I am trying to get a certain voltage to an voltage comparator which is made by an OPA. I wonder if that's possible to get a certain voltage in this case. I am trying to use digital potentiometer but I don't know if there is any ic deal with this case. I am trying to compare to voltages. That's why I need a certain voltage.
This "voltage" you're trying to get to compare it to? where's it source...
What's the goal?
sorry, I should make is more clear. I am using pt100 and make it work with a 16-bit ADC. I want to set up a certain temperature to 0 v. Therefore, I use LM317 to support a constant current source to get a voltage, from pt100. And then, use this voltage to compare the voltage that I intent to treat as lowest temperature, which is 0V. I use an OPA to do it, but the resistors have different torrent. I can make the output not as what I expect.
So I choose to provide a certain voltage.
What I am trying to do is providing a reference voltage to let the voltage comparator have a base line voltage.
A picture (circuit diagram) is worth a thousand words (and is less ambiguous!)...
Digital pots are for gain control in analog amplifiers, to generate a voltage you
use a DAC.
What voltage range and accuracy are you wanting. What do you mean by "OPA"?
(opamp?)
Can use a digital pot as voltage divider as well to output a reference voltage to an op amp.
that's a good idea, thank you so much. 
Office of Population Administration? Official Public Analysis?
I'm very curious, what is OPA?
Hi, I think what is trying to be said is that he has a voltage comparator made with an OPAMP, Operational Amplifier.
Tom.... 
This method works simply with Arduino code and a 10 min effort with Excel sheet.
What ever pullup or pull down resistor value you have chosen, finally calculate 2 values -> Temperature and its corresponding ADC count, that's in then your job with microsoft excel is 2 mins.
Make a graph of your table such that temperature in the x-axis and adc count in the y-axis, after a curve is plotted, right click on it and select 'Format Trendline' there you select which ever fits you. For me 'polynomial' with order 2 fits. Then apply 'apply formula on the chart'. Thus you will get the formula, apply it in the arduino coding, that it. It works
CrossRoads:
Can use a digital pot as voltage divider as well to output a reference voltage to an op amp.
Its the wrong tool for the job, high and varying output impedance and there aren't any
I can find with more than 10 bit resolution... Many DACs have an output buffer so can
drive arbitrary circuit configurations, with a digi pot you need to limit yourself to circuits
with high input impedance (not differential amplifier for instance)