The quantization error of an ADC such as the one in Figure 11-13 is always positive because

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The quantization error of an ADC such as the one in Figure 11-13 is always positive because the VAX value must exceed VA in order for the comparator output to switch states. This means that the value of VAX could be as much as 1 LSB greater than VA. This quantization error can be modified so that VAX would be within ±1/2LSB of VA. This can be done by adding a fixed voltage equal to ±1/2LSB (±1/2step) to the value of VA. Figure 11-37 shows this symbolically for a converter that has a resolution of 10 mV/step. A fixed voltage of +5 mV is added to the D/A output in the summing amplifier, and the result, VAY, is fed to the comparator, which has VT = 1 mV. For this modified converter, determine the digital output for the following VA values.

(a) VA = 5.022 V

(b) VA = 50.28 V

Determine the quantization error in each case by comparing VAX and VA. Note that the error is positive in one case and negative in the other


Figure 11-37

VAY Comp Sum amp VAY = VAX +5 mV EOC VAX +5 mV D/A converter 10 mV/step RESET Ten-bit counter CLOCK CLOCK


Figure 11-3

Clock Four-bit counter D C B A D/A converter Resolution = 1 V VOUT Full scale (input = 1111) 1 V 10 Input

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Digital Systems Principles And Application

ISBN: 9780134220130

12th Edition

Authors: Ronald Tocci, Neal Widmer, Gregory Moss

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