ADC ADC types Flash ADC SAR ADC h

ADC

ADC types • Flash ADC • SAR ADC h s Fla

Notations/Interface REF+, REFAGND, DGND EOC

The Comparator: A 1 -Bit ADC INL=DNL=0 http: //www. labbookpages. co. uk/electronics/res. Networks/comparator. html • • • Widely used as a building block in many higher resolution ADCs Comparator’s resolution needs to be able to support overall high resolution ADC Without hysteresis, a 1 -bit ADC is inherently linear, but with hysteresis, it is not Hysteresis size should be less than required resolution Constant offset does not harm linearity by itself, but may cause internal signals to go out of range, 4 thus causing errors

Flash ADC

Flash ADC • N bit string DAC • 2 N – 1 comparators • Thermometer to binary encoder • Logic latch • Clock signal • Vref to the DAC Very fast: just one clock cycle 6

1 1 0 0 1 1 1 Chapter 17 Figure 24

Bubbles 1 1 0 1 0 0 1 1 1 0 1 Chapter 17 Figure 24

Bubble/sparckle removal Single bubble correction Chapter 17 Figure 26 J. G. Peterson, “A monolithic video A/D converter, ” IEEE Journal of Solid-State Circuits, vol. 14, pp. 932 -937, issue 6, 1979.

Error Sources • Comparator offset • R-string mismatch • Input capacitance • Feedthrough of input signal to reference ladder • …

SAR ADC

SAR ADC Chapter 17 Figure 05

Binary Search