measuring transconductance(gm)

[walters]

How do u measure Transconductance?

Transconductance is the Ratio of output current to the input voltage

The Bias Current changes the Transconductance(gm) in microseconds or milliseconds in time?

The Bias Current changes the input and output impedance why and how?
(the input and output decrease as the bias current increases)

whats the difference between conductance VS transconductance?

conductances means how fast current flows?
Transconductance means ?

 

[akg]

How do u measure Transconductance?

why should we..?

Transconductance is the Ratio of output current to the input voltage

correct

The Bias Current changes the Transconductance(gm) in microseconds or milliseconds in time?

:shock:

 

[walters]

akg

Can u give me a Water analogy for "colour" in electronics ? what is "Colour water" in electronics?

What would be the water analogy for transconducance?

 

[akg]

What would be the water analogy for transconducance?

similar to a Dam , heigher the water (more pressure at bottom/voltage), more the water discharge from bottom (flow/current)

 

[walters]

Thanks alot akg

 

[audioguru]

My answers are all in the 1st few links in Google. Why didn't you look there?

How do u measure Transconductance?

Transconductance is the Ratio of output current to the input voltage

No. Transconductance is the Ratio of the change of output current to the change of input voltage. This corrected description answers your 1st question.

The Bias Current changes the Transconductance(gm) in microseconds or milliseconds in time?

Time has nothing to do with it. It is immediate. Transconductance is measured with a voltage input, not a bias current input.

The Bias Current changes the input and output impedance why and how?
(the input and output decrease as the bias current increases)

A lower impedance is required in order to pass more current.

whats the difference between conductance VS transconductance?

Conductance is a resistance. Transconductance is a voltage-controlled resistance.

conductances means how fast current flows?

No. Current flows a little or a lot at only one speed. Current is a quantity of amps. A low conductance passes a low current. A high conductance passes a high current.

 

[walters]

Thanks alot for the information and correcting me

What does (Gm) mean? they say in books that transconductance=gm

They say in my Book that Gm=time

example in my book

"The output current of an OTA is the input voltages times the transconductance"

OTA has a gm=1000us

What is the output currrent when the input voltage is 25mV

(Gm)(Vin)= I out

(1000us)(25mV)=25uA



Quote:
whats the difference between conductance VS transconductance?

Conductance is a resistance. Transconductance is a voltage-controlled resistance.


Transconductance= voltage controlled resistance
GM= Time

Does treansconductance= Gm

 

[walters]

Transconductance internet notes::

a bipolar device, transconductance is defined as the ratio of the change in collector current to the change in base voltage over a defined, arbitrarily small interval on the collector-current-versus-base-voltage curve. For an FET, transconductance is the ratio of the change in drain current to the change in gate voltage over a defined, arbitrarily small interval on the drain-current-versus-gate-voltage curve.

The symbol for transconductance is gm.

If dI represents a change in collector or drain current caused by a small change in base or gate voltage dE, then the transconductance is approximately:

gm = dI / dE

As the size of the interval approaches zero -- that is, the change in base or gate voltage becomes smaller and smaller -- the value of dI / dE approaches the slope of a line tangent to the curve at a specific point. The slope of this line represents the theoretical transconductance of a bipolar transistor for a given base voltage and collector current, or the theoretical transconductance of an FET for a given gate voltage and drain current.
Transconductance is a measure of the change in plate current to a change in grid voltage, with plate voltage held constant. The unit for conductance is the mho (siemens), pronounced "moe." Transconductance is normally expressed in either micromhos or millimhos.

Transconductance, also known as mutual conductance, is a property of certain electronic components. It is a contraction of "transfer conductance". Conductance is the flow of a current through two points when a voltage is applied as in a resistor, conductance being the reciprocal of resistance. In contrast, transconductance is the control of a current through two output points by a voltage at two input points, as if the conductance is transferred from the input points to the output points. When referring to a value, it is the ratio between these changes in voltage and current, and is written as gm:

In the world of vacuum 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.

Similarly, 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.

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.

the ratio of the tubes plate current to its grid voltage. The unit of transconductance is the "mho", which is measured in amps/volt, and is not surprisingly "ohm" spelled backwards, because one ohm is equal to one volt divided by one amp, so the unit of resistance, the ohm, is a volt/amp. Transconductance is one "figure of merit" for a tube. Higher transconductances mean higher gains and greater amplification from the tube.

 

[akg]

sorry walters , i missed a change

 

[walters]

its ok thanks for the help anyway

 

[audioguru]

They say in my Book that Gm=time

example in my book

"The output current of an OTA is the input voltages times the transconductance"

OTA has a gm=1000us

No. GM= 1000uS is one thousand micro-Siemens, not 1000us. "us" is micro-seconds and time has nothing to do with transconductance.

You and your book are confused with Gm= Greenwich mean time.
When your book says "times" it isn't talking about the time on a clock, it is talking about multiplying numbers in math.

Just look at the 1st few links in Google. Google. GOOGLE!

 

[walters]

Thanks for the information

GM= 1000uS is one thousand micro-Siemens

Siemens means how fast the current flows?

What does 1000us Siemens mean?

What does 350us Siemens mean?

What does 20us Siemens mean?

Telling how much Siemens are in current or the rate or flow of current ?

 

[Styx]

Seimens is the inverse of resistance, which if you bothered to pick up a dictorary or use google you would know by now :roll:

High Siemens means lower resistance

And hte Unit of Siemens is "G" not "s"

 

[Roff]

Seimens is the inverse of resistance, which if you bothered to pick up a dictorary or use google you would know by now :roll:

High Siemens means lower resistance

And hte Unit of Siemens is "G" not "s"

http://en.wikipedia.org/wiki/Siemens_(unit)

 

[walters]

Siemens= how much conductance

 

[akg]

Siemens= how much conductance

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]

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

now how does it differ ?

 

[walters]

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

 

[akg]

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

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.?