1. Jan 16, 2012

### Bassalisk

I've asked this question before. But still I got some unanswered ones.
I am really tired, but I cannot sleep if I got something laying there, tingling me.

http://pokit.org/get/cfb750b79f49cfc12dc51a74a37f576e.jpg [Broken]

This is digital ramp.

Can somebody explain to me, how does the counter-DAC part works. I though I understood it, but i am still not comfortable with the idea. What kind of DAC gives even steps, how come it increments so evenly, that ramp? How does this counting works? What is that counter essentially?

It is confusing me, because in succesive approximation, we have a "normal" DAC, like DAC with R2R.

http://pokit.org/get/b75abb641b183f5128aa50a8eacd0770.jpg [Broken]

Those jumps are uneven, and I understand that. But how come out of the digital ramp ADC, the DAC gives even steps.

It doesn't matter whether you go from LSB to MSB, or the other around, those steps cannot be even!!

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2. Jan 16, 2012

### jim hardy

""It doesn't matter whether you go from LSB to MSB, or the other around, those steps cannot be even!!""

i think in pictures.

if you're incrementing LSB the steps have to be same size,
0000=0
0001=1
0010=2
0011=3
0100=4
0101=5

one per step

but start from opposite end, MSB, and what happens ?

0000=0
1000=8
0100=4
1100=12

did i get the right question?

3. Jan 16, 2012

### Bassalisk

We think the same then :)

I though the increment was like this:
0000
0001
0011
0111
1111

or better yet,

this crossed my mind

0000
0001
0010
0100
1000

and accordingly for from MSB

0000
1000
1100
1110
1111

There was my problem. So the increment goes like you said? Really didn't know that.
Mr. Jim you are my savior.

How do you know so much about electronics, if you were a energetic-trained?(Power lines etc). Every question I asked, you knew the answer about electronics...

Last edited: Jan 16, 2012
4. Jan 16, 2012

### jim hardy

ahhh , logical enough.
in high school electronics class(ca 1963) teacher had us boys all build simple two transistor flip flops. We hooked them in cascade, to make a binary counter of about eleven or twelve bits and connected Simpson multimeters(analog) to show status of each stage. (LED's were only a dream then.) Drove LSB with a low frequency oscillator.

We watched the pattern on the meters as lsb ticked regularly and each successive stage of course ticked half speed. Took an hour to count up to all ones and we cheered as all eleven meters swung together back to zero...

so i guess that visual demonstration imprinted the progression of a binary count and the concept of carry .

i take it you're studying various ADC's. i like dual slope integrator the best.

5. Jan 17, 2012

### Bassalisk

You know what, I will to my college demand an access to laboratory, and do just that! Thank you mr. Jim.