Output Stage Circuit Body Effect Mitigation
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Solution Overview
Problem
Conventional operational amplifier circuits using a partition supply voltage structure experience abnormal operation due to the body effect, which is typically addressed by expensive special processes for independent P-well and N-well creation, increasing manufacturing costs.
Innovation Solution
An output stage circuit is designed with a first and second transistor, each with specific terminals for input and power connections, and a current source providing a constant current to mitigate the body effect, allowing normal operation without the need for special processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a partition supply voltage structure is used to reduce power consumption, then power consumption is reduced, but the body effect causes abnormal operation
Solution Approach 1:
A third transistor (N3 or P3) is introduced as an intermediary component between the output transistor and the body terminal. This intermediary transistor acts as a buffer that isolates the body effect influence while maintaining the half-supply voltage structure, allowing the output transistor to operate normally without direct exposure to the body effect caused by the voltage partitioning
2Reliability
If special processes for independent P-well and N-well are used to eliminate body effect, then body effect is eliminated, but manufacturing cost increases
Solution Approach 1:
Instead of using expensive special fabrication processes (independent P-well and N-well), the invention employs a simple circuit-level solution using additional standard transistors that can be manufactured using conventional CMOS processes. This replaces a costly manufacturing approach with a cheaper, more accessible alternative
3Reliability
If the gate voltage of the output transistor is significantly increased due to body effect, then the threshold voltage increases, but the output current is limited to extremely small current
Solution Approach 1:
The intermediary transistor (N3 or P3) is positioned between the output transistor and the body terminal, serving as a buffer that prevents the body effect from directly modulating the output transistor's threshold voltage. This intermediary structure maintains stable threshold voltage while preserving the ability to deliver large output currents required for driving post-stage loading
Data Source
AI summary
An output stage circuit includes: a first transistor, including a first terminal coupled to a first node, a second terminal coupled to an output terminal, a third terminal coupled to an input terminal for receiving an input voltage, and a fourth terminal coupled to a first power terminal for receiving a first voltage; a second transistor, including a first terminal coupled to a second node, a second terminal coupled to the output terminal, a third terminal coupled to the input terminal for receiving the input voltage, and a fourth terminal coupled to ground; and a current source, coupled to the output terminal for providing a constant current.