Here's my problem:
I'm planning to build the current to voltage converter below for measuring very low currents over a wide range (~1pA to ~1uA). The idea of the circuit is that initially Uout1 is used until ~3.5V develops across the limiter at which point resistor nR is bypassed and the second output Uout2 is then used for the higher current measurements.
The back to back zener diodes in the limiter have the following problems:
> High, non linear leakage current
> High capacitances
> Hard to switch off once conducting
I need to come up with a new diode network to remove resistor nR from the circuit with a threshold voltage of ~3.5V, low leakage current and capacitance.
Unfortunately I think this requires some very in-depth knowledge (which i don't have but am trying to learn!) and i'd be very grateful if any of you enthusiasts could point me in the right direction!
Thanks!
I'm planning to build the current to voltage converter below for measuring very low currents over a wide range (~1pA to ~1uA). The idea of the circuit is that initially Uout1 is used until ~3.5V develops across the limiter at which point resistor nR is bypassed and the second output Uout2 is then used for the higher current measurements.
The back to back zener diodes in the limiter have the following problems:
> High, non linear leakage current
> High capacitances
> Hard to switch off once conducting
I need to come up with a new diode network to remove resistor nR from the circuit with a threshold voltage of ~3.5V, low leakage current and capacitance.
Unfortunately I think this requires some very in-depth knowledge (which i don't have but am trying to learn!) and i'd be very grateful if any of you enthusiasts could point me in the right direction!
Thanks!