Help in Opamp Design-task: design a buffer amplifier

[dayang]

Help in Opamp Design

Hi.all,
I need to desgin an opamp to buffer my output voltage and to drive the load (10pf and 5K ohm),the buffer opamp seemed very tough for me:
1 3.3v power supply,0.18 cmos technology
2 0.2-1.6v input and output common mode range
3 when drive the load 9bit settling time is 1us from 0.5 to 1.5v

Pls give me some advice on the OP design or give me some kind of structure or some paper on the design of this kind of OP .

Regards

 

[paulux]

Re: Help in Opamp Design

You can get the performance by optimizing a simple two stage amp with PMOS input because 0.18um is fast enough in your application.

 

[vbhupendra]

Re: Help in Opamp Design

you can use folded cascode with pmos i/p pair. as it has the moderate gain and speed more than two stage.

 

[dayang]

Re: Help in Opamp Design

you can use folded cascode with pmos i/p pair. as it has the moderate gain and speed more than two stage.

Hi,vbhupendra
my plan is to use an pmos folded cascode with a source follower,the 1st pole(pole of first stage) is dominant pole,and source follower has the 2nd pole.from the settling time requirement,the bandwith of the OP is at least 6MHz,and the cap load and res load with reduce the bandwith and eat up the phase margin,this will greatly reduce the performance of the OP,don't you think so?

 

[vbhupendra]

Re: Help in Opamp Design

y u want to have source follower ?

 

[eezou]

Re: Help in Opamp Design

folded cascode or two stage

Added after 8 minutes:

folded cascode or two stage

 

[dayang]

Re: Help in Opamp Design

y u want to have source follower ?

directly add res and cap load to the output node of folded cascode will greatly
reduce its dynamic performance,I think.

 

[Shaber_Mezbah]

Help in Opamp Design

folded cascode with N-mos input can solve problem of desired commom mode voltage