Recyclic folded cascode

[simplsoft]

Hi

I have gone through a research article for flicker noise reduction Its mentioned in that research paper that recycling folded cascode reuse current and enhances transconductance saves power. Can some one help me in understanding how current is resused.

Thanks

 

[simplsoft]

Anyone who can help me? how current is reused?

 

[frankrose]

Probably the article should explain how it works or the references at the end. I think it is a created name by the writer, however I haven't seen this architecture before. Maybe it would have helped if you had shared the article too.

 

[Dominik Przyborowski]

There is a big number of articles on the RFC (this architecture is already 10 years old).
Consider IN+ → OUT- path. You can see that source of M5 is a summing point of two signal currents - main one from the MA1 transconductor and reused one from MB2, mirrored by MB3-MA3 current mirror. So, the total transconductance is Gm=gm_MA1+K·gm_MB2. The advantage of RFC over FC is as following.

Suppose the same current consumption and DC OPs - the gm of every device is then easily scaled with current.
The FC has M1 input device biased with 3·Ib and M3 with 4·Ib (total current is 8·Ib). The transconductance is equal to 3·gm (gm is a transconductance of mosfet biased with current Ib).

Now, consider the RFC with MA1/MB1 ratio equal to 2/1; K=3 and MB1 current set to Ib (the RFC current is the same as FC).
Now Gm=2·gm+3·gm=5·gm, which is 67% higher then for FC.

Of course, there is a trade-off between various parameters so in the real design you would obtain different numbers.

 

[simplsoft]

Consider IN+ → OUT- path. You can see that source of M5 is a summing point of two signal currents - main one from the MA1 transconductor and reused one from MB2, mirrored by MB3-MA3 current mirror. So, the total transconductance is Gm=gm_MA1+K·gm_MB2. The advantage of RFC over FC is as following.

Suppose the same current consumption and DC OPs - the gm of every device is then easily scaled with current.
The FC has M1 input device biased with 3·Ib and M3 with 4·Ib (total current is 8·Ib). The transconductance is equal to 3·gm (gm is a transconductance of mosfet biased with current Ib).

Thankyou for your reply. This reuse term I cant understand. How is it reused because the current in MB2 is 0.5IB flowing into the path of MB3 and mirrored to ma3. where is it reused aagain.? It is used for the first time.

Is this enhanced gm going to reduce noise?