Question

An 8- bit counter type ADC is operating at 1 MHz clock frequency. The full scale output voltage of DAC (in built with ADC) is 2.55 V. Determine the digital equivalent obtained for $V_{in}=1V$. The op-amp comparator used in the circuit has $V_T=6.1mV$

• A. ${\left(01100101\right)}_2$
• B. ${\left(11100101\right)}_2$
• C. ${\left(01101101\right)}_2$
• D. ${\left(11011011\right)}_2$

Answer 1

The correct option is A

${\left(01100101\right)}_2$

(a)
Step size = $\frac{V_{FS}}{2^n-1}=\frac{2.55}{255}=0.01$Volt

To switch off the clock and produce end of conversion signal the DAC should produce the voltage of

$V_{in}+V_T=1+6.1\times {10}^{-3}=1.0061V$

$Numberofsteps=\frac{V_{in}+V_T}{stepsize}=\frac{1.0061}{0.01}=100.61\approx 101$

Output binary =${\left(01100101\right)}_2$