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johndoe
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What is stack effect in cmos design and how would it affect the threshold voltages?
Stack Effect in CMOS Design: Threshold Voltage Impact
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Discussion Overview
The discussion centers around the concept of stack effect in CMOS design, particularly its impact on threshold voltages in the context of stacked NMOS transistors. Participants explore how the arrangement of transistors affects their electrical characteristics, especially during operation in circuits like NAND gates.
Discussion Character
- Technical explanation
- Homework-related
- Conceptual clarification
Main Points Raised
- Some participants describe the stack effect as involving two or more transistors in series, specifically referencing a CMOS inverter with stacked NMOS transistors.
- It is proposed that the threshold voltage (Vt) of the top NMOS transistor increases when the bottom NMOS is turned on, due to the source voltage (Vs) being at a higher voltage than its body.
- Questions are raised about whether the stack effect on Vt occurs only when the bottom NMOS is active, indicating a conditional relationship between the states of the transistors.
- One participant seeks clarification on the application context of the stack effect, specifically mentioning its relevance to a two-input NAND gate configuration.
- There is a suggestion that if the bottom NMOS is off, the top NMOS would be grounded, implying that the stack effect would not influence Vt in that scenario.
Areas of Agreement / Disagreement
Participants express uncertainty about the conditions under which the stack effect influences threshold voltages, with no consensus reached on the specifics of its impact in different operational states.
Contextual Notes
Participants do not fully explore the implications of body effect or other factors that may influence threshold voltage beyond the immediate discussion of the stack effect.
Who May Find This Useful
This discussion may be useful for individuals interested in CMOS design, particularly those studying the effects of transistor stacking on circuit performance and threshold voltage behavior.