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bgyan

How to design a 8-bit flash ADC using two 4-bit flash ADCs?

I thought and got this answer :
(any expertise, please check and comment about it . . . .) Explanation:
In above figure, two 4-bit ADC, a 4-bit DAC and a subtractor are used to design the 8-bit ADC.
Here, higher order 4 bits are directly determined by 4-bit ADC
and for the lower order 4-bits:
the analog equivalent of higher 4-bit is first determined using DAC
and then it is subtracted from the input signal using subtractor
(NOTE: o/p of subtractor is always less than resolution of 4-bit ADC ie. 1/16 * V(ref) of 1st ADC.
in fig. above we take V(ref)=8V so 1/16 * 8V = .5V)
Then, this o/p is fed to another ADC with reference voltage 0.5V
This gives lower order 4-bits of our final o/p
Thus, we get the 8-bit digital equivalent of an analog signal using two 4-bit ADCs..

Here,
Total conversion Time = 2 * Conversion time for 4-bit ADC + Conversion time for 4-bit DAC

Last edited by diadem59 on 29th April 2010, 2:31 am; edited 1 time in total

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Your idea is correct, but instead of dividing the reference voltage of the 2nd stage ADC you should use an amplifieing subtractor which gives you 16(Vin-V1)