nickexists
Active member
Does anyone know the impedance of the analog pins on the Teensy 3.1? I want to read a voltage from a voltage divider and I want to know how the current pulled in by the analog pin will affect my results.
Teensy 3.1 Analog pin/ADC impedance.
- Thread starter nickexists
- Start date
- Status
PaulStoffregen
Well-known member
It's not a simple resistance. There is a very small leakage current, which varies with temperature, and is not well specified. But that's not the main issue.
The input looks basically like a switch to a capacitor. When the ADC samples your signal, the switch connects, suddenly shorting the internal capacitance inside the chip to your signal. A current flows momentarily, to charge the capacitor to the same voltage (or close to the same voltage, if your signal has source impedance that causes a voltage drop between the true source and the internal ADC).
The internal capacitance is in the dozen pF range, and the switch on resistance is in the 1K range... approx.
The input looks basically like a switch to a capacitor. When the ADC samples your signal, the switch connects, suddenly shorting the internal capacitance inside the chip to your signal. A current flows momentarily, to charge the capacitor to the same voltage (or close to the same voltage, if your signal has source impedance that causes a voltage drop between the true source and the internal ADC).
The internal capacitance is in the dozen pF range, and the switch on resistance is in the 1K range... approx.
whollender
Well-known member
nickexists
Active member
Thanks. My signal is probably going to be around 2 volts with an impedance of 500k ohms so it sound like i'll definitely want to use some sort of buffer.
- Status