Question

With the Enhancement MOSFET, when gate input voltage is zero, drain current is

• A. At saturation
• B. Zero
• C. IDss
• D. Widening the channel

Hint:

E-MOSFET Operation. Normally OFF device. Requires \(|V_{GS|>|V_{th|\) to create a channel and conduct drain current. At \(V_{GS = 0\), \(I_D \approx 0\).

Answer 1

The Correct Option is B

Enhancement-mode MOSFETs (E-MOSFETs) are constructed without a physical channel between the source and drain regions initially
A voltage must be applied to the gate (relative to the source, \(V_{GS}\)) that exceeds a certain threshold voltage (\(V_{th}\)) to induce or "enhance" a conductive channel
If the gate input voltage is zero (\(V_{GS} = 0\)), this voltage is typically below the threshold voltage (\(V_{th}\) is usually positive for n-channel E-MOSFETs and negative for p-channel E-MOSFETs)
Without a gate voltage sufficient to form the channel, no significant current can flow between the drain and source
Therefore, the drain current (\(I_D\)) is ideally zero when \(V_{GS} = 0\)
IDss is the drain current at \(V_{GS}=0\) for depletion-mode devices, which are normally "on"