Lecture18a

# Lecture18a - Lecture 18 ANALOG-TO-DIGITAL INTERFACING...

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Lecture 18. ANALOG-TO-DIGITAL INTERFACING Objectives: Topics: Describe DAC operation Describe S&H operation Find analog and digital signals Digital-to-Analog Converters Sample-and-Hold Analog-to-Digital Conversion

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Digital-to-Analog Conversion Digital input (N bits) analog output (single value) Common Algorithm: v OUT ~ V ref If N=4bits, V ref =5V Input range – from 0000 (dec.0) to 1111 (dec.15) EXAMPLE 10-bit DAC, V ref =5V, input=01 0001 0101. v OUT -?
Summing Amplifier DAC i F - + Bit = 1 - switch up Bit = 0 - switch down v OUT =-R F i F i F = sum of all input currents Which input is the MSB? D 0 -D 3 are ‘1’ or ‘0’ What is a disadvantage?

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Resistive Ladder DAC v OUT V ref A - Also known as R-2R network Output buffer (could be a voltage follower) V ref R 2R 2R 2R 2R 2R 2R RR v 0 v 1 v 2 v 3 V ref 2R 2R 2R v 3 a) 0000 v 3 =0V b) D 3 =1 (1000)
V ref R 2R 2R 2R 2R 2R 2R RR v 0 v 1 v 2 v 3 V ref 2R 2R 2R v 2 c) D 2 =1 (0100) d) D 1 =1 (0010) e) D 0 =1 (0001) N-bit converter:

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Sample-and-Hold - used for analog-to-digital conversion. Conversion takes some

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Lecture18a - Lecture 18 ANALOG-TO-DIGITAL INTERFACING...

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