Hello, I would like to ask you some questions regarding DAC output.
1. When the DAC chip output is 0~5V Unipolar OUTPUT, for example, the DAC output is a discrete signal, so it is known that a filter is connected to the output terminal to receive a voltage without ripple or noise. Please explain how the output waveform changes to a pure analog voltage based on the related circuit.
2. If the DAC output is to drive a low-impedance load, add a voltage follower op amp to the output stage.
I am not sure of the concept of why I should put that amplifier in a low impedance load drive, so I ask for it. For example, when the resistance load is high or low, it may be said that it is not well organized.
It may be awkward because the question is in the learning stage, but please answer it widely. Thank you.
1. For CD, for example, 44.1 kHz sampling is used. Since the audible frequency that humans can hear is 20Hz~20kHz, the sampling frequency is about 20kHz x 2 times. The CD also has an analog filter at the output, but not all filters have very sharp characteristics at the cutoff frequency. So the way it came out is oversampling.
The picture above is the spectrum from the original DAC. The necessary part is the blue part, but it is very difficult to construct a filter that can be squeezed sharply at 20khz. So, over sampling is done inside the digital filter. In other words, by adding the average of the two values in the middle, it virtually increases 44.1 kHz by 4 or 8 times. Then, the spectrum appears as shown in the lower part of the picture above, and the sampling noise can be sufficiently removed with a general 1st-2nd order analog filter.
2.DAC itself is not so low in output impedance. If you connect a few kohms to tens of kohms to the DAC output, it's no problem, but if you connect a 15~32ohm speaker like a headset, the output voltage drops. In this case, it means to amplify the current by putting a buffer into the DAC output. Voltage Follower = As a buffer, there is no voltage gain, but it serves to amplify the current.