Electronic – Why is higher transconductance relates to faster transistor switch

switchestransconductancetransistors

Here is a quote from this site:

…higher 'transconductance' – a measure of the performance of a
transistor – than silicon transistors. The higher the
transconductance, the faster the transistor can switch on and off.

That means higher clock frequencies can be supported, and that lower
core voltages are necessary.

The above bold marked argument shows up in Oxford dictionary under the example sentences as well:
https://en.oxforddictionaries.com/definition/transconductance :

‘The higher the transconductance, the faster the transistor can switch
on and off.’

I know that the transconductance is the slope of Iout Vin curve. The steeper the curve the higher the transconductance of the transistor. But that curve doesn't have any time axis. It seems ∆Iout/∆Vin is about DC increments doesn't have anything related with time. Or does it? How is being faster switch can be related to higher transconductance?

There is no time in the below plot(Ic Vbe are DC values since they are capital letters, they are not instantaneous):

enter image description here

Best Answer

Quite often it is the gate-source capacitance of a MOSFET that is the dominant factor on how quickly a MOSFET can be turned on or off. Quite high currents have to be injected into the gate capacitance to quickly change the gate voltage so, if the transconductance is (say) twice as much on MOSFET A than MOSFET B then, to adequately switch a particular load current, you only need to change the gate voltage by half the amount compared to MOSFET B.

This usually results in an increase of switching speed for a given current injected into the gate.