Why is there no chapter about OTA in Razavi and Grey & Meyer?

[Jim cage]

Why isnt a chapter describing the OTA in both Razavi and Grey&Meyer?

There are chapters of OP amp but none of them discuss on the OTA.

Does anyone knows the answer?

Thanks

 

[DenisMark]

folder cascode ota

It's not true. OTA+output buffer=OPAMP. The term OTA can be applied to any of diff. stage configuration, e.g. CS with active load, telescopic, folder cascode... Their have large output resistance Rout for increase gain (A=Gm*Rout or A=(Gm*Rout)^2) and their isn't situable for drive resistive and large capacitive loads. That is why their is named as OTA. For drive resistive and large capacitive loads it's necessary to provide output buffer with low output resistance and such circuit is OPAMP.

 

[rajkumaru]

Re: OTA

Yes, denisMark is correct. Because without output buffer amplifier does not have low output resistance.

 

[leelamadhav]

Re: OTA

Even i am a bit confused.. so the telescopic/cascode opamp (and other opamps) discussed in razavi's book are OTAs... Please correct me...

 

[tandr]

Re: OTA

opamp means V input , V output ,
But ota means V input , I output , G=I/V
So , the difference is opamp 's output is a volatage signal
, but OTA is current for its' high output impendence , so If a OTA is followed
by a buffer and the buffer 's output impendece is low , it become a opamp

 

[qiushidaren]

OTA

According to the defination, OTA means "operational transconductance amplifier" which has a high output resistance.

Added after 1 minutes:

And I agree with tandr's explanation.