adcdacmultisim
Here is schematic for Analog to Digital conversion:
Here are two Digital to Analog converters in Multisim:
Which one should I use? I want to connect it at output of ADC to get original sine wave. How should I connect it (which pins should I use)?
EDIT:
I found answer, however, other problem occurs 🙂
Here is schematic with 8bit DAC:
Here is transient analysis, showing input and output sine wave:
What are voltage spikes at output signal?
In general, your analog signals should stay in the analog section of the board and your digital signals should stay in the digital section of the board. You should have separate ground planes for each. However, these ground planes must connect to provide a consistent reference point to both sections.
Ideally, the analog sections and the digital sections should connect at a single point. The "star" connection mentioned in your links and by MoJo. Though sometimes this is not possible. But basically what you want is a small "bridge" to connect the two sections. Any signals that must cross between the sections should be routed over this bridge.
The reason for doing this is to prevent or minimize any noise from switching signals on the digital section from disturbing or corrupting any analog signals that you are trying to generate or measure. The split prevents digital currents from flowing into the analog ground plane. While the "bridge" connects the two ground planes so the ground reference is at a consistent level in both sections.
A good reference for why and how to ground mixed signal systems is Henry Ott's Grounding of Mixed Signal PCBs. Some diagrams from that page will help to explain some best practices:
As for the power supplies, they can come from the same source. Usually the bypass capacitors specified in the datasheets are sufficient to decouple the power between the sections. However, if the noise on the board is particularly bad, sometimes additional filter circuitry is necessary. For instance the one seen here:
Or, you could have a separate regulator to provide clean, stable power to any of your analog devices. This will most likely provide the best accuracy but at extra expense, board area, and circuit complexity.
[For the most part, below is just my conjecture. Then again, troubleshooting often involves conjectures.]
When you connect the amplifier to the A/D pin, you may be increasing the load capacitance. which the amplifier output is "seeing". It could be due to the capacitance of the A/D input, or dues to the capacitance of the cable. This (suspected) capacitive load may be causing your amplifier to oscillate.
We don't know the model of the amplifier (?), so we don't know how much load capacitance it should be able to drive. We also don't know what you cabling looks like: is it 200mm or 20m?
A quick & dirty fix would be to add as series resistor (say, 1kΩ) between the output of the amplifier and the cable. I'm calling this a "dirty" fix, because you are increasing the impedance that the A/D converter will see.
A serious fix would be to drive the cable with a buffer.
Best Answer
Since your ADC is only 8 bits, and the DACs you show are 16 bits, I'd say neither - look for an 8 bit DAC (although you could use the 16 bit parts, and tie the lowest 8 bits to ground).
Read the datasheets for those parts (or any other you might find) to find the features of each, and how to use them.