Designer’s Guide Community

samiran

Junior Member

Offline

Posts: 15

Designing an output stage!
May 20^th, 2010, 6:06am

Dear All,

I need to design an output stage (third stage) for a two-stage compensated opamp. I have gone through some related papers and text. After reading them, I have built-up some interpretations:

1. The main design specifications whilst designing the o/p stage are a) output swing, b) power dissipation (or efficiency), c) linearity (or THD). Please let me know are there anything else I need to consider.

2. My 2stage diff-amp works with 1.8 V - 0 V supply rail. So, the output stage also need to be designed among those. Which topology should I go for?

3. After inserting the third stage is it required to again compensate the whole circuit? And any other design metric dependent upon both the driver stage and output stage needs to be considered?

4. Any simple design guideline is very much appreciated.

Please help me.

Thanks & regards
Samiran

Back to top

IP Logged

Mayank

Community Fellow

Offline

Posts: 334

Re: Designing an output stage!
Reply #1 - May 20^th, 2010, 7:20pm

Quote:

The main design specifications whilst designing the o/p stage are a) output swing, b) power dissipation (or efficiency), c) linearity (or THD). Please let me know are there anything else I need to consider.

Yes, The kind of load it needs to drive & how much of it ?

Quote:

2. My 2stage diff-amp works with 1.8 V - 0 V supply rail. So, the output stage also need to be designed among those. Which topology should I go for?

Depends on the above mentioned factors + the answer.

Quote:

3. After inserting the third stage is it required to again compensate the whole circuit? And any other design metric dependent upon both the driver stage and output stage needs to be considered?

Yes, Esp. if the output driver's a gain stage.

Quote:

4. Any simple design guideline is very much appreciated.

Again there are numerous topologies ranging from a simple common drain config to complex drivers like class AB & others. Choose the one which fits your specs. There's plenty of material on output stages.

--
Mayank

Back to top

IP Logged

love_analog Senior Member Offline Posts: 101	Re: Designing an output stage! Reply #2 - May 31^st, 2010, 7:48am You need to tells us what kind of load and gain you desire. Typically you put a 3rd stage if you have to drive a low resistance and prevent that from loading the 2 stage opamp.
Back to top	loveanalog.blogspot.com The Power of Analog IP Logged

ampbuilder New Member Offline Posts: 6	Re: Designing an output stage! Reply #3 - Jun 22^nd, 2010, 2:29pm Can try Common Emitter/Source; it alone can swing to +/-sat voltage off the rail which is about 0.2V for a BJT but watch out, gain depends on load.
Back to top	IP Logged