Question

1. (3 points) Review the conceptual operation of an ADC and use the given parameters to find the desired value. parameteint so e ine resourceptuele operation of an adc and use the given a. Your 8-bit ADC has Hi and Lo reference voltages of 1V and 4V, what digital number would result from sampling a 2.0V? b. Your 5-bit ADC has Hi and Lo reference voltages of O and 5V, what input voltage would yield a digital number of 12? c. Your 6-bit ADC has a Lo reference voltages of 2v. A voltage is sampled at 2.4V and the digital result is 26. What was the Hi reference voltage used by the ADC?

Answer 1

V Hi=4V Vio= 1 8-bit ADC step size of ADC - VHi-Vio 08-1 A = 0.01176 V Digital number for av is. "N" N.= 2-12 q-1 0.01176 - 0.01176 outs N = 85

I b 5 bit apo Vhi = 5v ViO FOV in 5-bit ADC possible digitala are 0 to 31 Step size of 5-bit 90c () V Hi-VLO 5-0. 5 -0.161291 31 o= 31 91 - Vin-Vio mbes (N) = Digital Numbes (N) - a Given N=12, we need to find uin 12 - Vinco 0.10129 Vin = 12 x 0.16124 TVim = 1.9355 VĮ

2 6-bit ADC Veo=av at Vin = 2.4, N= 26 step size of 6-bit ADC (A) = VHI - 96 s - Viti-2 - 63 Vin_Vi .: N= Vin - VLO 26 = 2.4-2 A. 0:4 - 0.01538V 26 .: De VHF = 2 63 V Hi = 630 +2 = 63 X 0.01538 72 VHI 22.97 V.

Answer 2

Answer a)

First some explanation:

For an 8-bit ADC, the minimum out number is 00000000 Binary and the maximum is 1111 1111 Binary (i.e. 255 decimal or FF hex). Therefore the equation that relates the ADC output to voltage input is:

Output_number = (255/3) (Vin-1) (You can verify this by putting in the two extreme values of Vin, that is 4V and 1V)

Therefore for Vin =2V, we have

Output_number =(255/3)*(2-1) = 255/3 = 85 decimal or 55 Hex

Answer b) For this 5-bit ADC the input-output relationship is

Output_number=(31/5)*Vin (the max. value in 5-bits is 11111 binary of 31 decimal)

Therefore the input voltage for an output of 12

12 = (31/5)*Vin

Vin = 60/31 = 1.935 volts

Answer c) For this 6-bit ADC the input-output relation is

output_number = (63/(VrefH - VerfL)) *(Vin-VrefL)

Substituting the given values we get

26 = (63/(VrefH-2))*(2.4-2)

0.4/(VrefH-2) = 26/63

VrefH-2 = 0.4*63/26 = 0.97

Therefore VrefH = 2.97 volts or almost 3V

Answer d)

ADATE is ADC Auto Trigger Enable bit. If we set it to 1 then auto-triggering of ADC is enabled.

The three lower-most bits of ADCSRB select the auto-trigger source as shown below. If ADCSRB is unchanged then ADC is in free-running mode, that is it will start the next conversion on its own after one conversion is over.

Bit (0x7B) Read/Write Initial Value - R | ACME RW ADTS2 ADTS1 R/ W R /W ADTSO ADCSR R/W

ADC Auto Trigger Source Selections ADTS2 ANTC1 FO+-O Triager Source Free running mode >> Analoy comparator External interrupt request o Timer/Countero compare match A Timer/Counter overflow Timer/Counter1 compare match B Timer/Counter1 overflow Timer/Counter1 capture event 1 1

Hope this helps.