Simple and basic opamp designs.

[saad]

Can anyone recommend me a solved example for design of given type of opamp? OR

List the steps while designing one of the opamps like this one?


Just use dummy design specifications. I can then use it for my own requirements.

Regards,
Saad

 

[skythunder]

Re: OPamp design!!

haha , I saw that you are located in Southampton, UK. And I am familiar with your OPAMP architecture, so I guess you are working on an opamp design assignment.
I got my own report which has the same topic as you want . Hope it's helpful.

PS: I studied at southampton last year

 

[skythunder]

Re: OPamp design!!

this is a single stage opamp.

Gain = gm1* ro6//r07;

GB= gm1* CL ;

Pay attention to those current mirrors, they have bad effects on DC offset and bandwidth .

 

[saad]

Re: OPamp design!!

Hi skythunder!

Thanks for your help. This infact isnt the assignment but a part of my project.

1. Can you explain how does pmos mirror add DC offset to the amplifier and affect its bandwidth? Any relation in support to that?

2. How does this offset affect the performance if opamp is to be used as "voltage comparator"?

Thanks

 

[ambreesh]

Re: OPamp design!!

the mirroring in not perfect, vds difference in the 2 PMOS.
You cannot fix the output voltage to some number, not possible.
The offset would add offset to the differential voltage required to cause the comparator to flip.
The offset would also be added by the input pair.

 

[skythunder]

Re: OPamp design!!

Hi, saad ,

to be honest, I think this structure is not so good .
There are three simple current mirrors. Vds mismatch leads to DC offset, and current mirror introduce mirror poles and zeros which affect the frequency response of the OPAMP.

I admit that the biasing cascode output stage scheme in my report is not feasible, you have to set up a practical biasing network .

By the way, at that time I was taught by professor Redman. White, he is a very nice professor. If possible ,you can choose his class--- Analog and Mixed Signal CMOS design . you may get more help .

 

[aru_vlsi]

Re: OPamp design!!

hi
can anyone suggest me the design of high performence opamp alongwith the steps involved and the specifications. i need this urgently for my project work, plz if anyone can send to aruvlsi84@gmail.com

Added after 45 minutes:

hi
can anyone suggest me the design of high performence opamp alongwith the steps involved and the specifications. i need this urgently for my project work, plz if anyone can send to aruvlsi84@gmail.com

 

[ambreesh]

Re: OPamp design!!

Read allen and holbreg for comparator design.
And the architecture has no issues, have seen enough of them working properly on silicon.

 

[Sadegh.j]

Re: OPamp design!!

I did the same project in Hspice, only the second branch from the left was not there, do you want it, because if you do, I have to go through my files.

Let me know if you do.

 

[Sadegh.j]

Re: OPamp design!!

Found the file.

 

[saad]

Re: OPamp design!!

@ambreesh
The circuit seems fine but due to its non-symmetric nature, rise and fall times at the output are not equal. How to improve it?

@skythunder
Thanks alot for ur help. U mentioned the problem of improper cascode biasing. can you help me on that??


Regards

 

[ambreesh]

Re: OPamp design!!

Do you want to have rise time and fall time same across PVT then I cannot help you. they will change.
What are the specifications for your design?
What is the reponce time you need, what is the load your comparator sees.
For what input variation do you want the ouptut to flip.
I would still suggest that you go through the comparator design in Allen holberg

 

[saad]

Re: OPamp design!!

I have comeup with a design mentioned in Allen holberg book.. but that isnt symmetric..also sensitive to temperature and process variations..

infact i m trying to make a ramp generator that uses an opamp and comparator. the frequency of triangle wave is supposed to be 1MHz

Also, i m using the comparator in class-d modulation stage. if the comparator is non-symmetric; it introduces harmonic distortion in the amplifer (which is undesirable)

if you can give me suggestions to go through with this design.. also, the design of this kind of comparator (the schematic i hve uploaded) is not in the book by "Allen holberg"

thanks

 

[abhisheksbox]

Re: OPamp design!!

for to design an op amp or any analog circuit first you hav to decide the number of poles and zeros required and the location of these poles and zeros. then take a suitable configuration of desired circuit and find its transferfunction from its small signal configuration which also depends upon the operating frequency. after this match the desired number of poles and zeroes and compair the values with the transfer function, if u find lesser pole and zeros then try to indroduce more in ur circuit with the help of capacitors and resistors avoid usin inductors and if u get more poles and zeros then try so move the undesired one far from the operating region either to infinity or to zero axis. then after some ittration u can get a crude design with some values of evey component the apply kvl or kcl on ur design and try to find out the current and match it.

 

[eric.hanyq]

OPamp design!!

It's realy a simple circuit! With CMR,range of Vout ,else as GB,SR,then you can easly caculate it...
If you want large Av,try to use cascode..

 

[starrinesss]

OPamp design!!

It's a basic circuit, and some times is no good enough for application,

 

[joe_chen]

Re: OPamp design!!

how to get the offset voltage

 

[dewabantura]

OPamp design!!

its a good beginner circuit, it will provide you with the design feeling. Straight away jumping to a large and complex circuit will make u lost.

Juz my two cents, coz i am currently designing high performance op amp.

Regards!

 

[drifterz]

OPamp design!!

this is a good basic op amp to get started.