Why didn't you ask the interviewer for the answer? Since you didn't getHi,
I remember during my first interview (in which I got rejected ) I was asked a question of how to realise a 16-bit ADC using two 8-bit ADC and Mux(es)? One is free to use discretes and opamp.
Does anybody know the answer?
That is the method I know also. The first 8 bit A/D has to have 16 bit accuracy if you want true 16 bit accuracy on the output.Why didn't you ask the interviewer for the answer? Since you didn't get
the job at least you would have learned the answer ;-)
I have never heard of using two 8 bit ADCs to make a 16 bit ADC. I have
heard of using an ADC and a DAC to do a null-and-difference measurement
(which increases the resolution of the ADC).
You measure the input voltage (Vin) with the ADC. You then set the DAC to
the value measured on the ADC (Vdac). You change the gain of the ADC input and
then measure difference between Vin and Vdac.
You need to be careful with the DAC and ADC specs. An DAC with 8 bit resolution
does not usually have 8 bit accuracy. I would be surprised if connecting two
8 bit devices together would get you 16 bits.
(* jcl *)
Unless I misunderstand what you mean, this will only give you 512 separate levels, equivalent to a 9-bit A/D.He didn't say anything about accuracy, only resolution. You would need to split the signal into two halves, then apply them to the ADCs. If you can change references, you can use 1/2ref for the first ADC, then subtract the signal from the first reference. You'd then need to detect when the signal is negative to trigger the multiplexers to go to ground for the MSB.
Steve
note: clearly this is an impractical way to make a 16-bit ADC, since it would work like crap, take up a lot of space, and cost a lot more than any 16-bit adc