Question

EXERCISE 4: (30 MARKS) Given the following circuit in figure 3 of a flash analog-to-digital converter where VREF = 2.8V. Op-amp comparators Analog input Priority encoder A A 8. Parallel binary output A A A Sampling A pulses Figure 3 - Circuit of exercise 4 a) Determine the resolution of this converter. b) Determine the maximum error quantization error. c) If the sampling period is 10ms, calculate the number of bits per second bitrate) of the ADC. d) Determine the output code if the input voltage is 1 V. Justify your answer. e) The ADC is required to have a minimum resolution of 10 mV. What is the minimum number of bits needed for the ADC to provide this resolution? Justify your answer

Answer 1

Given data, KREP - 2.80 3-bit ADC a) Resolution - 2 nano. of bits. Resolution of ADC = 23 = 8. b) manimum quantizcetion erron - C A. Step size = VREF .. en? = 2.8 V = 0.35V .. marimum quantization erron = + 0.354 = t 0.1751 C) sampling period = noms from this sampling frequency afs= 1 loms fs = 10047, we know that, Bit rate - Mo = nxfs = 3x100 bps 970 = 300 bps )

d input voltage is v. arom diven data . we have concluded that Stepsize = A.0.35V From this, Input range output code 0 – 0.35V 000 0.35 -0.70 001 0.7 -1.05V 010 1.05 -hour ou 100 viu a tw750. 0675 - 2011 101 2.1. - 2.USU 110 2:45 - 2.8V 2 from above, we get oto as output for nu input This can be justified from the given figure. we know that for comparators, if vp > output = 1 » output co V SV.

- up for every op- amp is analog ill which is in. 1. No for top op- amp (let it be op- amp 1) = Veer ( 3 ) = 2.8% = 2.645V Up < VN & output = o Coutput of op- amp not digital output To for op-amp 2 - Veer rol = 2.11 Upc Un output zo foto op-amp 3 - Veep () - 9-75V Upevn → output = 0 vn for ope amp u E VREF ) = l.uv . Vpc vo → output =0 w for oſ ames a weef ( ) = 1,05V · Vp <WN → output 20 vw for opa amp 6 = VREF $) - 0.70 i Np > W > output = 1 As we are check for using priority encoder, we need not to op-ampy. The output of op- amp 6 is to "2' in the priority encoder. connected '2 in binary = 010 010 is the ourput for N analog il

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