current mirror very low current
The best way is to use a current mirror: It's made like an ECL port with the base of one transistor shorted with it's collector and a load on the collector of the other (Try to make a search for current mirror circuit). By acting on some parameters of this scheme you can make a certain current and duplicate it (even a fraction of it) with a very good accurancy. This is used into DAC IC to stabilize their performances against ageing and temp. drift.
Bye Mrm