Block Diagram of OP-AMP
Block Diagram of Op.Amp
An op-amp is a high quality amplifier. It contains four stages, which are connected in cascaded manner.
The first stage of an op.amp is a double ended differential amplifier. This stage provides maximum voltage gain. This stage should employ a current source at the common emitter node for good common mode rejection.
This second stage is an intermediate gain stage called single ended differential amplifier. It does not require a current source in the emitter. Normally the second stage is needed only to provide some additional gain. Its input resistance should be relatively high to prevent excessive loading of the first stage.
The third stage is an emitter follower, which produces unity gain. It has high input resistance and also low output resistance. It matches the output of amplifier stage and the input of output stage.
The fourth stage is a level translator and output driver. This stage is used for preventing any undesired dc current in the load and increasing the permissible output voltage swing. Hence it supplies large output voltage or current.