about resistor selection

[urian]

hi,there
i am designing a 4bit flash adc.
when considering the resistor-ladder reference,which kind of resistor should i take?
if the individual resistor should be 1k ohm ,can i use nwell resistor,for as i see,the poly-resistor has very low rec-resistor ,i.e,about 50 ohm.
any suggestion?thx

Best regards
urian

 

[erikl]

nwell resistors tend to own a rather high temperature coefficient, and especially a high voltage coefficient.
If your Design Kit allows for this option, use unsalicided poly resistor (using Salicide Blocking Layer). Its sheet resistance is in the order of several 100 to about 1kΩ/◻.

 

[urian]

hi,erikl
in the IBM_PDK manual, it says below:

The CMOS8RF (CMRF8SF) Design Manual technology currently provides eight types of resistors: OP N+ diffusion(opndres), OP P+ polysilicon (opppcres), OP RP polysilicon (oprppres), OP RR polysilicon (oprrpres),silicided polysilicon (silres), N-well (nwres), Kx (x = 2,3,4,5,6) BEOL (kxres) and L1 BEOL (l1res) resistors.We
note that the silicided polysilicon resistor is not yet qualified.

it seems that there are no unsalicided poly resistor within the PDK,so i have to choose silicided polysilicon instead? and what is OP polysilicon resistor? the comparison between these resistors shows that the L1 BEOL (l1res) resistor may be the better choice,but i dont know what this kind be.

 

[erikl]

... it seems that there are no unsalicided poly resistor within the PDK,so i have to choose silicided polysilicon instead? and what is OP polysilicon resistor? the comparison between these resistors shows that the L1 BEOL (l1res) resistor may be the better choice,but i dont know what this kind be.

I don't use this process, so I can't know. Should be documented in the IBM_PDK manual, however.

BTW: As long as your design relies on resistor ratios, the TC resp. VC don't play a big role if you match the engaged resistors closely.

 

[urian]

thanks,erikl
may be i should choose the best matching resistor