Current Mirror Immunity Threshold Voltage Variation
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Solution Overview
Problem
Conventional current mirrors are affected by threshold voltage variations, leading to inconsistent current magnitudes despite constant voltage sources and channel aspect ratios, due to the sensitivity of threshold voltage to processing conditions.
Innovation Solution
A current source with a feedback circuit that includes multiple MOS transistors and resistors, designed to increase the voltage difference between the source and gate of MOS transistors, thereby stabilizing the current magnitude by controlling the voltage difference and threshold voltage variations through negative feedback mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current mirror is used with fixed voltage source and channel aspect ratio, then current magnitude should be consistent, but threshold voltage variation causes current inconsistency
Solution Approach 1:
The patent employs a feedback circuit that includes a second MOS transistor, third MOS transistor, fourth MOS transistor, fifth MOS transistor, and resistors. The feedback circuit receives a control voltage and adjusts the voltage difference between source and gate of the first MOS transistor to compensate for threshold voltage variations, thereby maintaining consistent current output despite processing variations
Solution Approach 2:
The patent dynamically adjusts the voltage difference (VSG) between source and gate of the MOS transistor as a control parameter. By changing this voltage parameter through the feedback circuit, the system compensates for threshold voltage variations and maintains stable current magnitude
2Reliability
If feedback circuit with multiple MOS transistors and resistors is added, then threshold voltage variation impact is reduced, but device complexity increases
Solution Approach 1:
The feedback circuit uses multiple MOS transistors (second through fifth) and resistors to create a control mechanism that adjusts the voltage difference at the first MOS transistor. This feedback structure compensates for threshold voltage variations while maintaining manageable complexity through systematic transistor arrangement
Data Source
AI summary
A current mirror with immunity for the variation of threshold voltage includes raising the voltage difference between the gate and the source of a MOS in the current source, and increasing the channel length of the MOS for limiting the generated reference current.