Multi-Input Op-Amp Current Mirror Layout for Low Input Offset
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Solution Overview
Problem
Multi-input operational amplifiers suffer from input voltage offset issues due to interference between input pairs, which affects the accuracy and reliability of the amplifier's output.
Innovation Solution
The design incorporates a first and second transconductor, each with specific current generation characteristics based on input voltages and reference voltages, along with current mirrors and a current source to isolate and reduce input offset, ensuring that one input pair does not affect the other.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple differential input pairs are connected to transconductors and then to a primary amplifier, then the operational amplifier can process multiple input signals, but one input pair affects the other input pair causing input voltage offset
Solution Approach 1:
The patent divides the current generation function into multiple independent transconductors, where each transconductor processes one differential input pair independently. The current mirrors then combine these independent currents without causing voltage offset between input pairs, thus segmenting the signal processing paths to eliminate interference while maintaining multi-input capability.
Solution Approach 2:
The patent introduces current mirrors as intermediary elements between the transconductors and the primary amplifier. These current mirrors convert voltage signals to current signals and combine them in a way that prevents voltage offset propagation, acting as a mediator that decouples the input pairs and eliminates their mutual interference.
2Ease of operation
If one input terminal voltage level shifts, then the output curve transitions, but this shift causes input offset affecting other input terminals
Solution Approach 1:
The patent uses current mirrors to create copies of the currents generated by each transconductor. These mirrored currents are combined in the primary amplifier, allowing the output to respond to input changes while preventing the voltage offset from propagating to other input terminals, thus copying the functional response without copying the harmful offset.
Data Source
AI summary
A multi-input operational amplifier comprises two transconductors, two current mirrors, and a current source. Each transconductor generates a current according to a corresponding voltage difference. When the voltage difference is less than or equal to zero, the current is a constant. When the voltage difference exceeds zero, the current is proportional to the voltage difference.