measuring transconductance(gm)

TUBES:

transconductance is the change in the plate(anode)/cathode current divided by the corresponding change in the grid/cathode voltage, with a constant plate(anode)/cathode voltage. Typical values of gm for a small-signal vacuum tube are 1 to 10 millisiemens.

FETS:
in field effect transistors, transconductance is the change in the drain/source current divided by the change in the gate/drain voltage with a constant drain/source voltage. Typical values of gm for a small-signal field effect transistor are also 1 to 10 millisiemens.

TRANSITORS:
The gm of bipolar small-signal transistors varies widely, increasing exponentially with the emitter current. It has a typical range of 1 to 400 millisiemens. The input voltage change is applied between the base/emitter and the output is the change in collector current flowing between the collector/emitter with a constant collector/emitter voltage.
A transconductance amplifier outputs a current proportional to its input voltage.

OTA:

What are the differences? and why are the transconductance different?

i don't understand where is the difference..
transconductance is the change in o/p current wrt change in i/p voltage .
for each of the above devices the i/p and o/p method/pins(whatever u call it)
may be different . it doesn't mean the gm is different .

oh sorry i thought the (gm) would be different because of the different millisiemens from input to output

Because i thought the millisiemens (gm) is different from input to output for a tube VS OTA VS transistor VS FET

walters said:

oh sorry i thought the (gm) would be different because of the different millisiemens from input to output

Because i thought the millisiemens (gm) is different from input to output for a tube VS OTA VS transistor VS FET

Click to expand...

:shock: good thinking .. :x :x :evil:

The gm of bipolar small-signal transistors varies widely, increasing exponentially with the emitter current. It has a typical range of 1 to 400 millisiemens.

Typical values of gm for a small-signal field effect transistor are also 1 to 10 millisiemens.

Typical values of gm for a small-signal vacuum tube are 1 to 10 millisiemens.


See the bold see the difference of (gm) ? of the millisiemens why are they different?