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XRD8799 Datasheet(PDF) 9 Page - Exar Corporation |
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XRD8799 Datasheet(HTML) 9 Page - Exar Corporation |
9 / 23 page XRD8799 xr xr LOW POWER, 2 MSPS, 10-BIT, A/D CONVERTER WITH 8-CHANNEL MUX REV. 1.00 9 FIGURE 3. XRD8799 TIMING DIAGRAM THEORY OF OPERATION 1.0 ANALOG-TO-DIGITAL CONVERSION The XRD8799 converts analog voltages into 1024 digital codes by encoding the outputs of coarse and fine comparators. Digital logic is used to generate the overflow bit. The conversion is synchronous with the clock and it is accomplished in 2 clock periods. The reference resistance ladder is a series of resis- tors. The fine comparators use a patented interpola- tion circuit to generate the equivalent of 1024 evenly spaced reference voltages between VREF(-) and VREF(+). The clock signal generates the two internal phases, φB (CLK high) and φS (CLK low = sample) (See Fig- ure 1). The rising edge of the CLK input marks the end of the sampling phase ( φS). Internal delay of the clock circuitry will delay the actual instant when φS disconnects the latches from the comparators. This delay is called aperture delay (tAP). The coarse comparators make the first pass conver- sion and selects a ladder range for the fine compara- tors. The fine comparators are connected to the se- lected range during the next φB phase. FIGURE 4. XRD8799 COMPARATORS AIN Sampling, Ladder Sampling, and Conversion Timing Figure 3 shows this relationship as a timing chart. AIN sampling, ladder sampling and output data relation- ships are shown for the general case where the levels which drive the ladder need to change for each sam- pled AIN time point. The ladder is referenced for both last AIN sample and next AIN sample at the same time. If the ladder's levels change by more than 1 LSB, one of the samples must be discarded. Also note that the clock low period for the discarded AIN can be reduced to the minimum tS time. Auto Balance CLOCK Data Analog Input Sample N-1 Sample N Sample N+1 Auto Balance N-1 T S V IH V IL V OH V OL t F t B t R t S t DL t HLD t AP φ S B φ B φ S φ Latch Ref Ladder COARSE COMPARATOR S S B B φ φ φ φ Latch Selected Range FINE COMPARATOR VIN VIN VTAP VTAP |
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Similar Description - XRD8799 |
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