Need step by step guide for designing a balanced OTA

ota design

Hi

I am a beginner of analog circuit design
I like to learning by example but in a book don't have an example
for design a balanced cmos ota.

so, if I want to design a cmos balanced OTA.

I want to know that which paramter is most importance
such as gain , speed, power consumption , or anything ?
and each parameter have any effect to each other ?
such as
- increase gain but decrease speed..

and could you please to guide me a step by step to design a balance OTA..

because i want to know how to set an aspect ration of each mos in a circit ?

best regardly

ota design step by step

I think you might check Phillip Allen's book on p269
You can download the book from eBook forum

Re: OTA design step by step

I want to know that which paramter is most importance
such as gain , speed, power consumption , or anything ?
and each parameter have any effect to each other ?

Click to expand...

Which parameter is more important depends on the application that this amplifier will be used in , usually u will find trade-offs between the different specs and u will have to optimize ur design to achieve most if not all of the specs.

Re: OTA design step by step

these are some general steps for start:

1- if you have a limit for your power consumption, you can calculate your total allowalbe current (by knowing the value of your power supply)... if not,assume a reasonable limit, maybe around 5-10mw for 1.8v power supply

2- By writting the equations of Gain, settling time, unity-gain bandwidth and the poles of your system, you can find some limits for your currents and Gm.

3- for finding a transistor's W/L you need at least 2 of these parameters : I, Gm and Veff. so if you couldnt find 2of these from previous steps, you should start assuming some values....one of the values that can help is the Veff, which also effects your Maximum Swing and a typical value for a 1.8 power supply can be 200mv... by finding 2of these you can start calculating W/L.

4- by writting the equations you can find the relation between differet parameters, but for some help L has a considerable effect on Rds, you can increase it for more gain, but rememeber high W & L will increase the capacitances and the speed of your circuit.

5- for some constants like µC(oxide) and λ, simulation of a single transistor in your desired technology (like 0.18u or 0.13u) can help a lot, for 0.18u i usually consider an initial guess of µC(ox) = 200µ and µ(p)C(ox) = 50µ

hope it can help you for start
message me if you need more.....

Re: OTA design step by step

For proper understanding, you can use the Allen & Holberg book chapter 6 and 7. These chapter has spice code with model parameter also.
Example with solution, step-by-step is given.
You can copy and simulate the same code, which is given in chapter.
I hope........ in this way you could understand much
Thanks!

Raj