Class Project: When doing hand-analysis, where do I start?

In the usual practical differential amplifier design situation, what do you start assuming? The currents? the gm? the W/L ?

If you were told , you got a 500uA budget on a certain circuit, is there a possibility where you will not use the entire 500uA for better performance? Or is more current always better performance?

Please, any experience advises surely helps. This is a WISE TALK post .. you know, I'm sure all of you experienced analog designer have got this BIBLE of FACTS which never go wrong in any design .. share them

Re: Class Project: When doing hand-analysis, where do I star

Hi aoshater,

You are generally given a spec for the design with desired gain, GBW, slew rate, max current etc. In your case you have mentined a current budget of 500 uA, are there any more constraints specified.? if not you can decied on a spec of your own by deciding on reasonable values for the above mentioned parameters...say what is the load you want to drive, what is the GBW you want, how much gain etc..
Also you have to decide on the topology ..single stage or two stage..before u start your calculations...Refer to the Analog design book by Razavi or David Johns and Ken MArtin. Book by Allen/Holberg also is good. You will get a good idea on how to start..
And as far as increasing performance by increasing current is concerned..analog is always about trade-offs..you can increase speed by increasing current but you trade-off on gain etc.
hope this helps.
kr
cmos