Issues with resistor value variation

[srivatsan]

Resistor value variation

hi guys,
i have a resistor in my startup circuit. it seems that the value of the resistor after fab will be ±25% or more. (The art of analog Layout and so on). When I simulated with such a deviation. I had a 50% increase in current and 20 decrease in current (appropriately).

Now I wanted to know whether someone who has fabricated a op-amp, has really seen such deviations? If so, what did you do for adjusting the rest of the circuit?

reply. thanks in advance.
srivatsan

 

[flatulent]

Re: Resistor value variation

Can you use ion implantation? This will keep the tolerance down. Can you increase the physical size? This will decrease the effects of etching tolerance.

 

[sunking]

Re: Resistor value variation

if the fundry is good, it can control its value of Res. in +-10% or so.
If you want a right value of current, you can trimming the Res.

 

[srivatsan]

Re: Resistor value variation

I am using MOSIS AMIS C5N run. So, I have no control in choosing a process.

I am not sure about trimming resistors. Is it fabricable in the above process?

Reply. Thanks in advance.

srivatsan

 

[sunking]

Re: Resistor value variation

Dont worry about it.
it is fabricable in the above process.

And you can contact your fundry

 

[tlihu]

Resistor value variation

One way is to have some metal contacts for metal change. Trimming is another way and you may need some extra circuits.

 

[ArchAngel]

Re: Resistor value variation

if the fundry is good, it can control its value of Res. in +-10% or so.
If you want a right value of current, you can trimming the Res.

yeah, I think the best way to get absolutely Res. is trimming.

u can also use Cr-Si as resistor, get a Res. about 10%