbation into a useful compensation that maintains signal integrity while preserving the fast dynamic response enabled by the switching operation.
3Measurement precision
If RC networks are added to balance impedance seen by bypass switch, then the charge injection compensation is improved, but the device complexity increases
Solution Approach 1:
The patent modifies the impedance parameters seen by the bypass switch through carefully designed RC networks. By adjusting the resistance and capacitance values, the circuit achieves balanced impedance conditions that enable accurate charge injection compensation. This parameter optimization allows the perturbation limiter to effectively cancel charge injection effects without requiring overly complex circuit topologies, thus resolving the contradiction between compensation accuracy and device complexity.
Data Source
AI summary
A circuit may include or may be coupled to a precharge structure to reduce or minimize a net perturbation, caused by switching, in the input source. Apparatus and techniques shown herein may enable low input current operation in a signal chain of an analog circuit by such reduction or minimization of such perturbation.