Does anyone have experience with leakage current in your typical solderless breadboard?
I have a circuit with a +/- 10V supply. I am trying to build a current sink that is around 500nA. I am able to measure the current, but there is a current mirror in the design using matched NPN transistors, and the matching at 500nA is abysmal - for 500nA input I get ~900nA output from the current mirror. The current mirror is a special topology (emitter modulated) so the error is not due to the input side having to supply both collector and base current.
The matched transistors are precision matched audio BJTs, part number LS313 from Linear Systems, they arent just 2n3904s with similar betas.
This was just a quick job to see if the circuit worked (it does), and I was wondering what parasitics might be affecting the matching. I plan to move to a carefully laid out PCB soon, with guard rings and planes around sensitive nodes.
I have a circuit with a +/- 10V supply. I am trying to build a current sink that is around 500nA. I am able to measure the current, but there is a current mirror in the design using matched NPN transistors, and the matching at 500nA is abysmal - for 500nA input I get ~900nA output from the current mirror. The current mirror is a special topology (emitter modulated) so the error is not due to the input side having to supply both collector and base current.
The matched transistors are precision matched audio BJTs, part number LS313 from Linear Systems, they arent just 2n3904s with similar betas.
This was just a quick job to see if the circuit worked (it does), and I was wondering what parasitics might be affecting the matching. I plan to move to a carefully laid out PCB soon, with guard rings and planes around sensitive nodes.