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Thread: Short analog ground to ground

  1. #1
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    Short analog ground to ground

    Hello,

    I am working with a Teensy 3.5, which I am integrating into a PCB design. Due to the layout I am not able to use the analog ground for my analog signals. Would I see any change in performance by shorting the analog ground to the "regular" ground?

    Thanks!

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Usually using GND for analog signals is perfectly fine. In most cases it makes little or no difference. But in some cases, like PWM to LEDs or motors, separate grounds for analog and digital can reduce noise. Even in those cases, using GND is ok, if you're willing to accept some extra noise.

    The opposite is not true. Never use AGND for digital signals. There's an inductor between AGND and GND, which isn't good when you have fast changing low-to-high and high-to-low voltage of digital signals.

  3. #3
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    Thanks Paul. So are you saying that I would see a decrease in performance on the analog signals if I were to short AGND to GND? I don't think so, since that would short out the inductor. I was thinking maybe the performance would improve slightly, since whatever noise is on GND would be coupled to both the analog sensors and AGND and could cancel out?

    The analog sensors are resistive voltage dividers through an RC low pass filter and an op amp. Maybe there's too much of a phase shift through the filter and/or amplifier for this to make any difference?

  4. #4
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    Depends where your noise is coming from and how careful you have been with your sensor design. Best practice is to separate power supply for the sensors, that connected to the Aref and code changed to use same with sensors and shielding grounded through analog ground. This keeps everything seperate from the rest of the circuit and just leaves you with EMI to manage. It is possible if your design is very minimalisitc that not having the filtering will get a truer picture of what is happening on the sensor supply, but I think that would only apply if your sensor is sharing a return path with your major loads, or if your sensor actually consumes large and varying amount of current in operation.

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