Bean Nakamura
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Posts: 24
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Hello again!
I decided to continue here instead of making a new thread since what I'm about to ask is closely related to this post.
So, I have a question regarding the frequency response of CS/Diff/2-stage op amps and I hope you don't mind answering them. I have designed the amps using the gm/Id method and have met the target for the gain specs. However, I neglected to take into account the bandwidth (BW), slew rate (SR) and phase margin (PM) when designing them. Initially, I only wanted to familiarize myself with the gm/Id technique so my main focus was gain. Now I'm wondering how to design the amps taking into consideration the said specs.
Questions:- 1)How do I go about designing the amps while also taking into account the BW,SR and PM while getting the same amount of gain? Using the gm/ID method. I looked it up online and some have suggested to plot Cgs and fT when characterizing the transistor. How does this come into play?
2)I saw some formula for the transfer function of the amps posted online. In this formula, Cdb, Cgs and Cgd are also included. Would I have to plot this as well?
3)Is there an easy/intuitive way to design according to the specs for BW, SR and PM? The formula posted online looks really intimidating. I have watched several videos on the derivation and so I am familiar of the process. However, I do wish there was an easier way to do this, if possible. How is this (designing for BW, SR, PM) done in the IC design industry?
4)I will be using the designed op-amp to make a simple 3-bit ADC, is there a rule of thumb on what gain and BW I should shoot for?
Thanks in advance!
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