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hi, i want to make a circuit having following points

(1) it has input voltage in the range 0-20 mV

(2) it should give same voltage as applied at input upto 6 mV only i.e if i give 2 mv , output should be same (2mV) and for 5 it will give 5 and so on. but above 6 volt it should not give any output

(3) after this i have to amplify the voltage in mV to volts

i tried lots of methods but there are so many confusions while doing this as i am in my beginner stage please help me in sorting it out

Why not show us some of your ideas and attempts?

"... but above 6 volt ... "

Do you mean 6V or 6mV?

" ... it should not give any output"

Do you mean that above 6mV input the output should stick at 6mV or do you mean that the output drops back to zero?

How accurately do you need the output to follow the input before limiting?

Why can't you amplify the signal first and then limit it?

If you amplify first then limit, you can do this crudely using bjts like this (which works well at high frequencies):

or using an opamp like this:

http://www.ecircuitcenter.com/Circuits/op_limiter1/op_limiter1.htm

or a precision opamp circuit like this:

The last example can be used for very small input signals but it is still recommended to amplify the input first.

thank you for you quick response. i mean 6 millivolt. i cannot amplify before limiting because i need to calculate the values. actuually 0-6 mV is the output of Load cell. i need to save data before amplifying it. as per my requirement i have to limit the amplified out put to 3.3 v also this 3.3 v signal will be fed to the IOIO device. in short i am trying to make single circuit with multifunctionality. is it possible