How to measure the Gm of a transconductor?

[boooser]

how to measure gm of amplifier

A Gm cell can be made by a transconductor.

By how to measure the Gm of the cell for I do not know how to measure the output current of the Gm cell?

What kind of load can be used to plot the output current?

Can you give me a testbench schmetic to measure the Gm?


Thank you very much!!

 

[sissi]

I have the same questions

 

[harrytrinh]

There are some way that I am using can measure the Gm of a transconductor .
1. Use transient: You can use negative feedback and use ideal current source to source and sink a small current and measure the differential voltage input of input differential pair. Then use Gm=(delta Iout)/ (Delta Vin). Where the dellta Iout = (Iout1-Iout2) and delta Vin=Vin1-Vin2 (Where Vini=Vpi-Vni). This method you can ignore the offset of the error amplifier.
2. Use AC: Do AC simulation then look at the operating point. See the voltage at the inputs of the differential pair and the output current (Using .op command)
Thus, Gm=Delta Iout/Delta Vin

Hope it help. Goodluck!

 

[boooser]

There are some way that I am using can measure the Gm of a transconductor .
1. Use transient: You can use negative feedback and use ideal current source to source and sink a small current and measure the differential voltage input of input differential pair.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Can you tell me this with details. Thank!

Then use Gm=(delta Iout)/ (Delta Vin). Where the dellta Iout = (Iout1-Iout2) and delta Vin=Vin1-Vin2 (Where Vini=Vpi-Vni). This method you can ignore the offset of the error amplifier.
2. Use AC: Do AC simulation then look at the operating point. See the voltage at the inputs of the differential pair and the output current (Using .op command)
Thus, Gm=Delta Iout/Delta Vin

Hope it help. Goodluck!

How to measure the dellta Iout = (Iout1-Iout2)?

I now use two way to measure the dellta Iout.
1.use capacitor load between the two out put node and measure the current through it. But different value of cap will give big different THD.
And this method can not draw the Gm vs Vid waveform though .dc analysis,
For the cap will not pass dc current.

2. connecting a resistor between the two output and then measure the current through it.

Can you tell me your ways to measure Gm vs Vid waveform. and the right way to measure the Gm and THD of a specific circuit thanks!

 

[drake]

How to measure the dellta Iout = (Iout1-Iout2)?


Then use Gm=(delta Iout)/ (Delta Vin). Where the dellta Iout = (Iout1-Iout2) and delta Vin=Vin1-Vin2 (Where Vini=Vpi-Vni)

 

[harrytrinh]

I haven't ploted Gm vs Vid before yet. I just measure Gm at some condition and I think that is enough. For 1st method I mentioned, that is ideal current source so it is very easy to do (Iout1-Iout2) . You only see the different voltage at the input of differential pair. See the picture!
For measure the output current, you could use :

.Probe I(XMi.M1) where XMi is the MOSFETs at the output.

Added after 6 minutes:

sorry, Here is the picture!

Sorry, I can not post my picture! Tell me the way to post it!

 

[boooser]

You can upload you pic by clicking the browse button
And then click add attachment button to add you file.

At last you submit the reply.

I want to see your graph. Thanks

 

[wjlzhx]

you can use spectre ,it can see the gm

 

[qutang]

I think using hspice's extract parameter can get the gm easily.

 

[harrytrinh]

here is picture!