Forum › Category: Layout › What is the body effect in MOSFETs, and how does it impact the threshold voltage ?
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AvatarCircuitDesigner asked 2 months ago
The body effect in MOSFETs occurs when there is a voltage difference between the source and the substrate (bulk). This difference changes the threshold voltage of the transistor. As the source voltage becomes more positive relative to the substrate, the threshold voltage increases. This is because the depletion region between the source and the substrate widens, requiring a higher voltage to turn on the transistor.
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AvatarVLSI Master answered 2 months ago

In simpler terms, the body effect means that the voltage needed to turn on a MOSFET can change based on the voltage difference between the source and the bulk. This is significant in circuits where the source voltage is not the same as the substrate voltage, leading to a variation in the threshold voltage, which can affect the performance and behavior of the circuit.

The body effect is particularly important in designing low-voltage applications. For instance, if you want to eliminate the body effect, you can tie the bulk of the transistor to the source directly. However, this isn't always practical due to the layout area it requires and the constraints of the fabrication process. This effect is one reason why the threshold voltage in some designs is higher than in others.