akg

u have not bothered to look at
http://en.wikipedia.org/wiki/Siemens_(unit)

walters

yea i did but i still don't really understand what transconductance is

Because tube transconductance is different than transistor transconductance VS OTA transconductance VS FET transconductance

What are the 4 transconductance differences between all these

Tube transconductace?
Transistor transconductance?
OTA transconductance?
FET transconductance?

What are the differences please?

Transconductace means transfer conductance but also means Controlled conductance

akg

now how does it differ ?

walters

i don't know can u please tell me because i don't know

akg

You only told
"Because tube transconductance is different than transistor transconductance VS OTA transconductance VS FET transconductance"

thats y i asked , how do they differ.?

walters

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?

akg

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 .

walters

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

akg

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

walters

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?