Hi
I have this project in mind that involves my circuit going in between two line-level audio devices, essentially tapping off of the signal like a Y-splitter cable, i.e. hooking my device in parallel to the receiving device's line input. Inside my device, the signal is to be DC-biased and fed into a single-ended unipolar ADC inside of an MCU for further processing. The MCU in question is STM32L0 series that specifies the following parameters for ADC input impedance:
That's the first time I've seen ADC input Z specified like this; they don't tell the inherent ADC channel's input impedance but instead tell you what impedance should you put in front of it to get desired results? Not sure I get it...
Anyway, what I'm trying to ask is how should I design the input stage to the MCU as to not affect the signal quality in any perceptible way. My device should basically be as close to being "transparent" to the audio devices on both ends as practically possible. I am hoping for a basic solution like a voltage divider consisting of two 50k resistors for DC-biasing and a 10nF capacitor for AC-coupling. I'm reluctant of putting an op-amp in front due to power consumption considerations. Does a setup like this stand a chance of working properly and not messing up the audio signal? On the surface, due to the typically low output impedance of line-out sources and relatively high impedance of line-in inputs, I should should be able to get away with what is essentially Y-splitting the audio into two separate inputs so maybe I'm overthinking this?