cciarleg
Junior Member level 3
Hi,
I really need someone to walk me through this step by step. I'm just not getting it.
I understand the principle of the scaled resistors into an opamp-the very basics of the inside of a simplistic DAC. I have simulated an example R2R and see that it works.
I don't understand why though.
Most simulators do not include the DAC in their models-because it is trivial or not worth simulating. Why is this the case?
If there is no DAC in the simulator, and lets say you have a current output DAC, I want to feed a signal as though it came from the DAC into my opamp. How do I tell what current and voltage level to feed into the opamp? This is the question that I am really really stuck on and would like to figure out.
To make things complicated, I am desperately trying to understand the AD7538 and not having much luck. It is a combination R2R with other scaling resistors. The datasheet says that the input resistance at Vref (into the ladder) is constant-typically 6k. How can this be the case? I though we were using or putting to ground some resistors, thus changing the overall resistance. What do they mean by this? Or "there is always 2R and 2R in parallel"?
In line with the above, how then, since R is 3-10k, 6k typical, can I simulate with the internal feedback resistor? Should I have an opamp simulation for each of Rfb 750, 1500, and 2500 ohms?
Thanks.
I really need someone to walk me through this step by step. I'm just not getting it.
I understand the principle of the scaled resistors into an opamp-the very basics of the inside of a simplistic DAC. I have simulated an example R2R and see that it works.
I don't understand why though.
Most simulators do not include the DAC in their models-because it is trivial or not worth simulating. Why is this the case?
If there is no DAC in the simulator, and lets say you have a current output DAC, I want to feed a signal as though it came from the DAC into my opamp. How do I tell what current and voltage level to feed into the opamp? This is the question that I am really really stuck on and would like to figure out.
To make things complicated, I am desperately trying to understand the AD7538 and not having much luck. It is a combination R2R with other scaling resistors. The datasheet says that the input resistance at Vref (into the ladder) is constant-typically 6k. How can this be the case? I though we were using or putting to ground some resistors, thus changing the overall resistance. What do they mean by this? Or "there is always 2R and 2R in parallel"?
In line with the above, how then, since R is 3-10k, 6k typical, can I simulate with the internal feedback resistor? Should I have an opamp simulation for each of Rfb 750, 1500, and 2500 ohms?
Thanks.
