Loop gain of CFA Amp

Hello,

I cannot access any of the document links you have provided.

Please see if you can simply attach it to your E2E post.

Regards,

Hooman

Sorry, now I corrected the link.

I still cannot access the attachments.
You can just attach files to E2E directly. In order to do that, click "Use rich formatting" when you are posting.

Regards,
Hooman

I think now they have to be opened, I'm sorry for that.

Hello,

Here is one way to simulate the stability of the THS6022 (Current Feedback Amplifier) using TINA-TI.

I've "opened the loop" for AC using the large L and the large C. I am looking at the frequency where loop gain (Vout) is 0dB (77MHz) and reading the phase angle (86.3 degrees) to make sure there is enough phase margin (which there is according to these RF and RG values):

Here is the TINA-TI file for the simulation above:

THS6022 CFA (current feedback) Open loop Stabilty E2E Hooman 10_28_15.TSC

BTW, I have not done any verifications of the THS6022 TINA-TI model to make sure it adequately models the inverting input resistance (ri) and inverting input capacitance (Ci) which would surely affect the simulation results.

Regards,

Hooman

this is not "open loop gain" (= AVOL), is the "loop gain". Although of course it's suit for checking stability.
In this scheme, THS6022 unity gain frequency is 77 MHz?
How can you modify this method to test the stability of non-inverting circuit?

you simulate Loop Gain in TinaTI method Middlebrook / Tian? The LTspice it becomes relatively easy.

Hello,

The THS6022 simulated open loop response is Vout / I_inverting, as shown below in the plot labelled "Open_loop":

Here is the new simulation file including open loop gain / phase response of the THS6022:

THS6022 CFA (current feedback) Open loop Gain E2E Hooman 12_28_15.TSC

As you noted, in my previous post I had plotted "loop gain" to check for phase margin. I had shown the phase angle when loop gain is 0dB to be the phase margin.

I'm not sure what you mean by your comment about LT Spice. Please reiterate.

Regards,

Hooman

Your method is called "big LC", there is another method proposed by R. David Middlebrook (Tian and its modification). LTspice has built examples of using Middlebrook / Tian, with TinaTi I have not seen the implementation of this method.