# Rail-to-Rail Operational Amplifier

**URL:** <https://forum.core-electronics.com.au/t/rail-to-rail-operational-amplifier/14846>\
**Category:** Schematics & PCBs\
**Created:** [13 August 2022 20:00 UTC](https://forum.core-electronics.com.au/t/rail-to-rail-operational-amplifier/14846 "2022-08-13T20:00:00Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Benedick209316](https://avatars.discourse-cdn.com/v4/letter/b/fbc32d/32.png) [@Benedick209316](https://forum.core-electronics.com.au/u/Benedick209316)\
**Post date:** [13 August 2022 20:00 UTC](https://forum.core-electronics.com.au/t/rail-to-rail-operational-amplifier/14846/1 "2022-08-13T20:00:00Z")

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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.

Thank you all for your reply.

 ![r2r](https://canada1.discourse-cdn.com/flex028/uploads/core_electronics/original/2X/a/ad4fa9aa610deb86ed3792e74bd341265eeb088d.jpeg)

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**Author:** ![Robert93820](https://avatars.discourse-cdn.com/v4/letter/r/ac91a4/32.png) [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)\
**Post date:** [13 August 2022 22:51 UTC](https://forum.core-electronics.com.au/t/rail-to-rail-operational-amplifier/14846/2 "2022-08-13T22:51:42Z")

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Hi Benedick  
Could be a bit beyond hobby level.  
Cheers Bob

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**Author:** ![Trent5487676](https://yyz2.discourse-cdn.com/flex028/user_avatar/forum.core-electronics.com.au/trent5487676/32/4583_2.png) [@Trent5487676](https://forum.core-electronics.com.au/u/Trent5487676)\
**Post date:** [15 August 2022 06:46 UTC](https://forum.core-electronics.com.au/t/rail-to-rail-operational-amplifier/14846/3 "2022-08-15T06:46:09Z")

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Hi Benedick,

Welcome to the forum 🙂

This is well in the deep end of analog electronics so I don’t have an answer for you. I can however recommend [The Art of Electronics](https://artofelectronics.net/) as a reasonably accessible textbook that I’m confident would cover how to answer your question as it also goes well into the deep end of analog circuit behaviour.