Where to put the resistor series in a hybrid 10 bits SAR ADC

[mists]

about hybrid SAR adc

I want to design a hybrid 10 bits SAR ADC that use capacitor and resistor. But I don't know where should I put the resistor series, in MSB or LSB as the attached map? Who can tell me where should I put, and why. How does this choice affect the ADC performance such as INL, DNL and SNR. thanks! [/img]

 

[bastos4321]

Re: about hybrid SAR adc

In the paper you show they use the resistors as MSB. This ensures monoticity in the MSB and improve INL.

Bastos

 

[Humungus]

Re: about hybrid SAR adc

Well, actually the resistive net is connected to a calibration capacitor of same size that the capacitive LSB (not the ADC's LSB). If your ADC were only capacitive, the last capacitor, of same size than the LSB one, should be connected to Vref-. In this case, you apply a voltage proportional to the code of the resistive DAC to add more resolution bits to your ADC.

Bastos, why do you think it is the MSB?

 

[bastos4321]

Re: about hybrid SAR adc

Well, actually the resistive net is connected to a calibration capacitor of same size that the capacitive LSB (not the ADC's LSB). If your ADC were only capacitive, the last capacitor, of same size than the LSB one, should be connected to Vref-. In this case, you apply a voltage proportional to the code of the resistive DAC to add more resolution bits to your ADC.

Bastos, why do you think it is the MSB?

Well, recently I have workd in a SAR ADC like this and the resistors were the MSB due to its monotoniticity. The area of the resistors needs to be higher than the one of the capacitor array for matching.

Bastos