We usually measure the current with a shunt or a Hall sensor. Compared to Hall sensors, measuring current with a shunt can keep good dynamic. However, the shunt has equivalent resistance. And the shunt resistance is usually high, e.g., 100Ω, for the weak current (uA~mA) measurement to make enough SNR, which may lead to very long stable time of the current during the measurement. So how can we measure the weak current with ultra low input impedance? Is there a reference circuit to realize it?
Perhaps you can use transmedance amplifier. It is opamp configured for converting current to voltage. E.g. if you use 1 Megaohm feedback resistor you will get 1 V/uA ouput , same as using 1 Megaohm shunt, however your impedance will be 1 Megaohm / Amplifier_Gain so less than 1 ohm for >1e6 amplifier gain (typical for low freq opamp). However, you will also introduce some few uV / tens uV voltage offset (can be trimmed to be compensated). E.g. https://electronics.stackexchange.com/questions/594570/transimpedance-amplifier-for-very-low-currents
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry
- Polymer Chemistry