Offset voltage in op-amps (Amplifiers #8)

There's a pin called OFFSET. What's it for? Why is it important for op-amps to have an adjustment for the offset voltage? Let's design some circuits that correct for the offset error.

Aaron Danner is a professor in the Department of Electrical and Computer Engineering at the National University of Singapore.

Video filmed and edited by Cheryl Lim.
@randomcheryl

[GOLDN]

this is one of the best analog circuit videos I ever watched

[Hgkbukk]

These are really educational, but I was really hoping you'd release the next video in your 10 - Oscillators series.
Those are the most interesting ones!

[jimzweighaft]

Given how important amplification is electronics, this video and others like it should be required for all EE students.

[arizali_]

Thank you 👏. You made me remember a lot of things that I learned at school years ago and forgot because I didn't use them.

[JohnnyJohnson]

absolutely terrific videos and explanations. Very well presented and so easy to understand. Thank you!

[comeflywithme]

Great job in explaining. Keep it up. Thank you.

[vahagnmelikyan]

When you say applying zero voltage to the inverting and non inverting inputs at 16:17, you mean making a short circuit between them, or not attaching anything to them?

[mohaaabdi]

sir you have explained it very well, thank you

[chococookie]

Thank you professor, that was very helpful

[ivolol]

Given that almost no modern opamps include offset null pins and even many you'd want to use are in dual packages which also has no offset functionality, it'd be nice to include some other designs for fixing offset "externally". Every time I see this problem taught about, it's always only in relation to a single opamp that includes those pins whereas I'd find in most practical cases other design considerations mean I can never use such an 'old' opamp with the 'academic' fix available.

[karkigann]

I built some active crossovers for my stereo system. They used a generic op-amp and I upgraded to the AD 712 high-speed, bi-FET op amp. Far lower noise than even the "upgrade" of the TL 0072. Biggest difference? The AD 712 was laser trimmed each chip to achieve a zero offset. DEAD QUIET!

[pir]

I have a preamp and buffer to design for an audio preamplifier, the choice was for a TL072, but realistically two TL071s would be better, giving better component placement.

The offset null components would add to the real estate use i have and to be honest i need as much space as is possible due to the main amplifying devices being vacuum tubes, heat constraints and EMI, there are smps boost, voltage inverter, smps buck circuits so space needs to be thought out carefully wasting as little as possible.
Then i thought the TL071 ics should be fine leaving offset null alone, i'll be running them on +-10Vdc regulated from 12Vdc after the inverter the negative will be just over 11Vdc, so regulated to 10Vdc for a signal window of 20pk(10vpk-pk) more than enough for a preamp to avoid clipping.
Any offset dc and people need to understand the offset controls dc leakage at the opamp output, will be blocked by a dc blocking cap input and output.

As for dc bias shifts due to offset the signal window is large and i see no problems in any bias shifts, this is for guitar and without any specialised equipment to monitor the signal i doubt anyone would know.

The TL072 has no function to null the dc offset and there is no reason why two TL072 ics could not be used instead anyway, both are 8 pin dip or soic so8.

Were i designing a piece of medical equipment or a radio telescope then i'd use the offset control but for a mid to low fidelity audio amplifier i see no issues.

I just have to regularly convince myself of this.

[erikw-uy]

Chopper op-amps are another way to remedy the offset problem. But only for slow signals.

[johnwilson]

It looks like the offset voltage only affects the DC signal processing. If I were for example designing an audio amplifier then it seems like the offsets would get destroyed by any coupling caps. Is this true in general? can I mostly ignore offset voltage if I am not depending on accurate DC levels? I still get the same AC gains and bandwidths right?

[SHREYASHSONI-nd]

what to do if offset null pin is not there in the IC. For example, in LM358 IC offset null pins are not there.

[vahagnmelikyan]

I have dual op amp lm358, but when I connect my metering prob to output and the other probe to negative ground source without anything attached(no resistors attached) it shows full vcc voltage. Wasn't it supposed to be zero or close to zero volts? And when I do the same thing on the other outlet of op amp (since it's dual op amp) I get 0.0011v something like that. Aren't they supposed to be both zero?

[CLAUDE-jt]

What does 'hook the wiper to the minus VCC' means, which voltage dose VCC stands for? I'm confused, help me out please.

[ashkananisi]

How we can fix offset voltage in single supply op amp circuits?

[vahagnmelikyan]

Is there a minimum voltage difference required for op amp to give any signal? I'm trying to make 0.003v difference voltage (using metering device shows 0.003v between two points of input voltages) into 3v output. So far no success. I used formulas vout=Rf/R1×(V2-V1). My vout is 3v, V2-V1=0.003V, R1=1, 000ohm, So
Rf/1kohm=3÷0.003
Rf/1, 000=1000
Rf=1, 000, 000ohm.
I used two 1k resistors for both inverting and non inverting, and two 1million ohm. So far no results, the output shows close to 5v vcc when I use metering device connecting one prope to output, the other probe to negative ground, and when I connect to positive instead of ground I get 0.5v something like that... I was supposed to have 3v or something near that number.