working of chopper....problem

The manufacturers' data sheets do a good job of explaining it. (I assume you're talking about a chopper amplifier) Basically, the inputs are shorted, and a capacitor is charged to the value of residual offset voltage; then the inputs are connected to the signal and the offset value on the capacitor is subtracted from that.

I have come across an RF millivoltmeter that used a proper mechanical chopper - like a sealed relay that buzzed all the time. Basically the RF was applied to a special diode that produced pico-amps of current at millivolts. The chopper then switched this DC on and off which produced AC which was amplified with a high gain AC amplifier. Its output was then rectified and fed the meter.
Frank

how to collect particular datasheet for any component...can u suggest me any site.....thank you

Honestly speaking, although the other contributor where able to imagine a possible meaning of the original question, I'm not yet sure, to which kind of "chopper" the question refers, particularly because it's posted in the RF forum. How about starting a thread with a clear question?

Ah, I didn't even notice this original post was from the RF forum. If you're talking about an RF chopper, forget about what I said.

i m sorry for my inconvenience to you....actually i was talking about AC & dc chopper....used in POWER electronics.....now clear?