# How to find digital input for given output value of a DAC ?

Discussion in 'Homework Help' started by thar07, Feb 3, 2015.

1. ### thar07 Thread Starter Member

Jan 3, 2015
71
0
The n-bit R/2R digital-to-analog converter (DAC) has a reference of 16 V and the analog
output for the input code 1 is 15.625 mV. how to find the digital input value for the output
9.140625 V ??

2. ### MrChips Moderator

Oct 2, 2009
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If 1 count is 15.625mV how many counts in 9.140625V?

3. ### thar07 Thread Starter Member

Jan 3, 2015
71
0
It did not give any other details. If you could please explain the theory behind this.

4. ### MrChips Moderator

Oct 2, 2009
12,638
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If one potato weighs 100g how many potatoes in a 1kg bag of potatoes?

5. ### WBahn Moderator

Mar 31, 2012
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What will be the analog output for the input code of 2? Of 3?

See the pattern?

6. ### thar07 Thread Starter Member

Jan 3, 2015
71
0
if that so, why they given the reference voltage ?

7. ### MrChips Moderator

Oct 2, 2009
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Just to throw you off track.

Apr 5, 2008
15,806
2,389
Hello,

The reference value might be the maximum obtainable voltage.

Bertus

9. ### MikeML AAC Fanatic!

Oct 2, 2009
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Look up the concept of ratiometric. The output of a DAC is ratiometric with respect to the reference voltage.

10. ### WBahn Moderator

Mar 31, 2012
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Notice that they don't tell you how many bits the DAC is. Another question probably asks you to find that.

11. ### thar07 Thread Starter Member

Jan 3, 2015
71
0
They asked the following two questions and I don't clearly understand what it means.

12. ### WBahn Moderator

Mar 31, 2012
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What don't you understand?

Still waiting to see some attempt on your part.

13. ### isurunix New Member

Feb 3, 2015
21
0

for code 1 : 15.625 mV

1 V : 1000/15.625

9.140625V = (1000*9.140625)/15.625 = 585

in binary : 1001001001

14. ### thar07 Thread Starter Member

Jan 3, 2015
71
0
I don't understand the following things related to the question.

1) What is the reference voltage of DAC's (n bit R/2R).
2) How to find the number of bits in this DAC.
3) how to set reference voltage of ADC by using a DAC.

I tired find theories related abouve questions and found nothing. So I could not do anything to solve these.

Apr 5, 2008
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16. ### isurunix New Member

Feb 3, 2015
21
0
@Bertrus

Thanks for pointing it out. Can I post a link to a site containing relevant theories ?
Sorry for my mistake. I was browsing on the same question and most probably for the same home work. So I just hoped to make it easy for him to understand.

Apr 5, 2008
15,806
2,389
Hello,

Yes, linking to websites with the theoretical background are fine.

Bertus

18. ### thar07 Thread Starter Member

Jan 3, 2015
71
0
Do you have any theory notes related to this ?

19. ### isurunix New Member

Feb 3, 2015
21
0
@thar07 You can find the relevant theories here and here

I found them today. These seems to be good. Hope it will help them.

20. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
This is the Homework Help forum, not the Homework Done For You forum.

Please do NOT just do the poster's assignment for them -- in most cases it does them little good in terms of learning the material.