What is mos transconductance?
Similarly, in field effect transistors, and MOSFETs in particular, transconductance is the change in the drain current divided by the small change in the gate/source voltage with a constant drain/source voltage.
How does current flow in saturation?
The current can still flow through the “substrate” even though the channel is pinched. The reason why it saturates is that there will be a region of higher resistance of size proportional to the Drain-Source voltage, and therefore the resistance of this region will be proportional to the same voltage.
When is the drain current still zero in a transistor?
The drain current is still zero if the gate voltage is less than the threshold voltage. For negative drain-source voltages, the transistor is in the quadratic regime and is described by equation ( 7.3.9 ). However, it is possible to forward bias the drain-bulk p-n junction.
How is the conductance of a MOSFET related to voltage?
The slope of the curves equals the conductance of the device, which increases linearly with the applied gate voltage. The figure therefore illustrates the use of a MOSFET as a voltage-controlled resistor. 7.3.2. The quadratic model The quadratic model uses the same assumptions as the linear model.
What happens to the drain current as the voltage increases?
The drain current first increases linearly with the applied drain-to-source voltage, but then reaches a maximum value. According to the above equation the current would even decrease and eventually become negative. The charge density at the drain end of the channel is zero at that maximum and changes sign as the drain current decreases.
Why is the drain current in saturation not constant?
The measured drain current in saturation is not constant as predicted by the quadratic model. Instead it increases with drain-source voltage due to channel length modulation, drain induced barrier lowering or two-dimensional field distributions, as discussed in section 7.7.