How to make a ideal ota(Gota, Rout) ?

I just read paper "Design guidelines of CMOS class-AB output stages: a tutorial". In this paper, real output stage circuit and ideal first stage are combined to simulate.

My question is how to get the ideal OTA with two parameters: Gmota=100uuA/V and Rota=1M Ohm.

I have tried vccs(Gmota) with resistor(Rota). But I get wrong bode plot when doing stb analysis.

Can someone help me, thanks?

It seems that your ideal OTA is OK.

Perhaps the problem is not on your ideal OTA.

Real ideal OTA is only formed by E0. R7 is an extra load.

Dear angelote,

The first stage (ideal ota) I made with vccs and Rload has wrong stb result (no gain).

And if I replace ota with opamp (i.e., vcvs), it seems getting right dc operating point. But the bode plot still doesn't make snese.(phase margin <0)
But if I input sine wave and do transient simulation, "opamp (vcvs)+output stage" actually works with unit-gain feedback. And, the vcvs model can only represented by gain, not Gm and Rota.

So, what is the right behavioral ota model if given Gm and Rota ?

Thanks.

Hope the following link is helpful.
http://www.ecircuitcenter.com/Circuits/smps_buck_ac1/smps_buck_ac1.htm

twlin1 said:

My question is how to get the ideal OTA with two parameters: Gmota=100uuA/V and Rota=1M Ohm.

Click to expand...

I don't know much about your circuit, but I know that an OTA is a transconductance amplifier. It gives a current that depends on an input voltage (Iout=gm*Vin). This ideal behaviour is simulated using your E0(ggain).

The output voltage of an OTA depends on output load. If you use gm=100uA/V and an load of 1Mohm, the resulting voltage gain is 100. However, in your circuit, the OTA load isn't 1Mohm because it is in parallel to something else.

In OPAMPs, the first stage is an OTA, but you are trying to evaluate the output stage. I still think that the problem is not in the OTA implementation.

When you use E0(egain), R5 has no effect. Are you sure about that resistor?

I can't help you more that this becauso I don't know much about stability problems.

Good luck.