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How to design trimming for a given circuit?

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crazy4analog

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Trimming ciruit

How to design trimming for a given circuit?
I tired to find the material to refer for trim circuit design, but could not find..i think i am not looking for right words :|

Thanks
 

Re: Trimming ciruit

As Erikl said, if you need to trim an analogue voltage use a DAC.
Other trim techniques involve reading data into a shift register at powerup, the outputs of the shift register control individual nmos transistors that short out certain options, this could be shorting out sub-resistors that make up the complete resistor in the band gap reference PTAT.
Another option is fused links. These can be Top Metal - 1 shorts across all the sub-resistors except the base resistor used in BGap above. The ones that are needed to refine the BGap performance are laer fused to open the short and activate that resistor that was shorted out. The penalty is large layout requirements for the fuse & the cost of laser fuse at wafer probe. the benefit is it is very simple to implement.

Similar to this is the eFuse, a poly fuse used to say pull up (on) an nmos that shorts out an option. If the fuse is blown, the nmos is pulled off by a weak pull down and the shorted element becomes active. This is down without using external lasers by applying enough current across the poly fuse that it melts to an open condition. This is a one-time programmable trim similar to metal ;laser fuse but can be done after the part is packaged and possible after the part is bonded to its final PCB. Down side is the complex circuitry.
 

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