previous exams, ADC vs DAC levels

Ed Casas (edc@ece.ubc.ca) Tue, 5 Dec 2000 18:13:20 -0800 

Date: Tue, 5 Dec 2000 18:13:20 -0800
From: Ed Casas <edc@ece.ubc.ca>
Subject: previous exams, ADC vs DAC levels



Hi Azuma Hashimoto,

> I have a couple of questions.  First of all is there any
> possibility that solutions for old finals from APSC 380 will be
> posted on the web?

No.  The solutions were never typed up.

>  I was wondering because I am working
> through them and would like to double check my answers.  There
> is some stuff I can't find in the notes.

Not all of the material in previous years was covered this year.

> One example is question 5 part b from April 1998.  I couldn't
> find all the info in the notes to answer that one...

No, we didn't cover as many types of A/D converters this time
around.  You can look at that year's lecture notes for more
details if you're interested.

> When using "and" and "or" gates to draw schematic diagrams can
> we put more than two inputs to these?
...

Yes, multi-input gates are fine.  The internal circuitry in a PAL
actually uses multiple-input AND and OR gates.

> In the A/D and D/A notes there are two examples (49 and 51)
> where you solved them differently.  In one the resolution was
> the delta V over (2^N-1) and the other it was over just 2^N.
> I'm assuming that is because the minus 1 has a very small
> effect on the final answer but I just wanted to make sure that
> it doesn't have anything to do with the difference between ADC
> and DAC.  Since example 49 was a ADC and 51 a DAC.

Yes, it does have to do with the difference between an ADC and a DAC.

In both cases the number of levels is 2^N.

For the DAC we are interested in the step size and that the range
divided by one less than the number of output levels (2^N-1).

For the ADC, we can actually divide up the input range into 2^N
steps since we don't need to generate the maximum output level to
decide where the input lies.

Work it out for a small number (e.g. N=2) to see how this works.

-- 
Ed Casas   edc@ece.ubc.ca   http://casas.ece.ubc.ca   +1 604 822-2592