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Rail to rail circuit simulation

ibiteee

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Rail-to-rail circuit simulation

Hi,

I want to build a full rail to rail op amp, input and output but I don't really understand what and how I should simulate it. What simulation should I use exactly, DC to see the operating point of my transistors and Transient to see the input and output, also... what would the output look like? Is there something else I am missing?

I am sorry if I'm posting this in the wrong section, I just made the account!

Thank you!
 

danadakk

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Re: Rail-to-rail circuit simulation

Are you trying to use a RRIO in a design or do an actual discrete transistor RRIO design ?



Regards, Dana.
 

d123

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Re: Rail-to-rail circuit simulation

Hi,

Maybe you meant to post in the Analog Integrated Circuit Design section. I don't know about this stuff, presumably a Bode plot (AC analysis in simulator I use) would be useful, and capacitative load plus resistive load seems a benchmark. I guess r-2-r in and out would show a small 'dead zone' at lowest and highest Vin at Vout. A range of temperature analyses are good - where hopes of success after multiple promising simulations at +27C are chewed up (or not, hopefully) by undesirable things happening at max. -C and max. +C. Max. frequency before Vout looks hideously unrecognizable. There are lots of things to check. Did you mention step input and ringing?

- - - Updated - - -

I want to add, it depends on the kind of op amp aimed for... 1.8 to 5.5V CMOS or 2.7 to 36V bipolar, JFET inputs, etc. Other stuff like uA of quiescent current at max. operating temperature may matter to you or maybe need-for-speed bandwidth will matter more than Ferrari-level guzzler of supply current. Input offset voltage and current might be interesting, too. Any crossover distortion, I think it's called, too.
 

ibiteee

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Re: Rail-to-rail circuit simulation

Hi Dana,

I'm trying to design a RRIO, and I saw some schematics and I tried to build one myself, but I'm not sure how to check if it's ok.
 

ibiteee

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Re: Rail-to-rail circuit simulation

It has two supply voltages, Vdd and Vss with 3.3V and -3.3V with CMOS.

Sorry about the bad section, I thought I was in the right one, I'll try there.

Thank you!
 

ibiteee

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Hi,

I want to build a full rail to rail op amp, input and output but I don't really understand what and how I should simulate it. What simulation should I use exactly, DC to see the operating point of my transistors and Transient to see the input and output, also... what would the output look like? Is there something else I am missing?

I want to mention that I'm using a CMOS technology with two voltage supplies Vdd and Vss with 3.3V and -3.3V.

Thank you!
 

t4_v

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If you want to design CMOS IC opamp (because it is not clear to me what are you want to do) an example list of simulations may be as follows:

specification.png

Source: https://payhip.com/b/5Srt ("Preview" button in the top right)

It is rather full list of possible simulations. It depends on the design, to fully characterize an opamp or run chosen simulations. For sure you should start with AC characteristic to verify if your opamp is stable.

I also found following materials. Maybe they will help you:
- https://www.elprocus.com/operational-amplifiers/ (especially "5 Ideal characters of an Op Amp")
- https://www.youtube.com/watch?v=dTBUeugPxjE (around 27:24 there is AC characteristic)
- https://www.youtube.com/watch?v=RM-j-zSoEOc
- https://www2.eecs.berkeley.edu/Pubs/TechRpts/2016/EECS-2016-223.pdf
- https://www.researchgate.net/publication/291521532_Design_of_2_stage_CMOS_Operational_Amplifier

For sure, as always, books on CMOS IC design are good choice as Baker or Razavi.

Please tell if you need further help.
 

ibiteee

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Can someone confirm this to me, please?

For a transient simulation, is this how my input and output(in an ideal case) should look like?

For example, my Voltage supplies are 3.3V and -3.3V, first I try using a 1V peak to peak signal and then a 3.3.

sim.jpg
 

t4_v

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For opamp design, yes but you need PGA so an opamp with programmable gain as:
- Vin = +/-1 V -> Vout = +/- 3.3 V -> gain = 3.3V/V
- Vin = +/-3.3 V -> Vout = +/- 3.3 V -> gain = 1V/V

For comparator your picture is true, except the fact that output should be a rectangle signal (not sinusoidal).
 

ibiteee

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One last thing, how do I choose what current should go thought my circuit?
 

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