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Design >> Analog Design >> Which OTA architecture for this pipelined ADC
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Message started by kidman on Jun 11^th, 2009, 3:32pm

Title: Which OTA architecture for this pipelined ADC
Post by kidman on Jun 11^th, 2009, 3:32pm

I am to design an OTA for a pipelined ADC with 2.5 bits/stage.
These are the apparent specs of the OTA

Voltage swing = 1 Vp-p differential
Gain = 60db
GBW = 100MHz
PM=70 degrees
GM=10db
Current consumption = 300uA max

Title: Re: Which OTA architecture for this pipelined ADC
Post by jiesteve on Jun 11^th, 2009, 4:44pm

telescopic or folded cascode, depending on your supply.

Title: Re: Which OTA architecture for this pipelined ADC
Post by raja.cedt on Jun 11^th, 2009, 11:42pm

hi, you have to specify the load cap also, because you have around 300ua with this are you able to get required Ugb? And getting 70db gain also difficult in one stage but with your current spec you should bound with single stage so better use cascode with gain boosting.I understood all specification derivation but how did you come up with required gain margin?

thanks,
rajasekhar.

Title: Re: Which OTA architecture for this pipelined ADC
Post by kidman on Jun 12^th, 2009, 1:51am

1- I am using a 0.13u tech. Supply is 1.2v. Sorry for not mentioning that.

2- Actually there are still uncertainities concerning the exact value of the load cap. but I don't think it'll exceed 500fF.

3- Concerning the gain margin. I am part of a school project and making the specs isn't my task. My task is to take the specs and design the OTA.

Title: Re: Which OTA architecture for this pipelined ADC
Post by jiesteve on Jun 12^th, 2009, 8:19am

I think your supply is too low to do a cascoded one stage scheme. go with a two stage miller OTA. You will need to know what your load cap is, in order to compensate the amp.