Leakage Compensation Circuit Using Replica Current Subtraction
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Solution Overview
Problem
Existing leakage compensation circuits using current mirrors suffer from inaccurate compensation due to process mismatches and can introduce additional leakage current, especially when large device sizes are used, leading to issues like spurious jitter and static phase offset in phase-locked loops.
Innovation Solution
A leakage compensation circuit employing a replica circuit, an operational amplifier, and high resistance resistors to generate a compensation current equal in magnitude but opposite in polarity to the leakage current, ensuring accurate subtraction and minimizing injected current through a highly resistive path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current mirror is used to compensate leakage current, then leakage compensation is achieved, but process mismatches cause inaccurate compensation and the current mirror introduces its own leakage current
Solution Approach 1:
The patent uses a replica circuit that copies the leakage current characteristics of the original circuit. The replica circuit is designed to match the original circuit's leakage behavior, allowing accurate compensation without using a traditional current mirror that introduces its own leakage errors
Solution Approach 2:
The patent introduces an operational amplifier as an intermediary element to transfer and control the replica leakage current. The op-amp acts as a mediator that subtracts the replica current from the original circuit node, providing accurate compensation while avoiding the direct current mirror connection that causes leakage errors
2Measurement precision
If device size is increased to reduce process mismatches, then compensation accuracy improves, but leakage current from the current mirror increases
Solution Approach 1:
The replica circuit copies the leakage characteristics without requiring large device sizes. By using the operational amplifier to transfer the replica current signal rather than directly mirroring it with large transistors, the system achieves high compensation accuracy while keeping the compensation circuit's own leakage minimal
3Reliability
If a traditional current mirror approach is used, then leakage compensation is provided, but the circuit complexity and potential for introducing additional leakage increase
Solution Approach 1:
The operational amplifier serves as an intermediary that simplifies the overall circuit architecture. Instead of complex current mirror arrangements, the op-amp-based subtractor circuit provides a more straightforward implementation that reduces complexity while improving reliability
Solution Approach 2:
The patent replaces the traditional current mirror mechanism with an operational amplifier-based current subtraction system. This substitution transitions from a direct transistor-level current copying mechanism to a more flexible voltage-controlled current source approach, reducing complexity and improving performance
Data Source
AI summary
The leakage compensation circuit includes: a replica circuit of a circuit to be compensated, the replica circuit provides a replica leakage current equal to a leakage current of the circuit to be compensated; an amplifier having a first input coupled to the replica circuit and a second input coupled to a node to be compensated; a first resistance coupled between an output of the amplifier and the replica circuit; a second resistance coupled between the output of the amplifier and the node to be compensated; and wherein the replica leakage current is subtracted from the node to be compensated.