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Design >> Analog Design >> diff amp
https://designers-guide.org/forum/YaBB.pl?num=1254852155

Message started by sabawat on Oct 6^th, 2009, 11:02am

Title: diff amp
Post by sabawat on Oct 6^th, 2009, 11:02am

hello all,

when i simulated the dc opt of an diff amp(basic diff amp with diode connected load) i have seen a slightly different operating point(e.g if set 0.9v at the output it shows 970m) and the tail current is not at what i wanted to be,although individual components are designed perfectly.but when i combined transistors to form diff amp i have been facing the above mentioned prob.

can any one suggest a solution to solve the prob?

Title: Re: diff amp
Post by raja.cedt on Oct 6^th, 2009, 8:59pm

hi,
please post your schematic and show operating points...But basically it is very easy block to design, and first if some how set the tail current properly just by bias or aspect ratio of tail and then probably you may get what you want at each node.

thanks,
Rajasekhar.

Title: Re: diff amp
Post by Mayank on Oct 6^th, 2009, 9:54pm

hi,
Plz check if all your transistorss including your tail current source is in saturtation/sub-Vt region of Operation(MOS) as you intended them to be. Also check if the vds drop across 1/gm resistance of diode connected load is leaving enough vds across input MOS for it to be in saturation. And yeah, post your schematic with op points.

regards,
Mayank.