offset trim of Op-amp OPA177

Akhilesh,

The trim pins should be left unconnected if you are not trimming the offset voltage. Trimming is seldom used in modern designs and most newer op amps do not have trim pins.

The trim pins connect to internal nodes of the input stage of the op amp. Generally they connect to resistors in the load of the input stage and adjustment makes a very minor change in the current balance of the input stage. You can see a simple example on page 1 of the OPA27 data sheet.

I recommend the OPA277 as a more modern, higher performance, lower cost version of the OPA177.

Regards, Bruce

Sir, In modern design trim pins are not used So how do we achieve zero offset in newer op-amps ?

Akhilesh,

Many modern op amps have sufficiently low offset voltage that trimming is not required. Other methods involve injecting an offset voltage into the closed loop signal path. There are many ways to do this and they depend on the specific circuits being used.

Regards, Bruce

Sir may you recommend me some books/study material which can help me in understanding the advanced added features in  modern op-amps as compared to older (conventional) op-amps?

Akhilesh,

Based on the nature of your questions I recommend the book Op Amps for Everyone Design Guide by Mancini. It can be read on line on TI's web site and contains many practical details. Search for it by title. I also recommend that you read many data sheets for practical details on a variety of op amp types.

An old and reliable academic text is Analysis and Design of Analog Microcircuits by Gray and Meyer.

Regards, Bruce.

Akhilesh;

Laser trimming of an IC at the wafer level has been used in the past but new circuit techniques are giving such high performance that trimming is not usually needed, as Bruce indicated. This makes the IC production cost and selling price lower.