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why go for multistage amplifier?

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pforpashya

pforpashya

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Hello,

I am working on amplifier design so I had the question

In many amplifier design I see 3 stage or even 6-stage amplifier are involved.

I also seen 6-stage cascode amplifier for RF applications.

is it always necessary to go multistage for gain versus frequency matching or for other parameters such as noise figure
 

Hi,

There are a lot of discussions about multistage amplifiers in this forum.
Did you read through them?

See the box "similar threads" below.

Klaus
 

Hi,

I thought two-stage are basically only suitable for circuit internals due to weak power output capability, as they don't really have an output (buffer) stage, and > three stages are for op amps that interface with loads external to, for example, an IC; the multiple gain stages must be, I assume, based on a prior calculation as to how much gain is needed and how much gain each gain stage actually provides, and how much of an increasing nightmare the compensation begins to be for the designer as more poles and zeroes get added with each additional stage; I would guess it's not always necessary to use a multi-stage amplifier, especially looking at some IC "detailed" schematics, but couldn't answer about frequency or noise.
 

A single gain stage design has to trade gain for bandwidth.
This is technology-limited presuming you did the best
possible design. Often things other than performance
dictate technology selection.

If you need more bandwidth (albeit with a steeper "cliff"
past that point) cascading stages is the way to get
that along with the desired gain.

Show yourself - make a lineup of 1 and N stages, with
same GBWP amplifier, obtaining the same end-end gain.
Look at the Bode plot.
 

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