# Homework Help: How to calculate this 4 bit DAC

1. Jun 29, 2017

### michael1978

< Mentor Note -- thread moved to HH from the technical forums, so no Homework Help Template is shown >

please can somebody help me, how to calculate this 4 bit dac,
i know this one if input 1.1.1.1 5/2, 5/4 5/8 5/16 voltage

i dont understand nothing i search on the internet but i dont find some useful example,
my english is not so good....
please one more time can somebody explain me how to calculate, for formula thanks

Last edited by a moderator: Jun 29, 2017
2. Jun 29, 2017

### Staff: Mentor

Try again, using the search terms R-2R ladder DAC.

After you have done that reading, try again to work your schoolwork problem and post your work here so we can check it.

3. Jun 29, 2017

### Merlin3189

BTW, can you check your circuit, as I think the op-amp has the inputs reversed.

Berkeman beat me to the rest of the comment.

4. Jun 29, 2017

### Staff: Mentor

Good catch!

5. Jun 29, 2017

### michael1978

thank you a lot , it help me, thanks...
have nice night.

6. Jun 29, 2017

### Staff: Mentor

Also, you show the output component as a Comparator. It should be a Op-Amp, not a Comparator.

7. Jun 29, 2017

### willem2

You really should look up another version of the R 2R ladder.
-1 if key A is closed, the positive supply is short circuited to the output of the op-amp. That won't end well.
2 R1 shouldn't be there.
3 The ampiflier you connect the R-2R ladder to should have infinite (much larger than R) imput resistance.
4 The inputs should be connected to either 0 or 5 volts, and not left unconnected.

The last point is essential to make make the superposition principle work. If you have a network of resistors and voltage sources, you can calculate the effect of a single voltage source by replacing all the other voltage sources with a wire. You can than sum those indivudual effects to get the output voltage. Replacing the voltage sources by open circuits won't work.

8. Jun 30, 2017

### michael1978

Good Morning

i solve all the problme with voltage divider i find all the values.
but the problem is, when i push key D, the voltage of D is the same(like i find it with voltage divider), but the voltage on c,b,a they have other value?
how do i calculate ?because i draw the circuit in gsm (every circuit)
thanks...

9. Jun 30, 2017

### Baluncore

The circuit in post #1 is a weird mix of several ideas.

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Last edited: Jun 30, 2017