I'm about to design an ADC for unipolar inputs(positive and negative) using an 80C552... A couple of questions: We know that Vref=(Vref+ - Vref-) If Vref+ = 2.5V and Vref- =-2.5V Then Vref=(2.5 - 2.5)=0 OR Vref=(2.5 - (-2.5))=5 ? What will be the value of LSB? Is is still applying the LSB = Vref/1024? Thanks for your time John
I haven't looked at the specs for your particular chip, but most onboard ADCs can only measure voltage between their supply rails, and there is a spec saying Vref- cannoit be lower than ground. If this is the case, then you must externally level shift your voltage, either with resistor, or an opamp circuit.