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Design >> Analog Design >> Help needed on analog design issue
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Message started by limmo on Jun 22^nd, 2009, 11:03pm

Title: Help needed on analog design issue
Post by limmo on Jun 22^nd, 2009, 11:03pm

I am new to analog design. Currently doing a design project base on the circuit attached below, with all the spects included.

1) The problem now is that I do not have the skew rate given, so how to determine it?

2)I found this two design formula, Vic(max)= Vdd - Vgs3 + VT1
Vic(min)= -Vdd + Vgs1 +Vds13

How do I know what is my Vic(max) and Vic(min)??? As I do not know how to determine Vgs3 and Vds13 as well.

Title: Re: Help needed on analog design issue
Post by raja.cedt on Jun 23^rd, 2009, 1:18am

hi,
start your design with some fixed vov and vdsat (typically they will be 50mv,150mv), based on this values you allocate vds of every transistor. From the given BW spec find how much gm you want and with this gm find how much gds you want for the differential gain....So with the above design strategy you will some slew rate, from your spec i don't see any requirement to find slew rate here...

Thanks,
Rajasekhar.

Title: Re: Help needed on analog design issue
Post by limmo on Jun 23^rd, 2009, 3:02am

I am still not too sure how to assume the required values though having read some analog design related example. Can kindly provide me with more guidelines. Thank you

Title: Re: Help needed on analog design issue
Post by raja.cedt on Jun 23^rd, 2009, 4:34am

hi,
you can use razaavi as reference (see example 9.5), for voltage distribution before going to design you should think how much dc operating point at every node?your total supply is 1.8 and may be you can drop 400m at the tail node and 700m at each differential pair and pmos load such that 900m is the output dc voltage...again all these are depends on your process.

Thanks,
rajasekhar.

Title: Re: Help needed on analog design issue
Post by salty on Jun 24^th, 2009, 10:11am

Try this page, there is a good tutorial for opamp design.

http://www.zen118213.zen.co.uk/RFIC_Circuits_Page.htm