Rail-to-Rail Operational Amplifier - Page 1
Forum section: electronics / beginners

author: Micka999
author_rank: Newbie
timestamp: August 13, 2022, 08:19:41 pm
content: Hello everyone,I’m doing project on topic rail-to-rail Op Amp, my task is to explain how each part of the circuit works. I have encountered rail-to-rail op amps and know some techniques for gm constant. But I can’t find anywhere on the internet a situation for this type of gm-constant biasing case. Can anyone explain to me which gm-constant biasing circuit it is, I know it’s a self-biased wide swing current mirror in input stage which represent constant current for polarization diff amp, but I can’t understand how gm-constant is realized.Thanks all on your replys.

author: magic
author_rank: Super Contributor
timestamp: August 13, 2022, 08:52:29 pm
content: Ask whoever created this schematic.You are right, it looks dodgy. The circuit to the left of the blue line is a double-cascoded NMOS current mirror followed by a double-cascoded PMOS current mirror. The lowest NMOS pair both have their sources grounded and their gate potentials equal, so they conduct the same current (or a ratio equal to their channel width ratio). The rest works in common gate mode.The only way this could possibly make sense is if the transistors are of different construction, perhaps (?)I'm not familiar with CMOS so can't tell if that makes sense. I think it wouldn't make sense in bipolar, but CMOS is more varied.editMaybe the current source shown on the schematic is supposed to be temperature-dependent already, its implementation being left as an exercise for the reader.

author: floobydust
author_rank: Super Contributor
timestamp: August 13, 2022, 09:54:24 pm
content: Is a grad school "project"? I'd love to get a master's degree based on Internet forum's giving me answers.OP's cross posted the same question:https://www.edaboard.com/threads/rail-to-rail-operational-amplifier.403791/#post-1739454https://forum.allaboutcircuits.com/threads/rail-to-rail-operational-amplifier.188570/https://www.hobbytalk.com/threads/rail-to-rail-operational-amplifier.610082/#post-6661727https://maker.pro/forums/threads/rail-to-rail-operational-amplifier.297553/#post-1831951

author: CaptDon
author_rank: Super Contributor
timestamp: August 14, 2022, 01:31:32 pm
content: It does seem often 'students' come here looking for easy answers rather than investigating and using the course materials bought with student loans. Years ago I was working with a friend who was taking courses at one of those 'Technical Institutes'. They spent two full weeks doing FET transconductance curves!!! It was only a two year associates course. I felt it was way to much time spent on a narrow issue when there was so much more relevant issues to study. If I was going to spend that much time on transconductance as a teacher I would have shown the relationship of plate curves for triodes and tetrodes/pentodes as some of these students will no doubt migrate toward tube amplifiers of both musical instrument and home hi-fi. About half the students I've met got their interest in electronics by playing with broken musical amplifiers or home / car stereo.

author: floobydust
author_rank: Super Contributor
timestamp: August 14, 2022, 05:10:29 pm
content: How many (grad) students are trying IC design? I've seen many thesis from developing countries that were just regurgitating a datasheet, and that qualified for a MastersOP's amplifier is already explained in that 2021/9 paperhttps://www.mdpi.com/2079-9292/10/18/2311/pdf-vor

author: magic
author_rank: Super Contributor
timestamp: August 14, 2022, 05:17:02 pm
content: Good find but still no direct answer to OP's question(I'm starting to wonder if this post is perhaps some sort of spam?)