high output current, wide swing opamp

[viperpaki007]

Hi,

I need to design opamp which can deliver upto 600mA of output current, Vdd=4.2V, and peak to peak output voltage swing from 3.5V to 0.5V. I am using 1V gate oxide breakdown transistors.

I found the following circuit in [1] and authors have claimed high output current delivering ability. However, i am not able to completly understand this circuit. Few things are clear though. M9,M10, M2, M3, M7 ,M6, M11 and M12 form input differential stage. While M18 and M17 form output class AB structure. Rest of the circuit is unclear to me. Can somebody explain how the circuit works. Moreover, how i will be able to meet gateoxide break down conditions for M17 and M18 transistors.





[1] M.hassan, A combined series-parallel hybrid env-amp for env-tracking mobile terminal, IEEE journal solid state circuits, 2012

 

[erikl]

... Rest of the circuit is unclear to me. Can somebody explain how the circuit works.

Search for "Monticelli biasing", "folded mesh" and "minimum selector".

 

[Dominik Przyborowski]

Moreover, how i will be able to meet gateoxide break down conditions for M17 and M18 transistors.

For output stage it could be very hard. One of an idea is to insert diode connected fets between source and ground/vdd of output fets, but this solution could strongly limited your output current. Also You could design cascoded or double cascoded output stage, but this will probably boost your open loop gain too much and produce some problem with frequency compensation. I think, the easiest way is to use thick oxide devices as an output stage.

Why You're using 4 times higher supply voltage than nominal for technology? Is it really necessary?

 

[viperpaki007]

Hi Dominik,

Thanks for the help. My design requirement dictates that my output voltage swing should go upto 3.5V and as low as 0.5. Therefore, i need to use higher supply voltage. Even if i use a thick gate oxide transistor, i will have to use two of them in cascode. This is because thicker gate oxide transistor has breakdown voltage of 2.5V in technology. Can you give me any link for cascoded or double cascoded output stages.

regards