can u suggest some current amplifiers for me ah...i have to amplify 0-20mA to 0-120mA....

 

Need some better specs than that.

What kind of voltages are needed (what is the impedance of the intended load)?

How fast does the current need to be able to change.

 

200mA to a 500 ohm device at the o/p side.....
fastness of current change does not matter................
o/p open circuit voltage of 100V

 

Something like this perhaps?

 

what's M1 in this circuit...what type of mosfet

 

what type of mosfet

N-channel, with a voltage rating >100V and a low Rds(on), e.g. IRFP4668.
N.B the FET and load will have to dissipate up to 5W and 20W respectively, so both will need substantial heatsinks.
If the load has any inductive component a reverse-biased diode across it will be needed to protect the FET from voltage spikes.