ee3954_fall13_10_adc

500v i4 1875v i3 1250v 0625v i2 i1 i0 priority

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Unformatted text preview: 375V 3.750V Example: 3-bit ADC Vin I7 I6 3.125V I5 O0 2.500V I4 1.875V I3 1.250V 0.625V I2 I1 I0 Priority Encoder O1 Digital Value Out O2 Major drawback: An n-bit ADC Requires 2n-1 comparators, thus expensive Advantage: Highest speed ADC available ADC.14 ADC in 16F877 - Successive Approximation ADC Clock Oscillator Vin Successive Approximation Register Clear Data ready – End of conversion D7 D6 D5 D4 D3 D2 D1 D0 V Start DFlip Flops (Latche)s Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q0 Digital Output 8-bit D/A converter Note: for an n-bit ADC it will take n clock-cycles to find an output. ADC.15 ADC Successive Approximation – HW Flowchart Set all bits D7…D0 to ‘0’ Set D7 to ‘1’ and compare V to Vin Y V < Vin N Clear D7 Set D6 to ‘1’ and compare V to Vin Y V < Vin N Clear D6 Set D5 to ‘1’ and compare V to Vin Y Set D0 to ‘1’ and compare V to Vin V < Vin V < Vin N Clear D5 Clear D0 ADC.16 Successive Approximation Example – 4.3V – Step 1 – Bit 7 (D7) 5V 4.3V D7 = 1 (1XXX XXXX) Threshold = 2....
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