Re: ADC Problem
Hi.
A differential ADC has a positive (Vin+) and a negative (Vin+) analog input. These inputs require two equal drive signals that are 180° out of phase. The amplitude of each drive signal should equal the reference voltage, Vref, of the ADC to use the full dynamic range of the device. When a conversion occurs, the ADC converts only the difference between the two input signals on the Vin+ and Vin- pins. The ADC subtracts any portion of the signals that are in phase, such as noise, and these inphase signals thus disappear. The ADC adds the portion of the signals that is out of phase, which is the analog input. Thus, the amplitude of the converted signal is 2xVref.
The common-mode voltage, which you set up externally to the ADC, determines the value on which the differential analog inputs are centered. The reference level of the ADC determines the range of this
voltage. When an analog-to-digital conversion occurs, the ADC rejects this common-mode voltage.
(excerpt from EDN, June 12 2003, page 72)
So, you only have one Vref, that you set to Vref = 0.5 (in your example).
Arthur