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Telescopic OTA Design

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raditsme

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can anybody suggest transistor sizes for the same telescopic ota for gain >80db and ubg >300MHz . I decided my current Iss be 320uA according to my power Specs etc.I did calculations for the same but my all transistors are not working in saturations for those values of W and Ls. I wasted a lot of time to tweak the design in a logical manner but could not get success. My technology is UMC 0.18um in Cadence spectre and Vdd=1.8v. please help......
 

erikl , Thanks for reply........ i had read the paper you mentioned above . But this paper do not explain all steps clearly. I followed steps mentioned in Razavi book Page hNo.300 for Vdd=1.8v and UMC=0.18um. for the Sizes and Bias voltages that i got do not satisfy to make all the transistors in saturation..it is like a mission.....how much one would tweak the design...if i do then i loss my current and all other specifications........what sud i do...is there any thesis or article which may explain all steps clearly..
 

if u are using a basic current equation i=beta*w/l*(vgs-vth)^2 to calculate w/l then the you will have problems. at 0.18u the first order eqn is not so valid. i suggest you setup a testbench ( connect a current source into a diode connected device to setup ur bias and then have a mirror device whose w and vds u can vary to keep it in saturation). this way it will give a better picture ofwhat width and length u can use for ur mirrors and cascodes.
 

raditsme said:
... the Sizes and Bias voltages that i got do not satisfy to make all the transistors in saturation ...is there any thesis or article which may explain all steps clearly
Click to expand...
Perhaps studying this thread may be helpful?
 

Thanks eriki.. i would see this method simultaneously.....
.......sud i use Gm/Id methodology to achieve my Design of Two Stage Telescopic OTA Design for above mentioned specs...?
 

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